460 Ford Winnebego Fuel Pump & Carb Replaced - backfires going up Grade

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bigbryz

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Mar 17, 2014
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Just had the Fuel Pump and Carb replaced on this 1986 Minnie-Winnie Ford E350-460ci, Everything seemed to be running fine until I headed up the pass. As soon as I hit the grade doing about 60, started to backfire & lose power. If I floored it, it would downshift, and
try to regain speed, but, the backfiring comes back. Got off the freeway, headed back down the mountain,
and, it runs perfect otherwise. I was able to repeat this at the very same location on I90. 
Taking it back to mechanic, but, he is not sure what would cause this. I did notice that the gas tank is leaking, so, he must have left
something loose when he replaced the fuel pump. Not sure if that could be related?
Any ideas would be appreciated.
Bigbryz
 
First off what are you calling a backfire?
Is it at the exhaust or through the Carburetor?

Backfire out the exhaust is normally from a RICH fuel mixture.
If it is backfiring through the Carburetor ( I assume it is a Carburetor engine) it is probably too LEAN. If it ran good before you did the fuel pump I then would have a look at the fuel pressure.

If there is a leak at the tank you may not be getting full fuel supply to the Carb,if it is indeed running lean.
 
My 460 did that when the plugs and wires started breaking down.
 
Only at an incline like this?
Just seems strange.  Pretty sure the backfire was exhaust, but, need to check . it runs great except for up this mountain pass road,
at about the same place ?
 
Apparently the angle of incline is starving fuel pump. Probably has something to do with leak at fuel tank. How much fuel is in tank?  Remember, Grandpa had to turn his model A around and back up a steep hill if his fuel level was too low. I am not suggesting you try to back MH up the incline ( though it may work).
 
jubileee said:
Apparently the angle of incline is starving fuel pump. Probably has something to do with leak at fuel tank. How much fuel is in tank?  Remember, Grandpa had to turn his model A around and back up a steep hill if his fuel level was too low. I am not suggesting you try to back MH up the incline ( though it may work).
[/q

Grandpa had gravity feed and no fuel pump.
That was quite normal in those days.
Click to expand...
 
Today's mechanics really know very little about the old systems just like yesterdays mechanics know little or nothing about the new vehicles.

Yesterday you needed experience
Today you need training and test equipment.

Your description is quite vague.
In an 85 Winni is the fuel pump in the tank?
If the tank was removed to replace a pump, a fuel filter change would have been in order. There is lots of crud that could be disturbed in the tank of that vintage. Also I am not sure which Carburetor you have but look for a filter at the new carb also along the frame.

The condition you describe can be caused from a partially plugged filter.
Because I don't know the Carb is it new,rebuilt.?
It is possible the power circuit is not adjusted properly.

Good luck I am sure there is a simple fix as those systems were not complex.




 
Lawrence M said:
Today's mechanics really know very little about the old systems just like yesterdays mechanics know little or nothing about the new vehicles.

Yesterday you needed experience
Today you need training and test equipment
Click to expand...

Dialing in / tuning a carburetor is becoming a lost art. You can bolt on on, it will run good enough, but without adjusting and tuning the carburetor to your engines specific needs a great deal of performance can be lost. This is usually not evident until the engine is stressed. 

Was the carburetor a stock replacement or aftermarket? Read your spark plugs, they may tell the story.

I suspect float level too low.

Did you replace spark plugs and wires?

 
If the fuel pump is engine mounted it may be sucking air at that leak.  A high volume electric fuel pump might be a good option to replace an engine mounted pump.
 
You are going to get lots of Ideas but don't start throwing money at the problem.
Look at what you have changed and deal with that!
You always have to say.
What has changed?
In your case a carb and a pump.

Also why did you change them what was the problem that you saw fit to install a new carb.
Was your mechanic qualified? Or a back yard Bubba!!
 
After you get this figured out, you may want to check the roll pin on the Distributor as the backfire will break the pin securing the gear in place when this happens you will get one more backfire with flames about 5' out the exhaust then silence. Mine was a bad fuel pump relay, this was a class C Ford E350.
 
Just a thought, it happened to us, the vent tube for the tank when the tank got put back was pinched so we idled great and cruised ok, but died out when we needed to give some. So one thing to check if it happened after the pump replacement.
 
Thanks to everyone for the Inputs. The RV is at the mechanic getting checked now. I have passed on these
ideas for him to check.  I think the ideas about the filters may be on to it. The fuel pump is in the tanks, and,
I'm sure this is the first time in 30 years that tank has been dropped down. probably shook up some junk.
The carburetor was a rebuild/direct match to original.  The tank leaking is a smoking gun to me also!
I will pass on verdict when i get it!
bigbryz
 
Sounds like it is doing it under Load so I wouldnt hesitate to replace the coil
 
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