Platinum_Racing

I have an OS .12 cv bump start engine with the rotary carb. I am running Blue thunder 20 % with break in settings with a head shim. Motor savers air filter. I have checked for fuel leaks, pressure leaks, Im sure the piston is in the right way, it still has plenty of compression. The backplate is fine, the tank is fine, the lines are new, the bearings are fine. The internals have not been modified, the needles are clean and the glow plug is fresh. The problem is that as soon as the flywheel hits the bump starter, the engine takes off at 110% throttle. The bump starter is spinning in the right direction, and when it starts, I lift it off of the starter. It has had 2 carbs on it. Whats the matter with this engine????

Platinum_Racing

Please, I need to know Fast!

flack

iTrader: (1)

It sounds like the carberator is fully open when it starts or the idle screw is turned all the way in. Have you checked your servo to make sure they are not operating in reverse? They can usually be changed at the radio.

Doug

Platinum_Racing

Idle is fine, and the servos are properly working.

Pattojnr

iTrader: (19)

dont start it, but take the aircleaner off and see if the opening of the carb is about 1mm. then open the carb with the radio and see if the servo is workin gthe right way and opening the carb ?
hope this helps.

Platinum_Racing

did all that, the idle is 1mm and working right

Pattojnr

iTrader: (19)

try richening the bottom end mixture. try even returning to stock carb settings. flush with housing. and 4 turns on main needle

Pattojnr

iTrader: (19)

if the piston has a transfer port in the skirt, it should be opposite to the exhaust port.

Platinum_Racing

set for break in right now, and the piston is in the way os says it should be.

Pattojnr

iTrader: (19)

ok. so how old is the motor. and how do you know the bearings are ok? is there any fuel leakages. try running the engine for a few longer bursts on the starter box, without the glow warmer, and just note if any fuel leaks. sounds like a big air leak. possibly cracked crankcase ? bad seal, or bearing . you can also try over richening the bottom end , as this will compensate for air leaks, if it doesnt rev as high with extremely rich settings, then an air leak is evident.

Platinum_Racing

I have tried 2 os.12 cv motors. The same thing happens, i sealed up the gas tank with silicone sealent, and i tried 2 different pipes.

PoPRC

I had this same problem once at the track with a dynamite .12. But it was my throttle linkage that was causing it. Just curious though, why do you have the head shimmed? Did you install the shim yourself or was it a shim OS had put there already? 20% on a .12 shouldn't require a head shim for break in, unless it is there by factory default.

Platinum_Racing

Its factory shimmed.

sook

sounds like it is your throttle linkage that is causing this problem. Have you tried turning your radio system on and looking down the carb to see if it is opened more than your idle set of 1mm?