440-3 backfire

[The_Handier_Man1]

From: waylonsway53  (Original Message)
Sent: 1/28/2005 7:11 PM

Thanks for the previous thread answers.I look forward to being on the road and meeting everyone somedayLOL..I would like to know what would cause the engine to backfire like crazy when the gas pedal is pressed down.It runs like &%*&*%$ and backfires in the exhaust.Runs kinda smooth when idle.However the smell after is horrible smothering..Only started doing it after it warmed up.Thanks denison for you earlier response and the others as well..Glad you like the site..Waylon Rules



From: denison
Sent: 1/28/2005 8:37 PM

Well; You have a nice supply of problems that are actually common in 30 year old vehicles that sit 99.9% of the time. But we might need more info to be able to guess better.
I call the explosions out the exhaust “after-firing”, and popping back up through the carburetor I call “backfiring”. Both backfiring and after-firing could be caused by a carburetor that had sediment clogging up the cruise circuit and power circuits, or allowing way too much fuel to flow through â€" as from a needle valve into the carburetor float chamber that was not closing off completely, or even carburetor secondary throats that arent working right. If the carb hasn’t been rebuilt in the last 6 or more years, I would be suspicious of it.
Also, leaky valves, caused by sticky lifters, or by poor lubrication on the valve stems â€" again these symptoms often result from an engine that hasn’t been used enough for the valves to get properly lubricated, or for the oil sludge to work its way out of the lifters. Proper valve stem lubrication happens via oil mist, when the oil is fully warm. This requires the RV be driven on the highway, for maybe 30 minutes at least â€" not just running at a fast idle in neutral in the driveway. The space inside the valve covers is the last part of the engine to warm up. That’s why it is also the most grungy looking in there.
The problem could also be deteriorated ignition wires, or spark plugs that were really old. Even a cracked distributor cap, or dirty rotor, or faulty ignition coil. If the engine has ignition points, an old corroded set of points can cause misfiring whenever it feels like it, or a bad or poorly grounded condenser. This would not be true if yours has the electronic ignition. The electronic system has a pickup coil inside the distributor, not points. The 413 engines came with points until sometime in 73, then came with electronic ignition till they switched to the 440 engines. The 440s in Winnebagos always came with electronic ignition. Do you have any idea how old the ignition wires are?
The bad smell in the exhaust probably means unburned fuel, and that could be from poor ignition, low compression, or from the carb supplying too much fuel for amount of air â€" a rich mixture. It also wont help if the gasoline in the fuel tanks dates from more than 2 years ago. Fuel that old can spatter gummy varnish deposits onto spark plugs that will short them out, and which wont burn off easily. This never happens with fresh gasoline.
You might want to do a compression check, just to make sure that all of your valves are really opening. If there is one or more badly bent pushrods, it would mess up the flow of air into the intake manifold, which will also mess up the air/fuel mixture. Pushrods get bent when an engine sits for a few years, then is started. Some of the valves might not open at the first turn-over, due to having seized in place. The result is one or more bent pushrods. Its not at all uncommon. Luckily they can be replaced from inside the RV, and arent overly expensive or hard to find. And if they are only slightly bent, you can run it that way for a long time.
Low compression can also come from gummed up compression rings on the pistons, but using it at moderate speeds would normally free that up fairly quickly.



From: waylonsway53
Sent: 1/28/2005 11:23 PM

Thanks denison,the plug wires are new as is the electronic ign module and regulator.Also is the rotor and cap.Did the plugs on one side but got to cold and wet hrere to  do the other side.As I said it now starts up fine.Only after it has run idle for about 10 minutes it starts to after fire..when you depress the gas pedal.Can I use standard parts on the internal engine or do I have to buy oversize?I have a remanufact.Carter thermo quad carb. on it now but it has been on it for a while I think..Would like to put a 1407 edelbrock on it with electric choke if I can..
Thanks and look forward to hearing from you again..



From: west coast redneck
Sent: 1/29/2005 4:42 PM

I think your on the right track.If it's not electrical go to the carb.I have the same motor with the original old Carter carb..Had nothing but trouble with it , so I replaced it with a 750 Edlbrock.# 1411 with electrick choke. Made a big difference, & got rid of a few vacuum hose that were now needed with this carb.Less to go wrong.Good luck



From: jsn80
Sent: 2/3/2005 8:29 PM

I have a 318 that afterfires at idle only.  I've adjusted the timing and the carburator and filled the tank with ethenol gas.  This reduced the afterfire quite a bit, but not completely.  I know I have two exhaust leaks, could that be the culprit?

jsn80



From: denison
Sent: 2/3/2005 9:34 PM

By exhaust leaks do you mean leaky exhaust valves? I suppose they could be causing this. But it would also mean the engine was running pretty rich, or that there was some misfiring, leaving unburned gas/air mixture being pumped out of the cylinder and into the exhaust manifolds/exhaust pipe. This could happen if you had spark plugs that didnt have the correct -reach- (length) for the spark to be fully inside the combustion chamber. They might work fine at faster rpm and larger throttle openings.
If you mean exhaust gases leaking from the manifold, that would not itself cause the after-firing; but could make the slight amount of normal after-firing more noticeable.
You said you have it running on ethanol gas. Do you know what percentage of ethanol is in the gasoline. Usually an engine running rich enough to after-fire a lot would also be putting out some puffs of black smoke. I could suspect the carburetor of needing to be cleaned out and rebuilt.



From: jsn80
Sent: 2/3/2005 10:29 PM

My winnie has dual exhaust with headers, the leak is where the headers bolt onto the exhaust pipes.  The ethanol is 10%, which raises the octane from 87 to 89.5.  Also I'm not seeing black smoke coming out of the exhaust.  I haven't checked the spark plugs yet.  Hopefully I can work on that this weekend.

Thanks for the help denison,

jsn80



From: jsn80
Sent: 2/14/2005 9:58 PM

Changed out the spark plugs and wires yesterday....What a chore that was... The gaps were off on the old plugs and the wires just fell apart when I pulled them off of the distributer.  I want to recheck my timing again now that I have good plugs and wires.  I'm afraid I might have to do a carb rebuild.



From: mightybooboo
Sent: 2/16/2005 6:21 AM

"I'm afraid I might have to do a carb rebuild."

All I know is any maintenance/rebuilding you do,the happier you will be.These are fine trucks,very durable and dependable when done right.

BooBoo