ijpom

After struggling to tune a new SH 28 for the first several months, I have quickly and easily tuned a different SH 28 type engine (my EX 28, if your following from another thread).
This makes me conclude that the first engine has an air leak causing the tuning issues.

Work already done around the fuel and air system:
The fuel delivery tubing and pressure line was all replaced.
The carb's main needle (HSN) had been removed, cleaned re-tightened.

What else is the next most likely source of air leak. The carb to block interface? Other carb needles? Other block opennings?
I have a spare used SH28 carb that appears OK, and I could just replace it and retune, or am I better off trying to seal the engine using RTV?

BTW: the tune issue is that the engine bogs down under load, while just off idle.

1QwkSport2.5r

Sounds like a simple tuning problem and not an air leak. An air leak will cause erratic running and the inability to get it tuned; example: run fine for 5 minutes then all of the sudden go lean and quit/cut-out.

With the fuel systems these engines are equipped with, very rarely will air leak in, but actually fuel leak out. This is in part due to using the muffler to pressurize the fuel tank. Same goes for leaks around the backplate - fuel/oil will get pushed out during the positive pressure part of the stroke. Look for oil splatter around the engine on the chassis. This will be a dead giveaway if there's a leak.

The things to check are: are the o-ring(s) around the backplate in good condition and backplate screws are tight, o-ring in crankcase below carb and o-ring around bottom of carb itself in tact, carb pressed firmly against crankcase and pinch bolt tight, cylinder head screws tight, glow plug good?, and are the bearings good? The rubber seal on the front bearing means nothing - it doesn't seal the crankcase but actually the oil film between bearing race and crankshaft. If the bearings are loose/worn out, tuning will be difficult. Is the fuel fresh? Is the cylinder liner oriented properly? Are the needles holding their setting while running - or rather are the needles screwing themselves in when you rev the engine? I had this happen on my SH .28 and Mach 427 - the o-rings on the idle stop and main needle were dried out and shrunk and would screw themselves in when the engine revved up causing it to go lean and in one case the idle gap opened way up causing a really high idle.

If all checks out, open both needles a full turn and re-tune it. Also ensure the idle gap isn't closed too much or open too far. An improperly set slide gap (idle gap), the low speed needle setting will be incorrect. Usually, when too rich on the idle needle, the engine will rev slow and be really smokey. If it's lean, it will cut out or rather the rpm will sag. The idle needle controls fuel mixture until about 60-75% of the slides travel and the main needle controls fuel flow over the whole rpm range (if too lean will render the idle needle somewhat ineffective) but usually (if not set too lean) will control fuel mixture from about 75% throttle to wide open.

ijpom

Thanks for the input.

In response to your points:
I don't get any fuel leaking out of the engine, and I have not proved that air is getting in except through the air filter. I'm sure it's getting in there as there is dirt on the filter.
The engine sometimes runs without bogging down, but there is no certainty to it. It does not display the '5 minutes runs fine, then won't idle' business, as you describe the classic symptoms.

Additional to the bogging, I have been trying to keep the engine safe with temperatures (during break in and after). So I have an inexpensive temp gun, and it has been reading 300+ deg f by the middle of a tank of fuel, and sometimes higher. This is high by most accounts, but I still get plenty of smoke out of the exhaust on acceleration. I don't trust the temp gun as a consequence of these contrary indicators, but I keep the body off to keep the head/heatsink in as much air as possible.

On another tack, I've run out of Torco 20% (I think it has 14% lube) and ended up getting O'donnell 20% with 8 or 10% lube. I realize I probably will have to re-tune for a fuel change as well as everything else, but I was hoping maybe my engine didn't like Torco with lots of oil, and will prefer O'donnell.
So far I have based my fuel purchase on what can be had locally, or what Amazon will ship - I'm sure these are fails afe ways of buying fuel. Ha Ha.
Any experience of thoughts on what works well with the SH 28?
(From new the engine had 1quart of VP Racing SpeedMaster, 3/4 Gallon of Torco, yet to see any O'Donnells)

Thanks.

