[rebel715]

Hi all,
I am new here and have a 1984 D-100 shortbed fleetside with the leaning tower of power and a 4 speed manual A-833 transmission. I am having a problem with a SEVERE lean spot at about 1000-1500 rpms while under load. The truck wants to buck and jerk violently. I have replaced the carburetor, fuel filter, fuel pump, and adjusted timing, replaced distributor rotor button, cap, wires, and plugs. My electrical system is fine as well as the coil and ballast resistor. I am still using the old ECU that is hanging from the air filter, so it is controlling my spark advance since my distributor does not have a vacuum advance. My carburetor is a new Holley 1945 that seems to be fine, but is factory sealed for adjustment. Yes, the accelerator pump seems to be squirting fine also. I have replaced all vacuum lines and checked the intake manifold and carburetor base gasket for leaks. I just ran a compression check also, and all cylinders are around 125psi and within 8 % of one another. I just can't seem to fix this problem!!! Any tips on what to try???
Thanks!!!!:4-dontknow:

 

[Gen1dak]

Those carbs were already set up on the lean side. Now with gasahol, it's even more lean. Being non-adjustable, you'll probably need to consider an aftermarket solution, or an older Slant Six carb that is adjustable.

 

[rebel715]

Thanks for the reply. I am just so frustrated, and just purchased the new carburetor with no real improvement. I want to replace the distributor with one with a vacuum advance and install a Holley 1920 carburetor, and then "hopefully" I will resolve the drivability issue.

 

[Gen1dak]

Eeeeeek! I missed the reference to the Lean Burn computer. That's even worse! Yeah, you definitely should retrofit to a vacuum advance distributor at least, but a tunable carb would also be an improvement.

 

[4ontheFLOOR]

ditch the lean burn system,it bogs down the motor so much and was never a good system brand new, nevermind 30 years old.

 

[Delmivet]

Hello

Im actually new to this website, but i stumbled upon this forum and just wanted to say im having a very similar problem. I bought an 87 d100 cheap off of a friend and he was having problems. (vapor lock) lol so i got it and fixed it then it ran perfect with no problems at all. But after a week it wouldnt even make it up the smallest hill and just got worse. it starts and idles great but after about 2miles of driving it dosent even want to drive on a flat surface, jerking and wanting to stall the more gas you give it the faster it dies.

any help would be greatly appreciated, yes this has the lean burn system too, but im currently tight on cash so i cannot convert it just yet.

 

[Gen1dak]

Couple things come to mind. Symptoms and problems overlap. Fuel filter comes to mind. Could be loading up after a brief drive. If that's okay, I'd think maybe the coil and/or ballast resistor may need replacing. If those simpler things check out you must consider bigger issues like the lean burn being fried. I mean, people replace their pc every 2-4 years. That lean burn has been there for 25!

 

[Nabby]

After 2 miles of driving, your engine should be warm and your choke open. Up until that point, the choke being partially closed probably compensates for a lean condition. Spray carb cleaner around the engine to check for vac leaks, there's a lot of hoses that can crack, and I've had diaphragms fail in the EGR valve and in the choke pull-off on my slant, allowing air in. You might see if you can coax it up to speed by giving it gas very slowly once it's having these problems, as there may be a problem in your accelerator pump which means when you step on the gas, it will go super-lean until the engine can catch up. "The more gas you give it, the faster it dies." sounds a lot like an accelerator pump problem, either failed or improperly adjusted.

 

[anothernewb]

x2 on ditching the lean burn. it caused these kinds of issues when new, there are better products out there that do the same job, without the issues.