emjdrvr

Bill I need some help with my vspec. The engine ran fine for the first half gallon after break in averaging normal temps. Very shortly after break in I noticed the engine was starting to hesitate and bog slightly about mid to upper rpm but would clear itself out once in the higher rpm range still in the 200- 250 degree mark. However the engine will now hesitate, sputter and stall out as i throttle upto midrange. On the starter box i get full the full range of throttle authority but on the track when the engine is under any load the engine will only rev up to just under mid range stall out. I have tried everything i can think of. Re tune, change plugs ( p3 hot ) check for leaks, change fuel filter and all to no joy. Now i should mention that when i do put a new plug in the engine runs normal for about 3 laps ( 2-3 minutes )then the whole issue starts over again.

fuel is 20% with 14 % oil
os p3 hot plug
stock engine with no change
ofna jp 4 pipe

Thank you,

Shawn

Bax

My Feedback: (11)

Bogging in the midrange usually means that the idle mixture is too rich. You may need to lean it a bit. You may also have the high-speed needle improperly-set. Get the engine set first, and ignore temperatures. How does the engine run at full throttle? How does it idle? How does it transition? If the engine runs well throughout the throttle range, then you have it properly-set, regardless of any temp reading. If you set your engine based upon temps, then you'll never get it set correctly. If you are using a low-oil racing fuel, then you can count on needing to replace the piston/liner assembly after a few races or after a few gallons. Low-oil fuel contributes to good racing and short engine life.

The high-speed needle should be set just rich of peak RPM. When you accelerate up to full throttle the engine should come up and then hold. It should not come up and then drop in RPM. If it comes up and drops, the high-speed needle is too lean. The idle mixture should be set so that you get a good idle with good throttle-up. Adjust it as necessary to get a clean throttle transition.

Higher-oil fuels will give you longer engine life, but will also take a bit longer to clear when you punch the throttle. Top-end will be about the same. If you're not racing, then a regular airplane-type fuel would be the best all-around solution. You can get those fuels with nitro up to 30%...whatever you want, really.