Hey everyone.
I bought a used TT .61 gp. It runs okay. it has the air bleed style carb, and i cannot get to have a good idle and high end. I can get a good high end or a good idle, but not both. it seems as if adjusting the air bleed screw affects both the high end and low end performance. i am using an apc 12 x 6 prop with coolpower 15% nitro fuel. Any ideas? the muffler leaks a little bit of fuel in the middle where the front part attaches to the back part of it.

If i tune it to a good low idle where i can tilt it up 15 degrees and it wont die, once i run it all the way up, it is way too rich. then i have to lean out the air bleed screw some, and it no longer passes the tilt up test. i am all out of ideas.

Cruel Power and a bushing engine like the GP 61 are never going to get along in the long term. Put some castor oil in the fuel.

If they don't have castor oil at the hobby shop, get some at the drug store. About 4 oz in Cool Power or 2 oz in Omega.


Put the air bleed screw half way across the air hole. Run engine at wide open throttle and adjust high speed needle.

Then idle the engine and adjust the air bleed without touching the high speed needle.

These carbs are normally very trouble free

I tried that, I start it, then let go wide open and find the fastest rpm setting, then richen it about 200-300 rpms. THen i go down to adjust the low idle airbleed screw, with the engine still running, once i get it where it can idle down to about 4000 rpms, it will pass the 15 degree tilt up test. now that i set the high speed needle and have it idling good, it would seem as though i just tuned it out. BUT as now that it is idling good, as soon as a run it up to the high ends, it is running WAY to rich.

I set the high speed needle when the air bleed screw is about half covering the hole. when i idle it with the high speeds running GREAT, it will idle ON LEVEL GROUND forever, but as soon as i tilt it up, it runs rough and shuts off. to correct this, i have to screw the air bleed in about 1 full turn so that there is not as much air on the idles. BUT for some reason on this engine the air bleed screw also effects the high ends, becasue with the air bleed screw turned in, on the top ends, it is very rich, not enough air, so i have to lean out the high speeds, which then means on the low ends not enough fuel and too much air.

If i back the air bleed screw out a little bit so that is only covering about 1/4 th of the hole, i can get to idle good and the high speeds are really good, but in this state of tune, it will ONLY idle on level ground. when i tilt it up, it speeds up about 300 rpms and dies. this would normally indicate not enought fuel, so i close the air bleed screw some and start the whole process over.

there is no middle ground that i can find. correction on the fuel it is the pink 15% omega

If you tilt it up while idling and the engine speeds up 300 rpm before dying, The idle mixture was rich.

You may have a tank problem?

People rarely check the idle with a tilt up test. They only do the tilt up test with the engine at high speed.

if i tilt it up while idling and it dies it is rich? rich in air or fuel????? because to make pass the test, i have to close the air bleed screw in so that there is less air in the carb. but that always messes up the high ends.

So if i get it to where it has great high ends and doesn't increase rpms when it is tilted up at full throttle, and it will idle on level ground forever, it should be okay? i always was told to tilt it at full throttle and idle. if it does increase rpms when tilted up at full throttle, is that bad?

the fuel tank is a hayes 11 0z. tank. it sits right behind the firewall with the fuel outlet nipple slightly below the centerline of the carb, no more than 1/4 th of an inch. If tuned to run good at high ends, it runs great in all aspects, right side up or upside down.

by the way, the airplane is a hangar 9 .46 twist.

The H9 Twist planes are great flyers.

Instead of doing the tilt test at idle . . . . Tune your top end properly and do your tilt test. If the engine speeds up a little on the tilt test it is OK. --- Then tune your idle with the air bleed screw. Tune the engine for best idle . . . . Then check your transition back to high speed. If the engine immediately quits, the idle is too lean. If the engine stubles along for a while and eventually picks up and runs correctly, the idle is rich.

"Rich in fuel"

On most air bleed carburetors, the idle mixture circuit only works at a very low speed. It has no effect at higher speeds. The air bleed hole is covered up by the throttle barrel at greater openings than idle..

You should be able to get the engine to idle in the 2,000 - 3,000 range.

Matt,


Only a grossly misinformed, or uninformed person would use all-synthetic lube fuel in this type of engine.

'CruelPower' contains only 17% all-synthetic oil, which is too little and not good enough for this bronze bushing bearing, ABN engine.

Your engine will eventually perform 'user assisted' self destruction...

Who was it (...) that told you to use CoolPower in this engine???



You must use fuel that contains:

1. At least 20% oil.

2. At least half of the oil, preferably more, must be castor oil. All castor is even better.


There are commercially available fuels that don't cost very much and fit the bill.

PowerMaster GMA fuels contain 22% 50/50 blend of castor and synthetic oils and either 5%, or 10% nitro.
Sig Champion fuels contain 20% 50/50 blend of castor and synthetic oils with various nitro percentages.

