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Thread: Chevy 350 stumbling

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    Chevy 350 stumbling

    I know we have a van forum but since my 1972 Chevy C30 dump truck has a old Chevy 350 engine and some of you have these in your vans, I thought I would ask about a problem I am having. First I will tell you about the engine itself. It is a crate engine that matches the same year that I had because they took the numbers and matched it. I did change to electronic ignition years ago. The problem it stumbles sometime, it is almost like a electronic miss. When I switched the engine I put new wires , distributor cap , rotor , plugs and last summer I replaced the vacuum advance . I also bought a rebuilt carburetor ( 4 barrel ) thinking that was it but it still does it. It starts and idles perfect . It doesnít do it all the time but when it does it it does it when you are at a stop it will start like a hesitation and a miss and then it seems to run alright. It doesnít backfire which I have heard it wasnít a carburetor issue but I donít know about that. I would appreciate any suggestions. Thanks

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    VCVC Charter Member Vanner68's Avatar
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    Check for vacuum leaks at the intake and carb base. Spray a little ether in those areas with the engine running and listen for the rpms to pick up.
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

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    Quote Originally Posted by Vanner68 View Post
    Check for vacuum leaks at the intake and carb base. Spray a little ether in those areas with the engine running and listen for the rpms to pick up.
    Thanks Greg I will check that. I did retighten the carb bolts the other day but it didnít seem to make a difference .I did put a new gasket on when I put the rebuilt carb on it . It seemed pretty thick but it came with the carb.

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    Check for consistent fuel flow

    Also check your fuel filter for clogs and the rubber portion of your fuel lines for air leaks.
    Sitting on top of the wheel

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    Quote Originally Posted by Vanner68 View Post
    Check for vacuum leaks at the intake and carb base. Spray a little ether in those areas with the engine running and listen for the rpms to pick up.
    I had my knee replaced so this hasnít been a priority. Was messing with it today, when I sprayed starting fluid around the base at idle the rpms dropped. So I am guessing that it is sucking the starting fluid into it and getting to much fuel ? When I put the rebuild carb on I got last year the gave me a gasket which I put on but I am thinking it was thicker than the old one. Could the thickness be a issue ? Is there any way to seal the area between the carb and manifold better? Thanks

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    VCVC Charter Member Vanner68's Avatar
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    Quote Originally Posted by Mags View Post
    I had my knee replaced so this hasnít been a priority. Was messing with it today, when I sprayed starting fluid around the base at idle the rpms dropped. So I am guessing that it is sucking the starting fluid into it and getting to much fuel ? When I put the rebuild carb on I got last year the gave me a gasket which I put on but I am thinking it was thicker than the old one. Could the thickness be a issue ? Is there any way to seal the area between the carb and manifold better? Thanks
    First, make sure there isn't any old gasket stuck to the intake or carb base. Make sure there are no nicks or scratches on either. The thicker gasket helps isolate the carb from engine heat, if it is a hard phenolic it should have a gasket top and bottom as well. I will spray some WD40 on the gasket surfaces to soften them up a little so they seal better.
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

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    Quote Originally Posted by Vanner68 View Post
    First, make sure there isn't any old gasket stuck to the intake or carb base. Make sure there are no nicks or scratches on either. The thicker gasket helps isolate the carb from engine heat, if it is a hard phenolic it should have a gasket top and bottom as well. I will spray some WD40 on the gasket surfaces to soften them up a little so they seal better.
    Should I go ahead and get new gasket before taking the carb off ? Also I was checking it again this afternoon and I sprayed around the back of the carb where the distributor sits and it ignited . Is there a chance it could be maybe a crack in the distributor cap that is causing the stumbling? I canít figure what else could ignite the starting fluid. Thanks Greg P.S. howís the new job?

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    VCVC Charter Member Vanner68's Avatar
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    Definitely a spark leaking out there. I would change out the cap and rotor first.

    New job is working out ok, biggest hurdle is remembering what all the line names are and where they are located.
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

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    Quote Originally Posted by Vanner68 View Post
    Definitely a spark leaking out there. I would change out the cap and rotor first.

    New job is working out ok, biggest hurdle is remembering what all the line names are and where they are located.
    Thanks Greg I will try that. Good luck.

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    Remove the distributor car and rotor, after inspecting the "flywights and springs" mannually turn the mechanical advance to see if the weights move and return.

    while you are in there,make sure to clean the pads under each flyweight and clean the fly weight posts.


    this may help - - https://www.google.com/search?client...ghts#kpvalbx=1

    Check your vacuum advance connection for smooth operation. Some engines seem to run better with ported vacuum, (no vacuum at idle) others seem to run better with full manifold vacuum at idle.

    Many suspected carb issues often turn out to be ignition related issues

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