750cfm holley too big?

[87fox72mach]

so i got my car running to the point where i can drive it in my cul de sac a little bit seems to run ok. but i still think the 750 may be to big for my 351c 4v 4 speed car. engine has a moderate cam in it forged pistons intake etc. im not looking to drag race. i have tuned the engine with a friend who knows carbs and tuning well. i feel that the engine still smells really rich. my plugs carbon up easily. on cold starts it dies out completely with choke on. im thinking maybe i went to big on the carb. so i was wondering what jets do people recommend. my holley currently is a 0-3310s. primary jet is a 70 according to the manual. power valve is a 65. im running at 15 mmhg vacuum at idle any help is appreciated!

 

[Jeff73Mach1]

750 CFM is fine. If the cam causes a lumpy idle, the power valve can be bouncing open, you might need a lower number PV, but I would start by working with your choke settings. Where do you have the idle set and what does it idle at when the choke comes on?

 

[Don C]

I agree with Jeff, 750 is fine for a 4V Cleveland, they seem to like bigger carburetors than the charts and online calculators tell you.

Is your choke connected to a good 12 volt supply, so it comes off soon enough? And is the pull off adjusted right?

 

[87fox72mach]

my choke is manual so when its warmer out or the cars warm its just off. i have the car idle set at like 700-800 rpms when warmed up

 

[Jeff73Mach1]

Factory idle with a 4 speed was 1000 RPMs with timing set at 16degrees BTDC. Just raising the idle and readjusting the idle adjustment screws might make for significant improvements. The engine really needs to warm up completely before you can expect it to perform properly. Where is your timing set at?

 

[87fox72mach]

my timing is at 10 btdc currently. i will adjust idle and go from there. im also looking to get some new springs for my dizzy. long story short my timing was advancing to fast causing a spark knock. at some point someone changed the advance springs in my dizzy thats why i got it to run best at 10 btdc

 

[Don C]

What is the idle speed when the choke is on? There is a separate adjustment for it.

How old is the carburetor?

Check the float level.

Power valve could be bad.

Plugged idle air circuits can cause a rich condition.

Because you're in Pennsylvania I'm assuming you are at a low altitude, so your jets should be fine.

Is the choke linkage adjusted so the choke opens all the way?

 

[Jeff73Mach1]

I wasn't by any means saying you needed your timing at 16 degrees btdc-I was just giving the factory spec that I had available. With a cam change timing becomes specific to your car and what is right is right.

Just remember a idle change requires idle jet readjustment, which may require a timing tweak, which may result in a need to readjust the idle. . . its a wonder these cars ever left the factory

 

[87fox72mach]

people often say carbs are easy i beg to differ, especially if you not from the 70s! fuel injection is easy haha but the carb is brand new. we checked the floats and they were correct. idle air circuit im not sure what that is

 

[Jeff73Mach1]

2 screws on front of carb-typical initial adjustment, engine warm, choke off, is to turn them in until they lightly seat and them back them off 1 and 1/2 turn each. From there with the engine idling where you want it, you adjust them by backing each out an equal amount 1/4 turn at a time to achieve maximum engine rpm at idle, then adjust your idle back to where you want it and turn each in a 1/4 turn at a time until the engine just starts to stumble then back it off again a quarter turn. Try and keep the screws equally turned in/out

There is a more precise way to do it with a vacuum gauge, but this will get you in the ballpark if your carb was properly set up in the first place. from the factory

 

[87fox72mach]

this is what my friend and i did. currently is where i have it set at. im thinking maybe my rpms r just to low. i think with choke on it barely makes 500 rpm wants to cut out

 

[goodnigh]

My '71 M-code has a 770 Holley and some kind of cam.

We measured valve lift at near 0.6 inches.

The car has an auto choke and can be temperamental

when cold. When warm it has excellent low end torque

and will put you in the seat if you stomp the gas at 3500 rpm.

mike

 

[c9zx]

I suggest you fix the distributor advance problem, set initial timing at 16, idle speed at 800 RPM, and adjust the carb again. scroll down on the attached link for info on timing vs. cam duration (overlap). There is also a fast idle screw to set engine RPM when the choke is in use. http://www.4secondsflat.com/Carburetor%20Sizing%20and%20Series%20Charts.htm

Let us know what you find. Chuck

 

[87fox72mach]

I suggest you fix the distributor advance problem, set initial timing at 16, idle speed at 800 RPM, and adjust the carb again. scroll down on the attached link for info on timing vs. cam duration (overlap). There is also a fast idle screw to set engine RPM when the choke is in use. http://www.4secondsflat.com/Carburetor%20Sizing%20and%20Series%20Charts.htm

Let us know what you find. Chuck

I'm gonna fix the distributor. Problem is mallory no longer makes the advance spring kits. I wonder if an msd kit would work?

