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Discussion Starter · #1 ·
Hey guys,

Currently running a 750 d/p on a mild 351 clevo. Spec of engine are mild cam (unknown), Headers, Has 2v heads but the intakes have been ported out to 4v sizing. Engine goes well but the double pumper just doesnt seem to run great no matter how much tuning we do. Have taken it to many different tuners.

Was told a V/S would be the go so have bought a 670 s/a. Would it be a good idea to chuck on car and test before changing the jets or is there anyone running a similar set up that could offer a good place to start?

Thanks for any info :thumbup:
 

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Each carb will needed to be tuned for the engine. However, holleys tend to come jetted rich from the factory.

I would get some fuel bowl gaskets and open the carb to see what jets you have, then get 3 or 4 sets of jets smaller than what you have now.

I recommend to start leaning it out until the engine starts to complain then go back up 2 jet sizes from there.

For example, I use a lot of 3310's (750 vac secondary), and these carbs come with 72's up front. I found these carb run best with 69 or 70 jets on my engines. (from big cammed 350's to mild 454's).
 

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Discussion Starter · #3 ·
Awesome mate Cheers for that, Its funny cos I have seen on other posts they come lean from factory haha. Will open her up and see what she is running. Will get some Jets and have a play.

Cheers Jase
 

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Your holley comes with 65 front and 68 secondary and yes they are lean from the factory. I have read a lot about the famous holley street avenger stumble and the transition circuit being very lean and people having to jet up never down on a lot of different engine combinations. I have one but not on my engine at the moment and I went up to a 67 on the front and 68 is way to lean for the secondary since it does not run a power valve so I put 72 in the rear and my mild sbc with rhs 180 cc intake runner heads and a lunati voodoo 211/[email protected] 50 roller cam with 9 to 1 compression it ran just fine with no surging or off idle stumbles and runs excellent when I had it on. I currently have a holley 600 on my engine (jetted the same) which uses the same metering block and fuel curve as the street avenger on the front side and I have decent fuel mileage with mine. I would leave the front alone and see how it runs and check your plugs but I would definetly jet up the rear. Most holley carbs have a difference of 6 to 8 jet size numbers bigger on the rear from the front cause it does not use a power valve. Hope that helps out.
 

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Discussion Starter · #5 ·
Primo Will chnge the rear jets up as soon as I get it. Might change the front too while its off and try it. Can always put back in but I remember my d/p runs a biggish primary jet.
 

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Hey guys,

Currently running a 750 d/p on a mild 351 clevo. Spec of engine are mild cam (unknown), Headers, Has 2v heads but the intakes have been ported out to 4v sizing. Engine goes well but the double pumper just doesnt seem to run great no matter how much tuning we do. Have taken it to many different tuners.

Was told a V/S would be the go so have bought a 670 s/a. Would it be a good idea to chuck on car and test before changing the jets or is there anyone running a similar set up that could offer a good place to start?

Thanks for any info :thumbup:
I ran one on a 4V 351C. It can be made to work but takes some effort and frankly there are better choices out there if you haven't already bought it. Here is some insight into potential issues with a 670SA:

holley street avenger off idle bog fix - Ford Mustang Forums
 

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Discussion Starter · #7 ·
Ok thanks for that link thats awesome. I have already bought it as had good reviews from N Z sites and users. SO fixing these 3 things should stop the stumble? Did you find your one ran well after everything was sorted? Worth a swap from a petrol heavy d/pumper?
 

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Ok thanks for that link thats awesome. I have already bought it as had good reviews from N Z sites and users. SO fixing these 3 things should stop the stumble? Did you find your one ran well after everything was sorted? Worth a swap from a petrol heavy d/pumper?
It ran fine once it was dialed in. It just took a lot of trial and error. I even ran it on my 460 for a while.

If you have a heavy car with an automatic transmission the vacuum secondary carb is generally considered preferable but either could be made to work well on a cleveland.
 

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Discussion Starter · #9 ·
Yeah the XA is quite heavy and its auto. I runs ok but is a pig when cold and just feels like its just not running perfect. Wondering if a smaller carb would be the go but now wondering if I should have gone a 750 v/s
 
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