Hello all! I am having some problems I was hoping you more experienced motor heads could help me with. I am new to the hobby but I am familiar with the terminology and the basic operation of the engine. Here is the problem:

OS .40 LA
Sig kadet LT-40
Average outside temp 90 deg
Low humidity
About 1500 ft. elevation

On the first flight of the day the engine runs well until the tank is about 1/3 full. At 1/3 full the Engine dies. On subsequent flights the engine runs rough and does not produce the same amount of power as the first flight. It is also more prone to die before I get to the 1/3 full state. The amount of power it produces is pretty much unacceptable. It barley pulls my LT-40 around the patch and makes go-arounds a little scary. Another thing is that is seems worse when I don’t allow it to cool off between flights. Oh yeah, also when I place my finger over the carb and turn the prop to prime it, I notice a wet squish sound that I don't remember hearing before. It may have been there and I just wasn't listening. Also, when I look at the fuel lines after the engine dies they are full of fuel, but there are small bubles in the line.

Here is what I have done (not much): First I used my pump to be sure that the fuel could be drawn all the way to empty, which it can. Then I changed the tubing inside and out side of the tank anyway.

Could it be over heating? Bad fuel? Carb problems?

Here are some things I would try.

1) Change fuel tubing (sounds like you already did this)
2) Make sure you have good, fresh fuel
3) Make sure you have the tank positioned correctly (the lines coming out of the tank should be horizontal to the engine carb)
4) Make sure you don't have any air leaks (good seal on tank, good seal under carb, good seal at glo plug, good seal on backplate, etc.)
5) Make sure you have your engine running about 300 RPM's rich or peak

Now for the $75 "sure thing" fix. Buy a Thunder Tiger 46Pro and watch all your problems go away. The OS LA series is an underachiever. Just look through the threads in this forum. The TTPro is the best value in R/C 2-stroke engines - period.

Good luck

Check the head bolts. You may have run it hot a time or two and the bolts do stretch with the heat. The tip off is brown stuff around the head or on the head. Just had a new Magum .28XL and after the first two runs had a bunch or brown castor on the head. Wiped it off, tightened the head bolts (alot) and problem fixed.

Also, your description sounds suspiciously like a too lean setting that causes the engine to heat up and lose power as the flight goes on. Maybe that's why you need to let it cool down. What you can try is pulling the throttle back to 1/2 to 3/4 which causes (usually) a richer setting. When I'm losing power, its the first thing I do and the engine usually comes back in a half a minute or so.

Good luck!

What prop are you using?

After tightening the head bolts, see if it has any compression. You may have peeled the liner in it with that first lean run whereby it quit at 1/3 tank because it was too lean.

Good luck,

Jim

I checked the head bolts and they are all tight. Also, the wet squishy sound I mentioned is coming from the small hole in the carb next to the Idle mixture needle (I've never touched this needle). Is this normal?

Another thing is that my engine is covered with unspent fuel. More than I have noticed in the past.

How do I check for compression? Do I need a special tool? The prop (master airscrew 10x6) feels the same when I flip it over as it has in the past (after break-in).

Thank you all for your help so far. I appreciate your comments.

Jake C.

Do you have the fuel tank wrapped in foam? possible fuel foaming. Only my 2cents worth.

I have foam on the sides and top but not the bottom. Maybe I should put some under as well.

Jake C

filter your fuel mine is in the pump line try cleaning needle valve and carb where the fuel goes through if nothing works remove the head and ck the cyl for peeling look for brass at full th. quick pinch and release the fuel line adj the needle so you can hear the rpm increase 2 or 3 hundred ck all fuel lines for cracks hope this helps jack

Greetings all,

Well, I'm pretty sure I found the problem with the engine. I was tearing it down to check the sleeve and generally inspect it when I found a nice little crack in the case. I've applied JB weld to the crack and I am going to seal the back plate with high temp RTV. I am hoping that the JB weld is going to be sufficiently strong to hold up. It will be a nice experiment anyway. Here is a crude drawing of the crack. Maybe you all could give some input as to Whether or not you think JB weld is going to do the job. I applied it on the outside rather liberally and on the inside and back sealing surface I applied it in the crack and wiped away all of the excess.



Jake C.

Time to send that one back for a refill....

JB weld is good for the outside but will flake off on the inside and do a lot of bad things when it starts ratteling around inside the motor....
I'm not a guru in metals but from the look of where the crack is that you show it's a good probibility that the engine lug will go next causing a whole lot of problems and safety concerns...

Just two cents wirth...

I had very good luck with the JB Weld, I did however apply it with two layers....it was a pretty bad crack and has not given any trouble at all.

Well, I will have to see if it’s going to work. I think I will be sure to tie it down and run a tank through it while I’m standing well clear of it. Then I'll re-inspect it. Anyone else have experience with JB Welding an engine? I might post a new thread on the subject.

JakeC

had a enya it was cacked all the way to a opening cant remember if it was ft. or back looked like yours i had it tig welded
it ran about 1 tank of fuel and broke right through the weld i jb welded it and the same thing happen on the other hand i got a enya that had a small hole driller through the crank case and that held wt. jb i think most of the eng. are some kind of pot metal alum. it cant hurt to try wouldent spend much haveing it welded if the jb dont hold thats what happen to me if you could find a used crankcase adios jack

Send it in and get a new case for it. Cracks in engines do not get better and JB Weld (in this type of situation) is like a Band-Aid on a broken knee.
If that crack migrates and looses the mounting lug, you may have not only completly ruined the rest of your engine, but may in fact loose your airplane if the engine parts company with it.

Just my two cents worth.

Fuelman