Holley tuning??

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1972Dart

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I'm having carb problems and was reading through the tech stuff and think I need a blow proof power valve. I was running a Edelbrock 750cfm and it ran fine. I bolted on this Holly 4340 double pumper and its running like crap. I shot the timing and have it at 8deg retarded but when I set the idle at around 1000 rpm it runs pretty good, but in gear stalls. It backfired out the top several times and is running super rich. I think I should order a power valve in case I blew it out but I'm not certain that's the proper fix. What timing should I run. It's a 360, victor 340 intake, headers, msd 6a ignition. It's my first Holly carb so any help would be pretty nice so I can get to Carlisle this weekend.
 
It doesn't sound like this was a new carb. If it had been run for a while and then put on the shelf for a while, it needs to be rebuilt. The diaphrams in Holleys for the accelerator pump and power valves become hard when left to dry and they need to be replaced. A whole rebuild kit isn't that much. Try that and let us know how it is.

don
 
First off if your timing is 8 degrees retarded that is a major problem. You should be at least 8 degrees before. So in other words your timing is wayyyyyy slow. That will make it backfire. If your running a big cam you should be running probably more like 12-14 before. Also there is no such thing as a blow proof power valve. There is a anti-backfire kit that consists of basically a one way vacuum valve you install in the baseplate to keep the backfire from blowing out the power valve. This is what you need. It does sound like you trashed the power valve if it backfired several times and is now running way rich. What size cam are you running? You didn't mention that. That makes a difference on what size power valve you need. If your running a big cam you'll want to go with a lower rating on the power valve such as a 4.5 inch or 5.5 inch. (the bigger the cam the lower the rated power valve). The stock one is usually a 6.5 inch. If it ran good with the 750 Edelbrock why did you change it? If you really want to go to Carlisle why not just put the Edelbrock back on?
 
fishy68 said:
First off if your timing is 8 degrees retarded that is a major problem. You should be at least 8 degrees before. So in other words your timing is wayyyyyy slow. That will make it backfire. If your running a big cam you should be running probably more like 12-14 before. Also there is no such thing as a blow proof power valve. There is a anti-backfire kit that consists of basically a one way vacuum valve you install in the baseplate to keep the backfire from blowing out the power valve. This is what you need. It does sound like you trashed the power valve if it backfired several times and is now running way rich. What size cam are you running? You didn't mention that. That makes a difference on what size power valve you need. If your running a big cam you'll want to go with a lower rating on the power valve such as a 4.5 inch or 5.5 inch. (the bigger the cam the lower the rated power valve). The stock one is usually a 6.5 inch. If it ran good with the 750 Edelbrock why did you change it? If you really want to go to Carlisle why not just put the Edelbrock back on?
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ThanX fishy, I appreciate the assistance. After typing this quick last night I checked some things because after re-reading it didn't sound right. I'm running the timing at 8deg before not retarded as I previously stated. It's a 4150 holley carb and yes it was used and sat for a few months. My cam is a 284/484 purple shaft. And Yes, I agree with putting the Edelbrock back on which I plan to do after dinner. Will only take a few minutes anyway. I ordered a holley pro tuning kit, new pump nozzles, and new carb gasket from Jeg's today. The kit has 3.4, 4.5 and 5.0 power valves in it. So should I put the 4.5 in or go with the 3.4? I can put the line lock on and burn all 3 gears with the Edelbrock but noticed I can't even try that with this Holley as is.
 
When you get your Edelbrock back on it put a vacuum gauge on it and adjust your idle adjustments for max vacuum. If it's 9 inches of vacuum at idle the 4.5 inch power valve will be about right. In other words you want your power valve to be about 1/2 or slightly more of your idle vacuum.
 
If you're running an automatic tranny, you shouldn't probably be running a double pumper Holley. That Edelbrock 750 is more than enough carb for your 360, and "in my personal opinion", a much better daily driver carb than any of the Holley's. Set up the Edelbrock for your engine and leave it alone. Put the Holley on there and keep on tuning! That should get me some flack!! :)
 
OldVart said:
If you're running an automatic tranny, you shouldn't probably be running a double pumper Holley. That Edelbrock 750 is more than enough carb for your 360, and "in my personal opinion", a much better daily driver carb than any of the Holley's. Set up the Edelbrock for your engine and leave it alone. Put the Holley on there and keep on tuning! That should get me some flack!! :)
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Agreed, unless you are running a lot of stall, i would steer away from the d/p in a auto. I run a eddie on my car daily without any fuss. More than what i can say for the past 2 holleys ive owned
 
what are the jets? do your primaries about 70 and secondaries at about 74-76. but all in all, change to a vacuum secondary. put the eddy back on and trade that DP for a VS. in an auto, check your vacuum reading in gear, about 2 in. below. I run a 360 Mp short block 10:1, eddy heads, rpm AG intake, holley 3310 750VS with a 2.5 power valve, 70 primaries, 76 or 78(?) secondaries, light yellow spring with a quick change spring kit and a proform main body. from a standstill, i can put the hammer down and hit about 5200rpm and get sideways and take off like hell. I need more rubber back there. so either get the eddy back on or trade the holley, your engine will love you.
 
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