I just re-jetted my 750 double pumper. I used 71's primary and 76's secondary. I adjusted the float bowl through the site window with just a trickle coming out the hole and started the fuel mixture adjustment out 1-1/2 turns. It was still running rich. So I turned each one in a quarter tune. Still running rich. Now I repeated the quarter again. It's not as bad on the EYE'S. Question is how far can I lean these? I know there has to be some mixture. So zero turns out is out of the question. I still get a slight black smoke out both sides.

 

2 things here.
1, With the car off gently turn the idle screws in all the way then out 2 full turns.
Start the car and start on the drivers side first, and screw it in slow until the engine starts to run bad, then screw out easy until it smooths out, give er some gas and do the other side the same way, you might have to do it a couple of time until your satisfied.
Or use a vacuum gauge and do the same until you see the highest vacuum reading for each screw..
2: While you have the vacuum gauge hooked up to full vacuum at idle, see what it says in gear.
Your front power valve should be 1.5 numbers less than the reading, example, if the gauge says 9 in gear then you need a 7.5 power valve in front.
the back on I think should be about 2 numbers lower than the front one.
With a Holley you will always have a slight or more rich condition, they are made to run on a 305 to a 502!
You have to build them to your engine.

 

I had a similar problem with my new out-of-the-box 600 cfm double-pumper. It idled too rich with the mixture screws all the way in. Fuel was dripping down the secondaries! I took the carb apart, cleaned out all the passages with carb cleaner using the red tube that comes with the can and reassembled it with new gaskets. After that it ran like it should. It might be worth checking that you don't have fuel leaking somewhere making the idle too rich.
Pete

 

Set up rich race car double pumper, everything in the sob is that way.

 

Question I start on the front drivers side. Where do I go next. Right front or left rear.

 

Lars just adjusted the 850 double pumper Holley on my new '73 big block. He found the tiny adjustment screw on the secondary throttle plate was missing causing the secondary plate to be completely closed. He stated the secondary plate has to be open slightly to let a little air pass and lean up the mixture. I could not get my idle screws to have an effect until he adjusted the secondarys.

I also think he said the jets on the primary and secondary sides should be about the same if you have a power valve on the secondary.

Just some comments I thought I'd share, if I haven't gotten them confused.

Ralph.

 

tttp

 

Just a normal 750 DP should have #70s in front and #80s in back.
Power valves should be 8.5s, which I can tell you will make it run RICH!!!!
Try to keep the jets 10 numbers apart.
Adjust the front idle screws then go to the back ones either side first

 

here"s a couple articals that will help you out read the holley carb and then read the bg set up paper
http://www.lbfun.com/Corvette/Tech/vettetech.html

 

The power valve will have no effect on your idle richness, the higher
8.5 opens earlier when you put it under light load vacuum drop, but all
the power valves enrich the fuel the same amount have nothing to
do with your idle richness.

 

Brown78 you have a PM.

 

If you have aftermarket inlet manifold have you checked to see carb pad is level. Most will slope forwards on Vettes. If not level (although only 5 degrees or so) your float level settings will not be correct i.e. primary level will be too high and secondary too low.

 

Well thats %100 wrong!
If you have an 8.5 power valve and only pulling 7 pounds of vacuum your car will run wide open rich, or if its got a hole in it you will be lucky to get the car to idle before you foul the plugs.
The lower the nimber on the power valve, the higher RPM you have to have to activate the system and a better chance of not bogging.

 

Thats true it only opens earlier, tell me how changing the main jets
or the power valve will effect the idle circut and his richness at idle??
the primary throttle blade is almost 100 percent closed, it has to be open a decent amount to pull air through the boosters that pull fuel
out the main jets. at idle the car is running on the fuel well of the idle
system of the metering block. Leaning out main jets only effects things
after the throttle plates are open wide enough to pull fuel from the boosters after the accelerator pump has added fuel to help transition
from idle circut to the main circut. the power valve, jet size in the
main circut has nothing to do with idle. the damn idle circut is different
on a double pumper then a calibrated for street car cams vacuum
carb. All the hot rodders don't mention the rich idle circut of a
double pumper on your high idle vacuum street cam.

