Johnny,
Vapor lock phenomenon develops any where between the tank and the
carburetor / throttle body.
Should one not address that, you will run into this issue at one time or
another.
I'll address it later as I have several things that need to be addressed
now.
On Wed, Nov 15, 2017 at 7:42 PM, Ken Henderson
wrote:
> Mike,
>
> Your valve seat failure was undoubtedly the source of your problems.
> Without knowing the history of the engine, I won't speculate on the cause
> of that, 'tho' obviously the head had been rebuilt, and probably by someone
> who didn't realize that the seats in the head were hardened from the
> factory, so shouldn't have needed seats.
>
> An alternate possibility for the symptoms you described is that the exhaust
> crossover in the intake manifold has not been blocked. Without that mod,
> vapor lock is MUCH more common with today's gasoline formulations. When
> you talk to Dick Paterson, talk to him about that: He sells blockoff
> plates and gaskets modified to work with them.
>
> Finally, 0.054" or 0.060" gaps are too wide for the 455, despite the 0.080"
> specified in the factory manuals. I think Dick will tell you to use
> 0.038". Wider gaps stress the ignition module (and other ignition
> components) too severely.
>
> Ken H.
>
>
>
> > Thanks Jim and to the others that responded, I guess I'm just as confused
> > by the decision to go with EFI over a properly tuned carb and which
> system
> > to go with (if I decide to go with fuel injection), as many others are.
> >
> > My issue began while on a trip to northern Ontario a couple of months
> ago.
> > 1975 26' Royale by Coachmen,I left and the coach was running fine,
> > temperature was around 75 degrees. A couple of hours into my drive I
> > decided to stop for fuel, when I pulled into the service center the coach
> > began
> > running rough, idle was off and for the first time the coach stalled.
> > After fuelling up it started fine but was clearly not running smooth,
> once
> > on
> > the highway it appeared to be running fine until I stopped again.
> >
> > I let it cool down and after a few hours I fired it up and same issue.
> > Next day same thing. Once I arrived home I noticed that the black soot
> left
> > from the tail pipe suggested it was running rich. Replaced plugs, gapped
> > at 54, wires, cap and rotor along with new air filter and fuel filters
> and
> > it
> > started and ran beautifully for a short run of ten minutes, then it
> > started running rough again.
> >
> > Replaced the coil and ignition module, installed a fresh set of plugs
> with
> > a gap of 60, set the timing, fired right up and idled smooth for a few
> > minutes then started acting up again, almost as though when getting to
> > temp caused the idle issue. At this stage decided to do a compression
> check,
> > everything was excellent except number 2 had ZERO compression, determined
> > to be exhaust valve, seat jumped out.
> >
> > Now I'm ready to have the heads and intake reinstalled after a valve job
> > with everything new and carb cleaned out, at this stage trying to decide
> > which way to go regarding EFI. I will do some research on the EBL system
> > and will get in touch with Dick Paterson.
> >
> > I would like to drive the coach out to California in the spring and
> > obviously hoping for a reliable set up. Any additional opinions are
> welcome
> > especially those which are based on experience with a particular system.
> >
> > All the best,
> > Mike
> >
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
