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#1 |
Senior Member
![]() Join Date: Jan 2012
Location: Austin, TX
Posts: 553
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GMC 305 v6 Holley 500 swap woes
For those on the gmcclub, this is a repeat post...
So, I got a factory refurb Holley 500 2bbl 4412S wallered out the opening a bit to match the opening on the bottom of the new Holley carb adapter plate, torqued everything to spec, hooked up the fuel, throttle linkage, choke and vacuum advance to the dist. It runs like ****, when I can even get it running. When it does run, the vacuum advance runs the RPMs up super high. I adjust the dist to lower the rpm but it seems to be slightly misfiring. All other vacuum ports are plugged. I've tried everything... setting the idle mixture screws out 1 1/2 turns from turned in all the way, messed with the ignition timing and I think I smoked my coil (and I'm sure my starter is about to go too). It ran decently with the Stromburg WW2 carburator. This is MADDENING. Any other ideas? The only other thing I can think of is the timing chain skipped at some point? It there an easy way to determine the initial timing of correct? Side question: with the new carb, how does anyone access the #3 spark plug to change it or seat the boot easily? Thanks for any help. |
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#2 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,575
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Re: GMC 305 v6 Holley 500 swap woes
Did you set the float level?
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#3 |
Senior Member
![]() Join Date: Jan 2012
Location: Austin, TX
Posts: 553
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Re: GMC 305 v6 Holley 500 swap woes
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#4 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,575
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Re: GMC 305 v6 Holley 500 swap woes
Be prepared for some fuel leakage when you open the window on the side.
And some leakage when you adjust the level screw and lock nut. I always set my float so that when you lean on the fender a little fuel leaks out. Any other questions just ask. |
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#5 |
Senior Member
![]() Join Date: Oct 2007
Location: Marietta, GA
Posts: 783
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Re: GMC 305 v6 Holley 500 swap woes
From looking at the photo, it looks like maybe you have an unused and unplugged vacuum port? Make sure any ports you aren't using are plugged. Also, if the vacuum advance is causing your idle speed to be too high, switch to a ported vacuum source. This will be the port high on the metering plate in most cases on a Holley.
Checking the float level is vital - fuel should just barely dribble out of the hole with engine idling. Finally, you'll need to adjust the accelerator pump cam clearance, and possibly the squirter size. You can google how to do that. All that said, it's CRITICAL to make sure you have no vacuum leaks,. so gotta make sure your seal/gasket to the intake is good. |
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