Four Barrel Miss

Got a 350 mercruser with a 650 holly spreadbore, vac secondary. Engine misses when the secondary opens all the way. Revs quick and hits all 8 with the secondary cracked. No vac leaks and ignition seems to be working fine. Had a Quadjet on the engine originally and it did the same thing. Any ideas????????????????

Re: Four Barrel Miss

gb, Possible water in fuel, check the fuel/water seperator?

Re: Four Barrel Miss

Could also be:
Wrong powervalve installed
Wrong main jets installed
Wrong secondary diaphragm spring installed

Is this carb. new? Is it the exact Holley number specified by Merc. for that engine? If not, a start would be to check the above against the service manual specs..

Re: Four Barrel Miss

can't tell from your description, but are you revving the motor in neutral or do you mean it revs up quick in gear when you give it throttle?
Assuming the latter, can you determine if the miss happens at a certain rpm?
The fact that you have the same problem with two different carb lessens the chance of it being a carb problem. It could still be an ignition problem at high rpms. Could also be fuel delivery is short at high rpms- check fuel filter, fuel pump, blockage in fuel lines/fittings, and fuel tank vent. If neither fixes it then begin looking at the valves. A non sealing or improperly adjusted valve many times that will cause a high rpm miss or backfire.

Re: Four Barrel Miss

Thanks for the suggestions, will change the seperator filter this weekend. This holly is classified by summit racing as a "marine quadrajet replacement carb"and is new out of the box. Had this boat repowered 2 summers ago with rebuilt 350, new quadrajet and delco marine electronic ignition. Engine had this miss from day one. It doesn't matter if you rev in or out of gear.Most prevalent when climbing back of an ocean wave and throttle is wide open, rpm tryin to get to 4800. I have to back up throttle allow minimum secondary and it will gain rpm and the miss goes away...don't know about the type of fuel pump they installed, thinking about a high volume pump as the suggestion fuel mix is leaning out with spreadbore air flow is possible.............

Re: Four Barrel Miss

Holley or Q-Jet ???

Re: Four Barrel Miss

I'm confused by your last post, too. If it's always been there, and it is in fact a Holley, you might want to order a trick or tuner kit for it. They come with multiple jet sizes, diaphragm springs, etc. and are designed to help you set the carb up to your specific application. Might be some screwing around, but might solve the problem, too. Check out this website:
http://www.bob2000.com/carb.htm

Found this on there:
"Question: Is the Holley spreadbore better than my Rochester Quadrajet?

Answer: Not at all. The Holley spreadbore carb is a poor imitation of the Rochester Quadrajet. Here's why.

The Rochester Quadrajet is a modern design, and uses some very forward-thinking features such as a central float bowl with one float, vacuum-operated metering rods for power enrichment, an air-door controlled secondary, and no gaskets below fuel level. A couple of disadvantages are its sliding cup accelerator pump, and hard-to-find parts.

So, how does this relate to Holleys, since this is a Holley page? The design of the Holley spreadbore replacement leaves out many of the good features Holleys are famous for, and leaves off most of the good features of Rochester Quadrajets.

The Holley spreadbore lacks these features, which are standard on its squarebores: Externally adjustable floats, standard accelerator pump nozzles, standard gaskets.

The Holley lacks these features, standard on a Rochester Quadrajet: Metering rods for power enrichment, air-door controlled secondary.

Since the Holley is lacking in so many things that the Quadrajet excels at, I recommend to anyone who is thinking of putting a Holley spreadbore on any engine: Don't! If you have a spreadbore intake, use a Rochester Quadrajet. If you really want a Holley, change the intake manifold to use a squarebore Holley. Don't use adapters, either! They are proven power robbers. "