383 "stumble"
 

I took my 18 Donzi out for the first time this weekend with my new 383 ( Scat, Pro action heads, 9.2 comp, crane 272 hydr flat cam). I was very pleased but it seems to have an off idle stumble that is pretty significant. If I nail it out of the hole there are no problems but if I try to accelerate gradually it stumbles and sputters between 1500-2500 rpm. It also stumbles coming off plane in the same rpm range or at about 200-2500 on a slow plane. I am not the best with carbs but it has been suggested to me that the float(s) are either mis adjusted or stuck. Does anyone have any feedback, things to try and maybe give me a hand walking through it?

Thanks

Chris

Carb is a brand new 650 mechanical secondairies double pumper

Have you tried reading the spark plugs? What type of carburator? Have you rebuilt the carb lately? Kinda sounds like a piece of chit is caught in the primary side of the carb and until you get into the secondaries it isn't getting enough fuel. Just a guess... need more info.

BT :cool:

Sorry... didn't see your last line. In the case of a new carb, I would say you clearly have too little or too much fuel on the primary side.... probably too much. Try reading the plugs for more clues. Too much will be black plugs.... too little white.

BT :cool:

My sugestion is to dump the Holley for a Barry Gant... but before I would run any new carb I disassemble and inspect the stuff I have found has turned me away from the new Holleys.

Your carb sounds lean to me. Try larger squirters, if that doesn't work fatten up the jets 2 sizes. As others have mentioned, check your plugs also.

Lean would suprise me. My engine builder and I discussed the carb choice. We settled on a box stock 650 holley and then I bumped the jet sizes up 2 on the primaries and secondaires for safety. I would have thought it was more a too rich thing.

Chris

I could be wrong...it happens every day

Thanks for the help guys. I really appreciate it.

Chris,
I agree with jdnca1, try going up a couple squirter sizes. Had the same problem on my 68 Camaro. Also verify your timing curve just to be sure everything's advancing when and where it should be.

I would check your idle transfer slot relationship

Turbo would you be so kind to explain that a little. Not quite sure what you mean.



Thanks

Chris

It has been suggested I need baffles for my fuel bowls? Anyone else have this?

Most HP carbs are set rich from the factory so they dont toast your motor and blame it on them. Too rich can cause bog also improper advance/ timing.. read your plugs

If your plugs are coal black and/or wet then you're probably not lean. Otherwise you might be. I had a 1050 Dominator on my previous modified 502 that did the same thing around 2500rpm. I tried many combinations of squirters, air bleeds etc. The only way I could get through the "transition" smoothly was to increase my jets...then of course I had the dreaded "black transom";) Try going both ways, leaner and richer, to see what it likes more. If you still have problems I agree with turbo...dump the holley for a Demon..they are much better carbs. :cool:

If your going to do this your self the best thing to do to start is get one of the books on Holly carbs that Peterson has published
and read and reread it several times if necessary then go back and look at your carb and ask questions. Because even after the book experance is needed but you will be ahead of the game compaired to most.

I will go get a book.

P.S. After 20 min my transom was more black then it ever had been with my stock motor all last year.

Chris

Yea Chris, stop fartin' around and get "the book"!!