Okay i have a 69 elky 396 and I'm useing a 780 cfm 4150 series holley carb. I've recently changed the jet sizes because of a cam and intake change. I belevied the car to be running rich prior to chaging them from 70 at the front(primary?) and 76 at the back (secondary>?) to 68 and 72. I started it and checked the floats , set idle and timing.It seem to running good until i give it a good shot fuel it boggs about 3000 rpm or soo. there is no back fire at this time but deffinatly hesitation. if i genlty give it gas it will rev up and no backfiring occuring. The also dosent appear to be any leaks i've replaced meter gaskets and bowl gaskets. i haven't been able to drive it there still and lot of snow on the ground. i know i should be able to get it running better than this. any suggestions??

Was it acting like this before the jet change?

NO . It it ran well all the way threw the power band. the sparks plugs looked alitte black and when i was running it at track (1/4 mile) my father said it look like it was expelling some smoke. not clear on the colour but i'm sure it' s was not oil. all of this was prior to the jet change.

So it ran fine before the cam and intake change or just before the jet change? What did you change from on the old set up to new set up? You may need to get a bigger shot of fuel with cam and squirter size on it.

I don't think the jet change is the cause of your problem.If the bog is coming in around 3000 rpm under load them I would be looking at the spring for the secondaries or the rubber diaphram itself. I'm assuming vacuum secondaries.

Unless the metering plate on the secondaries has been changed a vacuum secondary carb would not have jets.

Check your Vaccume at Manifold reading~~~ with the cam change, if you went in the direction of a power cam, you in most likley hood will have LESS manifold vaccume than before the cam change, that would lead me to looking at the Power Valve size in the front bowl, it may require a change due to the lower vaccume.

okay.actually the cam and the intake change was over a year ago i hadn't drivin it much so i didn't get around to changing the jets till now.So it ran okay after the cam and intake were changed but not after the jets were. 4150 series i think are all double pumper and have mechanical secondarys. So far i have been reading on the holley website and I'm leaning towards the secondary shooters or the throttle advance screw needs adjustment I'm not sure yet though.. And i've heard this is a common problem with double pumper and mechinical secondaries

sorry

okay.actually the cam and the intake change was over a year ago i hadn't drivin it much so i didn't get around to changing the jets till now.So it ran okay after the cam and intake were changed but not after the jets were. 4150 series i think are all double pumper and have mechanical secondarys. So far i have been reading on the holley website and I'm leaning towards the secondary shooters or the throttle advance screw needs adjustment I'm not sure yet though.. And i've heard this is a common problem with double pumper and mechinical secondaries

okay.actually the cam and the intake change was over a year ago i hadn't drivin it much so i didn't get around to changing the jets till now.So it ran okay after the cam and intake were changed but not after the jets were. 4150 series i think are all double pumper and have mechanical secondarys. So far i have been reading on the holley website and I'm leaning towards the secondary shooters or the throttle advance screw needs adjustment I'm not sure yet though.. And i've heard this is a common problem with double pumper and mechinical secondaries

If it wasn't BROKE ! WHY fix it ? Put the other Jets back.

Well actaully I'm in pursuit of a quicker 1/4 mile time. and like i said it was running rich so maybe not broken but could be improved. and its not that important i guess but I'm trying to learn about carbs along the way. bye the way it ran 14.1 at 96 mph last yeah and i'd really like to hit 13's this year.