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carb tuning

aliensecretion

Full Member
Joined
May 28, 2009
Messages
323
Have finished putting everything back together after replacing intake manifold gasket, rebuilding carb (2100) and a few other things. It wouldn't start without the accelerator pushed way in so I went back and changed the float from 7/16 to 1/2". First try it fired right up but after that i still had to hold the accelerator in a bit to get it to start. When it fires up it's running very rich. This is my first time doing all this and I can't seem to figure out how to get it where it needs to be. I've been at it for about 3 days now so I'd appreciate any ideas! Should I go even further with the float?
 

Smokeater11

Bronco Guru
Joined
Jun 14, 2006
Messages
1,971
Loc.
Auburndale,FL
Did you forget you're starting a carbed vehicle? You almost have to push the gas pedal in some form or fashion to get one to fire. I just did the exact same thing you did last weekend, I changed the intake and put on a rebuilt 2100 and i have to give mine 2 quick pumps to get it to start. This isn't EFI bro!!;) As far as fixing the running rich, with the engine off turn in each mixture screw until it seats lightly(you'll be able to feel it get snug) then back it off 1&1/2 turns. Fire up the truck and let it get up to operating temp(190* or so) then turn each screw back in until the motor starts to stumble, then turn it out until it stumbles. Do this slowly and listen to the idle as you do so, it'll get smoother and faster then slower and rougher as you loosen the screw. Once it starts to stumble after turning the screw out turn it back in until the smoothest and fastest idle ia achieved then stop. Do each screw 2 or three times alternating sides until you feel good about it. Then reset the base idle to around 800-900 rpms. If it still seems to be rich then turn each screw in at 1/4 turn increments until it leans out. If it won't lean out before you get back to stumble again then you did something wrong in the rebuild or have a faulty part. These 2100s are about the easiest carbs to tune that I've come across. Also make sure your base timing is set correctly if you pulled the dizzy out when doing the swap.
 

TBS-POPS

Bronco Guru
Joined
Jun 16, 2007
Messages
1,388
Loc.
valley springs, ca
Start with the 2 idle fuel adj screws backed out from all the way in 1 1/2 turns. set the idle speed screw at about 3/4 of a turn in from the throttle fully closed. should get you close
 
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aliensecretion

aliensecretion

Full Member
Joined
May 28, 2009
Messages
323
Mixture screws were 1.5 turns out and I tried all kinds of variation with them and idle screws. Oh, Looks like i didnt describe the main problem in the original post... My problem is that it won't stay running if I let off the throttle. That's where I'm still stuck.
 

jdamach1

Full Member
Joined
Jul 26, 2007
Messages
273
Loc.
Tyler, Texas
It is most likely a vacuum leak at the base of the carb. Make sure you are running the correct carb to intake gasket. If you are running a factory 1" aluminum 2V carb spacer, you need two gaskets. One between the carb and spacer and the other between the spacer and intake. The correct Fel-Pro 2V gasket number is 600941. Most of the aftermarket gaskets are not cut correctly for the spacer and will cause a vacuum leak. I have had this happen to me a couple of times and have seen it many times working on other Fords.
 
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aliensecretion

aliensecretion

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Joined
May 28, 2009
Messages
323
Ok, Easy enough to check. I don't have the spacer so I do have an extra gasket from the rebuild kit. No rtv on these right? On this one I had just used the gasket and the blue tacky stuff to hold it in place during assembly. Will check for leaks as soon as I finish lunch.
 
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aliensecretion

aliensecretion

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May 28, 2009
Messages
323
Ok, so just came back up from the garage... re-gasketing the carb seemed to help with the dying unless the throttle is pushed back issue but I still have really bad black smoke when it runs that I can't seem to cure with any idle adjustments. Also, twice it was like the throttle stuck down and the engine just kept spinning faster. I had to run to the key to kill it!
 
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aliensecretion

aliensecretion

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May 28, 2009
Messages
323
Been researching an answer to this... would the jets maybe need to replaced with a smaller size? I bought the biggest screwdriver i could find but was still unable to get them out during the rebuild and i couldn't see any markings so i don't know what size the current ones are. It seemed to run a little rich before and know it just pumps black smoke out the back.
 
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aliensecretion

aliensecretion

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May 28, 2009
Messages
323
Hmm, just read a post on a mustang site where the guy said he had a backfire through the carb and it blew out the power valve. Is that common? i did have it happen when I was reinstalling the dist. and got it 180 out. Any way to test?
 

jdamach1

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Joined
Jul 26, 2007
Messages
273
Loc.
Tyler, Texas
Yes, a backfire can blow out a power valve, but it is more common in Holly carbs than in Autolite carbs. They are hard to test unless you have a hand vacuum pump like a Mityvac MV8000. My Mityvac came with a kit with various adapters. One is a rubber cupped adapter that fits against the power valve where you can pull a vacuum on it. If it holds vacuum, the diaphragm is good. If it will not hold vacuum, the diaphragm is bad.
 
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aliensecretion

aliensecretion

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May 28, 2009
Messages
323
Changed the parts you guys talked about and it solved the issues. Thanks to everyone who replied! Took it out for a spin and the thing runs smooth as can be now. I think it even cured my overheating issue! Major improvement on how it ran before I started all this. Everything I've done during this was my first time doing it so I definitely appreciate the help!
 

Justafordguy

Contributor
Bronco Guru
Joined
Sep 26, 2009
Messages
6,253
That's good to hear, I just rebuilt a 2100 and I'll be replacing the holley on mine this weekend.
 
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aliensecretion

aliensecretion

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Joined
May 28, 2009
Messages
323
Ha! Wouldn't you know it... the new timing chain cover gasket didn't hold and sprung a nice little leak right out the top today. It's always something. Hmm, didn't use rtv on that one, maybe i should have.

jdamach, thanks again for the help getting me in the right direction!
Fordguy, It seems a lot of people prefer that little 2100.
 

jdamach1

Full Member
Joined
Jul 26, 2007
Messages
273
Loc.
Tyler, Texas
You're very welcome on the carb. You did good especially since this was your first time messing with one.

On the timing chain cover gasket, yes, definitely use RTV.
 

idhawkdriver

Jr. Member
Joined
Mar 7, 2008
Messages
144
Loc.
Boise, Idaho
I know this is an old thread, but I'm having very similar issues but I didn't exactly catch what aliensecretion replaced. Mine is a 302 that "lopes" at idle to the point of almost dying. At stoplights, i have to my foot on the gas or it will sputter and die. Just did a carb rebuild, tried spraying carb cleaner around looking for leaks (nothing). Have tried mixture screws, idle speed adj (idles at 650), timing is adv at 15 deg. All the plugs are a darker gray, as is the exhaust. I'm about ready to take it to a pro because I'm going crazy.
 
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