Need some serious help

[D150dude]

ok, I thought I’d post this here instead of the engine forum. So last week my 81 d150 with the slant six and lean burn started to chug, well the truck was parked from Thursday till this Monday so I took it out and noticed that it was chugging along I took it on the hwy and it wouldn’t go over 70km/hr. I changed the plugs,cap,rotor,fuel pump and filter check the timing and it still won’t go over 50 now, when I floor it it spits and sputters and backfired and even seems like it dies but as I lift my foot off the pedal it sounds fine, what is going on here? I’m pulling my hair out guessing. If anyone needs a video of it running to see what I mean text me at+18078614536 and I’ll send you a video

 

[hotrod45]

Sounds like a carburetor issue, as if the high speed jets are at least partially plugged. Will the vehicle speed eventually increase if you go easy on the throttle?

 

[D150dude]

Kind of but around 50 she wants to die

 

[hotrod45]

Take the air cleaner off. Do not start the engine. Look down into the carburetor and operate the throttle with your hand. See if it is squirting a strong shot of gas into the throat of the carb when you operate the throttle. By the way, never, ever put your face over an open carburetor if the engine is running.
Your description of the vehicle stumbling and backfiring when you put the gas pedal down is typical of a failure of the accelerator pump, the little mechanism in the carburetor that gives that extra squirt of gas. If the throttle can move any substantial amount before it squirts gas, that's bad. I don't know what is available these days for carburetor repair, but if you can find a rebuilt carb, that is probably the best choice. A "zip kit" to rebuild/clean a carb is probably going to include an accelerator pump, but it will not address what I think is a problem with the high speed jets, or perhaps a port in the casting that goes to the jets. That's why looking for a rebuilt first seems like the better choice.

 

[D150dude]

Ok I’m gonna go do that right now, I will keep you informed

 

[D150dude]

Take the air cleaner off. Do not start the engine. Look down into the carburetor and operate the throttle with your hand. See if it is squirting a strong shot of gas into the throat of the carb when you operate the throttle. By the way, never, ever put your face over an open carburetor if the engine is running.
Your description of the vehicle stumbling and backfiring when you put the gas pedal down is typical of a failure of the accelerator pump, the little mechanism in the carburetor that gives that extra squirt of gas. If the throttle can move any substantial amount before it squirts gas, that's bad. I don't know what is available these days for carburetor repair, but if you can find a rebuilt carb, that is probably the best choice. A "zip kit" to rebuild/clean a carb is probably going to include an accelerator pump, but it will not address what I think is a problem with the high speed jets, or perhaps a port in the casting that goes to the jets. That's why looking for a rebuilt first seems like the better choice.

I went and had a look see and what I saw was when the accelerator is pushed just a little I can see the fuel dribble down inside of the throat of the carb

 

[hotrod45]

The accelerator pump should put a forceful stream (think: "squirt gun") into the throat. Less than that = flunks the test. It seems like you might have been cautious. Operate the throttle in a full stroke, from closed to full open in a count of "1."

Added: if that accelerator pump is operating all right, the next best guess I have is that the fuel is contaminated. Water would be the first normal guess, as long as you can eliminate the chance of kerosene or diesel having gotten into it.

 

[D150dude]

The accelerator pump should put a forceful stream (think: "squirt gun") into the throat. Less than that = flunks the test. It seems like you might have been cautious. Operate the throttle in a full stroke, from closed to full open in a count of "1."

Added: if that accelerator pump is operating all right, the next best guess I have is that the fuel is contaminated. Water would be the first normal guess, as long as you can eliminate the chance of kerosene or diesel having gotten into it.

I pulled the fuel fitting out and I also pulled this, it’s in the pic. Looks like that little rubber knob is broke

 

[Elevated 2013]

If Hotrod45 isn't right about the carb or the gas (and I don't know that much about carbs and rebuilding them as I only ever rebuilt 2 and I had help) then my next question would be if you still have a cat on the truck? If so, it could be clogged.

 

[hotrod45]

That's newer than what I'm used to seeing. Did you take the top off the carburetor?

 

[D150dude]

If Hotrod45 isn't right about the carb or the gas (and I don't know that much about carbs and rebuilding them as I only ever rebuilt 2 and I had help) then my next question would be if you still have a cat on the truck? If so, it could be clogged.

No cat

 

[Elevated 2013]

Just a thought as I've seen clogged cats doing the same thing. As of right now stick with hotrod's advice.

 

[D150dude]

Just a thought as I've seen clogged cats doing the same thing. As of right now stick with hotrod's advice.

I was hoping for a clogged cat because I’ve experienced those symptoms before

 

[D150dude]

So I took it out again to see and it feels like I have a deadbolt spot around 50km where the truck feels like it just died but it’s still running what would cause it to feel like a dead spot?

 

[hotrod45]

So I took it out again to see and it feels like I have a deadbolt spot around 50km where the truck feels like it just died but it’s still running what would cause it to feel like a dead spot?

Water in the gas can produce a symptom similar. The water droplet will sit wherever it is and bump up against the small orifice that gas can pass through, but water can not. Usually, you'll get a series of stumbles in the engine, almost as if it is surging. Will the vehicle now go faster than that, whereas it would not before? If so, it would seem to be the case that you have touched whatever it is that is wrong. Get a new one.

Added: It probably would be a good idea to get a proper diagram of the vacuum hoses and make sure that they are all there, in good condition, and hooked up where they are supposed to be.

 

[TigreST]

Shot in the dark: This thing got a ballast resistor on the firewall? If yes it may be shot? It’s part of the ignition coil set up on some old school Mopars.

T.

 

[D150dude]

I was also thing bad egr valve and or solenoid

 

[crazzywolfie]

do you drive it much? i would recommend using shell 91 octane gas if you don't drive it much. it is all i trust in my carbed engines. no ethanol. may also want to convert it to 4 pin ignition system. i am kind of surprised the lean burn system is still working. you don't see many vehicles with it anymore for a good reason.

 

[D150dude]

It is my daily driver, yes I’d like to convert it to a better ignition, when I bought it I had to redo my wiring and I also put on a remand ecm unit but the truck ran perfectly and would drive it 150km round trip to work every now and again

 

[crazzywolfie]

are you sure you set the timing right? pretty sure you have to disconnect the computers temp sensor and vacuum line that runs to the computer and plug the line with the engine at operating temp.