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Thread: Chevy 350 Motor Problem

  1. #1

    Default Chevy 350 Motor Problem

    I have done everything that I can to figure out what the problem is. My boat has a rebuilt chevy 350 in it. It will get on step but I cannot get it to go over 3,000 rpms, it will fall falt on its face. I have replaced the starter, alternator, and coil. I have checked the timing and adjusted it to book specifications. I have not replaced the distributor but it is the last thing that I can think of that might be causing the problem. Fuel is fine, fuel filter is new. What can it be?

  2. #2
    Member Laker Taker's Avatar
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    Low pressure fuel pump?

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    Moderator stid2677's Avatar
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    Have seen similar behavior before. I would replace the plug wires, they get really hot in the enclosed area and can break down and get very fine cracks that will allow them to short out against any metallic surface. Fairly cheap and easy to replace and is not a bad idea to change every few years anyway. Sometimes you can actually see the sparks in the complete darkness. Another much more painful way is to run your hands over the wires while the engine is running, you will know without question if you get the snot shocked out of you, I would just replace them.

    Just a SWAG, but have seen it more than once on both vehicles and boats.

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    Member Frostbitten's Avatar
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    Have you checked compression? I had a 5.0 a few years back act the same way. Compression checked revealed there was a need to tear the motor down, and it got reallllly spendy after that!! Long story shortened, it was cheaper to do a complete re-power at that point. For your sake, I hope it's something simpler (and cheaper).

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    Moderator stid2677's Avatar
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    Quote Originally Posted by Frostbitten View Post
    Have you checked compression? I had a 5.0 a few years back act the same way. Compression checked revealed there was a need to tear the motor down, and it got reallllly spendy after that!! Long story shortened, it was cheaper to do a complete re-power at that point. For your sake, I hope it's something simpler (and cheaper).
    A compression check is a solid recommendation, especially if it is burning oil. Suck, bang, blow, basic mechanical troubleshooting.
    An exhaust restriction will also cause these type symptoms.

    Had a jeep that got to where it would not get faster than 40 mph after a complete rebuild. Drove me crazy and threw away a bunch of money troubleshooting it. Finally in desperation I disconnected the exhaust pipe from the manifold and it ran like a raped ape.
    During break in oil fouled the muffler and catalytic converter. Replaced both and solved problem.

    Steve
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    What boat is this on? Is it a jet or a prop? Post a pic.

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    Carb or EFI ?

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    Member SusitnaAk's Avatar
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    maybe the vacume advance in the dist. ck plates springs see not rusted or gummed up Hook timing light up to it and watch the marks as get higher rpm they should advance with..

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    Member hoose35's Avatar
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    I say start with the distributor, plugs, and wires. Sounds like it is not hitting on all cylinders. Also as was mentioned before, a compression check is a good idea as well, it can be very informative
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  10. #10

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    Wrong Prop pitch & dia will do the same thing!

  11. #11

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    Thank you all for the great advice. The motor has great compression so I think a new set of wires, a high performance distributor and new plugs is my next step. Will keep you all posted. Oh, my outdrive is a volve penta 280 duo prop and it's a carb motor.

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    Quote Originally Posted by Laker Taker View Post
    Low pressure fuel pump?
    How much is it?

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    Member Laker Taker's Avatar
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    Quote Originally Posted by fishmen View Post
    How much is it?
    I should have asked more questions about his set up before I threw in my .02 but I just had the same symptoms on my 5.7 EFI motor. My problem ended up being the high pressure pump which was $400. I was able to check my low pressure pump and it was ok. They run about $250. Everyone that I talked to about my problem thought it was fuel pressure related, and when I finally hooked a gauge up to it, it was.

  14. #14

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    Why would you replace the starter and alternator because the engine won't rev? Sounds like a loose nut behind the sterring wheel.

  15. #15

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    Dogfish,
    I was just letting anyone willing to assist me with information that I have completed on the engine, I know the starter and alternator have nothing to do with the engine problem. However, I'm not a mechanic just looking for assistance not a smartass answer.

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    I thought the same thing so Dogfish is not along. Anyway one common mistake people make setting the timing is not removing the vacuum from the distributor. Before I set the timing I would check to make sure the timing TDC mark is at TDC.


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    Same engine, same problem. Replaced pretty much the same things that you have... after replacing the carb, to no avail, we found a slight blockage in the fuel lines... little compressed air and voila! Check all the screens and filters as it don't take much to knock down those rpms.

  18. #18
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    What carb? We got a VP 5.7L with the Rochester Qjet. Wouldn't hardly get on step at the begining of this season. Appeared that the secondaries were not opening up fully and a carb rebuild fixed the problem.

  19. #19
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    Assuming it's a Q jet carb, there is an internal fuel filter in the carb under the fitting the gas line screws into. Replace that if you haven't. If it's reving to 3000 and then falling off rpms, it sounds more like a fuel problem than ignition. Faulty ignition will usually rev to a certain point and then start missing but not loose rpm. Wrong timing usually causes a loss of power without missing and will rev to a certain point and then not climb further. I'm assuming that it performed ok prior to the rebuild so improper prop pitch is out. And a plugged exhaust is unlikely as there is no muffler or cat conv to plug. Be careful when replacing the internal filter as there is a front and back end to the filter and the carb side of the gasline fitting has very fine threads and is easy to cross thread. Also, after tightening the fitting, hold the fitting with a wrench while tightening the fuel line to prevent destroying the threads in the carb. I believe you have a fuel delivery problem and the internal filter is often overlooked. Good Luck!

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    Agree it sounds like a fuel starvation problem. Check your anti-siphon valve on the top of your fuel tank. They're notorious for plugging up.

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