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Carb Cleaner tuning trick

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Not sure if this is well known or not, maybe I am the last to know. I saw a trick done today by a neighbor who was kind enough to come take a look at my car. I have been having problems with it running rich for a while now. My buddy (also my neighbor) asked his neighbor to come take a look because he is a long time mechanic and muscle car guy. I started the car, he listened to it, smelled the exhaust, then asked for a can of carb cleaner.


He alternated spraying carb cleaner at the air horn from about 3 feet away, so just a misting, and tweaking the air screws. He was listening to what the engine did when he hit it with the cleaner. If the engine slowed down it meant it was running rich and tweaked it down, when it sped the engine up it meant he had gone too far and it was lean. after about 2 minutes tweaking, listening, and spraying he had the car running better and sounding better. So that is a little trick for anyone looking for a new tool in the box.


I took it for a run and it sounded pretty good. I may come back a little bit to the rich side as the car had a stumble at lower speeds.


Another thing I noticed was the transmission was off. taking off at the first stop sign the car came out of 1st half way through the intersection. I am wondering if I just need to adjust the clutch. It has sometimes had an issue getting into 2nd as well. Then, with the car running in 3rd if I let off the gas sometimes it will come out of gear. Seems kind of odd, I figure it is in the gear levers under the car and outside the tranny. anyone have any thoughts?

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Check your transmission fluid levels. Your tranny will behave poorly if the fluid level is too low.


The toploader is tricky to get topped off, but I know it is close. Any tips?

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he did kind of a vacuum tune,, but he didn't use a vacuum gauge and he did not tune the car when it was in gear.


when you tune like this the engine must be under load. so if he did this with the car in neutral then the mixture will be completely off when the car is in gear and most likely your vacuum is lower now then it was before he adjusted it.


Basically he adjusted the idle bleed screws. the recommend starting point is 1.5 turns out from closed. normal tuning can be anywhere from .5 turns to 3 turns out depending on the engine.


when you tune the bleeds you want to adjust them with the engine in gear, foot on the brake and headlights on. this loads the engine down. you then hook up a vacuum gauge and a rpm meter.

and you adjust the bleeds to highest vacuum reading before the rpms start moving up or down. additionally after you discover this highest Vacuum point you are suppose to back off 1-2HG vacuum to compensate for road conditions. you always find you need to richen the mixer back up if you leave it at highest Vacuum.


The method he used i wouldn't of recommended. my guess is you are now too lean or he dropped the vaccum a bit.


as for how this may effect the transmission , if you had a automatic it would. for a top loader i have no idea unless a top loader has a vacuum modulator on it that may cause the shifting to change, or you have a separate transmission issue. I would lean more towards the trans is a separate issue from the tuning trick he tried.



the method he used would make more sense if he was looking for a vacuum leak around the carb base or intake manifold.

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How would you load the engine with a manual transmission to tune the bleeds? Me thinks I would either be working with a stalled engine or chasing after it with my tiny screwdriver ;)

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you would have to let the clutch out lightly, or so i'm told with a manual.


you need 2 people obviously. this method takes forever to get right which is why you pretty much avoid it. if you ever try this method on the double pumpers with 4 corner bleeds you will drive yourself crazy.


what you find is you tune an engine perfectly for a set RPM once you come off that RPM the engine would not run well.


the best way,, is a vac gauge on the dash and the seat of your pants. you can try a color tune but it is equally a pain in the but.


if your start stalling more open up the screws 1/2 turn and go from there. make sure what ever change you make to one side you repeat on the other. the best is start with 1.5 turns, drive it,, smells rich, drop 1/4 turn go out again. keep an eye on the rpms if it start to go up then open it back up 1/8 a turn.


your aiming for a general good tune in a larger rpm range basically. with a vacuum tune the engine has a very narrow range where it holds correct air/fuel mix. carbs basically give you the incorrect air/fuel mixture at every throttle position so the idea is try to stay on the rich side if possible.

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Understandable, and I knew that this was only going to get me close. I agree that it is on the lean side now because of the stumbles in a couple spots, but now I can fine tune. I don't like matrixx's idea about chasing the car and making adjustments though, there's gotta be a better way. :D

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Tune on a dyno? That's the only answer I can think of for this.

1931 Ford Model A Station Wagon
1969 Mach 1 - 351C, TKO-600, 4WDB, R&P, A/C, Shaker, Fold Down, etc.
1972 Mach 1 - 351C, FMX, PDB, PS, A/C, Fold Down, Console
1996 Mustang Cobra Convertible - 10psi Procharger, 436rwhp

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