1977 Dodge M880

Hi Everyone. I'm the (somewhat) proud owner of a 1977 Dodge M880, which is the military surplus version of the Dodge W200.

I've owned the truck for about six years and have had the most consistent running problem with it. I posted about it over at Steel Soldiers but I figure I'd ask here as well.

Instead of re-writing everything, here's a copy of the issue as I posted it over there. Hopefully some of you guys might have some ideas?

"This old 77 has had a persistent fuel problem for several years. It just chokes out of fuel and stops running. Here's what does NOT appear to be the cause:

1. Dirty fuel tank - removed, cleaned, reattached fuel tank
2. Bad fuel lines - all lines have been replaced
3. Bad rollover valve - removed rollover valve from the system altogether
4. Fuel sending unit - replaced it and made sure its vending properly
5. Bad fuel pump - replaced mechanical fuel pump TWICE and even just put an electric pump on to no avail
6. Bad cam/eccentric - the thing pumps fuel like mad when its not connected to the carb
7. Bad fuel filter - replaced fuel filter twice
8. Vapor lock - insulated all fuel lines and even experimented with a three-port valve

Sometimes she fires up fine. You can watch the fuel almost fill the clear filter. There's always a little bubble in there though. Then, over the course of an hour or so idling - or faster if you're driving - you can watch the fuel filter empty out of fuel and see the bubble get bigger until the carb sucks air and the truck stalls out.

Any ideas lads? Cuz I'm out of them."

Thanks in advance,

Will

Bypass that fuel filter and see what happens

PW2018PW said:

Bypass that fuel filter and see what happens

Click to expand...

Same issue. Doesn't seem to be the filter.

My first guess would of also been the fuel filter. I had a glass fuel filter on my 71 Z28 that would vapor lock when ever the engine got hot.

It sure sound like a vapor lock issue. Either the fuel is boiling in the carb bowl or the fuel line somewhere. Is this engine stock? What engine is in the W200, 318? Is the carb choke heated by the exhaust? Where was your fuel filter located? Make sure all the fuel lines are routed as far as possible from a high heat source (like exhaust).

If can post some photos of your carb / intake / fuel lines that might help fine the issue.

Suggest as a test hooking up an auxiliary fuel tank such as one used for a V8 marine engine. If you can find one. Normally the gasoline lines are 1/4" fittings and so you may have to use an adapter for larger lines.

MJockey said:

Either the fuel is boiling in the carb bowl or the fuel line somewhere. Is this engine stock? What engine is in the W200, 318? Is the carb choke heated by the exhaust? Where was your fuel filter located? Make sure all the fuel lines are routed as far as possible from a high heat source (like exhaust).

If can post some photos of your carb / intake / fuel lines that might help fine the issue.

Click to expand...

I'm starting to think the carb is the issue. I've insulated all the lines and run the truck with the hood open. Plus there's a heat shield in there, so I don't think its locking in the line. The fuel filter sits about six inches south of the carb.

Now, the fella that owned it before me put a Holley four barrel performance on it. I'm going two swap back in the two barrel to see what happens.

And yeah it's a 318.

Carburetor floats need either adjustment or go bad over time. It probably is sinking due to age or saturation. Check the float level to specification.

Also, my 1978 Chevrolet pickup gas cap is pressurized once the fuel pump builds up pressure. Not certain that a 1977 Dodge has a similar pressurized gas cap. Worked at a Dodge dealership in 1975 and have mechanical knowledge of 1967 to 1975 Dodge vehicles.

Pull your carb float off and check it by floating it in a jar of gas

Potomac Valley said:

Hi Everyone. I'm the (somewhat) proud owner of a 1977 Dodge M880, which is the military surplus version of the Dodge W200.

I've owned the truck for about six years and have had the most consistent running problem with it. I posted about it over at Steel Soldiers but I figure I'd ask here as well.

Instead of re-writing everything, here's a copy of the issue as I posted it over there. Hopefully some of you guys might have some ideas?

"This old 77 has had a persistent fuel problem for several years. It just chokes out of fuel and stops running. Here's what does NOT appear to be the cause:

1. Dirty fuel tank - removed, cleaned, reattached fuel tank
2. Bad fuel lines - all lines have been replaced
3. Bad rollover valve - removed rollover valve from the system altogether
4. Fuel sending unit - replaced it and made sure its vending properly
5. Bad fuel pump - replaced mechanical fuel pump TWICE and even just put an electric pump on to no avail
6. Bad cam/eccentric - the thing pumps fuel like mad when its not connected to the carb
7. Bad fuel filter - replaced fuel filter twice
8. Vapor lock - insulated all fuel lines and even experimented with a three-port valve

Sometimes she fires up fine. You can watch the fuel almost fill the clear filter. There's always a little bubble in there though. Then, over the course of an hour or so idling - or faster if you're driving - you can watch the fuel filter empty out of fuel and see the bubble get bigger until the carb sucks air and the truck stalls out.

Any ideas lads? Cuz I'm out of them."

Thanks in advance,

Will

Click to expand...

Post a bunch of pictures so we can help you a lil better.
Might need to put a manual choke on it and a carb spacer. Is it the stock size carb? Are there any vacuum lines missing that go to the carb?


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Grand Mesa said:

Carburetor floats need either adjustment or go bad over time. It probably is sinking due to age or saturation. Check the float level to specification.

Also, my 1978 Chevrolet pickup gas cap is pressurized once the fuel pump builds up pressure. Not certain that a 1977 Dodge has a similar pressurized gas cap. Worked at a Dodge dealership in 1975 and have mechanical knowledge of 1967 to 1975 Dodge vehicles.

Click to expand...

They’re still the same till around 88 if memory serves me correctly


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I have Scout's but there all 79' and less. If it's a Holley carb then a rebuild and setting the float is critical. Also, at least with IH engines being over carbed is a bad deal (if it came with a 2 barrel 350cfm then that's what you need). The proper power valve and jets are also critical based on elevation. Another thought is for the emissions equipment. Is there a smog pump, evap canister, vacuum switches, egr still in place or has some or all of this been deleted? If so the evap canister needs to be plumbed in with a non-vented gas cap (also helps with gas smell when driving but I digress). You can delete all of the other smog crap if your state allows for it to minimize vacuum issues etc when troubleshooting this. Finally vacuum plays a part in timing advancement depending on what type of dizzy you are running. You obviously have fire but it needs to advance as well. My fuel filters (one in line from the tank and one between the fuel pump and the carb are never full so that isn't always a good indication of what is happening.

For me I would do the following:

Compression check (just because too much fuel or old fuel can cause damage)
Buy a mityvac so you can test vacuum
Install a "T" in the vacuum line between the main vacuum port and the brake booster to use the mityvac (assuming you have power brakes and a Holly this port should be on the back side towards the fire wall.
Do a full rebuild on the carb (including PV, jets and float)
Check the flow pressure after the pump to the carb (find the correct pressure but assuming 3psi but everyone is different and then increase/decrease as necessary)
Buy and install the holley heat dam gasket and install regardless.

Last thing, how exactly did the PO add a 4 barrel without swapping the manifold? Spread bore vs square bore intakes can have issues with the wrong carb type being installed as well.