1QwkSport2.5r

You need to re-tune the needles when you change fuels. Likely your 300F temps is due to a lean setting. Lower oil means more fuel is being burned which runs hotter, especially if you didn't richen the needles. Lean fuel mixture advances ignition timing which will cause higher engine temps as well. If the engine truly overheats, it will usually just quit and need to cool down a little before it will restart. Smoke amount and color has little to do with anything because every fuel will smoke differently because of using different kinds of oil and other additives the fuel company uses. 300F by the middle of the tank tells me it's lean - WAY lean - regardless of what fuel you use. The needles should be adjusted with changes in fuel, different heat range glow plugs, and should be checked every time you run the truck/car.

I've used fuel blends ranging from 0% nitro 20% oil to 30% nitro 8% oil with my normal preference being 20-25% nitro and 11% oil. I mix my own fuel and use castor oil only. 30% nitro is a bit much without adding a head shim, but it will run okay if you run it richer. I feel anything less than 10% oil isn't enough for a basher truck. I usually break-in my engines on 15% nitro 15-18% oil and I always use hot plugs like Enya 3s or McCoy MC59. Hot plugs will tolerate richer mixtures as they retain more heat after combustion. Richer mixture means cooler engine temps. However, if the engine runs correctly and throttles nicely and rpm doesn't sag in a long WOT run, don't worry about what temperature the engine is running at. If you tune the engine to run at say 250F, you're wasting fuel and power. The needles should be set just a teeny bit rich - say 1/16th-1/8th turn richer than absolute peak power.

ijpom

Thanks again for your full responses Tim. Always something useful to re-consider.

Unfortunately I selected the "Racing Fuel" from the O'Donnell range which is their 8% lube. I'll opt for the "RTR fuel" at 12% lube next time .... if I have a choice.

Thinking again about the temperature, I believe now that the temp gun and you are right, and I'm running too lean. The final clue was that I can't restart right away if the engine stalls. With the high running temps, the fuel will evaporate at the carb while trying to prime it (good old fashioned vapor lock).

Anyway, I'm back at square one with the needles at 3+ turns out, and one tank of mild adjusting completed. Not so much bogging so far. :-)

1QwkSport2.5r

See if your hobby shop sells castor oil or Klotz Benol. If they do, grab a bottle and add 4-6oz of oil to the gallon of 8% oil fuel. A 4oz bottle of medicinal castor oil will work too, just look at the label and ensure it doesn't have sugar or other additives in it. 6oz of oil to a mostly full gallon of fuel will add about 3-4% to the oil content. The aircraft guys do this all the time.

Anthoop

I can only really echo what Tim has already said..

I have used fuels with below 10% oil content and whilst they are powerful/clean burning....it is very easy to damage an engine by running too lean....and a temperature gauge is never a tuning guide, it can be useful when there is a problem or you are trying something new or for break in but that is all.

Again as already said...back off from the ultimate performance on each needle...for having fun you do not need the engine to be on the edge of the tune....just make it happy.

Anyways...let us know how you get on after the retune with the new fuel Erin...and good luck.

ijpom

So it's been a few weeks, and I did get a chance to re-tune all engines with the new fuel.

Here is an response from your posts:
Thanks for the suggestion of using additional oils, but with all the wrenching and sourcing of parts, I've decided not to become a mixer of fuel as well. This leaves me with the re-tune for fuel change, combined with the general re-tune. I'll tweak it all again when I go back to the safer 10-12% lubrication.
Anthony, thanks for your input too. Nice to have multiple confirmations on an idea.

