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Discussion Starter #1 (Edited)
I am running a AED 750 double pumper race carb on a 408 stroker. Runs great at the track. So, I don't want to screw with it. However, when driving around town it's loading up and wetting the plugs. I have adjusted the air screws slightly and it helped a little. But, I have a Holley 4160c duel line I am thinking about using on it for local driving and putting the the AED on for the track. It only take a few minutes to change them out. Any commits?

tony

7'44 on my last 1/8 run
youtube tnealp2
 

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How's the fuel pressure? Is it blowing fuel past the needle and seat from too much pressure? Float level correct?
If it's not right on the street, it's probably not right at the track either.
 

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Discussion Starter #3
fuel pressure

The carb came on the engine (crate engine) and its been wetting the plugs since new. It came with 3922's and it went up to 3923's which help some. It had a mechanical pump which I change later to a procomp 140 gph with the reg set at 7.5 lbs. It is not as bad as when I first installed the engine, but I am afraid I going to wash the rings out. When I run at the track and check the plugs there not wet, but they are smutty.

tony
 

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Something is wrong with the carb; I run the coldest plugs I can find and NEVER have a wetting or fouling problem whether I'm running the 975 Demon or 1050 Dominator. It will sit in traffic for hours with no problems. Check the needle and seat for microscopic debris--I had a 600 Holley years ago that would foul plugs driving to work; I'd pull the needle and seat, blow it off even though there was nothing visible, and I could usually get home before it fouled another set! I had 3 filters on the car trying to keep out dirt, but it still fouled the plugs--I tossed the carb before trying a new needle and seat assembly--maybe you could try that, they are cheap. My Demon seems less susceptible to higher pressure than the Holley's, but I don't know why as they use the same parts. I've run over 9 psi without problems, but most Holley's don't like so much--try backing down to about 6 psi and see if it makes a difference. You may need to re-adjust the float level after a pressure change.
 

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I agree that if the carb was working perfectly at the strip it wouldn't load-up and run like crap on the street.

Sounds to me like you might have the wrong size power valve. Demons come with lower value power valves in them from the factory which is why you may have had more success with it.

What is your vacuum signal at idle (in gear if it's an automatic)?

Take that number and divide it in half. Replace your power valve (which is probably a 6.5) with the new value.
 

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Discussion Starter #7
Thanks guys for the input. You can crank the car in the shop and it will chock you in just a minute or two.

tony
 

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Have you tried the other carb yet? Your car sounds like it is doing pretty much the same thing as mine. I have had several carbs on mine and can not get the rich idle out of it. I have changed air bleeds, fuel pressure, p/v's and other things. I have used stock Holley's, a Demon, an APD and currently run a Quick Fuel. APD actually sent me a couple carbs.
 

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Discussion Starter #9
I had the 4160 on a 355 with a medium flat tappet cam and it ran perfect. But, I have not tried it on this engine. The 4160 is not a double pumper. That is why I thought about using it for going to meets and around town.
I am planning on starting on a true pro stock for competition in a few weeks. I am looking at a few Nova's now.
My Nova is not race ready. It doesn't have roll cage or a lot of the other safety equipment to qualify for competition. I only run it on test and tune days when anything goes. You could ride a rocket without a helmet if you want.

tony
 

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Discussion Starter #10
vacuum

I lowered the fuel psi to 6.5 lb and check floats they were at the right levels. Tightened the fuel bowls. The vacuum in gear was running between 7 & 5. I don't know that size power valves I have in the carb. Someone said I likely have 6.5. If so, that should be my problem. Would 4.5 be the size I need? I think the power valves are the problem.

tony
 

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Discussion Starter #11
Just took the carb apart. It has a 45 in the front and a plug in the back. How can you tell if the valve is blown? any suggestions?


tony:confused:
 

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Just took the carb apart. It has a 45 in the front and a plug in the back. How can you tell if the valve is blown? any suggestions?


tony:confused:
with a 5-7 vac, that power valve is too large. I would think a 3 or 3.5 would be better.
 

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Discussion Starter #13
Just put the carb back together with a 3.5. Made it worse. It is still puffing black smoke at idle, and now it's bogging.
Must have trash in metering blocks somewhere. I am about to give up. I will call AED tomorrow. The carb has less than 1000 miles on it, and it has never ran right.:confused:
 

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Quickfuel has always told me to plug both power valves and square jet the carb. I have done this a few time on different carbs and never had a problem.
 

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Discussion Starter #15
AED tech support

I emailed AED yesterday (Sunday)about my problems with my carb. They emailed me back the same day (Sunday), and told me how to fix my carb. The techs name was John, and he is great. We exchanged quit a few emails. It is good to know that there are companies like AED that really care about their customers.:)

tony

74 Nova SS
 

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Discussion Starter #17
The tech from AED said to raise my timing first. Lower my throtle body idle screw until the engine is barely running. Then readjust all four air mixer screws. He said too do this at lest twice. He also said to upgrade to a MDS ignition system. It would make the car run much better than the HEI that I am using now.

tony
 

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What he's telling you is that you don't have the engine tuned properly. What was your initial and total mechanical advance? What cam are you running?

You should probably have a higher vacuum signal at idle than 6.5-7 unless you are running an all-out super-radical cam. I have 9-10 inches of vacuum at idle with a 255/255 @ .050 mechanical roller cam. Once you drop below 7-8 inches of vacuum due to a race cam, that's when you need to start thinking about blocking-off your power valves because the spring will be so light they won't really work.

As you advance your timing the engine RPM will increase at idle which will enable you to close the throttle blades further to bring the idle RPM back down. This will increase your vacuum signal and the 4.5 power valve will then stay closed at idle.
 

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Discussion Starter #19
Here are my cam specs
CAMSHAFT - Comp Cams hydraulic roller
DURATION - 236 IN / 242 EX at .050
LIFT - .555 IN / .576 EX with 1.6 rocker
Since I moved up in timing and readjust the air mixer the car is running much better. The vacuum is between 9 & 7 now. I had the time lowered because I was trying a new nitrous kit. Before we figure it out, I replace the 4.5 with a 3.5. Do you think I should go back to the 4.5? If I can sneak the money by my, wife I will go to an adjustable MSD system.
Thanks everyone for the input.:eek:

tony
 

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He also said to upgrade to a MDS ignition system. It would make the car run much better than the HEI that I am using now.
Sounds to me like a guy that sells MSD products--If you have a decent module and coil in your HEI, you won't see ANY difference except for the lighter wallet. If the ignition is so weak it can't fire the plugs, I'd think it would pretty damn hard to start too.
And unless the timing is so far off that the car barely runs, how is that going to wet your plugs? I'd keep looking at the carb. Bolt on the other one and see if the problem goes away.
 
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