I am working on a friends engine. Its almost new and he has had two flameouts with it with awful results. The engine starts right up and runs fine until it warms up (just prior to take off) and then dies as if starved for fuel. I have put a new carb on it, checked and sealed the backplate, made sure the head bolts are tight and tried a variety of carb mixtures with both the low and high speed needle valves. I am running a 12x6 prop on it and an OS A3 plug. Any ideas out there?
That is too large a prop for that engine. Yer gonna kill it. Also, they take about a gallon or so to fully break in and tend to lean out till then even with the correct sized prop. I ran a 10X6 prop with an OS #8 plug on mine for my Kaos. After the gallon, its a real screamer. From the Tower Hobbies website: Suggested Prop size: 10x6, 9-1/2x6 I would try the 10x6.
At RCuniverse I came across a thread (search - bean counter) about the ST45 having problems with transition from idle to full speed. The largest prop I run on my ST51 is an 11-5.
Are you able to get the motor to run fine at idle and at top end and it stalls on the transition?
I placed a brass sleeve inside the throttle barrel which took care of this stalling condition. I obtained the sleeve at Homedepot in the plastic tube, plumbing section.
I completely agree. ST recommends a 10x8 or 11x6 prop for break-in. This is NOT an ABC engine. It is ringed and therefore requires a careful break-in period. I also recommend the OS #8 plug. The A3 is too cold for this engine. Once you get this set up and broken in it is sure to become one of your favorites. Lots of power for the money!
What is the correct/best fuel to use during the breakin? I'm having th
same problem as mentioned above. I have a 10X6 plastic prop on m phaeton with a G51. I got about 1/2 gallon run through it (15% nitro) I am running it slightly rich to help with the break-in.
The old standard way of running in a ringed engine was to use a slightly smaller prop with a fair percent of nitro with the engine running very rich at the target rpm for the broken-in engine.
You won't hurt anything by using 5% nitro and an 11x6, but according to the old ways, the engine will just be average and not as peppy as it would be with the old racing break-in procedure employed.
Once broken-in, an 11x6-7 or 12x5-6 would be fine. Even a 10x7 or 8 would be good for faster models. Just don't get crazy with an 11x8 or higher, or a
12x7 or higher. A 12x4-5 or a 13x4 would be okay. If you must run slower/higher pitched props than those just recommended, listen carefully for sounds indicating preignition. Sometimes just richening the high speed needle is enough to avoid preignition. Preignition mostly occurs toward the end of a flight when the fuel level drops in the tank. It is still damaging to the engine, even then.
More load on the engine advances the timing. It can be advanced to a point where the engine overheats. Lowering nitro content, switching to a smaller prop or going to a colder plug can help delay the point where damaging advanced timing occurs.
The G51 is a tough engine, but why stress it unnecessarily?
I have a ST 51 and experienced the same thing for a while. The 15% nitro is fine but use something with castor in it. ST recommends that. Definitely go with th OS 8 plug.it makes a world of difference. I was running a Master Airscrew 11x6 prop but found that it spends more time beating the air than pulling the plane. Switched to an APC
11x6 and got better results with less RPM. One last thiong... ST 51 is very sensitive to the location of the fuel tank to the spray bar. Adjust things until they are as close as possible. Other than that, they just require lots of tinkreing to get them right but once you do they will be one of your favorite engines.
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