So the bog issue is non-existent after some tuning, but some of this has questions over it.
1) Basic start, idle, throttle blips were done on my 80ft x 16ft driveway. The buggy with the bog issue got slightly lower gearing with on-road tires, and never got up to full speed under these conditions.
2) Full throttle runs were done in a larger parking lot where the car could make full speed and not run out of space (2 or so seconds at full throttle and we are already there). Temps remained stubbornly high when things were running well (270 - 300 F).
3) Truggy with no bog, remained without bog after richening, and incrementally re-leaning to account for the new fuel. This was done at the large parking lot also. Temps were always better with this engine at 250-270F.

The worst bog was always at the big professional track (long straight, 3ft+ double and triple jumps, hard packed clay) and technical stuff I suck at navigating. It was always made worse by being stuck near the bottom of a large jump and getting engine bog (lean or other-wise). The small track I now frequent (backyard, loose soil, 1ft bumps) was always less difficult and less prone any bog. I assume these are related, or should steep uphill starts have no bearing on tune?

Since I think my HSN's are better, and start and idle are functional, I re-read the Paris Enigine Bible and came up with two lines of questioning:
A) "Set the low end or idle. After getting top end set close, bring model in, listen to the idle. If it is
idling fast then it slows down in a few seconds, it is probably too RICH on the bottom (minimum
spray bar). In that case, make it more lean (turn clockwise ¼ turn), then run another lap and
bring the car in again. Repeat this procedure until the idle stays high for at least 10 to 20
seconds; at this point readjust the aircrew so the idle is at a moderate speed. The wheels should
not turn, and the clutch should be fully engaged."
Does this work for you guy's? I don't have the 10 sec of high idle. According to this I may be running the LSN too rich. That seems like it would not be the cause of my over temps, but ill try to lean it out a little and see what happens.

B) "1. Wire and surrounding bottom of plug wet, with like new shiny wire = rich side of optimum power 85%
2. Wire and surrounding bottom of plug starting to dry and wire starting to gray = Very close to optimum power 95%
3. Wire and surrounding bottom of plug dry, wire totally gray but not distorted optimum power 100%
4. Wire and surrounding bottom of plug dry, wire distorted = slightly lean DANGER!
5. Wire and surrounding bottom of plug dry, wire broken and distorted or burnt up = extremely lean possible engine damage!"

Whenever I have pulled the plug after a run (for ARO or igniter check) I see the base of the plug is wet and the wire is greyed and lightly distorted. Seems like a mix of results from lean and rich settings. Do these plug indicators work for you guys? I'll put in a new plug and re-assess using the current tune.

Thanks for any insight you can give.

Anthoop

Far be it for me to knock the Ron Paris method...but is this really correct "idling fast then it slows down in a few seconds, it is probably too RICH on the bottom (minimum
spray bar). In that case, make it more lean (turn clockwise ¼ turn)" ?

The LSN is generally adjusted in very small adjustments...like 1/16 and less once in the ballpark....and the throttle gap and LSN work in conjunction (so...say I lean the LSN then I will have to reduce the gap to compensate and vice versa).

From your description of the plug I am guessing that your needles are imbalanced....so the HSN is set lean and the LSN is rich...very easy to do.

I think you are trying to combine too many methods of tuning and that is one reason why you are struggling, also the temp. gun can not tell you if one needle is lean and the other rich...eg...lean HSN and rich LSN- you run round using full throttle then use low throttle to bring it in and measure temp...all could look ok yet it could be dangerously lean.

Personally I use a set procedure that has always worked for me with any engine I have used....listening to the engine is an important part...
I run around for a few minutes gently to warm it...both needles are on the rich side and gap is 1mm.

Bring it in when warm and top up fuel.

Then full throttle-high rpm runs...to adjust the HSN...(HSN governs the total amount of fuel allowed so the engine needs the most fuel when it has the most air available- full throttle/max rpm)...adjust in necessary increments depending on how rich it was from the start....once the maximum full throttle performance is found then you can set the HSN back a little richer.
(Note- you may have to open the throttle slowly in order to reach the high rpm depending on how rich the LSN is...and you can go past the maximum full throttle performance to find when the HSN is too lean (just do not repeat too often as it will be cooking)).

