Holley 68 jets rich??

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dans4door1970

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Running 68's in front and 75's in rears. I'm at 4500 feet with 10 to1 and headers. 408 engine. My plugs are still fairly black so, it's rich. what would you all suggest to try next> Its a holley 770 Avenger on an M-1 manifold. Go down 2 in front and leave rear's?? just want to get some educated advice as I haven't played with jetting for a few years. The setup now is according with Holley's tables
 
I am sure you have ensured your floats are adjusted correctly, you have the right power valve, and your ignition system is good....all can give you a rich fuel mixture.
 
check your idle mixture screws...where are they at.....

and timing....what is the initial timing?
 
timing is at 20. idle screws adj. power valve is medium or middle of three. floats are dead on. msd coil, runs like a bat but loads up a bit on idle
 
It runs better on ethanol than non-ethanol, yes you read it right, My buddy says jet it for one or the other but difficult for both. Loads up worse on non-ethanol. I'm running NGK Iridium's. Should I try a standard plug?
 
Get rid of those specialty plugs, or gap the heck out of them. These plugs have very low firing voltage requirement,at normal gaps.They are designed for long life applications, with weak-azz coils that won't burn off the tips so they can bury them in the engine and say they are 100,000 mile plugs, and the poor third owner has to pay a million bucks to swap them all out, and the coils that drive them, too. Now that's a mouthful!
Ok so, get yourself some RN12YCs(stock type heads). Gap them at .045, and start over. If the coil craps out, install a better one.
My RN12YCs are circa 2004. Not a typo. 100,000plus miles. I run the sq-top Accell yellow puppy and Jacobs wires. Goes 7200 everyday as often as I get a chance to. With a 276/286/110 cam it will idle all day in 95* heat; that's about as hot as it gets around here, seldom more.
I run Holley 72s up front on my 367 at 900ft, burning 87E10.Allowing one jet size per 2000 ft, I imagine my engine might like 68s at 4500. Depending on your cam, I imagine 68s might be pretty close.
So What cam is in that beast?
 
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dans4door1970 said:
It runs better on ethanol than non-ethanol, yes you read it right, My buddy says jet it for one or the other but difficult for both. Loads up worse on non-ethanol. I'm running NGK Iridium's. Should I try a standard plug?
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You answered your own question, if it runs better on ethanol it needs to be leaned out. The more ethanol the leaner you get with the same jet size. But where you lean it out is the question, idle, transition, cruise or wot. If it loads up at idle I would start there.
 
gtsdude said:
You answered your own question, if it runs better on ethanol it needs to be leaned out. The more ethanol the leaner you get with the same jet size. But where you lean it out is the question, idle, transition, cruise or wot. If it loads up at idle I would start there.
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Yes, I know. I'm going to run ethanol and check the plugs. we have 2 gas stations with ethanol free and it's tough to get to them every fill up, so i'll not run it anymore. The 68's may still be a bit rich. would you go down 2 more sizes or one?
 
I would try one size in the primary first and see how it acts
 
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Remember that main jet changes don't have much effect on idle and cruise mixtures, they have more effect on WOT
 
So is the power valve spring what effects the idle?? on rich or lean. That's my last problem. I have the medium spring in now
 
No, power valve opens to richen mixture during low vacuum situations.....
 
here is what worked for me in my 416 with rich idle I went 3 #'s bigger on the primary air bleeds then reset the idle mixture screws . sometimes the airbleads will plug up and cause a rich idle condition take the float bowl and metering plate off and run a fine wire down through the air bleed hole you should see the wire and dirt if any .
 
dans4door1970 said:
So maybe I need the stiff spring so as not to open on idle which has low vacuum
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Your vacuum is HIGHEST at idle....power valve should have no effect on idle unless you have the wrong one. You need to know your idle vacuum to know that
 
Hold onaminute. Are you saying your "power valve" has interchangeable springs? Does that carb then have power pistons and metering rods? Then start with the weakest spring(s) in the kit, and make sure the metering rods are properly installed.Then make sure those rods stay down at idle, and also at part throttle/low throttle openings.
If the engine idles in neutral,at very low manifold vacuum, then as rpm increases on a performance engine,manifold vacuum will increase and keep those power valves closed.Then somewhere around 2000 rpm the vacuum will peak(street cam). She may hold that peak(still in neutral) for a long ways.
Different story when the engine is pulling a load.
So with the weak springs in, take it out for a cruise.Get her up to about 30mph in second, and then gently roll into the throttle, like you are just going for a leisurely cruise up to 40 mph. No hesitation?,slow back to 30. Repeat with a bit more throttle opening. Keep repeating until you get a hesitation. If the engine actually sags, as in kindof does nothing for a bit, then it's running out of gas. If you give it a bit more throttle at this time and it then goes back to pulling, then the main jets have come on line. So you will need to add gas during this transition. This is what those springs are for; put the next more powerful on(s) in, and repeat.If the engine gets to popping through the carb then it is very lean and may also need more MJ. An overly large MJ can mask a lean metering rod condition.
But if you don't have metering rods, no biggie, just pretend. It's the same procedure.But instead of springs, normally the entire PV is swapped out.
 
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AJ/FormS said:
Hold onaminute. Are you saying your "power valve" has interchangeable springs? Does that carb then have power pistons and metering rods? Then start with the weakest spring(s) in the kit, and make sure the metering rods are properly installed.Then make sure those rods stay down at idle, and also at part throttle/low throttle openings.
If the engine idles in neutral,at very low manifold vacuum, then as rpm increases on a performance engine,manifold vacuum will increase and keep those power valves closed.Then somewhere around 2000 rpm the vacuum will peak(street cam). She may hold that peak(still in neutral) for a long ways.
Different story when the engine is pulling a load.
So with the weak springs in, take it out for a cruise.Get her up to about 30mph in second, and then gently roll into the throttle, like you are just going for a leisurely cruise up to 40 mph. No hesitation?,slow back to 30. Repeat with a bit more throttle opening. Keep repeating until you get a hesitation. If the engine actually sags, as in kindof does nothing for a bit, then it's running out of gas. If you give it a bit more throttle at this time and it then goes back to pulling, then the main jets have come on line. So you will need to add gas during this transition. This is what those springs are for; put the next more powerful on(s) in, and repeat.If the engine gets to popping through the carb then it is very lean and may also need more MJ. An overly large MJ can mask a lean metering rod condition.
But if you don't have metering rods, no biggie, just pretend. It's the same procedure.But instead of springs, normally the entire PV is swapped out.
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Good info. thanks
 
He said in the first post it's a holley 770 avenger, I don't think that has metering rods or springs
 
replicaracer43 said:
I wonder if he is talking about the secondary diaphragm spring?
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Good call!
In that case they should be color coded,. Put the stiffest one you got in there, for now. But if you have the middle one in there now,and you don't have the quick change cover on the pot,then leave it be for awhile.
I just like to tune the primaries first, and usually block the secondaries closed until I have the front dialed in.
 
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