There are similar blends available from nearly all model fuel manufacturers.

This engine doesn't need any more nitro than 5-10% max and you pay less for it and use less of it.


...I second what Jim (w8ye) wrote and put more emphasis on the fuel blend.

Matt,


Not only the above, but fuel with a lot of castor oil will also make your engine run better and will help in solving the problem that convinced you to start this thread...


Ask me how I know.

...Personal experience.

The nose-up test at idle is a bit pointless -- since your plane will be incapable of maintaining a nose-up attitude for more than a very short period of time with the engine idling anyway -- it will stall and the nose will drop.

The best thing that ever happened to the throttling on my TT61GP was the mousse-can muffler I now use. Man, it's so sharp you'd swear it was a twin-needle carb.

With the standard muffler my 61GP would tend to load up at idle (even with the air bleed as open as practical) but with the mousse can fitted it transitions almost as fast as the throttle servo can move, even after extended idling. It also puts out a heap more power and is quieter with a nice raspy crackle to the exhaust note.

The 42GP and 61GP are two TT engines that are vastly under-rated as sport motors. I've never had to replace a bearing in either :-)

But, as Dar and others have said, you *must* use castor oil in the fuel. If you don't, you'll wear out the busing the crankshaft runs in and that'll produce *real* problems because it'll suck air through the front and it'll also wear out the big-end of your conrod which will effectively mess with your engine's compression ratio and timing just a little.

My GP61 is now a couple of years old and gets *thrashed* on my racing trainer. Running a hi-castor fuel means that its' still so unworn, even after more than 10 gallons, my electric starter won't even turn it over on a cold day due to the piston/liner pinch.

about the castor fuel......... i dont know how long this engine has been around or what fuel was running in it before i bought it. is it good that my starter, any time, sometime struggles to turn it over. when i stick the starter on the spinner, the starter is actually slipping on the spinner. it will turn it over if i put the engine at the bottom of the compression cycle, (bottom i think, just the most travel on the prop before it reaches the next compression), and stick it on, it will start it.

i will change the fuel and see what happens

The starter's ability (or lack thereof) is normal for this size engine.

Enjoy

Jim

I should put about 2 oz. of pure casor oil into the gallon fuel bottle i have?

I was wrong, the fuel i have is the pink Omega 15%

i think i got it almost tuned out last night, i tuned the high ends to where it slightly increases rpms on the high ends, in this setting, i can get to idle down to 4,300 rpms. not as low as i would like, but i will work. it still when i tilt it up while idling, the rpms increase and then i eventually (about 10-15 seconds) flames out.

Matt,


First of all, an engine will never have to pull the fuel up to its carburettor, while it is idling.

You are checking the engine in an unrealistic condition. Nose-straight-up test is only done while the engine is running full-bore, or in a 3-D plane, when the engine is running in hovering throttle setting...

Your engine will never be very good for a 3-D plane, so just ignore this statement and adjust the idle mixture, with the model in level attitude.

First of all, back off the idle-stop screw in the carburettor, so the throttle can close fully. Now,close the throttle until the engine is running below 3,000 RPM and use the 'pinch test'.

If you pinch the fuel-line, the RPM should increase momentarily and the engine should quit within 1-2 seconds.

If the engine quits almost immediately, it is too lean; close the air-bleed screw 1/4 turn and try again.

If the engine runs longer than 2 seconds before quitting, it is too rich; open the air-bleed screw 1/4 turn and try again.


If the air-bleed screw has unmasked the entire air-bleed hole, you must use less nitro and this will allow the high-speed needle to be closed further, or you will have to disassemble the carburettor and drill the air-bleed hole one size larger.

After getting the right 'quit-time', check the transition from idle to full power. This should be done with the model level and at servo-speed - not whacking it open as fast as your fingers can do it, just as fast as your throttle servo will do it.

If it 'chokes' quietly and dies (or chokes momentarily and advances afterward), it is too lean. If it hesitates, sputters and then advances over a couple of seconds (or dies), it is too rich. Make these adjustments smaller than before (1/8th of a turn).


Second, a reciprocating internal-combustion engine does not flame-out... This is a very descriptive term, reserved for jet engines only. Don't over-estimate yourself...
Your engine will only quit, die, shut-down, cut-out, conk-out, or whatever, but will not flame-out. Look elsewhere in this forum...

4300 rpm is too high to be able to land the airplane. You need to be below 3,000.

2 oz castor is about right for Omega.

Matt,


4 oz. of castor oil will bring your gallon of Omega fuel to 20% total oil...
Yet, for this engine you would want at least 50% of that oil to be castor... These 4 oz. do come close, but no cigar...

For your next gallon of fuel, shop elsewhere, unless your LHS can bring you the fuel your engine needs; like Sig Champion, or PM GMA.

Thanks i put the castor in the fuel...... it helped some but i was still unable to get it to run right.

