I've been having idling trouble on my '76 20R. I have the stock Aisan carb and pretty much stock everything else, except for the fuel pump. Although the fuel pump on these is supposed to be an electric in-tank unit, apparently that failed at some point because a previous owner installed a small aftermarket unit in the engine bay.

SO, even with the air/fuel adjustment screw leaned all the way out the ENGINE STILL RUNS FINE?! (with the idle screw turned up, of course) Plenty of fuel dumping down the carb with it all leaned out says too high of fuel pressure to me. I've searched the site several times and can't seem to find a figure for the stock carb fuel pressure. I'm thinking I'll put some sort of in-line fuel pressure regulator in, but I need to know the range. Anyone know what's up?

 

Most standard carby cars run around 5-8psi of pressure. Any fuel pump will do. Do you have a return line to the tank? You could try putting the return line into a bottle and start the engine briefly to check the regulator is still working.

Maybe the float is set incorrectly (too high). Is there an inspection window for the float?

Don't leave your truck running too lean and drive it. You'll burn holes in the top of your pistons.

 

A regulator in some cases it's hard on the pump to push against the regulator

holly low psi fuel pressure regulater jegs.com

Part numbers
1 to 4psi 510-12-804. < I'm using this one on a weber
4.5 to 9psi 510-12-803bp Look at your pump for identification or psi rating and search for specs

Or you can swap to a carter low pressure electric street pump 4-6 psi part number 180- p4070. Jegs.com. If your pump turns out to be to powerful

 

I'll dig around and see if I can determine if there is a return line to the tank. I assume you mean from the carb... And as far as inspecting the float, when I look at the glass window on the front side of the carb, the fuel level is right in the middle, which would say to me that it is OK? I'm not sure how to tell what is "too lean", but right now I'm running at 2.5 turns out on the air/fuel mixture screw and there's no smoke coming out the tailpipe.

Thanks for doing the research for me! Hahaa I guess I'm going to have to check out what my little aftermarket pump says on the sides of it. I'll post back up here after some digging...

 

No prob m actually using the holly part and have the carter pump n the box waiting for a holly carb setup

 

Sound like you have a vaccumm leak

 

Any ideas on where to start looking?

I had a buddy over and we systematically removed each of the vacuum tubes that run to the EGR master box on the passenger wheel well. We hardly got any response or change in the sound of the engine no matter what we did. I'm thinking it may be time for the EGR to hit the road if I can raise the funds for a carb upgrade...

 

You can get a can of 'Start ya bastard' or any other type of carby cleaner in a can and spray around the base of the carby. It should pick up in revs from the higher octane from the can. Then you know if you have a leak. back firing can sometimes cause gaskets to blow out.

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