tuning dual holleys on a 355 w/ high rise intake? - Team Camaro Tech
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post #1 of 3 (permalink) Old Feb 17th, 07, 08:15 PM Thread Starter
Senior Tech
Darko
 
Join Date: Feb 2007
Location: Detroit
Posts: 606
tuning dual holleys on a 355 w/ high rise intake?

I bought a 67 camaro with dual vac secondary holleys on a weiand high rise intake.

Its got camelback heads
11:1 compression
somewhat lumpy cam
headers
350 trans
3.55 rear gear

There is hesitation when driving it around, and if you nail the throttle when the car is at a stop the carb will backfire and the motor will shut off. When I took off the bonnet & air filters the tops of the carbs looked black & oily. It has an adjustable fuel pressure guage and thats set around 10psi if I remember right.

Any idea what the cause of the backfiring is? How to start tuning it?
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post #2 of 3 (permalink) Old Feb 18th, 07, 04:18 AM
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Steve
 
Join Date: Jun 2005
Location: Melbourne, Australia
Posts: 2,864
Re: tuning dual holleys on a 355 w/ high rise intake?

That's a lean back fire. You need to richen the accelerator pump's shooters/squirters.

Nov 68 Van Nuys. 327 floor-shift-auto, Frost Green and not much else when new.

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post #3 of 3 (permalink) Old Feb 18th, 07, 08:05 AM
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Join Date: Aug 2004
Location: New York
Posts: 166
Re: tuning dual holleys on a 355 w/ high rise intake?

10 PSI is a lot I am suprised you are not dumping fuel the needle and seat usualy hold to 9 PSI I always set a street [email protected] 7 to 8 PSI. BlackoutSteve is right you probably have a lean bacfire. You can buy a tune kit that changes the accel. pump ramp to a more agreesive ramp. Also you really need to set the timing up correctly first before you tune the carbs. To much initial timing will also cause carb spitting. Alot of people turn up the timing to compensate for a flat spot or hesitation in the fuel curve. I like running a timing curve on eng. like yours that has 15 degrees initial 36 total and I bring full centrifigal adv. in as early as I can without making the eng ping. You do that by adj. spring rate. Once that is set you can tune the fuel curve properly. If I were you I would contact Pro systems carb shop in Spring Lake Mi. 727-490-5717. They will be more then happy to point you in the right direction and get you tuned in they can sell you all the tunning kits and help dial you in. They are about the best at what they do and I dont think they are to far from you.
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