Now the LSN...I use a method of stop and go...whereby I will run it up and down a few times and then bring it to a standstill next to me for a number of seconds (this time can be anything from five to twenty and can be variable due to engines/conditions)...once it has stood for a number of seconds I apply full throttle....I keep adjusting the LSN until it will take off clean and fast...again only adjusting in necessary increments...

When I am leaning the LSN then the idle rpm will rise...so invariably I will reduce the slide gap and once I have adjusted the slide gap then I will check/readjust the LSN...and then the gap...and LSN....generally I will do this a few times to check.

ijpom

Resting idle seems like the most sensible method, with real world application. I don't understand the methodology behind the high idle for 10-20 sec. Perhaps it will do that when I get things set up perfectly.

Regarding fueling while hot, I've been very cautious despite it being done in competition by everyone. I run hotter temps than normal, and my aim and bottle squeeze are of the novice variety.
(Just looking up the auto-ignition temp of nitro-methane and methanol perhaps I shouldn't be worried, 417C and 470C respectively).

Anthoop

I have not heard of or seen/experienced a fireball whilst refuelling.....but it would always make sense not to put your face right over the car whilst refuelling.....other than that I feel safe doing it.

Tweak them needles next time you are out and let us know how you get on.....I am a fan of adjusting to make the engine perform properly and in my mind that is achieved when adjusting it by gauging how it performs.

There are so many tuning methods...and many I just wonder how on earth would that tell you anything....the "pinch test" is one thing that always gets me...I have tried it out of curiosity but to be frank it is almost meaningless, it might put you nearly in the ballpark but that is all...better to just accelerate and say "ah...that is not right" then if in doubt go richer....if it is better then you are going the right way.

Another point to make is that you can only set the needle position (LSN) in one place pertaining to the slide....so between idle and when the needle leaves the jet then you are at the mercy of the taper of the needle. Primitive carbs...make the best of it.

ijpom

The good news of the weekend is that the current problem engine is now not requiring a tune. The bad news is that it requires a rebuild.

Short story:
Running rich and idling poorly when cold. Engine went from full throttle 60 ft down straight, and then cut out dead. Could not turn flywheel to find BDC.
Pull engine down and find connecting rod broken at small end. It appears that the bearing is fully intact on the piston end, but the dis-assembly is not complete. It also appears that the lower portion of rod has beat the hell out of the bottom of the piston to make it un-salvageable.

The blown engine has a non-scored liner from top to below the valve openings, and I would like to salvage it for re-use. With great effort I can move the damaged piston from below opening to have half way closing the exhaust openings. I can also more easily press it back down using a plastic protector and a vice
Since I have a complete old engine with poor piston to liner fit, I figured I may have a complete engine between them.

I need some input on removing liner.
As described the piston is damaged and thats probably why it fits so tightly at the lower portion of the liner. At neither top nor bottom of its motion can I move the liner at all. I did try to heat the block (to above comfortable holding temps) but that didn't free up the liner.

Any suggestions on removal? Or is there no point since a worn piston is unlikely to work well with a non original paired liner?
Also, is there any indicators I should look for in the carnage that might indicate if the fault is of a user/tuner origin.

Anthoop

Booo...bad luck.

To get the liner out I would strip everything off of it and then put it in the oven for 10-15 minutes at 150 deg. celcius...then using oven gloves take it out and try to push the bottom of the sleeve up through the backplate hole (will need a tool with a curve to make it easier) and/or try to lever it up through the exhaust port hole (if the liner is not totally matched with the casing).
You should only have to move it up a few mm and then you can get something under the top lip to lever it up and out.

I would think you will be very lucky if that other piston is a decent fit...but always worth a shot....and SH parts/engines are well priced should all else fail.

I can only think that you will find some traces of heat discolouration on the damaged bits....but try to get it apart and have a look/see...put some pictures up if you can.

