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AL 2100. rebuilt by Pony Carbs yrs ago

had it set. car running nice
yesterday I decided to get on the gas hard and abuse it a little, normally i baby it.

car ran fine and pulled no issue. Rpms strong.

25 mile drive up the expressway and back home

i pull off the expy get to a red light and its shaking and stalling, vacuum is low, idle dropping below 400

nurse it back home throwing it in neutral at lights to keep it idling. was idling fine in neutral



Checked all the vac hoses and ran through the basics. fuel filter is new, timing is spot on.

back out the mixtures 1/2 turn. idle comes up vacuum steady at 20 and back running strong again

go figure.
 

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I had a small piece of metal shaving (probably from the transfer tube) on a Holley 4bbl come loose and stick inside the needle valve. I drove into town with no problem, but on the way home, it wouldn't hold an idle. I was flooding my engine at idle because the valve wouldn't close. Of course it happened the day of getting ready to go on a road trip to cruise Route 66 in Northern AZ.
 

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If you blew the power valve it would also exhibit very poor running conditions.

Did it backfire at anytime?

Another thing that might have happened (not necessarily the carb) is the distributor hold down could have been loose and allowed the distributor to slip, drastically altering your timing. I've had both of the above happen to me....AS WELL as the debris causing the float valve to not be able to close LeeFred mentioned.

All of this reminds we my I switched to EFI and never looked back.

Phil
 

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Junk in the carb - wouldn't hurt to clean it out and re-gasket it.
 
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67 coupe, 69 Sportsroof, 86 hatchback
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I'll go with the flow and agree a loose piece of something in the carb. Your main concern is that it may still be rattling around in there waiting to cause more trouble.

Post above reminds me one of my drivers is overdue for me to pull all the injectors out so I can clean the built up silt out of them. Again. I just did the same job on my RV a couple of months ago and ordered an extra set of the injector o-rings for the other truck while I was at it. So it's not like I'm waiting on parts or anything. The o-rings sometimes harden and leak and so need replacing every ten years or so anyway but often they don't survive the injector removal. Wish I had one of those snazzy ultrasonic injector "bath" cleaners though. Just mentioning this for the folks who seem to think you can slam the hood on EFI and never touch it again.
 

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I'll go with the flow and agree a loose piece of something in the carb. Your main concern is that it may still be rattling around in there waiting to cause more trouble.

Post above reminds me one of my drivers is overdue for me to pull all the injectors out so I can clean the built up silt out of them. Again. I just did the same job on my RV a couple of months ago and ordered an extra set of the injector o-rings for the other truck while I was at it. So it's not like I'm waiting on parts or anything. The o-rings sometimes harden and leak and so need replacing every ten years or so anyway but often they don't survive the injector removal. Wish I had one of those snazzy ultrasonic injector "bath" cleaners though. Just mentioning this for the folks who seem to think you can slam the hood on EFI and never touch it again.
Huh, I've had my Toyota for 31 Years now and never touched an injector. I'm either overdue, or have just been lucky to not have any problems ?
 

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An old carb ran fine one day, next day it ran like shart. After a lengthy troubleshoot, I found that tiny pieces of rubber were blocking the jets. Ran perfect again after cleaning.


Mark
 

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Huh, I've had my Toyota for 31 Years now and never touched an injector. I'm either overdue, or have just been lucky to not have any problems ?
Absolutely monster super duper lucky. Because we all know how all cars are all the same things. VW's, Coupe Deville's, Pintos, Peterbilts, all same same. Yep.
All that said, I heard at a seminar that over 50% of the vehicles on the road have some sort of miniscule (at least) head gasket leakage and like 75% are estimated to have dirty and underperforming injectors. Some pretty surprising numbers there, especially the head gasket statistics.
 
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Last year I sent the factory OEM injectors from my kid's 1989 Fox body to be rebuilt. 6 of 8 checked in spec as received. These injectors were as delivered from Ford in 1989 with 145,000 miles on them.

One was not delivering any fuel. One was delivering fuel but not in spec. The engine was down on power, idled rough, but actually drove "OK" even on 7 cylinders after 29 years of zero maintenance.

So...yes...not maintenance free....but maintenance minimus. And, if you have a completely failed injector, not only will it get you home, but it got my kid through about 2 years of college before it made it back to my garage for repair.

EFI>Carb IHMO...which is obviously why I went that route...but others will disagree...and they have valid points too.

Phil
 

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Last year I sent the factory OEM injectors from my kid's 1989 Fox body to be rebuilt. 6 of 8 checked in spec as received. These injectors were as delivered from Ford in 1989 with 145,000 miles on them.

One was not delivering any fuel. One was delivering fuel but not in spec. The engine was down on power, idled rough, but actually drove "OK" even on 7 cylinders after 29 years of zero maintenance.

So...yes...not maintenance free....but maintenance minimus. And, if you have a completely failed injector, not only will it get you home, but it got my kid through about 2 years of college before it made it back to my garage for repair.

EFI>Carb IHMO...which is obviously why I went that route...but others will disagree...and they have valid points too.

Phil
I think its pretty hard to argue that EFI is worse, but a lot of people are uncomfortable with the idea of using a laptop rather than a set of hand tools to tune. I prefer EFI on a lot of my project cars, but carbed engines have their own appeal and I don't hesitate to go carbed for some builds.

As for "underperforming injectors" that is a vague statement if I have ever heard one.....pretty sure most carbs out there are "underperforming" too, but it doesn't mean they aren't working just fine by most standards. There is a saying about statistics that I always remember. "Statistics mean nothing to the individual". A perfect example being package delivery services like UPS or Fed-Ex, they both have the same rate of lost or damaged packages, but ask anyone and they will have their own favorite carrier because in their individual case one or the other damaged some package of theirs at some point, setting their minds against that carrier forever. The point as it applies to carb vs EFI is that everyone has their own preference based on their own experiences.

As for the original topic..the OP never actually stated the number of miles put on the carb since rebuild....I agree that debris of some sort is likely if it was continuing to run normally while not idling(one of those situations a wideband would prove invaluable to see if it just suddenly went rich over the whole RPM band or just down at idle..not something you can easily check by reading plugs unless you make a hard run and immediately shut it off)
 

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A blown PV would leak fuel into the carb continually. Since the OP fixed it by mixture enrichment, I would say that's not the issue. More likely some junk has found a tiny port and is partially or completely blocking one of the many tiny holes in that carb. I'd take the top off the carb and have a good look in the fuel bowl for stuff that shouldn't be there. Rust/dust, flakes of shellac, bits of gasket, stuff like that. It did it once, it will do it again. Screws don't suddenly decide to turn on their own on the mixture.
 

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Replaced a pretty new Holley 600 one time that went "bonkers." We never did figure it out..... the end conclusion was that something had
shaken loose internally and had changed the idle characteristics. After a few hours of fiddling, cleaning the carb, etc. we replaced it with
another and that was the end of the problems.
 

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AS WELL as the debris causing the float valve to not be able to close LeeFred mentioned.
Had the same problem myself with the Holley carb on the Pantera. Pulled the bowls, cleaned everything, new gaskets and problem gone!
 

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Sounds like debris in the idle circuit. I would remove the venturi cluster and backflush the idle circuits on the cluster with carb cleaner.
 
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