jet down 750 or get 670 holley????

[z ya]

After my run on the dyno and finding out that my

750 was pig rich. I have to decide on if I should

jet down my 750 or get a 650 or 670 carb. My a/f

ratio was 10 to 1 across the board. Need some ideas here guys?????

[660Z]

need more info....what jets,#powervalve,vacuum reading,dp or vac secondarys,jets in the rear?......mark

[z ya]

The carb is a 3310 s vac sec Holley. It is straight out of the box. I beleive the jets

are 72's and not sure on the p/valve.

[z ya]

Thanks for the insight Pete. I drilled the blades

and that helped a bunch! But the carb is way rich

at wot. I will play with the jets for a while and

see what I come up with.

[pparaska]

Ron,

I'm having problems with my 3310 being too rich as well. I think most of the problem is that the transfer slot is being uncovered too far at idle and loading up. Alot of overlap in the cam will do that. I'm going to drill holes in the throttle plates to let more air in to lean out the idle mixture and allow more of the transfer slot to me covered up.

 

Other than that, the 3310 is typically rich out of the box. You may need to reduce the effective size of the idle fuel restrictions (IFRs) (with .014 to .016 dia wire in the IFR hole in the metering block) or increase the idle and/or main air bleed holes.

 

I was reading my new copy of Vizards' book on intakes and manifolds and came across an interesting philosophical discussion of the Holley "Main" metering circuit. Vizard thinks its more aptly called a cruise circuit, because it is only part of the fuel circuit for any application of the throttle that creates less manifold vacuum than the power valve rating. His advice is to adjust the main jet size for cruise mixture and to play with the power valve circuit restriction (PVCR) size to get the mid to high load mixture correct.

 

All of this would be easier with an O2 sensor, and a wide band one at that.

 

Again and again recognized high performance V8 experts tell me that a 750 carb is NOT too big for my 327, and will make more power. They say all it takes is correct tuning. Then again, others say I need a 650 and any more is not going to make more power, just make idle and throttle response different. I think there's truth to both arguments. I think a 750 on my 327 or your engine could work well, if the correct venturi boosters, throttle plate holes, powervalve, PVCR, IFR and jet sizes, etc. are used - but probably not an out of the box 750. But that's a TON of tuning.

 

EFI would be SO much easier. If only the money would fall off a tree or something!