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Old 10-20-2011, 03:18 PM
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No mixture adjument

BEFORE YOU GO AN SAY
Your Past the idle slots.
check vaccum leaks
timing
overjetted
I"VE TRIED THEM ALL

TIMING 14ADC at idle
JETTED AT 68 IM 5280 above sea
vacuum leak non only time i got adjustment was with a vacuum leak

About the engine.
Stock 350 target master engine with crown 2.02 heads
stock cam 390ish 402
8.5:1 compression.
HEI
Accel U GROVE plugs
th350 trans

Ok so this is starting to piss me off. I've tried everything from a spread bore to a 750 double pumper. I can not get a idle mixture to adjust. Ive tried rejetting it from 64-73 an nothing. I live 5280 above sea level. In Holleys instructions go two jet sizes down for every 2000 feet from .72. The only time I have ever got a idle adjustment was when i had the 64s or 68s in front 64 to lean ran out of adjustment. so i put 68s in an i forgot to plug the vac on the back of the 750 for the pcv on both64 an 68. But as soon as i plug that nothing my mixture screw went bye bye. I thought ok maybe its to rich so i put 64s in same thing made it run like **** cause how lean it was but with the pcv vac uncapped had idle mixture then once it was capped nothing. Ive tried this with a 650dp x2 700sb 750vac secondaires

I've tried opening the rear plate so i can get the front to close to get into the idle slots. Same thing nothing I dont know what would be causing this. I thought maybe i have my valves to tight an it was leaving the intake open so i checked them an backed them off started over an went a 1/8 of a turn insted of 1/2-3/4 after zero lash. It made a difference an the engine ran smoother but i still had no mixture screws. Please if anyone has any idea why I can only get a adjustment with the rear pcv open please let me know

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Old 10-20-2011, 04:47 PM
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There`s two things that cause them to be non responsive.
Fuel pressure too high. Anything over 5 psi is too much. If you don`t know what it is your shooting blind.
Timing too low resulting in what you have already discribed which is the butterflies aren`t on the idle slots. When you opened the rear butterflies you made it idle off the rear boosters. The vac advance needs to be connected to a manifold vacuum source. Your base timing at idle should be around 20 - 24 degrees before top dead center, when it`s set here, it raises the idle speed and thus you slow down on the carb which places it on the idle slots. Pretty simple to figure.
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Old 10-20-2011, 05:02 PM
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Are using a VAC Guage? If you have a mild cam - should read any where from 15 to 20 ", steady needle. Wish I could give you the link but there are charts online that can tell you what is happening with your motor by reading the VAC guage. I use it as a troubleshooting tool everytime that I have a issue. Plus, read plugs, you have checked valve lash, the only other I can think of is correct timing. Was your CAM/Crank synced to TDC?
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Old 10-20-2011, 06:01 PM
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Have you tried a different PCV valve?
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Old 10-20-2011, 07:09 PM
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Quote:
Originally Posted by ssmonty
Have you tried a different PCV valve?
im not running one i just have it plugged. I got it to respond today now i just need new plugs. Its just not touchy as my 650 on my 396. but im still going to bump my timing up an get new plugs an see how that affects it.
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Old 10-21-2011, 08:14 AM
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Quote:
Originally Posted by matt921
TIMING 14ADC at idle

I assume that is a mis-type and should actually read 14 BTDC at idle.

I also assume that figure is with the vacuum advance hose dis-connected from the vacuum canister and plugged off.

Raise the initial timing to about 16-18 degrees BTDC with no vacuum added.

This should be set with the engine idle RPM below 800. You may have to close the secondary butterflies back down as well to get the correct RPM range.

Then re-connect the vacuum advance hose to a FULL manifold source.

Re-adjust the idle RPM back down to below 800 RPM with the throttle stop screw.

At this point you should be able to adjust the air/idle screws. If the RPM is set too high, the air/idle screws will not show any change because you will be out of (above the RPM range) of the idle circuit.

NOTE:

Setting the idle RPM and the initial timing is best done with the trans in DRIVE if you have an automatic trans. If checking this way, extreme care should be taken to prevent the vehicle from moving. All wheels should be blocked. Parking brake fully applied. Helper with foot on brake pedal and firmly pressing down to apply the brakes. The engine RPM should not be increased (revved up) during this procedure.

After adjustments to the initial timing and the idle RPM have been made, the idle RPM will increase about 200 additional RPM's when the trans is in PARK.
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Old 10-21-2011, 08:47 AM
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Quote:
Originally Posted by matt921
im not running one i just have it plugged. I got it to respond today now i just need new plugs. Its just not touchy as my 650 on my 396. but im still going to bump my timing up an get new plugs an see how that affects it.
You need to have the PCV system correctly plumbed and working, Matt. The carb is calibrated to have it working and if you don't I'd expect there to be a richer than normal condition at idle because despite what some think, the PCV valve is drawing even at idle.
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Old 10-21-2011, 03:52 PM
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Yeah hahahah bdc lol i had to think about that hahahaha. But ill give it a shot i put a pcv in today an it helped i didnt know that its pretty much a regulated vaccum leak. But ill try bumping that timing up a hair an change these crappy plugs out. I have got a idle adjustment now though so now im just trying to get it correct


Quote:
Originally Posted by Frisco
I assume that is a mis-type and should actually read 14 BTDC at idle.

I also assume that figure is with the vacuum advance hose dis-connected from the vacuum canister and plugged off.

Raise the initial timing to about 16-18 degrees BTDC with no vacuum added.

This should be set with the engine idle RPM below 800. You may have to close the secondary butterflies back down as well to get the correct RPM range.

Then re-connect the vacuum advance hose to a FULL manifold source.

Re-adjust the idle RPM back down to below 800 RPM with the throttle stop screw.

At this point you should be able to adjust the air/idle screws. If the RPM is set too high, the air/idle screws will not show any change because you will be out of (above the RPM range) of the idle circuit.

NOTE:

Setting the idle RPM and the initial timing is best done with the trans in DRIVE if you have an automatic trans. If checking this way, extreme care should be taken to prevent the vehicle from moving. All wheels should be blocked. Parking brake fully applied. Helper with foot on brake pedal and firmly pressing down to apply the brakes. The engine RPM should not be increased (revved up) during this procedure.

After adjustments to the initial timing and the idle RPM have been made, the idle RPM will increase about 200 additional RPM's when the trans is in PARK.
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