I noticed that there was a significant amount of fuel/oil residue on the bottom of the crankcase. I unmounted the engine an started the tightening all the screws process. I found that the two bottom screws on the back plate were loose. I tightened them a good 3 turns before they were again tight. I think air might have been leaking in through the back plate, which is why i think i found it so difficult to tune. I also drilled the air bleed hole one size larger.

Between these three things, the fuel, backplate, and bigger air bleed hole,...... I was able to tune out the engine in 20 minutes!!! When i was drilling the air bleed hole, i noticed some residue in the original hole..... I dont know which of these things fixed it, but it now idles at 3000 rpms, passes the tilt up test on both idle and full throttle!!!!
It is FINALLY in tune.

Thanks to everyone for all of the advice!!!! :-)

I have heard that term used by the gurus down at the club field before....... being new to the hobby, i assumed that was the correct term, sorry about that, now i can tell the club gurus they are wrong :-) with the use of that term. I would have asked them to tune the engine for me,, but i am not a member, and have only flown there 3 times as a guest.

I am still confused about the fuel though, i went in to my LHS today and asked the guy what fuel i should be using on my motor, believe it or not, he said i should be using 20% nitro fuel (all they had in 20% was cool power)...... i did pick up a quart of 10% sig champion fuel. havent tried it yet, but i will once my gallon of omega runs out.

again thanks everyone.

The guy in the hobby shop is going to try to SELL YOU SOMETHING. The 20% nitro costs more and he gets rid of it. If it tears up your engine, he can sell you a new engine?

I doubt if he's ever used a bushing engine? Or even knows which ones have bushings and which ones have ball bearings? Or knows that they need more oil in the fuel?

Back in the "old days" almost all model engines had bronze main bearings and also had cast iron pistons. Fox Super Fuel was 5% nitro and 25% oil back then.

Don't use Cool Power in a Thunder Tiger GP series engine. I don't use it in anything. I like the fuels with a blend of castor and synthetic oils for everything. However, I do not own any plain bearing engines anymore.

However, you can put caster oil in Cool Power fuel.

You can buy castor oil (Usually the Sig brand) in quart bottles at the better hobby shops. You can also buy Morgan's Cool power oil and Omega oils. There is also the Klotz brand of oil. You can also go to the discount store and buy castor oil in little 2 oz and 4 oz bottles but it usually costs you more money than the hobby shop kind unless the hobby shop is trying to charge you too much.

Hey guys, I need some help with the same engine. I just read this post before lunch and during lunch I went and picked up a gallon, of 5% nitro with 11% syn and 11% castor. Should this fuel be sufficient? Also, I need an idea of where to start with the high speed needle, I was going to start out at 2.5 turns an d work from there, but if anyone has a better place to start out at then that would be great.

I kind of inherited the engine along with the Senior Telemaster that it was mounted in so I do not know the history on it, but I do not believe that it has been run much. It had a 13-6 MA prop on it but at the recommendation of the LHS I bought a 12-6. Any other suggestions? Thanks.

Joey,


The fuel you have sounds like PowerMaster GMA 5%.

It is a good fuel for this engine.

The Senior Telemaster is a pretty slow flying plane.
With a 13x6 prop you would have the engine spinning more slowly and making somewhat more static and low-speed thrust.

It is better for the big Telemaster, than a 12x6.
The smaller prop, due to spinning faster, has a pitch-speed ~15% higher and the model may dive a bit faster, but will lose speed when you try to climb.

The bigger prop will also make the take-off run shorter.

Explain please. 15% faster requires 32.25% more thrust.

Brian,


I was talking about pitch-speed.
When a prop with the same pitch is spinning 15% faster, the pitch-speed is increased by the same amount...

Naah! The drag produced by the Telemaster will not allow the plane to get close to pitch-speed.

It many be like the PBY Catalina; i.e., take-off at 90, cruise at 90, land at 90...

I'll make the correction.

Fair enough...I can accept that the original "level flight speed" was a typo

Brian,


Not exactly a typo...

The 12x6 prop will be spinning faster and will output more HP than the 13x6.
And since speed, thrust and HP are related (HP is a multiplication of thrust and speed, stated in the correct units), the faster spinning 12x6 prop will make more thrust at higher flight speed, in turn enabling an even higher flight speed, until the equation becomes one <GGG>.

In static conditions and lower flight speeds, the larger diameter prop will have more thrust, because of its lower disk-loading and thus higher efficiency.

A 12x6 is not the wrong prop. It is just that in the typical flight profile of the Senior Telemaster, higher static and low-speed thrust levels are more important than high-speed thrust; thus making the 13x6 a more appropriate prop.

Thanks! I got her running last night, seems to do pretty well. I think that it should fly the telemaster just fine, and I did find a 13-6 sitting around so I will try both. Might have the airplane finished this weekend.