Good Evening Everyone,
I am looking for some troubleshooting help with using a stock carb on a modified preadator engine.
First, this is not on a minibike, but a motorized bicycle that I race occasionally here in southern california. The rules for this engine are stock rod, stock piston, 18lb. springs, stock cam, governor removed, stock valves, custom header, billet flywheel, custom intake, but stock carb. I currently have the 18lb. springs, ARC adjustable finless flywheel set to 8 degree advance, governor removed, straight 1" pipe exhaust with RLV muffler, and a custom intake manifold that incorporates the stock black plastic spacer between the carb and the intake manifold.
I originally was using the stock carb with stock pilot jet, but switched out the emulsion tube with a GX140 tube and a 36 main jet. With this set-up I get a good idle and no hesitation in all rpm ranges, but lacks a little on the top end. I then purchased an ARC stock carb bored to .625" with a 22 pilot and a 35 main jet. On this carb the bike has a very uneven idle bordering on the engine stopping. The 1/8 - 1/4 range of throttle also has hesitation/missing. On WOT the bike takes off like a bat out of hell and works much better than the stock carb that is not bored.
I am asking if anyone has ideas for getting it to idle correctly and not hesitate at low throttle. I first changed the main jet to 38 but not much change. I also drilled the pilot jet out to the equivalent of a 25 pilot, but still did not really remedy the idle/low throttle problem.
I am using the same stock black plastic spacer between the carb and the intake manifold, but I wonder if that is contributing to the problem. I could not get the stock carb to run without the spacer.
Thank you in advance for any advice,
Gilbert
I am looking for some troubleshooting help with using a stock carb on a modified preadator engine.
First, this is not on a minibike, but a motorized bicycle that I race occasionally here in southern california. The rules for this engine are stock rod, stock piston, 18lb. springs, stock cam, governor removed, stock valves, custom header, billet flywheel, custom intake, but stock carb. I currently have the 18lb. springs, ARC adjustable finless flywheel set to 8 degree advance, governor removed, straight 1" pipe exhaust with RLV muffler, and a custom intake manifold that incorporates the stock black plastic spacer between the carb and the intake manifold.
I originally was using the stock carb with stock pilot jet, but switched out the emulsion tube with a GX140 tube and a 36 main jet. With this set-up I get a good idle and no hesitation in all rpm ranges, but lacks a little on the top end. I then purchased an ARC stock carb bored to .625" with a 22 pilot and a 35 main jet. On this carb the bike has a very uneven idle bordering on the engine stopping. The 1/8 - 1/4 range of throttle also has hesitation/missing. On WOT the bike takes off like a bat out of hell and works much better than the stock carb that is not bored.
I am asking if anyone has ideas for getting it to idle correctly and not hesitate at low throttle. I first changed the main jet to 38 but not much change. I also drilled the pilot jet out to the equivalent of a 25 pilot, but still did not really remedy the idle/low throttle problem.
I am using the same stock black plastic spacer between the carb and the intake manifold, but I wonder if that is contributing to the problem. I could not get the stock carb to run without the spacer.
Thank you in advance for any advice,
Gilbert
