Yesterday we rebuilt my Holley 750 mech. secondary carb and now we can't get the car to run right.

We took the metering plates off, cleaned with carb & choke cleaner and air dried them with the air compressor. We also took the main body apart and cleaned it all up. We replaced the gaskets, and replaced my jets.

OLD JETS 72's up front, and 78's in the back
NEW JETS 70's up front, and 76's in the back.

We also replaced the accelerator pump.

We have gotten the car to fire a few times but it just spits out black smoke, LOTS of black smoke.

We then took the float bowls off again, and saw that they should be flipped upside down and set level. We have the air fuel screws 1 1/2 turn out to 2 1/12 turn out.

We are just stumped, PLEASE ANY HELP its my only transporatation and its stranded.

Was checking some other posts, not sure if this has anything to do with it @ all.

The accellerator pump that we put on had a green gasket, the one that we took off had a black gastket. I jus tnoticed someone saying that there are different accellerator pumps, how can you tell??

The gasket color on the accelerator pump doesn't matter.

I'd double check the float levels with the carb on the car. The fuel should come up to the bottom of the sight plug holes. I set mine so that If I just bump the car a little, a tiny bit will dribble out. You need to check the floats with the car running, or with your electric pump running if you have one.

I'd start with the float level and see what happens from there.

chris

Originally posted by gUmBaLL68Malibu:

We took the metering plates off, cleaned with carb & choke cleaner and air dried them with the air compressor. We also took the main body apart and cleaned it all up. We replaced the gaskets, and replaced my jets.No harm here...BUT- did you put the GASKETS on the right way? Best to double check...I doubt the Jet Change has anything to do with it- unless they or the PV are not tight enough causing an internal leak. In fact, it has nothing to do with it. A Holley has a separate Idle circuit. Pull it apart and double check everything. Holley gaskets are reusable a few times.

Originally posted by gUmBaLL68Malibu:
We also replaced the accelerator pump...No harm here. The green pump is the same pump. Did you look in the bore when you hit the gas? Does it squirt?- you cant miss it on a Holley? If so, THATS fine.

Originally posted by gUmBaLL68Malibu:
We have gotten the car to fire a few times but it just spits out black smoke, LOTS of black smoke..Sounds like an internal leak or too high of a float level. Are the plugs wet with gas?

Originally posted by gUmBaLL68Malibu:
We then took the float bowls off again, and saw that they should be flipped upside down and set level. ..Take the float bowls off again, and MAKE SURE they are set level- this is only to start. THen when the cars running, set it to just barely trickle out of the hole.

Originally posted by gUmBaLL68Malibu:
We have the air fuel screws 1 1/2 turn out to 2 1/12 turn out...BOTH screws should be the same number of turns out. Not sure what you mean here. IN any case, unscrew the screws, blow out the holes just in case, and seat the screws LIGHTLY. THEN screw both screws out 1.5 turns out and stop. THis is only a pre-tune setting, really.

I hate to ask, but did you count the number of turns the screws were out AS you took them out for the rebuild?

Holleys are actually pretty darned simple- if it was running before, it will run again.

Sounds like you have the wrong combination of power valve and power valve gasket...

There's 2 styles of power valves (one with 2 "windows" and one with a bunch of holes), and 2 styles of gasket (one with a round inner hole and one with little tabs sticking inward, and they're different OD too). If you use the wrong gasket style for the PV, it will leak severely between the fuel bowl and intake vacuum. The instruction sheet will tell you which gasket to use with whichever style of PV came in the kit.

Check that carefully.

We have disassembled the carb about 3 times, complety checked the gaskets made sure they were the same as the old, in the exact same way with no holes covered up.

I HAVE PLENTY OF GAS, the accellerator pump is squirting just fine.

The float level, we are going to set again right now. We thought last night that the gas had to be comming out of the hole,


The mixture screws we both start out @ 1 1/2 turns out, DID NOT count before rebuild. We are moving them both the same amount, but have adjusted from 1 1/2 to 2 1/2.

RECHECKING FLOAT LEVELS

WISH ME LUCK!!

Ok we set the float levels pretty low, turned the mixture screws to 1 1/2 turn,

Got it to start again (its not backfireing anymore). Still smoke comming out of the pipes. The car is so much more violent now that the gas kind of comes out because the car is shaking.

Adjusting the float bowls didn't seem to affect how violent it is.

About the powervalve gasket, had no idea there was a difference. We are going to look @ that now.

I will let ya know

THANKS GUYS!! & GALS!!!

BTW, the powervalve in there is a plug, the carb had a plug in it and we just left it in there. We did change the gasket though. WE are going to take mine off now and see about dots or windows. I think all the new ones we have are windows, might have wrong gastket.

vacum leak maybe...had one of those till yesterday, cause the whole car to shake and sputter violently. then i figured out that it was just a vacum line that had somehow popped off. make sure all lines are plugged in and that all other ports are plugged...sometimes you can miss a couple ports due to the throttle linkage covering it up or in my case the electric choke. good luck to you let us know how it turns out.

Ok, we were out there and noticed that on the passenger side, we were able to move the secondaries open. And they were open quite a bit, ALL the time. So we mounted the bracket so it wouldn't move the secondaries and they were closed. We had taken that thing off and looked @ it yesterday. Now its back to where it was.

