How do I adjust Holley Carb from ...

[Chris'69Mach 23]

running rich? Do I adjust the air/fuel mixture screws or is it the electronic choke I need to adjust?

 

If the choke is where I adjust the carb from running rich, how do I do that?

Currently the electronic choke is sitting in the middle of the adjustment scale. Turning it towards the front of the engine or towards the back of the engine.

 

I have a new Holly 770cfm 4 barrel w/vaccum assist secondary sitting on a 351 Cleveland.

 

If I need to play with the air/fuel screws, I know that with the engine off, I turn them back 1 1/2 turns from being bottom'd out.

 

Where do I go from here?

[70Mach03 12]

Some people tune by ear, some by rpms, and some with a vacuum gauge. What you're trying to do is get the rpms up to their highest level before they start going down again. I use a vacuum gauge and tune for the highest manifold vacuum it can pull. It's usually the highest rpm it can pull also. Once I get the highest vacuum I then reset the idle speed screw back down to specs.

 

I also have a Cleveland but with the Holley 670 CFM Street Avenger carb. I noticed mine was a little lean from the factory so I bumped the jets up a few numbers.

[Chris'69Mach 23]

I use the vacuum pressue guage .... question ..... if I use the vacuum gauge and adjust the screws accordingly, would that take care of the running rich promlem? Or is that via choke adjustment?

[Brian Conway 264]

You think it is running rich because you have pulled a few plugs and they are fouled or wet with gas. Right ?

 

If after the car is warmed up the throttle plate is vertical your done with the choke adjustments.

If your idle is at 750-850 and you think that is as good as is going to get. Your done with the idle adj. screws.

You have two moves left; Jetting or contact the HOLLEY Tech.

I have spoken with Kevin at the Holley Tech site and he answered ALL my questions. Brian

Edited September 15, 2013 by Brian Conway

[Chris'69Mach 23]

Dont have to pull the pulgs if the exhaust is black ... it is running rich

[Chris'69Mach 23]

I am just wanting to know if I need to adjust the screws or choke. and how to make the adjustments

[Chris'69Mach 23]

Ok, I firgured out that I needed to tighten the air/fuel screws to take care of the carb running rich.

 

Now I have a different issue. I got it to idle at 825 rpm but when I put it in gear, it wants to and sometimes stalls.

 

Do I need to adjust the idle screw to a higher rpm to counter this stalling issue?

 

What is the correct idle rpm for a 1970 351 Cleveland engine? What should the rpm's be while in gear at a stop?

[jholmes217 65]

1st thing is to ensure you timing is good before making final carb adjustments.

 

As said earlier, set your idle mixture screws for highest vacuum with a vacuum gauge 2nd. If you have an automatic, set the idle with the car in gear with all accessories on full blast and high beams on. Either have a friend hold the brakes down, or what I do is nose the front wheels into a curb and set the parking brake. Set you idle in gear to about 650 RPM for a mostly stock engine. If your engine is modified, then you will have to play around to find out what it likes. Your idle in park will probably be around 1000 to 1200 RPM when warmed up. Idle may be as high as 1500 RPM if the engine is cold and first started with an electric choke.

 

By the way, if your 351 is mostly stock, I think your carb is too big. It would probably run better with something in the 600-670 cfm range. A 428 Cobra Jet came with a smaller carb (735 CFM) than you have on your 351.

Edited September 16, 2013 by jholmes217

[RogerC 136]

By the way, if your 351 is mostly stock, I think your carb is too big. It would probably run better with something in the 600-670 cfm range. A 428 Cobra Jet came with a smaller carb (735 CFM) than you have on your 351.

 

Carb recommendations for 351C are:

"The usual carburetor choices for a 351C 2V usually range from 650cfm to 750cfm; for the 351C 4V those choices usually range from 750cfm to 850cfm."

 

See my post (post 6) in this thread:

http://www.1969stang.com/mustang/forum/showthread.php?t=13733

 

OP,

Haven't adjusted one in years so, sorry , can't help there.

[Chris'69Mach 23]

Carb recommendations for 351C are:

"The usual carburetor choices for a 351C 2V usually range from 650cfm to 750cfm; for the 351C 4V those choices usually range from 750cfm to 850cfm."

