Thread: Choking at 1000-2000 rpms

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Hey guys, I'm new here and need some assistance. My father has a 65 Mustang with a small block V8. I drove it to my house to wax it for him. It was low on gas and had been sitting in his driveway for a few months. I drove it a few miles and put some gas in it. After about a mile it started back firing and really struggling off the line and in the lower rpms. I knew something was up and went back to my house. A neighbor suggested bad gas so we drain it and put new in. Still the same. Next I checked the screen in the carb but it was clean as a whistle. It idles fine but when reved at 1000 - 1800 rpms it ramps up and down. I ran out of time and haven't had chance to do anything else. What would be my next step? Thanks for any suggestions.

in line fuel filter????Vacumn hose off???

I couldn't find an in-line filter and was told they didn't have them back then. Where might it be? I'll have to look when I get home from work.

does`nt the filter screw into the carb where you hook your rubber gas line hose to it ? what do you mean by screen ? look at the points ..

Yes, the filter is in the carb where the fuel line goes in. It looks like a screen to me. Sorry wrong wordage. We pulled off the cap and everything looked good. Looked in the carb, hit the throttle, fuel streamed out at low rpms and when holding the throttle there the fuel stream gets weak. When on the throttle at the higher rpms the fuel turns to a fine mist and roars. This is all in the driveway mind you. When I took it for another drive it could barely get moving. When I finally got into second and third gear it sputters and backfires. But again at the higher rpms it runs. Maybe a bad fuel pump or the line clogged at it?

Maybe a bunch of gunk in the carb...

Did you check the point gap, condition, and the dwell??

What are the idle screws set at on the base of the carb??? 1 1/2 to 2 turns out should be a good starting point.

Is the choke plate wide open when the engine is warmed up??

for a 65' mustang im gunna guess it's stock? if it is it's probably got the 2100 motorcraft carb on it. they were common in that era of mustangs. and since you backfired the car the first thing i would go to is the pump diaphram. they blow out real easy with any kind of backfiring. i went through this on a jeep a had, changed out everything, fuel pump, filter, plugs, cap, wires, even dropped the gas tank and cleaned it cause the dang thing had just been rebuilt, but low and behold i had another bad diaphram from a small backfire when installing and setting up the new motor. it was really frustrating to boot! cause i had every diagnostic test done on my ignition system i could think of, replaced everything (course it was due so i wasn't too miffed going to NAPA) but as it would turn out the power valve again was the issue. after that she ran like new again

Bad gas (ethanol) only takes a couple months to break down 90 days is the shelf life on gas with ethanol (standard at the pump these days) and since it breaks down so fast it doesnt take much to harm the older carbs. all the issues as you describe are the same as my jeep which had the same/simliar motorcraft carb on it. it costs about 20 bucks to buy the power valve at NAPA or 25 bucks to buy the rebuild kit online and comes with the power valve the part number 4008 is typically the 2100/2150 motorcraft one you'll end up needing to get. just make sure you check the vaccum lines before you replace it. sometimes backfiring will also cause one of your lines to go kabloowee. not sure if you need it or not but i can email you a PDF file on the motorcraft to rebuild it. not sure when the last time you rebuilt the carb but it maybe a good idea to go ahead and do that as long as your replacing the power valve. there maybe some gunk from the bad gas (which can crystalize) these particles can get caught up in the jets.

Dave - I did not check the point gap and don't know what the dwell is. Do you know what the gap should be? It's an MSD.

OSK - It has a 650 Holley on 'er. A buddy also mentioned the power valve too. I'll have to get it apart to check. I've never worked on any carb before but I'm pretty mechanical so I guess it's a good time to learn.

Thanks guys for all the sugg's. I won't get to play with her til the weekend so I'll get back to you with any results . . . or failures!!

a holley will also be the power valve, they too are notorious for blowing those dang lil parts. the power valve is right on the front of the carb

If it has been sitting for a few months there is a good chance varnish has built up in the carb. Gas turns to crap very quickly these days, even sometimes with stabilizer in it.

Recently happened to my 27, hadn't driven it for a month or more and took it to a show downtown. It started running rough and I had to keep the idle up to keep it running at lights. Finally, when coming down the street to the shop I cranked it wide open through the gears and it started running good and has been ok since then. I think whatever was plugging up the jets got blown through from running it hard.

The new gasolines really take their toll on carb and fuel systems.

Don

yeah
if i dont start my willys regularly i end up having to tinker with the carb.

Well the good thing is that the Holley power valves are cheaper and more readily available than the motorcrafts, but thats just my own experience.

If it's an older Holley and the power valve is blown you should put the power valve blow out kit in. It's a ball check mounted in a brass tube that goes in the power valve circuit at the base of the carb. And if it set for a length of time at all the carb should be rebuilt.

On Sat. I pulled the air cleaner off. The inside was sticky in the carb. I sprayed some carb cleaner in it a couple of times and it seemed to cut out about 70% of the lower rpm stutter but not all. I played with the idle screws and set them at 1 1/2 turns on both sides. Isn't there a test if you turn them all the way in and the car dies your power valve is good? Well when I turned in the idle screw in the passenger side it kept running and on the driver side it died.? I took it for a drive and it was the same. It could barely get going and sounded like complete crap. It looks like I'll have to pull the carb. My neighbor has an AFB carb we're going to throw on to see if that's the prob. He says it should bolt right on. We'll see what happens.

From the sound of it I'd say your carb is full of varnish.