I have tried numerous things to get the 455 running right. My carb has been totally rebuilt and I can get proper vaccuum when idling for 15 minutes or so then it just bogs out and the vac steadily decreases. I have tried timing, idle screws, vapor cannister, etc and still can't figure out my issue. I don't believe the float is damaged or the accelator pump is damaged. I experienced this flooding before the carb was rebuilt as well. Does anyone have any ideas what could increase the fuel pressure to the carb??? What about a damaged fuel line sucking air??? Anybody have any ideas. Thanks, btw this is pushing two years of an upper half rebuild. Fun.

Gee, it sounds like your carb problem is ignition module related. The
modules and mechanical fuel pumps are about the same price, and the module
is easier to change than the pump. As the engine warms up, the module
sometimes will act up, and then as the engine gets warmer than that, will
quit altogether. The coil will do the same thing. Ask Ken Henderson about
his issues that he thought were carb related. At least check for spark when
the engine quits the next time. If it isn't burning the fuel, it will mimic
carb flooding. Just saying.
Jim Hupy
Salem, Oregon
78 GMC ROYALE 403
On Apr 2, 2015 3:45 PM, "Bob de Kruyff" wrote:

> budworks521 wrote on Thu, 02 April 2015 16:28
>> I have tried numerous things to get the 455 running right. My carb has
> been totally rebuilt and I can get proper vaccuum when idling for 15
>> minutes or so then it just bogs out and the vac steadily decreases. I
> have tried timing, idle screws, vapor cannister, etc and still can't figure
>> out my issue. I don't believe the float is damaged or the accelator pump
> is damaged. I experienced this flooding before the carb was rebuilt as
>> well. Does anyone have any ideas what could increase the fuel pressure
> to the carb??? What about a damaged fuel line sucking air??? Anybody have
> any
>> ideas. Thanks, btw this is pushing two years of an upper half rebuild.
> Fun.
> It sounds like you are pretty sure it is flooding and getting too much
> fuel. If it is, it's pretty difficult for a mechanical pump to supply too
> much
> pressure assuming it was the correct one in the first place. They are
> pretty cheap so replacing it is much easier if you remove the RH inner
> fender
> panel.
>
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
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I have tried numerous things to get the 455 running right. My carb has been totally rebuilt and I can get proper vaccuum when idling for 15 minutes or so then it just bogs out and the vac steadily decreases. I have tried timing, idle screws, vapor cannister, etc and still can't figure out my issue. I don't believe the float is damaged or the accelator pump is damaged. I experienced this flooding before the carb was rebuilt as well. Does anyone have any ideas what could increase the fuel pressure to the carb??? What about a damaged fuel line sucking air??? Anybody have any ideas. Thanks, btw this is pushing two years of an upper half rebuild. Fun.

I have tried numerous things to get the 455 running right. My carb has been totally rebuilt and I can get proper vaccuum when idling for 15 minutes or so then it just bogs out and the vac steadily decreases. I have tried timing, idle screws, vapor cannister, etc and still can't figure out my issue. I don't believe the float is damaged or the accelator pump is damaged. I experienced this flooding before the carb was rebuilt as well. Does anyone have any ideas what could increase the fuel pressure to the carb??? What about a damaged fuel line sucking air??? Anybody have any ideas. Thanks, btw this is pushing two years of an upper half rebuild. Fun.

Larry, I was looking back over your original question regarding replacement
of a mechanical fuel pump. Realized that we have strayed a tiny bit off of
that, so I had a thought that no one had mentioned that when you have the
pump off, you ought to use a piece of 1/8 " welding rod or plain old
bailing wire with a "j" bent in the very end to get a hold of the timing
chain to check for excessive slack in the chain. 1/8 to 3/16" movement in
the chain while pulling and pushing with the hook is normal. Any more than
that indicates a worn chain and something to keep your eye on. If there is
a great deal of slack, 1/2" or more, you might need a new set of chain and
sprockets pretty soon. This will account for retarded cam timing, and
erattic ignition timing as well because the distributor gear is driven with
the cam, and slack, or more accurately slap in the chain will cause that.
Jim Hupy
a couple of other easy items to check:

Is your fuel tank venting properly? you might try loosening the gas cap
to see if it makes any difference.

is your mechanical spark advance working properly?


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