carb problem
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Senior User
Joined: Aug 2006
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carb problem
I have a holley 750 vac. sec. on my 302 it works fine but when i floor it it backfires just on pop and then takes off does anyone know what causes this. Im thinking the carb may be too big for my 302 or maybe im not adjusting the carb right. Any help will be appreciated.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
750 is too large for your 302 if it's a street motor. But if you can slow down the opening of the secondaries you might be OK. There are some guys on the site that are Holley experts who might be able to tell you how to do that. Try posting in the carb forum.
Post Fiend
Joined: Oct 2003
Posts: 9,176
Likes: 4
From: Western Central NV
If all the mechanics are OK. Then you are most likely getting TOO much gas when you stand on it. There are a couple of things you need to know. One is the check ball in the secondary housing? If that is missing that could be most of your problem. Second what color is the secondary spring? TOO light a spring causes the secondaries to open too quickly. Third, what jetting do you have? Remember the 289 & 302 Hi Pros ran 750s. so if your in the 300 HP area a 750 isn't too much. If not it maybe alittle much but with jetting & P.V. right, and right secondary springs you can run it. At 5500 Ft elev. on a 460 4160 Holley 600 CFM I run .622 primary jets and could run .612s. with a Blk seconday spring which is the heaviest. 6.5 P.V.
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Senior User
Joined: Aug 2006
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I got .70 jets in the front and a 28 squirter, the back spring I have no idea its just silver but its pretty stiff, what I noticed is that when I do give it gas it does throw a lot of gas out of the squirter so maybe I should go with a smaller one and re jetting
Post Fiend
Joined: Oct 2003
Posts: 9,176
Likes: 4
From: Western Central NV
Did you check to see that the check ball is the secondary housing? .070 jets IMO are way to0 big. The silver spring according to my Holley secondary tuning chart is called a plain spring which is standard spring on small blocks starts opening at 2240 is fully opened at 8160 RPMs. so that should be OK. I think you are dumping TOO much gas. Provided everything else is in proper working order.
