bikeordie092

ok, so i have tuned and tuned and tuned... oh did i mention that i have tuned on this motor? it has this weird idle, hard to describe, so i took a video! please watch it and see if you have any idea as to what the problem is?

[youtube]http://www.youtube.com/watch?v=tG3agkmiTvA[/youtube]

JohnP2

What sort of engine is that? How does it run? Does it bog at idle like that once it is fully heated up? Do the RMP change when you apply the brakes? What is the carb gap size?

Sorry for so many questions, just curious as to what has been ruled out. Thanks

bikeordie092

its an ofna force .26, when it actually runs it runs great, but that is usually only for about 5-10 minutes, then it wont run well at all. like it wont run much above idle, it just wont open up... and the warmer it gets, the worse it gets, it doesnt seem like its bogging down but that its jumping up... idk the size of the gap exactly, i adjust it accordingly when needed...

JohnP2

Hmmm...perhaps it is too lean. You noted you've "tuned and tuned. Below is a clip I got off the InformationSuper Highway, fromEd Bridges (sorry Neal,I'm sure you respect him anyway).I subscribe to much of this when I tune my engines.

Performance Tuning Guide
There are many ways to tune a nitro engine but I figure this is the most simple way to do it. This technique is for a fully broken in engine that is ready for a full performance tune. This tuning procedure will set your needles to where they need to be for optimum performance, the engine will tell you all you need to know.

For this method to work the engine has to be at running temperature (or as close to it as possible) as well as having the standard 1mm gap for the carburetor opening.

High Speed Needle
Pull a full throttle pass a couple of times and listen to what the engine does when you let off the throttle. If the it drops right to idle, the HSN is either good or on the rich side. At this point you can lean the HSN in 1/12 turn increments until the idle seems to hang a little after a full throttle pass. If it starts to idle high after a pass it is just on the lean side of a perfect tune. Back the HSN out 1/12 turn at a time after a wot pass until the engine drops right to idle after a pass. Now your HSN is set.

An explanation to what is happening is simple - if your HSN is too lean, after a full throttle pass when you let off the throttle the engine is still lean causing the idle to hang and idle high until the LSN has a chance to take over and meter the right amount of fuel to bring the idle down to normal running speed (given the LSN is set correctly).

If the opposite happens, after a full throttle pass when you let off the throttle it drops to a good idle right away and then starts to idle back up too high, this is a sign that the LSN is too lean. If it comes off full throttle with a good tune and will drop RPM nicely then the HSN is metering the fuel properly but once it hits idle the LSN being too lean will quickly take over causing the RPM to go back up.

Low Speed Needle
Most of this setting was explained above but there are a few little tricks you can use to make sure the LSN is adjusted perfectly. We all know that you don't tune for temperatures, but a temperature gun is very handy for this part. After some full throttle passes with the engine good and warm, bring it in and let it sit for about 10 seconds. At this point take your temperature gauge and hold it as steady as possible on the head, what you want to see is the temp dropping a degree every 4-5 seconds. You want the temp to drop very slightly at idle because when your off throttle the engine should be cooling, if not, the temps will keep pushing higher during on and off throttle running and will cause temperature issues.

This is how I do it and I have tuned a lot of engines for people, whether bashing or racing. I have seen across the board from beginners to veterans that when they hear the high idle after a pull, the first thing they go for is the LSN when in fact it is the HSN causing the issue.

1QwkSport2.5r

It's hard to tell, but it sounds a bit lean on the needle, and possibly a noisy bearing.

bikeordie092

it was lean, i kept thinking it was rich so i kept leaning it out and finally it got too lean and quit lol... i tuned a little on it earlier and got it really close to how i want it.

JohnP2

Man, it happens. I've tuned probably 12 new engines (and re-tuned too many different one to count), My last new one (OS .25 xz) I had too lean even though it was showing some signs of being too rich - so I actually learned something on that one!

When all else fails, just go back to stock settings and start over.

Glad you got it worked out. Remember, there is a never a perfect tune (or at least I've not found it). ;-)

JoeMaxx

Where I live it is always a new tuning day

I spend the firsttank of each time I run my nitros tuning then find the tune for the day. Some days I have to make as much as a 1/2 turn rich or lean before I get it right for the day. Other days it is just a fine tune with a 1/8 or 1/4 turn. I live in high altitude and the days between running can vary from 5 degrees to 20 degrees on outdoor temps. Humidity is always low but can spike after a rainy day. Most days 20 to 30 percent humidity but after a rain can jump to 80 percent.

Well I have alot of fun tuning for the days I run in spring and fall but summer time is fairly consistant.

An engine Temp gauge is what I use most of the time to assist with these radical changes in weather.I never use a temp guage to tune the engine but use it as a reference point whether the engine is too lean or rich during the first tank. Then when I know I am in the zone between 220 degrees to 270 degrees on the engine temps I than fine tune it for performance of that day because of weather conditions.

Sound,performance and smoke trail is what I use each time out. Lots of smoke from the pipe keeps the engineprotected from too lean of a fuel mixture but too much will run too rich than spit too much oil and fuel out of the exhaust.

