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Re: [GMCnet] EFI vs Carb [message #326056 is a reply to message #326054] Wed, 15 November 2017 22:45 Go to previous messageGo to previous message
jimk is currently offline  jimk   United States
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma:
Senior Member
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.
>
>
> On Wed, Nov 15, 2017 at 10:02 PM, Mike wrote:
>
>> 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@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

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