 

See my post (post 6) in this thread:

http://www.1969stang.com/mustang/forum/showthread.php?t=13733

 

OP,

Haven't adjusted one in years so, sorry , can't help there.

 

Thanks RacerX.... I have had a few people tell me that my carb is too big for my engine. I believe they are thinking I have a winsor and not a cleveland. There is deffinately a difference between the engines.

 

On another note, I have not messed with timing for nearly 30 years on an engine.

 

To clear the fog out of my head here, doesn't timing affect the idle and also if the timing is not set correctly, couldn't that cause the engine to run hot and other things?

[70Mach03 12]

Thanks RacerX.... I have had a few people tell me that my carb is too big for my engine. I believe they are thinking I have a winsor and not a cleveland. There is deffinately a difference between the engines.

 

On another note' date=' I have not messed with timing for nearly 30 years on an engine.

 

To clear the fog out of my head here, doesn't timing affect the idle and also if the timing is not set correctly, couldn't that cause the engine to run hot and other things?[/quote']

 

Yes, if the timing is retarted or advanced it will lower or raise your idle speed. Also if you still have points in the ignition, it will advance the timing as the points wear and the gap decreases. Retarted timing can cause one to run hotter. Insure you have the vacuum lines plugged prior to setting timing. With your bigger carb, you may want to try advancing the timing a bit.

 

 

Normally the best way to go is set the points, the timing, and then carb adjustments.

[Max Power 74]

Timing does effect the idle speed, and you have to go back and forth.

 

If you are running rich at idle, it could be the choke setting or idle jet screw adjustments. If you are running rich at all engine speeds, main jets and float level come into play. Since the carb is new, I will assume power valve and such is all fine, and if you have a big cam, you should have told us by now.

 

Probably the best way to tell if you are running rich only at idle would be to swap plugs when the car is warm, make sure choke is full open and go for a drive. Do not let it idle around after returning from your drive, and pull the plugs before doing another cold start. In other words, get a fresh set of plugs and run em without using the choke and idling as little as possible. Not scientific, but you get the idea.

 

Another way is to take it to the dyno room and have em run a wide band on it and see what they come up with.

 

You aren't really overcarbed that much, especially with vacuum secondaries. Holley seems to err on the side of rich these days, so this does not surprise me.

[Chris'69Mach 23]

The only thing I know about the history of the car is, the engine was rebuilt some years ago and has approx. 5k miles on it. I do not know if any upgrades were done to it when it was rebuilt but by the sounds of it when idling, it sounds as if it has a stock size cam in it.

 

When I found it, it was in a mechanic's lot with work being done on it every so often over a couple years. Prior to it being at the mechanic's lot, it had been sitting in a garage for about 20 years. During that time in the garage, the engine was rebuilt. The car was all primer with all the interior missing except for aftermarket toyota seats. I have had to piece together the fold down seat and trap door out of my pocket. Not to mention the rear window is leaking even after new rubber was installed by this mechanic ... gotta fix that too. It has a new paint job with the colors I requested but that too was done sub-par and not painted in a booth .... just imagine the imperfections in the paint and you're right on. Gonna have it repainted correctly once I scrape funds together after I find some seats that I don't have to wedge myself under the steering wheel.

 

I was told it had a C6 transmission in it by the mechanic but when I got it home I finally was able to get under it and look it over a lot better and found that it has a C4 transmission and not the C6 that I was told.

 

The mechanic where I got it from does do good work but far from it on this car. So far I have replaced everything involving the power steering except the pump, the shocks, the carb, everything in the fuel system except the steel lines to include new tank filler neck and hose.

 

Certainly too much that I had to replace / work on to have had to pay 21k.

 

Needless to say, even though I have had to put in an additional 10k above the agreed price, I am still tickled pink that after 30 years of looking, I have my 69 Mach 1.

 

Funny tidbit here .... When I first drove it around with the wife, she said "turn off that damn stereo, I want to hear the engine!" Gotta love that woman!!

[MikeStang 247]

look up infor on reading plugs correctly

Edited September 17, 2013 by MikeStang