Hi All,
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I have finally got back to it and rebuilt my 351W, Holley Carb and outdrive.
I followed all instructions that came with any parts or kits, and followed good practices that I could find in my Ford, Holley and <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comffice:smarttags" /><st1:stockticker>OMC</st1:stockticker> manuals. I took my time ( 1-1/2 years ) and tried to do everything "just right".
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These are in a fairly heavy 24' 1976 Winner Flybridge Sportfisherman.
Carb is Holley 4 bbl, vac secs, elec choke.
I first ran and tuned the unit in my shop. I built a steel stringer mock up, and had all units together. I even built a steel drum of water for the outdrive to run in, including circulated cold water for the drive to draw from and a fan vented top to vent exhaust outside.
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I ran the boat for the first time and developed this problem:
Backfire through carb at or above 3000 rpm.
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It started just fine, idles down ok, temp never breaks 140 degrees, beautiful oil pressure. Timing is 10 btc, gap and dwell are right on, right out of the book.
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What can cause this?
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From my teenage years of old ford pickups, my experience is to suspect bad timing, though my numbers seem just right OR not enough fuel to air running down the beast's throat. I do have a slightly rough idle <700 rpm, but I think that is a different prob ( I may have a minute vacuum issue that I am trying to track down.)
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I am starting to chase my own tail with this, and am looking for a fresh view point.
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Any suggestions?
Thanks

 

BTW- Does anyone know what the actual names for these parts are called?
They are not referenced to or pictured at all in any of the 2 OMC manuals, OMC cd rom, Ford engine rebuilding, and several Holley books that I have referenced for this project.

1) Between the carb mounting flange and the intake manifold, there is a hollow block spacer. It has vacuum access, as there is a hose barb that comes out of it. That point is connected via rubber tubing to the PCV in the rear of the starb head.

2) Once the name of the above part is learned, might help with this. There is an extremely heavy gasket between this hollow block and the intake itself. This gasket must be heat resistant or retardant as it is about the same make up as an exhaust manifold gasket, meaning it has gasketing as well as a metallic side.

Everything I have just shows the carb along with a flange gasket (8R-1398), which would be the gasket that I used to mount carb flange to this hollow block. I had to reuse the heavy gasket (I cringed, but have had no other choice yet, untill I can identify it) between the hollow block and the intake manifold.

1976 OMC electric shift stringer 235 HP 351 winsor Holley list 7163 4bbl<!-- / message --><!-- edit note -->