Another Holley 750 jetting question

[chlngr1970]

I tore my Holley 3310-2 down for a rebuild and found 4 different sized jets in it. The fonts are 70/75, and the rears are 73/77. This was built by a Mopar Guru I trust. He pulled it off his 77 ( ? ) Roadrunner 360 race car and put it on my 340 when we took it racing wow..more than 10 years ago :-? Anyway, the accelerator pump was leaking, and I was having issues getting the car to start. I went ahead and pulled the carb off, tore it down, and upon reassembly, I found the Holley trick kit doesn't have the caskets for a secondary metering block that is on my carb #-o Anyway...I never took the jets from my primary side, but did take them out of the secondary side. But, having 4 different jet sizes has me completely at a loss.

So, my question is, what should I start as a good base line for jetting?

• 340
• mild port work on heads
• 9.5:1 compression
• LD340 intake
• MP 284/.484 cam
• 727 with shift kit
• low stall converter ( probably a stock one )
• 3.23:1 open rear
• 295/50-15 tires
• Hooker/off brand headers ( long story )
• 2.5" exhaust through x-pipe dumped at rear axel

Is there anything else I need to post for a good base?

Thanks!

j

 

[idrift]

I vote for 68's or 70's. I think they would be just about right.
I am running a little hotter set up than you, and 72's are just
about right to slightly rich.

 

[rumblefish360]

What you have there is an OL'School "Stager Jetting" trick designed to help balance out the rich/lean conditions inside the intake manifold and the balanceing of the intake charge due to some cylinders fireing next to each other and the intakes inperfect air and fuel distibution.

It seems like the jetting is following the MP books suggestion of this stagger jetting for the intake you have. I'd bet that the intake is modified like the MP book says to modify it.

A milled centerdivider?

idrift makes a good suggestion. That is what I would do. 70's up front for a try with a new set up. Otherwise, if a MoPar guru built it, just leave it.

 

[chlngr1970]

Unfortunately, I removed the rear jets not knowing they were different. The front jets are black, so I am going to replace them anyway, but now that I have a reason, I just need to get the secondary jets back in the right way. I'll pop over to the local parts shop that has Holley parts. I need to run over to Monroe to check out a 3310-3 from Craigslist. Hopefully I can come up with the funds to get it if it is in good enough shape.

j

 

[crackedback]

I'd go back to a baseline jetting the carb came with and go from there.

72 primary
75 secondary equivalent to a 134-21 metering plate

That's from the holley reference library.

 

[braveseal]

back in the old days We always staggered the jets on a LD 340,I read it somewhere in a tech article.
When you looked at the plugs,it seemed to even out how it burned.
I'd put 73's in front and 78's in the rear in my opinion ,to start.

 

[mullinax95]

First time I've ever heard of staggering the jets.... dang it boy..learned something today. I have seen numerous intakes with the center divider cut on some old Mopar intakes that's for sure.

 

[chlngr1970]

Picked up some new jets. The local Holley guru ( the parts guy told me he was 8) ) sold me a pair of 72s for the front, and 78s for the rear. I might just pick up the same jets in there now, but new ones as the old ones look burnt. I'm hoping to have it back together next weekend, and running. That would be nice

j