Another “a truck pulls into a garage and stumbles out” issue

[Mac2Night]

I know we are here to help old and new on CB.com, but I always seem to have the same question a hundred others before me had but mine is always somehow a different situation. Because I don’t always find the answers I need, bare with me once again.

I have a new-to-me ‘77 that has developed a stumbling idle issue that leads to it dying altogether. What happens is that it fires up first crack without feathering the pedal even. Sits there and idles beautifully for 10 minutes but then develops a stumble that gradually gets more progressive until it dies. It’s not a convulsive stumble, it’s gradual and calm, but the idle roughens until it cuts completely off. It does the same when I try to drive it.

Being a Duraspark electronic ignition, I have changed everything (wires, plugs, cap, rotor, coil, vacuum advance) including the ignition module. Checked all my vacuum ports. I changed the fuel filter and fuel pump. New gas tank and sending unit. New carb base gaskets and rebuilt carb.

Fuel, fire and air but I can’t figure it out. Ideas and opinions welcome.

 

[B RON CO]

Hi, first thing take the air cleaner off. Make sure the choke is opening. Do the idle mixture screws make any difference? Post a picture of the engine. Good luck

 

[raleigh_bronco]

Sounds like a heat issue, like when the engine is warm the fuel or air isn’t being delivered. Vapor lock?

 

[Speedrdr]

I know we are here to help old and new on CB.com, but I always seem to have the same question a hundred others before me had but mine is always somehow a different situation. Because I don’t always find the answers I need, bare with me once again.

I have a new-to-me ‘77 that has developed a stumbling idle issue that leads to it dying altogether. What happens is that it fires up first crack without feathering the pedal even. Sits there and idles beautifully for 10 minutes but then develops a stumble that gradually gets more progressive until it dies. It’s not a convulsive stumble, it’s gradual and calm, but the idle roughens until it cuts completely off. It does the same when I try to drive it.

Being a Duraspark electronic ignition, I have changed everything (wires, plugs, cap, rotor, coil, vacuum advance) including the ignition module. Checked all my vacuum ports. I changed the fuel filter and fuel pump. New gas tank and sending unit. New carb base gaskets and rebuilt carb.

Fuel, fire and air but I can’t figure it out. Ideas and opinions welcome.

Like I found out recently, one or more of the ‘new’ parts may not be good. Electrical parts can heat up and either open a pathway (think wires separating) and lose fire. I went through several Duraspark modules before getting one that worked. If you have a volt meter, I’d suggest you check the individual wires in the module when you first fire it up. You may be able to find your “problem child”.
Or I could be all wrong.

Randy

 

[Brush Hog]

Maybe an Electric choke issue. Had the same problem. That and I had to open up the air fuel screws to 2 1/2 turns maybe a little more. Drove fine until it warmed up.

 

[dmoses42]

I had a similar issue on a '73, I'd get a mile or so down the road and it would act like it was out of gas. I put 2 new mechanical fuel pumps on, new rubber fuel hose, new tank selector valve, new gas tank, new filters. Then I was replacing the fuel pump a 3rd time and the plastic fuel line on the frame broke off in my hand. As I was replacing that fuel line, the part near the header broke in probably 4 places. I figure it was cracked and sucking air the whole time. I even put a bigger phenolic spacer between the carb and intake thinking it might be the issue.

 

[TX-ZACH]

Verified carb is getting fuel, jets are squirting? You checked vacuum for leak?

 

[gr8scott]

Being a Duraspark electronic ignition, I have changed everything (wires, plugs, cap, rotor, coil, vacuum advance) including the ignition module. Checked all my vacuum ports.

Fuel, fire and air but I can’t figure it out. Ideas and opinions welcome.

One more thing to check on the ignition side: the distributor pickup.

Disconnect the distributor and ohm test between the two colored wires. Should be within 400-800 ohms. Test it cold and then hot after it starts to stumble.