Thread: Holley Jets, WHAT the heck???

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THANKS Erik, Mizlplix, Denny, C9x & Nitrowarrior, Sorry I didn't check this earilier to re-post. It's a Holley #4779 double pumper that was gone through by the Carb Shop in Ontario to 'match' my engine {they didn't tune it on the motor, just built it to match my motor}. I gave the place all the spec's on my motor as per my engine builder. I don't have the paper work from them so I don't have that much info {it got lost somewhere between the engine builder & the car builder}. I do know they cut off the choke horn. The plugs show it running rich {tons of black soot on them} so I thought I'd put in smaller jets. I showed up an hour or so into the dyno tuning of my motor so I'm not sure if the Carb Shop or the dyno operator put the 70/82 jets in. But it didn't put out anymore HP or TQ with the 71/83 jets than it did with the 70/82's so I thought I'd go back to the 70/82's.
My dyno sheet has Zero's under the A/F ratio . But it does show FHp Hp, ME%, FB 1b/fr, BSFC 1b/Hphr, CAT & Wat. Will any of these figures help??? Oh Eric, what does EGT's mean??? Mizlplix & Denny, I'll get a vacuum gauge & check the vacuum but is there a way I can measure what power jet I have in there now??? I'll look up in my Holley book r/e where is the power jet! THANKS All, Bill

Originally Posted by billlsbird

THANKS Erik, Mizlplix, Denny, C9x & Nitrowarrior, Sorry I didn't check this earilier to re-post. It's a Holley #4779 double pumper that was gone through by the Carb Shop in Ontario to 'match' my engine {they didn't tune it on the motor, just built it to match my motor}. I gave the place all the spec's on my motor as per my engine builder. I don't have the paper work from them so I don't have that much info {it got lost somewhere between the engine builder & the car builder}. I do know they cut off the choke horn. The plugs show it running rich {tons of black soot on them} so I thought I'd put in smaller jets. I showed up an hour or so into the dyno tuning of my motor so I'm not sure if the Carb Shop or the dyno operator put the 70/82 jets in. But it didn't put out anymore HP or TQ with the 71/83 jets than it did with the 70/82's so I thought I'd go back to the 70/82's.
My dyno sheet has Zero's under the A/F ratio . But it does show FHp Hp, ME%, FB 1b/fr, BSFC 1b/Hphr, CAT & Wat. Will any of these figures help??? Oh Eric, what does EGT's mean??? Mizlplix & Denny, I'll get a vacuum gauge & check the vacuum but is there a way I can measure what power jet I have in there now??? I'll look up in my Holley book r/e where is the power jet! THANKS All, Bill

Twenty years ago or more all we ever went off of was EGT'S or exhaust gas temp.
We use use 1,350 F for good pistons in a drag application and 1,275 F for circle track application.
We would lean the carb. down until we got those numbers or very close to those numbers in each hole.

So what you're saying is not all 750's are not the same?.....wow, what a concept.....who'd a thunk it!?!? I'm sorry but it takes a bit more to help if some of the "better" info is included.

Here's the pic again for jets and PV location. The power valve is on the reverse side of the block that contains the jets.

.....Wow, got the carb somewhere around 15 years ago so I have no idea which one it is. I'm going out to start changing jets in a few minutes & I'll look for numbers. If I remember right there were some numbers on the choke horn that the Carb Shop cut off .... Denny so it looks like the jets I have in 71/83 could be close to what the factory put in some of the 750 Holley's??? THANKS, Bill

I have the holley recommendations for you here. I too have some 4779's and some 3310's around so I thought you might need this. As you can see the jetting can be stock set at 75 primaries and 76 secondaries or the next two 4779 sets would be 70 pri and 80 sec. Have you measured the venturies and throttle plate bore? It would be helpful to know those. That would differentiate the two styles of the 4779.

Cool Denny, you can upstage me when ever you wish......I care about the info for good results.

Yah, I always change out the secondary metering plate for a block, just so I have adjustability. BTW: at this stage of life, if I need a carb, I just pour out my 4 buckets of Holley parts and assemble one to suit my application.

One thing good about having a "Carb Shop" carb, is that they usually convert them to screw-in air corrector restriction jets. These make removing an off idle stumble a snap.

ALSO: Look on the side of the base section. They sometimes have the carb list and model stamped there too. (For when the air horn is cut off.)

....Ok up-date, I installed my MSD cut to fit plug wires last night & the car doesn't seem to stumble at all. A couple of my old plug wires were cut up. MUCH better throddle response! Then tonight I put in jets that were one size smaller {70/83}. And while I was at it put in a new needle & seat {the Vitro tipped one} & the two washers that go with it {my old one stuck & I washed it out with water a while back. I also had two home made gasgets on the needle seat assembly so I also put new washers on. Then I re-adjusted the fuel level in the secondaries. So tomorrow I will test drive it & if it seems to runs ok then I'll put the new plugs in & see if it's running a little leaner. Oh I also noticed a vacuum plug on my carb that was rotten away so it had to be leaking. I pluged that up also.... Oh to seal the fuel lines I used that white plumbing tape. Is this ok??? I looked over the entire carb & didn't see any numbers. If my car doesn't run right tomorrow I'll try to measure the ventures & throttle plate bore to figure out what carb it is. What's a screw in air correction restrictor jet??? Yeah, it was actually fun changing jets! Never done it before! I even identified all my carb parts by the pictures that were posted!!! THANKS again all, Bill

I too am curious why such a spread? Is a spredbore double pumper? I remember these having sim. #s on the jets. A rich setting is better than lean from a longevity point. With unleaded fuels, a wideband A/F is critical to get it right on the edge. EGT's are too slow but will get you there. As other have said, plug color is hard to use unless it's spotting -which is piston matter from detonation.

Bill, keep truckin'. Go for everything you have read here. Falcon....no......Spreadbores have a huge difference between primary and secondary metering. I only wish to see all that follow this to understand A/F mixtures and that tuning is not that hard, but there is some patience involved.