Need help on proper adjustment to carb for my 70's 250 single barrel

[mikey2409]

Hello everyone
Needs some input on adjusting my carb it a 1 barrel monojet right now I'm running it around 800 rpms at idle with a timing of 6° running rpms high during idle due to engine cutting off at times right now its running super rich from the smell in the cab at times and burning the 1/4 tank on 60mi round trip to work or around town up to a 1/8 in about 15-20mi and also deciding whether to try to find a 2bb and intake to replace the old 1 barrel and and stock intake any input on how I can get my truck running better

[bill3rail]

Originally Posted by mikey2409

Hello everyone
Needs some input on adjusting my carb it a 1 barrel monojet right now I'm running it around 800 rpms at idle with a timing of 6° running rpms high during idle due to engine cutting off at times right now its running super rich from the smell in the cab at times and burning the 1/4 tank on 60mi round trip to work or around town up to a 1/8 in about 15-20mi and also deciding whether to try to find a 2bb and intake to replace the old 1 barrel and and stock intake any input on how I can get my truck running better

I'm surprised there are no replies to this yet. We have some very experienced carburetor repair people on here. Unfortunately, I am not one of them to assist you!

Have you rebuilt the carburetor? I wouldn't jump into the 2Bbl that fast, I would try a rebuild first. Some of the kits available have all details on adjustments and settings, which may solve your problem.

Bill

[BMERDOC]

Tell us more about when it cuts off at times. It doesn't surprise me with the lack of performance if you are trying to cover up a problem. Any history? Any pics of the carb and engine you are working on? Have you sorted the basics like vacuum leaks and clogged fuel filters?

[mikey2409]

Originally Posted by BMERDOC

Tell us more about when it cuts off at times. It doesn't surprise me with the lack of performance if you are trying to cover up a problem. Any history? Any pics of the carb and engine you are working on? Have you sorted the basics like vacuum leaks and clogged fuel filters?

Yes just found that I have a massive exhaust leak at the manifold at the head and where it bolts to the intake mounting and also at the exhaust pipe plus also found out that in possibly running a mid 70'S head blue in color if that means anything with the proper date manifold if correct

[mikey2409]

Alright another question regarding my truck now that I've determined my exhaust manifold is shot I'm going towards the header route now here's the question is there a delete plate to cover the bottom of the intake manifold where the gasket goes between the exhaust and intake bolt down to each other or do I have to invest on a new intake as well

[j_cst_10]

I've rebuilt a couple of those style carbs, not that one in particular but they all operate similarly. Float height is a big deal on that style of carburetor and can dump unwanted fuel into the engine if set improperly. I pulled my 1bbl apart on my old 59 chevy and the floats were put in upside down.

Sound like you may have a float issue and/or a vacuum issue. Check for vacuum leaks and look down the carb when it's running. Is the idle set high because of a stumble when trying to accelerate or because it won't idle? Some more details are needed to nail down your issue.

As for carb adjustments, you have 2. Idle speed and mixture and it sound like your problem won't be fixed with a simple idle screw adjustment, but you can try. Turn the screw in and count the turns, then set it back where it was. Adjust it in 1/2 turn increments, if the truck responds better then great, if it doesn't try adjusting it out the same way. If you find this is your problem, get out a vacuum gage and connect to manifold vacuum and set the screw for the highest vacuum setting and best signal while maintaining a constant idle rpm.

[Kell]

Originally Posted by j_cst_10

Float height is a big deal on that style of carburetor and can dump unwanted fuel into the engine if set improperly....Sound like you may have a float issue and/or a vacuum issue.

X2, if you can actually smell excess gas (that is actually coming from the carb) I would start there. Once you have this set properly, then adjust air mixture if needed.

Increasing RPM to "keep it running" is common for a float set too high. Whatever the problem, it is a pretty easy fix and no need to drive it as is, good luck.

BTW, I clocked mine at 13mpg with the same setup as you. I need taller tires or an overdrive transmission (SCREAMING at 60mph), still, hardly any difference from this and my newer Silverado, my wifes Honda Pilot only gets 17.5 and that's with a ton of gas saving technology, pathetic.

[geezer#99]

As always and forever more, just follow the golden rule!!
Timing first, carb second!!

Bump your timing up to 12 degrees initial.

Then turn your idle down and adjust the mix screw.
Get your idle down to 700 rpm or less.
THat should cure the hiccups and the rich running smell.

[91rcsb]

What do you guys suggest the float height be set at? I bought a carb rebuild kit for mine and it has vague instructions in regards to adjustments.