Thread: holley Jetting

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got my engine together and running , 472 cadillac alum heads single plane intake 850 double pumper cam etc running 80s in the front and 90s in the rear. Very rich to the point that the engine misfires and flames out of the pipes needs to be leaned out for shure, any suggestions what i should start with, holley standard jetting is 80s on both ends, thinking of dropping to a 78 in the front and 82 in the back.
Any ideas for jetting idles great and can adjust easliy with screws i would think comparableto a 496 with 300 cfm heads
anybody ruunning a big block and know what jets they have, I need to start somewhere and i know i need to go down not up.

Hey, Al! Getting ready for the Speedy Creek drags if it ever warms up?
If it's that rich, you will not see much improvement with that small a jet change.
Is it a new carb? Did it pop out the carb a few times? The power valve could have ruptured, letting gas flow directly into the engine, a common thing with Holleys. Or the body could be warped, doing the same thing. I had that happen on a brand new Holley.
You've likely been through all that before, but sometimes the obvious gets overlooked.

Reread your post and got to wondering....How long are your pipes? A lean carb can cause hot blue flames out an open header. Rich exhaust plumes are usually big intermittent balls of red or orange fire. A rich engine will generally rev up and run better, lean will snap and pop more the faster it runs, with a bogging moan when it runs right out of gas.
Just some idle thoughts on your problem, hard to tell what's happening without being there!

thanks fro the reply pope hate to say it but its my 1st holley so i am learning
i have got my pipes on ,individual 18 inches long
shure seems rich as the shop fill sup with fumes
if the power valves are damged will it still idle and can one still adjust the idle scews to the point that the engine will die?
I might pull he bowles today and confirm what i have in there was jsut told 80 s front and 90s rear
Will be back in speedy creek this year if it ever stops snowing

Did you set the floats before putting it in service ? They may need adjustment just from shipping and it being bounced around.

Yeah, the float level is the first thing to check. Easy on Holleys, just pull the little plugs.
Shop full of fumes sounds rich, all right! Almost too rich to just be jets. If the carb sat on the shelf for a long time, the gaskets could have dried out and shrunk, causing fuel to get to places it shouldn't. Not so common now, with composite gaskets, but it still happens.

You don't have enough motor for that big a carb, you can jet down to lean it but the bores are big enough that the air will be lazy going thru the carb and that will make for a poor fuel signal. You'd be happier with a 750dp and the motor would be more responsive. Don't worry about the power valve, modern carbs have a check valve so if the motor backfires thru the carb it won't waste the power valve. Trying to get that thing tuned proper will drive you nuts, you'll learn a lot and be good experience but it'll be frustrating. As an example, the high HP hemi crate motor comes with a 750 double pumper, a big cam and tall single plane intake.

I'm running a 670 cfm Street Avenger Holley on my 468 chevy (mild cam), rpm intake and have had no problems. I pulled a 750 Ebrock off that would put your eyes out from the fumes!

The CFM has nothing to do with it running rich. Sure, it's a bit big for a stock engine, but jetting it right will get it running better. I had a Holley 3-barrel on a 283 with Power Pack heads and a Duntov cam that didn't run rich but you couldn't open that big trap door below 3000 RPM without a huge backfire. When it caught all hell broke loose!
The Caddy in question isn't a stocker, either.

its not a stock engine anymore mts heads flowing 335 cfm roller rockers, big mts single plane intake 1 1/2 spacer biggest comp cam they make for the engine.
I did some checking today confirmed 80 in the front and 90s in the rear. 8 individual 18 inch weedburner style pipes Fiddled with the timing and adanced it a bit all came in better but still rich misfire is now a lot less My timing light is at my dads so i cant see what it shows) . scary wicked off throttle response now car just about hops when you hit the gas.
Still think rich but is better. float levels are fine power valves are good
am going to pick up some 78 79 80s jets monday and put the factory jetting back in to start with and see how that goes.

Well so much for jetting figured it out, has a pertronics electronic ignition kit(runs off the cam lobes how i dont know?) its bad 2nd one this time its like the thing is too rich and misfires all over the place.
Had enough ordered a new hei h/o unit for the caddy should light its fire and then i can figure the carb.

Weedburners really kill torque, takes some decent length tubes 32" to 34" with a 3.5" or 4" collector, probably in the 10" to 12" length. Used to carry a set of weedburners for the sprint cars, put them on the car on dry slick afternoon races to kill the engine power!!!!!

yeh i knowthey are not the best ,but torque has never been my problem
they look and sound cool.

I don't know but I have had plenty of holley's that ran rich and have never heard them make the car back fire unless the timming was way off and then you could blow a power valve in the older holley's. But in general to me it sound more like a timming issue more then a carb issue. And I used to run those big old caddy's all the time with 472 cid's or the 501 cid's I love em they have all kinds of torque. Also could you have a sticky valve hanging up or open??? Maybe a broken spring but you would probably hear that.
Kurt

The miss is all over cause i can hear it in the seperate pipes did comp check all good spark is big and strong . will find out once i get my new hei distibutor and toss the petronix.I have run this thing really rich before and it ran without this kind of farting around.
1st spark then i can work on fuel