1QwkSport2.5r

Stick a zip tie or wooden toothpick through the exhaust port and turn the crankshaft so the piston pushes up against the zip tie or toothpick. This usually pushes the liner up high enough to get under it with something to lift it further. Heating the case may be necessary to soften the varnished oil that gets trapped between the liner and case.

ijpom

So here are the pics of the broken conrod and piston. Piston is in the lowest position it can be in with the rod blocking its motion - gives best view of skirt damage. Besides from being broken, I see no bad signs like overheating discoloration or wear. Tried all the tricks mentioned without success. The broken rod mushroomed the skirt of the piston, and now there is an interference fit, even at the bottom of the liner.

Next dis-assembly step is destructive, and since the rod is already broken, I plan to cut through it with a Dremel sized cut off wheel. This will allow some free room to slip off lower rod portion and hopefully push the piston low and away from the liner. Failing that I may need to drill out the piston. All this really means is that I had better get a replacement engine, as this is not likely to end in many good parts.

Anthoop

From the pictures...that glow plug coil looks to be very distorted....top of piston looks very clean....if I had just those two pictures I would say the engine has been using fuel that does not contain castor oil and has been running lean.

1QwkSport2.5r

I think, based on the look of the glow plug, that it was being run fairly rich. If you're at the peak mixture, the coil will usually have a frosted appearance and the bottom of the plug will be a dark copper brown color. If the coils are still round, then the shape of the coil is likely just the way it was manufactured. It's not crumpled or misshapen from what I see. When the piston is that clean after any real amount of fuel, I'd bet it was ran pretty rich.

Another observation, is the liner appears to be nickel plated and not chrome. Is all of the plating inside the bore look good without any peeling?

Usually conrods break for a few reasons... Manufacturer defect, hydraulic lock, too tight of a pinch, not running at operating temp, and any combination of these. Usually what I see being the biggest problem is the latter two problems together. That isn't to say this was the issue here though. I will bet if you could dremel down with a sanding drum the high spots where the skirt is mushroomed out that you could then move the piston up to push the liner out. You will want to heat the crankcase up to probably 300F to expand the case enough to get the liner out if it won't move otherwise. That piston might be salvageable. I think I have a good SH rod I could give you if all else is okay in the engine. I'd just need to know the center to center of the rod bushings is.

ijpom

Hey guys,
Thanks for your input. I'm still looking for answers, so maybe these pictures can help.
Tim, appreciate the generous offer of a rod, but I believe that this engine has gotten in to the 'spare parts' category.
I would say that the liner has no flaking and is of standard chrome plated construction. It was not possible to picture well.

So there is a little confusion about the pictures. I'll try to clear it up.

The broken conrod is in the SH28 in the upper pictures.
The lower pictures showing the glow plug and driveway after running the working EX28 in the truggy. Glow plug and broken engine are not related. ( I was going to mention the rich fuel streaks on the driveway, and the shiny plug element after 1 tank with a new plug, but thought adding to the requests for diagnosis was going to confuse things. My bad for leaving the pictures attached.)

These next pictures are of the break down of the SH28 with the broken conrod. As the back of the engine was too deep to get the dremel comfortably in there, I did a progressive drill-out of the rod.

Some of the marks internal to the block are from my dis-assembly.


This is the drilled out lower rod portion.


Piston looks nice on top to me, but has rod damage to sides and removal damage to the area near the pin. The color of the very edge of the skirt (3 mm or so) appears 'blued', perhaps with heat?


Crank, carb and bearings are all undamaged and will be in my parts collection.



In case anyone is wondering, piston would not go up and liner would not budge, so I removed all obstacles from pushing it down. First rod, then crank, then large bearing (small bearing was before large). Then the piston came right out.
Liner still not removed from block! But I believe I scratched it trying to pry it out after heating it up, and now there is little point.

1QwkSport2.5r

Okay, seeing more of the piston now, I agree. It's junk. The "blue" area is staining from the fuel; that area is never exposed to an open port; the stain line basically tells you where the the piston is exposed to an open port when at TDC. It will be more noticeable on the exhaust side since that side is the hottest and the oil varnishes on the piston more.

