Thread: Timing Questions

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Last writer asked about dumping fuel. You need a vacuum guage, just something cheap to help you adjust the idle screws. They're cheap. If that Holley is a double pumper, you have two(2) power valves that open when the vacuum drops. They are probably 6.5's if nobody else has messed up this carb for you already. All street Holleys seem to come with 6.5's. You need to know your vacuum at idle in drive. If it drops below 6.5, you are very rich and dumping fuel. You need to be 1-1.5 below your idle vacuum. If you read 6, you need a 5 or 4.5. This is one reason why vacuum secondaries are recommended for automatic street cars. It took me a long time to figure this out for myself because nobody could give me an answer. I picked up a free Holley catalog at a World of Wheels show and before that I probably had five other books on Holleys. I now run a 750 vacuum vacuum secondary 3310 and it runs great. That doesn't mean you should ditch the double pumper. It just means you have to buy twice as many power valves. It helps to know your fuel pressure but if you know that your pump is rated less than 7-8 psi, than you should be OK. Holleys can take up to that before the needles are overcome by too much pressure. You can regulate it, but why add all that extra plumbing if you just change to the right pump to begin with. Here's my setup. Chevy 355, Turbo 350, 10" converter, Holley 3310 750cfm, Comp XE274H, Carter street fuel pump rated 6 1/2 psi. Idle vacuum in drive around 6-6.5. I run a 5hg power valve. Runs great. Alot of fun. Hope this helps.

The 280H is supposed to have some what of a lopey Idle???? In bigger cubic inches it will loose some of it but for a 355 it should have a rough idle???? Maybe your trying to tune it out??? You will definitely need a vacuum guage to tune also. You will also need a tach to set rpm. First off I would say your rpm is to high.