As JohnP says there is no perfect tune and an engine will run different most of the time.

bikeordie092

exactly lol... thats why i said "really close to how i want it" instead of perfect haha

bikeordie092

right now, thats how it is here in tn with the weather jumping from 25-70 every other day lol

JoeMaxx

I used to live in Georgia so I know even worse in Colorado. R/Cs are parked for 5 months out of the year. Today when I drove into work 3 degrees outside by noon it was 50 degrees.

bikeordie092

lol here weve been having days where its 70 for the high and then the next its 31 or 32 for the high.. crazy weather.. everyone always says "if you dont like the weather, stick around for 5 minutes, itll change."

JohnP2

NE Texas is the same way. Snow one day, 70 degrees the next day. Of course from May-October, it's just HOT. I always ask Andrew "why do we need weather men? Just say 'it's hot today, it will be hot tomorrow and for the rest of the month'" ;-) One day I'm going to train a parrot to do this, and then pit him up against the areas top Meteorologists for accuracy.

But I digress....I think JoeMaxx nailed it. Just go by sight and sound (with a little check of the temp guage to validate your thoughts), and you'll be fine. I've also learned every engine is different. As long as it runs fine (and you are seeing that smoke). you'll have no issues.

supertib

How big is your idle gap ? You cannot properly tune a engine if the idle gap is too big or too small....it is actually one of the most important needles to adjust...................Anything over a 0.7 mm idle gap is too big to get a proper tune...... So stop chasing your needles and measure your idle gap...if your over .7 mm there is your issue !

Anthoop

Surely you can alter the amount of fuel entering to be correct for any (static) size gap? Whether the gap is so large that the correct mixture will cause a idle speed high enough to engage the clutch is another thing.

supertib

Well you can adjust the fuel to give a proper mixture of course, but that still wont help this guys issues any....You cant properly tune a nitro engine around a large idle gap......it simply does not work well at all............a 1 mm gap is too big and will cause all sorts of weird idle issues........

Anthoop

Seems strange to me. I would of thought the amount of air we let in will govern the RPM and the amount of fuel we provide will be as close to correct as possible throughout the entire travel of the throttle slide?
Would the 0.7mm rule apply to every engine and any weather/alltitude conditions?

JohnP2

Neal, one question. I've always heard that you should get the venturi gap as small as you can without affecting performance (i.e. choking).

Is it possible to set your gap TOO small (even though it does not choke)?

Thanks!

supertib

we are not talking about mixture...we are talking about having the right idle gap size...the old school advice of running a 1mm gap is wrong and results in a engine that wont run correctly, especially in a race environment...........You cant have a large idle gap and compensate with enriching the LSN mixture.....well you can, but the engine wont run right....................Idle gap is the most critical needle to set....as the entire tune of the engine is based off the idle gap.....If the idle gap is off, the rest of the needles will be off.......Anyone who says to preset the idle gap to one position then adjust the LSN day to day to compensate is wrong........

supertib

yes it is.... too small of a idle gap will result in a overly lean LSN and a overly rich HSN to compensate......... I see this all the time with guys who insist on tuning on the starterbox................ they tune the LSN around a tiny idle gap and then fatten up the HSN to prevent the bogging.....

Anthoop

I am most definately not saying anyone should set the idle gap to a specific setting...and that is what I am getting at.
I will try to ask the question another way:-
We adjust the position of the needle that moves with the slide, if we get the needle in the correct position when the slide gap is 0.7 why would opening the slide to 1mm then make the needle incorrect?

supertib

1mm is quite large..I am not sure of any engine or condition that would require a engine to have such a large idle gap..........Usually engines like a idle gap of roughly .5 mm...........Now of course at high altitude and a possibly dragging bearing a engine may require a 1 mm idle gap....... However that is not normal conditions............The most common mistakes I see people make when tuning is not having the right sized idle gap for the conditions.....

Also to add, the OP's symptoms 100% match having a too large idle gap......so this is why I am telling him to reduce his gap instead of fattening the needle like you are suggesting....

Anthoop

I am not suggesting anyone should reduce gap/fatten nor lean needles.
I am simply asking why the LSN would need to be set differently pertaining to the gap?
If the position of the needle is correct when the slide is at 0.7 then it will be in the correct position when we open the slide to 1.0...only the RPM will change?

supertib

day to day usually the first needle I touch is the idle gap...........many times you can tweak the idle gap and not touch the needles....of course not always....

JohnP2

I was the one who suggested he fatten his gap, merely to rule out having too small of a gap (and we ALL see that too often). However. this has been a FASCINATING thread concerning idle gap I'm spendin my Saturday night talking idle gap on an Internet forum. I am proudly hooked! ;-) We always hear .5mm can be too small and 1.0mm too big, so I agree that sounds ideal. .7mm sounds about right (at worst the best starting point). In thinking about it, most of my best tunes had ~.7mm gap.

Anthoop (and I LOVE your avatar by the way!) you posed some great questions. If i'm to deduce this thread, it's that you work your mixture around the idle-stop gap. i.e., that is what you start with and go from there. Only assume this is the first entry way of air, and you stabilize that and work in the fule mixture.