Not it that it helps, but the conrod I have spare is from a Mach 427 which is an SH based .26. I believe the .26 and .28 use the same rod; the bores are different. Too bad your engine couldn't be salvaged!

supertib

How big is your idle gap ? thats likely the first issues you have


second issue is your too lean ! way too lean

third bit of advice is ignore these guys on their fuel advice, they will have you running garbage high oil fuel that wont tune correctly ! stay with the fuel you have, just richen the needles and lower the idle gap down to 0.5 mm


I hate high oil fuel, it doesn't ever run correctly and more often then not it hurts engines more then it helps them !

supertib

Also a rich tune does not cause the idle to hang, that is 100% ass backwards...... a high hanging idle is a sign the mixture is too lean.... any time the RPM hangs it means there is too much air and not enough fuel ! many tuning guides are horrendously bad and do not properly describe engine behavior !


Your idle needle to be low and slow..almost like a Harley........if your idle sounds buzzy like a hive of bee's your too lean !

Your engine damage is from being too lean, hanging idle for 10 seconds means your idle gap is too big, your linkage is binding or your just too lean or a combination of all of the above

supertib

Tuning a LRP 30 the Nitroshop way
Here is my way to tune the LRP 30... My name is Neal Smith, I Am the owner of www.thenitroshop.com , I was formerly with Clockwork Racing Engines... I go by several names on the forums, Nitrojedi being one of them, sometimes Maximo.... Anyways I have been running nitro since 1984 and over the years become very proficient at tuning and have developed somewhat of of my system that works extremely well for short needle carbs like the LRP has... I promote tuning by sound over tuning by temperature and often times I don't even bother to use a temp gun... Once you learn what to listen for there is no better way to tune then by sound, it is without question the most accurate and consistent method.... When train yourself to listen to the engine you will find that the sounds it makes never lie, a lean engine will always sound like a lean engine no matter what the temp says..and if a engine doesn't sound lean then it isn't lean.......doesn't matter if your temp gun is telling you the engine is 400 degrees, if the engine sounds proper then it is proper.... a overheating or over lean engine will have telltale sounds that always will be present no matter what...there is no way to make a lean engine sound rich and no way to make a rich engine sound lean
So first and foremost is you need to set your idle gap size as well as make sure your linkage is functioning correctly........When I say functioning correctly I mean that when your radio is at neutral your throttle slide is closed 100%, with no further possible movement....It then has to pass the throttle down test..that where you hold full throttle then let go of the trigger, the throttle slide needs to snap shut 100%...it cannot hang open even the tiniest amount...this is non negotiable, if your linkage is not closing 100% during this test you will never be able to properly tune your engine.. So this means hold full throttle, let off the trigger....then check your slide and try to push to closed further, if you can closer it further then your linkage is hanging open.... i CANNOT STRESS TO YOU ENOUGH THE IMPORTANCE OF A PROPERLY FUNCTIONING THROTTLE LINKAGE !!!! YOUR LINKAGE MUST BE CLOSING 100% WHEN YOUR TRIGGER IS AT NEUTRAL !!!!! Do not rely on using your brakes to close the throttle slide, it has to do it at neutral with no further movement when you hit the brakes..... Also its a good idea to have some deadband on your throttle slides, meaning your throttle servo has some free play before it opens the carb slide...If your dont have any free play your throttle can get feathered opened by the servo twitching... SO always be sure there is free play in the linkage when at neutral...
So once we know your linkage is working and snapping itself *censored* we want to set a 0.5 mm idle gap...0.5 mm is the thickness of a exacto blade... if you have calipers measure a piece of wire or a needle or pin and use that as a feeler gauge to set the gap..if not look at the thickness of the X-Acto blade and use it as a guide to set your idle gap.... Even use a feeler gauge to test to make sure your linkage closes correctly...this here is without question the #1 reason most guys fail at tuning a nitro..their throttle slides are not operating perfectly and they have to large of a idle gap..... these 2 critical things are the #1 overlooked issue and the source of 1000's of phantom air leaks.......I cannot stress enought, make sure you have a 0.5 mm idle gap and that your throttle is operating correctly ! till these 2 things are absolutely perfect we cannot properly tune your engine, no ifs ands or butts about it ! your wasting your time adjusting the engines needles till you know for sure these 2 areas are correct !
