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Thread: Thoughts

  1. #1
    19cobaltcd
    Been fighting this thing for a year now. 260 Mercruiser with old alpha drive. 350 chevy with comp marine cam (460 lift), edlebrock performer intake, 650 spreadbore marine holley, roller tip rockers, stock exhaust. Thing runs like a dream until the back barrels open then it overheats, it is almost as if the throttle is connected to the temp gauge. Even with the changes I cant get anymore rpm or speed using the exact same prop. Also, end of last summer, stopped and picked up 3 friends, so its 4 adults, 1 kid and my cooler with refreshment and could not get it on plane, it was a dog and overheated. Tore it down again this winter, nothing to explain it. Cam degreed perfectly, no visible leaks in any gaskets. Only thing funny I found was the intake, the runners off the right side of the manifold had soot at the heads, the runners off the left side were clean. I'm starting to believe this brand new Holley carb is crap. Talked to Holley about it, basically there is nothing I can do to it. I think now it is leaning out when the back barrels open. Now I think I will replace it with an Edelbrock marine carb but I'm confused here too. Edelbrock says use the 600 cfm, Crockett from the mag says use a 750, (there was a question a couple of months ago and I thought the guy was describing my engine). Any thoughts?

  2. #2
    canuck1
    Can you borrow another carb to try? A 600 will work the best on the specs you listed

  3. #3
    blown428fe
    I also would try to barrow a carb before buying another. My friend changed his prop and had overheating problems only when he was on it, changed it back and it was fine. Maybe try a prop change. Just my opinon, I dont know shit about props.

  4. #4
    fourspeednup
    Aside from tearing into the carb and figuring out what's up, I only have 1 suggestion.
    If you're going with edelbrock, get the 750. That's probably more cfm than you need, but in my experience, the edelbrocks perform like a smaller holley and you shouldn't lose much if any throttle response.
    Soot on only right side+dual plane intake=left side of carb is goofy. This should lead to an quick solution once one of the carb gurus get on here

  5. #5
    19cobaltcd
    Yea, I've built hot rod engines for years and this one is kicking my ass. Dont have anyone to borrow a carb from, everyone here I know are running hugh double pumpers. Hope to hear from one of the experts out there with suggestions. I've stumped the best engine people I know in this neck of the woods.

  6. #6
    327,jet
    Maybe you have the wrong plugs for that year engine . It also could be a restricted exhaust or problems with water circulation in the block .good luck

  7. #7
    Senior Member
    Join Date
    Feb 2009
    Posts
    4,169
    I'll throw a couple things out there. Check your total advance... make sure it's not retarded. Have you fattened up the secondary jets? The Chevy fans will know what timing specs should be.... what advance, and in at what rpm. If you have a distributor with mechanical advance, do the weights move freely? A combination of retarded timing and lean secondaries will heat it up in a hurry.
    Just curious.... why are you using a spread bore, and not a square bore carb?

  8. #8
    19cobaltcd
    I had the dist spun on a machine. It was exactly as it was supposed to be. Never been able to do a high rpm check on the timing, engine cover in the way, I'm gonna leave it home the first couple of trips and do that but I have moved the timing around within 2 or 3 degrees of the idle setting, made no difference. The carb is a spreadbore with the metering plate on the secondary's, holley tells me that is the biggest one they make, so there is nothing I can do make it flow more gas thru the back barrels.

  9. #9
    19cobaltcd
    I got the spread bore cause it fit the manifold I had. I dont want to run a double pumper and I thought this one would work okay. I didnt know when I bought it but I ended up putting a 1" spacer under the carb to get clearance for the thermostat housing. Thats part of the reason I'm leaning toward the edlebrock carb next, I think they will fit even a spreadbore mainfold without an adapter. Even with a spreadbore to square adapter it will be much thinner than the 1" one that I was using. With that spacer my spark arrestor (K&N) only missed the engine cover by about a 1/2 inch. Really dont want to cut a hole in my engine cover for the air filter. Mine is old style, box over engine with jump seats on each side, but it's all one molded fiberglass piece, lifts up and back like a car hood.

  10. #10
    DetroitJim
    Cobalt:
    What have you done to check out the cooling system? It sounds like you have a restriction in the water intake, a shot water impeller, or a plugged up hose somewhere. As soon as the engine sees a load, it overheats due to no water flow. Why do you think the carburetor or ignition would make it overheat? In a marine engine you have an unlimited supply of cold water. Late timing or lean mixture will have very little effect on temperature.

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