Carb trouble I think

[Longhorn21]

I took my 87 Supra Comp out today and it ran great for an hour then it started pulsating between 1000 to 2000 rpm's. If I go at idle in gear it runs great and if I'm over 2000 rpm's it fine. By pulsating i mean it will rev-up and then rev-down over and over again. I think it may have something to do with the Holley carb but not sure what. Any help would be appreciate thanks

[michael hunter]

When was the last time the carb was overhauled?

[foxriverat]

Have you checked the fuel filter? my 96 efi comp started surging. And the fuel filter was the culprit.

[Longhorn21]

I got the boat about three years ago and the previous owner said the carb was 1 year old. If the fuel filter is the screen that is hooked to the carb from the fuel line then I have checked it and it is clean. It also floods if I keep it off for long period of time, so I'm thinking that my floats are not stopping the gas after the engine is off. That doesn't explain the pulsating though

[michael hunter]

Also check the power valve. Check the fuel filter/water separator. If its go points check the point gap.

[Longhorn21]

Less then a year ago I had the timing, new distributor cap, points, wires, and a new starter. I'm guessing I need a carb rebuild

[Longhorn21]

I don't have a fuel filter on this boat only a screen at the carb. How do I check the fuel/water separator. I don't want to take the carb apart if that's not the answer. I think it has to do with the carb, but what in the carb could cause it to flood other than the floats. Sorry this may sound stupid but I am a novice and trying to learn. The pulsating or surging between 1000 & 2000 rpms only is driving me crazy what could it be

[wideopen]

Rebuild the carb and you will fix the problem. I have an 88 comp, and the exact problem has happened to me more than once. Now, I rebuild the carb about every 2 to 3 years and it works great. Pay particular attention to the jets and needles, use lots of carb cleaner, and remove the sediment you find in the float bowls--you may have to gently scrape it away. Hope this helps.

[wideopen]

Also, you should have a fuel filter/water separator on the stringer at the front of the motor, left hand side. Replace this every season. It's a canister filter--Wix part #33110. Most automotive parts stores have them. If your boat doesn't have this filter, install one. Skidim should have it.

[Longhorn21]

That's Wideopen for the reply. When you talk about rebuillding the carb are you saying to get a kit or just open it up and clean everything with carb cleaner. I can open it up and clean it with carb cleaner, but getting a rebuild kit may be alittle hard for somebody like me that's never done it, but I would try If that's what your talking about.With the fuel/water separator are you saying to replace the filter or the whole unit. Sorry if these are stupid questions

[haugy]

Replace the Fuel filter first, just the filter, unscrew it and carefully remove it. Remember, you're unscrewing it upside down so to unscrew it, the filter should turn clockwise if you are looking down from above it. If it hasn't been changed in a while, an oil filter wrench will free it up.

Take it out. Pour out the fuel into a clear container, or a very clean bucket. Look for little air bubbles that never actually pop. That's water. Or you could just have a fuel filter that needed replacing, and the fuel looks clean.

Before putting your new one on, fill it with clean fresh fuel. This will help prime it so the pump and the engine are turning over constantly trying to get it full of fuel before it will start.

After that, if it still does it, time to get into the Carb. My first guess would be the power valve.

[wideopen]

Get a rebuild kit when you open up the carb. Discount Inboard Marine will get you the parts you need. The Holley carb is not hard to rebuild, just watch the little parts. The fuel filter/water separater on the stringer--just replace the canister filter inside. There is one bolt on top of the filter housing--unscrew that and the canister comes out the bottom. There is a gasket that seals the rim of the canister that you will have to remove with a little screwdriver, and just make sure the new one stays up in the groove.

[Longhorn21]

Thanks wideopen I'll do that this weekend. What size jets are in your carb cause the Holley guys said for my 4160 double barrel 600 cfm carb the jet size should be a size 74 and the one in their now is 65. That's a big difference. Your boat year and model is close to mine so I'm wondering what size your jets are.

[wideopen]

I believe my jets are 65's, I played around with different sizes, but 65's seemed to work the best. You could call Discount Inboard Marine to be sure--those guys are helpful and spot on what you need.

[Longhorn21]

Thanks I'll call them today. It kind of confused me when Holley told me 74. I check it out and keep everyone posted