I'm having some trouble with my 1980 with the 20R engine. It has terrible acceleration, and kinda stutters when taking off from a stop, the engine misses, and backfires, and I'm getting horrible gas mileage. The plugs are oily looking, and fouled, after roughly 800 miles. I'm thinking it is running way too rich, but am clueless when it comes to carbs. Anyone have any advice?

Thanks!

Do you smell fuel?

Run a compression test & post the results.

Dave

Considering what you say are oily plugs as opposed to dry/sooty plugs which would indicate a "rich" situation I would probably have to say you have an engine on the way out.

I finally had a chance to mess with the truck today. I ran a compression test, and it came out fine, #1 160, #2 165, #3 155, #4 155. The plugs weren't oily, but they were black and sooty. The threads were really oily though. I was warming the truck up, and when I shut it off after around 5 minutes at idle, there was a huge backfire with lots of black smoke. Scared the crap outa me! After I did the test and put everything back, it ran with black smoke coming out of the tailpipe. When it was warmed up, and I was opening the throtle for the test, smoke came from the carb every time I opened the throttle. The carb was rebuilt before I bought the truck, I'm thinking it wasn't done right. Any thoughts?

Thanks!

You might want to have a leakdown test performed on it. Had no outward evidence of a bad head gasket on my '80 20R, but when compression was applied to #1 cylinder, bubbles came up through the intake manifold's choke hose <img src="/forums/images/graemlins/angry.gif" alt="" />! Your symptoms sound very similar to mine.
Good luck.

Check for decent spark. Basically turn it over with a spark plug pulled, see if there is a decent arc on the end of the electrode.

Your compression is ok. If you're not losing coolant or oil, I wouldn't worry about it.

If you suspect individual cylinders, pull spark plug wires, one at a time, replacing as you go. Listen for the cylinder that doesn't drop idle.


On the carb side - check for vac leaks. Get it running and spray down that carb base (or anywhere else that could leak) with cleaner. If it changes RPM, you've got a leak.

I'm no carb expert, I went to webers which were for me a bit easier to work on.

After whatyou've described I'd go for the float and needle. The backfire your getting is raw fuel in the exhaust that will ignite when the situation is right. Check for a punctured float, stuck float, misadjusted float and or leaking needle.

Yeah, when I used to shut mine off after a somewhat high idle,
about 2 seconds later a huge backfire. And my dalmatian, well, I wouldn't find her under 5 minutes <img src="/forums/images/graemlins/scared.gif" alt="" />!
It was the carb.

Thanks for the info guys. I have a FSM on the way, and will start tinkering with the carb once that gets here. On a related note, anyone know where I can get a used 20R carb to play with? I'm kinda leary of tearing into the one on the truck. If I had a spare to practice on, I'd feel better.

Choke possibly stuck on?