hi there
i have a TTgp42,once started it goes ok but when i throttle up half way its ok but as soon as i try full throttle the engine just throttles down to idle then stops
it dose it every time.i stripped it down and cleaned it, back plate gasket is ok but the carb gasket was not so i used .25mm gasket paper but just done the same
thing so i tried grease proof oven paper and still the same,a lot of oil is also collecting in the fuel tank compartment,ive checked the fuel tank and is pressurised
ok i just cant get it to throttle up,air has to be getting in from somewhere, i can see bubbling in the carb so the engine is overheating as well it gets really hot,can
anyone help-regards kumkumking

Your first objective is to get the engine running slowly with the throttle wide open. Start the engine with the throttle wide-open and the needle valve open just barely enough for the engine to run slowly. It will be a blubbering low-speed 4-stroke mode. Now screw-in the needle valve until the engine speeds-up. Keep doing this until you reach the point where the engine starts breaking into the high-speed 2 stroke mode. Stop adjusting the needle valve at this point. When the plane starts flying there will be less load on the engine and it will break into the 2 stroke mode. This is the adjustment you want it when it is in the air. On the ground you want the throttle wide open and the engine alternating between a slower blubbering speed and breaking into a higher speed scream. Now throttle back to idle. You are now ready for take off

ok thanks very much i will give it a try tomorrow and hope it gets rid of the engine compression problem

Is the oil in the tank compartment a light or dark color?

its not light or dark its like a medium grey colour,i think the prop is blowing it through the holes in the fire wall but where the oil is coming from
i dont know but its not from the carb seal,the engine is fitted upside down,im more concerned that i cant get the engine to throttle up as it just
throttles down to idle itself when the throttle is fully open,is the oil a sign that its escaping from some where it shouldnt,ive checked the needle
assembly and its ok.

Maybe your fuel tank has a leak? Leaving the oil in the fuel compartment. Plus less pressure in the tank to supply fuel to the engine.

Being that the oil is a grayish color to me means that it is exhaust residue. I would however seal the fuel tank compartment if not already done and attempt to keep the residue from getting in. Try tuning the engine with the airplane upside down. More details such as prop size, fuel brand, nitro content and age of fuel, glow plug make and number. Are you running muffler pressure? The more we know about your setup the better we can help.

A change in starting procedure will not get rid of a compression problem.... sorry. If you have inadequate compression pressure, confirmed by measurement, and if you want to correct it, mechanical alterations to the engine, will have to be made. Or, it is time for a new engine.

Bingo

no the fuel tank dosnt have a leak and is fully pressurised

thanks for that method it did work but once the engine stopped it wouldnt start again till it cooled down but i think your right
time for a new engine as the TT-gp42 is discontinued and hard to get parts for-kind regards kkk

Just for something to think about, I've seen engines with worn bearings leak through the bearings with similar results:

• The grey color of the oil was from minute metal particles in the fuel
• The hard to get to run was due to running lean due to air being pulled through the bearing, resulting in a hard to adjust needle

The one thing no one has mentioned yet has to do with the outside of the engine. Is there fuel or oily residue on the outside of the engine anywhere after it was running?

Good point about bearings. With a gray oil residue it’s either burnt fuel or as Hydro states it could be from metal particles . Typically aluminum. This could be caused by the bearings being loose enough for the crank to rub the front housing or it could be a poor fit between the case and muffler.

The compression issue I doubt is a lack of compression. Remember the engine is inverted. Too much fuel in the cylinder will keep it from turning over when inverted. This is why I suggested to tune the engine with the airplane upside down. The situation gets much worse if while upright the fuel tank center is higher then the needle valve. The tank will naturally siphon into the carb and easily flood the engine. One of the reasons why I avoid inverted installations with a 2 stroke.

yes speed i think you are right about it being exhaust residue as the bottom of the compartment is open a bit so thanks for that but it still dies away at
full throttle,i tried lees suggestion and it did work but after stopping it wouldnt start again until it cooled down but when i did start it again it still did the
same thing die away at full throttle.my prop is a master airscrew 11x6 as for the fuel what i do is use liquid gold 2000 pro synth 15% nitro 1 gallon and
split that gallon in half and mix it with a half gallon of methanol and castor oil so now i have half synthetic half castor with a 7.5% nitro content,the fuel
is only 2 weeks old ive tried the fastrax No5 platinum the os No8 and No 3 glow plugs,i dont know what you mean by running muffler pressure but i do
have a tube from the tank to the muffler

yes the needle valve is lower than the tank centre due to the engine being upside down

yes there is oil on the outside after runnin

Where is the oil?