So lets talk about tune shifting and how heat affects the engines tune...Many tuning guides make no mention of this and its also a huge source of tuning issues.... These engines go thru a massive tune shift as they warm up, and the hotter they get the leaner they get, as well not only that but the harder you run them the leaner they get.. A good race engine will take 10 minutes of hard driving on a track to become thermally stable and for the tune to stabilize, up until that point the tune continually shifts leaner and leaner... When first fired a properly tuned engine will be sputter rich often with a very high idle and often want to stall easily... However as you continue running the enegine the idle will start to stabilize and as you get the engine on the ground and under load you will see the tune slowly start to clear up, and the longer you run it the better and better the tune becomes, till after roughly 10 hard minutes you will have the tune right back to where you left it the day before when you tuned it.... As i say the tune shift these engines will go thru is massive, from initial fire up to final hot tune you are talking a huge shift in engine mixture....l see soo many guys tuning their engines too soon and end up with a overly lean engine once everything heat saturates...... On a race track how hard a engine is run determines the ideal needle settings... Meaning I can set the needles perfectly for a average racer and he could race all day with a perfect tune..but if i gave the same car to a faster driver the tune would very quickly become too lean as the engine is being worked harder with the faster racer.......... this holds true for your MT's...meaning the perfect tune may vary depending on what your doing with the truck and how hard you are running it..... Wide open top end runs in heavy grass is going to want a much richer needle position then popping short wheelies in your front yard...So understand that the tune is going to move around on you and thats its perfectly normal....... what your going to need to do is learn to listen to the engine and make the appropriate adjustments..... And truly once you know what to listen for its super simple to tune these engines !!!! I mean it, its really really really simple !
Idle speed ! that's right, that's what we use to tune the engine, we listen to its idle speed both when we let off the throttle as well as its idle speed after sitting still for several specific time tests...... A lean engine will always, and I mean always want to high idle ... you will do a top end pass and when you let off the trigger the engine will carry RPM before it drops down, in severe cases it will make Chewbacka sounds...What you want to happen is for the engine to drop down to idle the instant you let off the trigger, then sit at a steady idle for 1-2 seconds then to drop a slower slightly lopey idle, relaxed and almost like a Harley Davidson...A lean idle will sound like a buzzing bee, it will be steady and buzzy and have no lope to it, very not sound relaxed..... Now if your linkage is hanging open or your idle gap is too big it can simulate the lean buzzy sound....this si why soo many guys get their needles all mixxed up, as their linkage and idle gap issues are creating a false lean ( well it is actually lean due to too much air ) ................. So As I say listen to what the engine does when you let off trigger, if it carries RPM your HSN is getting too lean ( or your idle gap is is still too open ).............
On these carbs preset a 0.5 mm idle gap..use the LSN solely as a idle mixture control..meaning do not use the LSN to adjust the engines low speed performance...the LSN is to be treated only as a way to adjust the engines fuel mixture while at idle....nothing else, All performance tuning is to be done using the HSN.... if you have a rich bog out of the corner lean the HSN, if you have a lean bog off the line fatten the HSN.....do not whatever you do use the LSN for anything but idle mixture control !
