I have an 88 Gulf Stream Sunsport that I recently bought. It has been sitting for 2 years and it runs good except at about 50 to 55mph it back fires thru the exhaust. E have changed plugs and wires and rebuilt carb. Does anyone know if it has an inline fuel filter? Also the distributor and coil looks new inside?

There should be a large in line filter along frame rail just in front of right rear wheels.Carb getting rebuilt should have taken care of filter in the inlet port there. Backfiring is more likely to be electrical. Check to make sure the plug wires go to the correct one.Check the EGR valve and vacuum control lines.Does the back firing happen during acceleration or deceleration?

A filter isn't going to make it backfire through the exhaust.Did it do that before the new plugs? Does it do it more under a load? Is there a stumble feeling? (EGR)If a plug gets cracked during installation it can act like that. You could also have one or more valves sticking because it sat so long. Running some good fresh fuel with a can or two of Seafoam through it may take care of that if it's the case.

It does the back fire during acceleration of 50 to 55. It did it before and after changing new plugs and wires

Crossed plug wire.Verify firing order and wiring.

Thank you for you help! Will try these things and get back with you both. Hopefully I can get this fixed by wed nite. Suppose to leave on a short 2 hour trip on thurs morning?

454 Back fire thru exhaust | Good Sam Community

Gale_Hawkins
Explorer
Jul 09, 2014
wa8yxm wrote:
Though I do admit that on many vehicles the exhaust is to the rear and thus "BACK FIRE" might be proper.

In automotive terms a back fire is a fire backwards (Out the air intake instead of the exhaust)..

That said.. Good advice above.. I can not improve on it.

I guess I call After Fire Back Fire :)
wa8yxm
Explorer III
Jul 08, 2014
Though I do admit that on many vehicles the exhaust is to the rear and thus "BACK FIRE" might be proper.

In automotive terms a back fire is a fire backwards (Out the air intake instead of the exhaust)..

That said.. Good advice above.. I can not improve on it.
Gale_Hawkins
Explorer
Jul 08, 2014
saulfun1971 wrote:
It does the back fire during acceleration of 50 to 55. It did it before and after changing new plugs and wires

Had back firing twice with our 1992 454 TBI. First time it was the pick up coil under the distributor. We did the labor and the part cost $13 but I would just with a rebuilt distributor next time I think.

The second time it turned out to be a dirty fuel filter .

Both problems had the identical symptoms. As noted with a carb you should have two fuel filters.
Jayco23FB
Explorer
Jul 08, 2014
Does your truck have an air pump as part of the emmisions system? A bad diverter valve and or check valves on the air manifold will cause this. This is a 1988 and it still has a carb? Most of GM trucks switched to throttle body injection in 1987.
ernie1
Explorer
Jul 08, 2014
GM distributors are known for the centrifugal advance, which is fastened to a rotating plate, gumming up and not rotating anymore or being balky. Grab the plate by hand and see if it'll rotate. If not, the distributor has to be disassembled and cleaned. You can also check the operation by removing the vacuum line to the vacuum advance and then using a timing light and revving the engine to see if the timing changes.
powderman426
Explorer
Jul 08, 2014
darsben wrote:
454 engines are notorious for collapsing the vacuum advance tubing. Please replace the tubing going to the distributor with new tubing.

X2 and listen for vaccum leaks.
darsben
Explorer II
Jul 08, 2014
454 engines are notorious for collapsing the vacuum advance tubing. Please replace the tubing going to the distributor with new tubing.
EDIT:
Also to answer your question My carb has a filter at the inle
saulfun1971
Explorer
Jul 08, 2014
Thank you for you help! Will try these things and get back with you both. Hopefully I can get this fixed by wed nite. Suppose to leave on a short 2 hour trip on thurs morning?
enblethen
Nomad
Jul 08, 2014
Crossed plug wire.
Verify firing order and wiring.
saulfun1971
Explorer
Jul 08, 2014
It does the back fire during acceleration of 50 to 55. It did it before and after changing new plugs and wires

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454 Back fire thru exhaust

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