 

[clevelandcoupe]

Alex,

Whats up with the the Mallory Unilite advance ?

I have a spare distributor for parts if you need it. I could drop it in the mail if needed.

Let me know.

Thanks, Jay

 

[c9zx]

I suggest you fix the distributor advance problem, set initial timing at 16, idle speed at 800 RPM, and adjust the carb again. scroll down on the attached link for info on timing vs. cam duration (overlap). There is also a fast idle screw to set engine RPM when the choke is in use. http://www.4secondsflat.com/Carburetor%20Sizing%20and%20Series%20Charts.htm

Let us know what you find. Chuck

I'm gonna fix the distributor. Problem is mallory no longer makes the advance spring kits. I wonder if an msd kit would work?

Is this a possible source for parts? http://www.summitracing.com/parts/maa-29014

The mallory instruction sheet said most distributors have 24 degrees of mechanical advance. That may be too much if you are using more than 12-14 degrees of initial advance. Chuck

 

[87fox72mach]

I suggest you fix the distributor advance problem, set initial timing at 16, idle speed at 800 RPM, and adjust the carb again. scroll down on the attached link for info on timing vs. cam duration (overlap). There is also a fast idle screw to set engine RPM when the choke is in use. http://www.4secondsflat.com/Carburetor%20Sizing%20and%20Series%20Charts.htm

Let us know what you find. Chuck

I'm gonna fix the distributor. Problem is mallory no longer makes the advance spring kits. I wonder if an msd kit would work?

Is this a possible source for parts? http://www.summitracing.com/parts/maa-29014

The mallory instruction sheet said most distributors have 24 degrees of mechanical advance. That may be too much if you are using more than 12-14 degrees of initial advance. Chuck

That is the part I need but is no longer available. I even called mallory or msd now and they said that part didn't carry over. So I'm just wondering if the msd kit may be close. I bought the dizzy offline. Someone changed the springs to advance the timing quicker. This led to spark knock occurring from 2500 to 2800 rpm. If I retard the initial timing a bit. The spark knock is not present

 

[TommyK]

I'm gonna fix the distributor. Problem is mallory no longer makes the advance spring kits. I wonder if an msd kit would work?

Is this a possible source for parts? http://www.summitracing.com/parts/maa-29014

The mallory instruction sheet said most distributors have 24 degrees of mechanical advance. That may be too much if you are using more than 12-14 degrees of initial advance. Chuck

That is the part I need but is no longer available. I even called mallory or msd now and they said that part didn't carry over. So I'm just wondering if the msd kit may be close. I bought the dizzy offline. Someone changed the springs to advance the timing quicker. This led to spark knock occurring from 2500 to 2800 rpm. If I retard the initial timing a bit. The spark knock is not present

Not sure how reliable this is but Autozone shows the spring kit in stock.

http://www.autozone.com/1/products/20553-yt-yh-series-distributor-advance-curve-change-kit-29014-mallory-29014.html

 

[87fox72mach]

Is this a possible source for parts? http://www.summitracing.com/parts/maa-29014

The mallory instruction sheet said most distributors have 24 degrees of mechanical advance. That may be too much if you are using more than 12-14 degrees of initial advance. Chuck

That is the part I need but is no longer available. I even called mallory or msd now and they said that part didn't carry over. So I'm just wondering if the msd kit may be close. I bought the dizzy offline. Someone changed the springs to advance the timing quicker. This led to spark knock occurring from 2500 to 2800 rpm. If I retard the initial timing a bit. The spark knock is not present

Not sure how reliable this is but Autozone shows the spring kit in stock.

http://www.autozone.com/1/products/20553-yt-yh-series-distributor-advance-curve-change-kit-29014-mallory-29014.html

Tried that to. Says in stock till you go to checkout then it says item not available. I don't get how no one sells little springs for these lol my only hope is to find someone who has a spare set or a broken dizzy