Gave it a fire, and still quite a bit of black smoke, let it run for a few minutes, and seem to rev good, but still black smoke.

Any other suggestions???

Jet it down......

70's for a 350 that is not wild is alot. go to 66's or so. 750CFM is alot for a 350...

I have a 406 running 750 Vac. with 68's, I think you are overjetted. Also it seems there might be an internal leak.

Clean your plugs and jet down. GO drive it. Then look at your plugs again. The black smoke shouldnt happen at idle unless the PV is coming in. I think you popped your powervalve. I have never heard of both of them beening plugged...

Originally posted by gUmBaLL68Malibu:
BTW, the powervalve in there is a plug, the carb had a plug in it and we just left it in there. We did change the gasket though. WE are going to take mine off now and see about dots or windows. I think all the new ones we have are windows, might have wrong gastket. I wouldnt ever run a PV plug on a Street car- especially on the primary side! IN order do that (still wouldnt do it)you REALLY need to FATTEN the jets up- we're talking 10 plus jet sizes! Take that plug out, and put a 6.5 Power Valve in there, or better yet go to Holley.com and put what was STOCK in there to start- it is after all a 750 double pumper, right? Thats no emissions carb! Get a NEW POWER VALVE and use the RIGHT gasket. Its in the instructions as a previous poster said.

"Ok we set the float levels pretty low, turned the mixture screws to 1 1/2 turn"

Good on the mixture screws, but why set the float "pretty low" by low do you mean low to the bowl BOTTOM or to the TOP?

SET IT EVEN (Parallel to the TOP OF THE BOWL) to start-OFF THE CAR-

you know; hold the bowl at at eye level UPSIDE DOWN and set it till you have it EVEN WITH THE TOP,

THEN set it to barely trickle out of the hole WHEN its running right.

The secondaries should at most be BARELY cracked open...

Sounds like the carb was "wOrKeD OvEr" by the prior owner tongue.gif ..

IMHO, dont worry about the jets UNTIL you have a REAL powervalve in there.

What is the idle speed, BTW?

WOOHOO!!

Well we went in there and took out the plug power valve and replaced it with a 6.5 powervalve with correct gasket & VOILLA!!!!


Smoked a bit got the idle set and mixture screws, its crusing time, then going to change plugs and air cleaner.


THANKS A TON GUYS!!1

We learned a ton doing this so its good smile.gif

Originally posted by gUmBaLL68Malibu:
WOOHOO!!

Well we went in there and took out the plug power valve and replaced it with a 6.5 powervalve with correct gasket & VOILLA!!!!


Smoked a bit got the idle set and mixture screws, its crusing time, then going to change plugs and air cleaner.


THANKS A TON GUYS!!1

We learned a ton doing this so its good smile.gif You know, I doubt the gasket was wrong..REason being- the thing was a PLUG, AND the pinhole style PV's havent been made in YEARS. Still, I suppose the gasket could have been wrong- but Im not so sure- just use the circular washer looking gasket from now on.

Smart man replacing that PLUG with a PV. Im sure youre mileage will go UP, as will general "feel". NEVER use that plug again- they aint worth it on a street car.

ALso, now that its running, you might want to rejet smile.gif . Look at a stock chart and see what jets were in there to start with. Since youre at sea level (uhhh DIRT level tongue.gif ), just use the stockers to start. You might not be that far off, actually.

Glad you got it going, set the idle with a vacuum gauge..

Just wanted to THANK YOU guys for getting me going again on Sunday, we were out of ideas before we started posting here.

THANK YOU THANK YOU THANK YOU

Well anyway got the car running, the car runs AWESOME, instead of bogging when i kick in the 4bbl it just goes, no hesitation just GO. Its real nice. Redid all of the linkage from the pedal to the carb, now much smoother and quite a bit less slack. The only gasket we didn't change (carb to intake) i think has a small vacum leak going to change that out next weekend.

Took a little bit of adjusting to get when i wanted the mechanical secondaries to kick in, had them way to early for a bit and kept killing the car, had forgotton that i moved that for about an hour graemlins/clonk.gif .

Also took this time to replace plugs, dist cap, rotor, and got a new K&N air filter with new air cleaner assembly.

I have already noticed better gas mileage, i was getting TERRIBLE mileage for the longest time and it just seems like it takes a lot less gas to get where i need to go now.

THANKS AGAIN GUYS!!! & GALS!!

GUMBALL68MALIBU,

I was just wondering if you were using a vaccuum guage to set the mixture screws and if so how much vaccuum did you have?????

We did tune the car with a vacum gauge. It had 15 psi. It was a little low, but i believe i have a vacum leak on the gaskets between the intake & carb.

I was just curious cuz my buddy's combo is real similar to yours but w/ about 9.5.1 comp and we ended up w/ 70 mains in his and had about 12hg of vaccuum so far...thanx

I found a real cool site on reading a vacum gauge.

http://www.gmcpauls.com/Tech%20Tips1.htm

scroll to the bottom of the page. It tells you all kinds of things you can find out with a vacum guage.