issue with hercules engine reving up on HG

[racerjim]

I'm working on a cletrac crawler and have got the hercules IXK3 motor running. We rebuilt the carb, put new tune-up parts in the wico c magneto, put in new spark plugs and new oil. When we try to rev the motor from idle on up to 1700 rpm it stalls out about halfway there and dies or will continue to run if you back it off quickly to idle again. it seems to have a good spark and the timing in righ on the mark on the flywheel when running checking with a timing light.

We suspect a fuel or spark issue but are unsure how to troubleshoot. any suggestions?

[Eric N]

Check your exhaust, might be plugged.  I've had that with a couple barn finds.

[John Schwiebert]

Looks like I posted my answer on the thread below this. Sorry about that.

[oliverchris]

As John said, likely a carb problem. I had a similar problem on my OC3. Messed about tweaking this and that with no great effect. Then put some time aside, cleaned out gas tank which was full of rust chips and dust and then put a newly professionally rebuilt carb on it, and I could not believe the difference! WOW! You may have some similar gunk in fuel line stopping full flow of gas, but just enough 'leakage' though to the carb to idle.

[hotratz]

You might try hooking the carb up to a portable tank and line like a boat tank just to see if the delivery system is the problem. I've rebuilt several of the carbs and always had excellent results. There isn't much to them so if you were fairly attentive when you rebuilt it they usually work fine.

If you think it might be spark, try leaving the timing light hooked up and see if the spark goes away when it revs up and stalls.