 

If your power valve has a hole in it or is lower than your idle vacuum you will have a rich condition and foul the plugs real fast.
This is why they make replacement power valves.

 

Tim -
I used to think that, too, until I was corrected: If the carb is idling on the idle circuit, the power valve can be wide open and it will not cause the idle to go rich. If you trace out the PV fuel circuit you will see that the PV circuit (and the primary metering jets) will not dump fuel through the carb at idle (I had to tear a Holley down and trace the circuits out before I believed it...). However, once you're off the idle circuit, a power valve that opens prematurely will cause plug fouling and other problems. But it won't affect idle.

 

Lars can you tell brown78 what to do to the metering block
restriction for the idle circut, I always just put up with the rich
condition, I assuum you have to make the restriction hole
smaller.

 

lars
thanks for taking the time to study the idle circuit.
let's go 1 more step:
kind of a test,
say a guy has a big cam with 7" idle vac.
and he likes to cruise at 1500 rpm in 4th, and only has 10", and it is flowing on the main boosters(most don't, but lets say his does like my 4165)
and he uses a 12" pv! what will happen?
idle- nothing
transition- nothing
1500- pv opens and if the carb is tuned right, it will be 12-13:1 a/f AND it will have terrific throttle response, but mpg will suffer. Do u think the plugs will get black at 12.5:1 AF? I admit I never tried light throttle cruise at 12.5:1 AF, this is why i call it a test
BUT(if poorly tuned ie. the pvrc is way too rich, like 9-11:1 well, it is poorly tuned and it will spew black smoke for sure and have black plugs)
.So , what do u think? can 12.5:1 turn plugs black?
.
as he speeds up, it accelerates briskly as the pv is open(no delay), as he reaches a higher cruise, say 2000 rpm, vac goes up when he lets off to cruise, pv closes at 12", a/f goes up to 15-17 or so, and mpg is real good.

 

Oh boy he we go again!
So if you have a blowed out power valve you will never even know it because it doesn't affect a car sitting at idle at all.
Well this time everybody can think what they want because I am NOT going to argue over every little thing on this site all the time.
So far we have learned a power valve will not make a carb smoke black, foul the plugs or even be noticable.
The Q-jet is the best carb ever built but hotrodders are missing the best thing since the Corvair.
Cars will ONLY run with timing hooked to full time vacuum, all other cars are sitting on the side of the road out of time.
Vortec heads are 100% better than any aftermarket head and cheaper even after buying a different intake, valve covers and rockers, getting them machined for a cam over 490 lift, this must be all free somewhere?
Edelbrock's intakes are better than anyone elses because they cost more.
No wonder people don't like Corvette people, you guys ideas are so backwards from anyone else.
I invite you to my house to listen to my car run and if its not up to your standards we will turn it your way and see if there is an improvement
Then after you leave I will have to pull the engine and rebuild it because running it backwards did not result in 500 horses like you said!
*Strait off a chevelle site that runs the same SBC that everyone else does here but knows what they are talking about.
Now to me checking the float levels because of flooding means at idle, not WOT???

 

[QUOTE=Tim H;1561848282]Oh boy he we go again!
So if you have a blowed out power valve you will never even know it because it doesn't affect a car sitting at idle at all.
.
ANSWER:WRONG! BLOWN VALVE IS LIKE HAVING NO PV, JUST A HOLE FOR GAS TO POUR THRU!
NO ARGUMENT HERE! BLOWN VALVE CAUSES INSTANT STALL. NO IDLE.
.......
a good pv allows both excellent mpg at cruise and max power upon acceleration. very cool.

http://community.webtv.net/MATTGRU/pv more details, PAGE UPDATED TODAY