hi,

im tuning my carb atm and got some problems.
sometimes when i hold the rpm at around 2000 and mash the gas down quickly there comes a huge flame out of the carb. (in neutral, not driving)
what is causing this? right now, i have 78 pri. and 71 sec. main jets and 35 pri. and 32 sec. squirters. throttle response is a little better with the bigger shooters. (in neutral, too). i dont think that the valves are causing this. i adjusted them a 3/4 turn from zero lash. distributor has new weights, bushings etc.
i have 10° initial with 30° max at 2800 rpm. the crane vacuum can is 9 turns tighter than the loosest setting. (as described in the hei setup article). is that ok?

when driving it is very lean at part throttle and stutters around. do i need to get bigger main jets or another powervalve? i have a 6,5" PV and its pulling around 14" of vacuum at idle.

any advice for this?

thanks,
nebu

 

Backfiring is typically an excessively lean mixture. So is the cruise surging.

Are you sure about your numbers? Since the primaries have a power valve, they are usually jetted leaner than the secondaries. 78 doesn't sound too lean for the primaries by any means, although 71 primaries and 78 secondaries would make sense.

If it is in fact 71 primaries and 78 secondaries, try going up a couple of jet sizes in the primaries.

 

yes the numbers are right. i drilled up the pri. jets to around 78-80 because my biggest jets i have are 75.
im trying to get the pri. side tuned in and then move up to the sec. side. dont know if this will work...