Now when at idle you want the engine to have a lope to to it, not almost stalling, but with a definite and audible miss ... you want it to slowly load up the longer it idles , meaning the longer it idles the lower and lower the idle gets, eventually tot he point it will stall out, however the longer it can sit low and slow ans still stay running the better...a lean LSN Will never allow this to happen..if the LSN is lean the engine will always have a steady buzzy idle and will not load up just sitting there idling.... when I tune a engine I continually check the idle, how it idles, how it idles down and how long it takes to load up........ Always listening for a fast idle down to a slow steady idle then a quick transition down to a slower lopey idle............... A lean engine will never be able to properly idle down..if the HSN is too lean it will carry RPM and if the LSN is too lean the idle will stay high and buzzy............ most videos I see online have a high buzzy lean idle......
So when I tune I baseline a 0.5 mm idle gap, I fire the engine, adjust the LSN to get a reasonable starting point for idle speed, then I fatten the top end till she sputters and then run by run slowly lean it down..little by little I lean down the top end always double checking my idle down then idle speed.... as I approach the engines sweet spot I make finer and finer adjustments, till the point I am only moving the needle a hair, like 1/48th of a turn.... when your near the sweet spot a 1 hour movement is too much..... as the closer you are the sweet spot the more sensitive the needles become.... So I basically lean my HSN till I start to notice the idle hanging when I let off, then I slowly fatten it back up till it goes away.... I do run after run after run always checking to make sure the engine idles down correctly and steps down to the correct idle stages..... it never lies, if the engine idles down cleanly then steps to a low slow idle you are not lean, no matter what the temp gun says..and visa versa, if your idle hangs and your engine does not step down you are lean, no matter what your temp gun says.....
Once you hae your tune set to where you think its close start doing some tests...first test is to do a wide open pass, bring the car to a abrupt stop..let the engine idle down to its second stage loping idle, then as soon is you hear it step down crack full throttle....If your are lean the engine will give you a lean bog right here... So if you get a lean bog fatten the HSN....retry the test till you can do a rapid throttle pull from a fast top off wide open............. then do this same test but doing a 3 count, then the same test with a 6 count, then a 10 count........ Once you are fully heated up you would like to see a slight loadup when you allow for a 6-10 second stop... not anywhere near enough to stall the engine, but a slight gurgle with extra smoke cloud is what we are after..........
So this is really it..listen to how the engine idles down..a properly tuned engine will idle down instantly, then quickly step from a smooth slow idle down to a slightly slower lopey idle...a lean HSN engine will always carry RPM and will want to idle high and idle will stay buzzy if the LSN is too lean....
Anyways coffee break and time to watch some TV..hopefully i dont have to many spelling issues
30% tunes easier then 20% runs cooler
lower oil tunes easier then higher oil, runs cooler and prefers a richer mixture..
I run 30/7 and it has a huge tuning window and can be run much richer then a fuel that is 20/14 , this is why the 30/7 fuel ends up performing much better and still protecting better then the 20/14...to get the 20/14 to run proper and crispy it needs to be run much leaner with a much hotter burn then what the 30/7 needs......I know this is backwards to common knowledge but is indeed accurate...

Listen to tune on this engine here for reference

https://www.youtube.com/watch?v=WgJR87HcRTE

1QwkSport2.5r

Oh here we go again....

supertib

sadly I got here too late and this fellow has already destroyed his engine !

Anthoop

Hehe...good to have you back Neal...always fun!

Shockingly I have been tuning my engines incorrectly for all these years...yet they still perform and last appropriately....I wonder if there is more than one way to skin a cat? :P

Personally I always start with a 1mm idle gap,,,and adjust the HSN first....and then the LSN and gap in conjunction......once the throttle is fully open then the gap/LSN has no bearing on the HSN setting...so yes...listen to the engine and how it performs...but set the HSN first and then leave it alone...once the engine performs correctly at WOT/high rpm then the HSN is set.....simples.

The setting of the LSN/gap is simply done with a series of acceleration tests/adjustments...


...but hey you should really know all this...and know how primitive the carbs are...and different locations affect the air....
I guess if we had EFI then the slide gap would be 0.5mm regardless though?...... lol

The shame is that many people look at you as an arrogant person Neal...I do not see you like that at all.