• If there is oil forward of the carb, you're leaking through the bearings. The needle setting isn't going to matter since you're sucking air through the bearings every time the piston rises toward the head button. Conversely, every time the piston goes down, fuel is pushed through the bearings, pushing out metal dust with it. The way the engine is supposed to work is piston up, sucks in air and fuel through carb while piston down forces fuel and air though the passages and into the combustion chamber. I'd bet that you're not getting enough fuel due to a worn/leaking bearing. To find out, take your spinner and try to move it(and the crank shaft) sideways. If it moves at all, bearings are shot
• If it's around the head or rear of the cylinder, it's probably leaking between the engine and the exhaust. If that's the case, you're not getting as much tank pressure as you think and the engine is starving.

One other thing. Your engine uses an air bleed carb. If you're not used to setting one, it can cause you problems as well since it works differently than a high and low speed needle carb.
Something else just got me thinking. You are mixing in straight castor oil. Are you filtering it or just dumping it in? I'd remove the needle valve and see if it's gummed up with castor fibers

the oil is all over the engine but i see fuel spray coming from the carb as the engine is upside down so the prop sprays it all over
and there is no bearings in this engine its a gp42,no fibres on the needle or inside and the castor canister says ready filtered

Okay, it's a bushed engine. A set of worn bushings will give the same results. If it was mine, I'd pull the crank and look for wear on it and the bushings. A quality caliper or similar would be good to check for either being our of round.
I have an old OS 25FP that I'm going to put in a Kadet Jr in the not too distant future. Other than being smaller than your GP 42, it's basically the same engine. It's getting torn down and checked over before it goes in. If the bushing or crank aren't in good shape, it's getting a new 25LA bushed or 25FX bearing engine instead.

What brand of is the castor oil? It has to be a certain type of refinement to work as an engine lube. I would bet that the engine would run better with the straight 15% nitro all synthetic oil fuel. Aside from that I’m going to say that you may be running too lean on the high speed needle. I would start over with fresh fuel, adjust the air bleed screw so the the screw covers 1/2 the air bleed hole and the high speed needle 2.5 turns from closed. When closing the high speed needle don’t close it down tight as that will damage the carb. Try to adjust the engine with the airplane upside down. I doubt anything is worn out as it is new, the only thing that could be wrong with it is a bent connecting rod from turning it over with a starter when it has too much fuel in it. Is there any way to remount the engine upright? If there is regardless of how bad it may look I would highly suggest doing so. I’m going to be flying in an aerobatics competition for the next two days but I will try to keep an eye on the thread and reply if I am able. Cell service is spotty at times where I fly.

the brand is geronimo 100% natural cold pressed castor oil for use as hair,nails and body massage,im gonna turn the engine
round today and try it with the 15% nitro synthetic oil and see how i get on-thanks

Yep, the castor oil is not the correct refinement. It’s gumming up your engine. It may take a few runs to get the engine to clear out. Set the carburetor to described settings and slowly cycle back bod forth on the throttle. Throttle up until it threatens to die and then back off a bit. After a tank or two you should be able to get to full throttle and fine tune the high speed needle. You want to close the needle just enough to break into a nice clean 2 stroke tone.

hi speed,
you knocked the nail on the head,it was the fuel causing the problem, now its running ok on the synthetic fuel 15% nitro.
now i was using 5% before and it was running ok with that but what i want to do is mix my 15% fuel to make it 7.5% as i
have 4 gallons of it and 20 litres of methanol,so what would be the best castor oil to mix with it-regards kkk

I’m not a fan of castor oil at all. I use strictly synthetic in all my engines. The argument is that in the event of a lean engine run the castor oil gives better protection. My view is that there is a higher potential for a lean run using castor as it leaves deposits. Many fuel formulations contain both but the castor content is typically not more then 5%. So where does that leave you? My suggestion is that if you feel you need to cut your fuel is to order both Klotz synthetic oil and castor oil from Sig Manufacturing and mix your fuel so that you have an oil content of 20%, 15% synthetic and 5% castor.

well speed thank you very much for all your help on this,you certainly got to the bottom of my problem
and i will most certainly take your advice-most kind regards KKK