Daily Parts Questions

I recently purchased a tillotson carb from you guys and I’m having trouble with it and was wondering if you could help. 196cc clone engine with stage 1 Bike worked great with jetted clone carb. When I put the tillotson carb on I couldn’t get it to run for more than about 5 seconds. Fires up but won’t idle. When it does run for a couple of seconds, it backfires huge out of the carb shooting smoke and flames. I’ve tried changing the low and high jets in the carb with mostly the same results. The .028 low seems to give best results but still huge backfire and gas and flames from the carb.

Any thoughts??

The backfire through the carb is more related to timing and valve lash than the carb. You would need to verify the lash is set at .003" on both sides and on the compression stroke. The other thing to inspect is the key that indexes the flywheel to the crank. If that key has sheared and the flywheel has moved, it could be firing the coil when the intake valve is open.

The PK-1B carbs are jettted a bit rich. You may want to bring the pilot down to a .020" jet

and bring the main down to a .037" jet

You could also have a vacuum leak between the carb and cylinder head. The black plastic spacer must be installed to get any stock style carburetor tuned. If that plastic spacer is not there, you will have a huge vacuum leak that you cannot tune around