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Old 07-29-2007, 02:33 PM
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Holley idle circuit tuning question

I have a holley spreadbore marine, which is something like a 4185 if I remember that right. It a vac secondary 670 cfm that I purchased from a reputable shop remanufactured. The engine is a 9.5:1 vortec 350 with a mild cam that is about 197/207

Its running tremendously on the boat but no matter what I do it runs very rich at idle. The idle screws were set 2 turns out and I had a nice idle but lots of black smoke. I now have them both 1/2 turn out and its slightly better but still black smoke. if I go any further in it gets really touchy. The difference between black smoke and lean stall is like 1/8 turn.

I'm sure the throttles are closed far enough (in the idle circuit) Idle is silky smooth at 400 and the idle stop screw is barely contacting the stop. Initial timing is 12*, total is 36* all in by 3000, no vacuum advance.

Is there something wrong, or am I just missing something? What is a typical bench setting for a Holley idle screws? What might I check to remedy this? I wouldn't mind except its making my transom ugly

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Old 07-29-2007, 02:58 PM
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Quote:
Originally Posted by curtis73
I have a holley spreadbore marine, which is something like a 4185 if I remember that right. It a vac secondary 670 cfm that I purchased from a reputable shop remanufactured. The engine is a 9.5:1 vortec 350 with a mild cam that is about 197/207

Its running tremendously on the boat but no matter what I do it runs very rich at idle. The idle screws were set 2 turns out and I had a nice idle but lots of black smoke. I now have them both 1/2 turn out and its slightly better but still black smoke. if I go any further in it gets really touchy. The difference between black smoke and lean stall is like 1/8 turn.

I'm sure the throttles are closed far enough (in the idle circuit) Idle is silky smooth at 400 and the idle stop screw is barely contacting the stop. Initial timing is 12*, total is 36* all in by 3000, no vacuum advance.

Is there something wrong, or am I just missing something? What is a typical bench setting for a Holley idle screws? What might I check to remedy this? I wouldn't mind except its making my transom ugly
Is there some reason you are not running the vacuum advance? this would definitely help but beyond that how are the float levels and fuel pressures set if either of these are to high it will likely run rich.
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Old 07-29-2007, 03:14 PM
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I'm not running vac advance because you don't use them on boats for two reasons; 1) throttle response isn't an issue, but heavy loading is always the case, and 2) it would defeat the spark-arresting requirements for an enclosed boat engine compartment.

Float levels are set and then epoxied to prevent leaks for the same reason. Gas fumes under the hood can make you into fish food. They are properly set, however I should verify fuel pressure. Its a Carter electric pump that WAS putting out 6 psi at the pump (probably a touch less at the seat) when I tested it, but it might be squeezing some past the seat.

Wouldn't an overfilling bowl issue be erratic? Wouldn't it come and go and make the idle hard to tune? Its so perfectly predictable. Always idles fine with the same exact smoke issue. I would think that after a full throttle run it would idle lean then suddenly rich as the bowls refilled.
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Old 07-29-2007, 04:31 PM
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If it were my boat, which I haven't had since my divorce in '97 , I would bump up the initial to 16 BTC. The cam tends to recycle the exhaust gas at idle which, as you know, will not burn twice. That tends to slow down the burn event at idle and low RPM. So you have to dial in alot more initial timing at idle to burn the fuel properly. With no vac adv. you'll only be at 40 total which should be fine.

I borrowed this tidbit of info from F-BIRD'88, (hope that was ok big daddy), This made quite a difference on my 350. Just something to try...........also, 400RPM??? Man, I don't think I could even get close to that low. Might try bumping it up just a tad. I know it probably sounds sweet in the water though.

My transom seemed to get dirty no matter what
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Old 07-29-2007, 08:31 PM
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Holley idle circuit tuning

Check the power valve in the carb and make sure it's not punctured. Also test for vacuum to see how much you have. At that low of an idle you may have so little vacuum that the power valve is opening too soon adding lots of extra fuel. There's a formula to figure what number power valve you need based on your engine vacuum. I don't know the formula offhand, but I'm sure someone here does.
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Old 07-29-2007, 10:19 PM
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check that powervalve, also most spreadbore Holley's with vacume secondaries had reverse idle circuits-(clockwise-rich, counterclockwise-lean on the a/f mixture screws)
I think the double pumper spreadbores had a regular idle circuit.
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Old 07-30-2007, 05:53 AM
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carb

Power valves have nothing to do with a rich idle. They are in the power circut and not the idle circut on a holley carb.


How much of the transfer slots are exposed in the primary throttle bores at idle??? If they are more the a square then that's the problem. You may need to get some more air through the carb. You can add a bit by setting the screw on the secondary side of the carb.

I personally DO-NOT drill holes in the throttle plates. If you can't get it to idle clean please PM me and i'll tell you how to add some more CLEAN air.

Keith
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Old 07-30-2007, 06:03 AM
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Holley idle circuit tuning

I'm sorry but you're wrong about the power valve not affecting performance at idle. The power valve on a Holley is designed to open as engine vacuum drops. For example the valve may be designed to open at 12 inches of vacuum, if you have a radical enough cam you'll have 10 inches or less of vacuum at idle and the power valve will allow fuel to flow. I had that problem on a built up Chevy engine. The exhaust from the tailpipes would make your eyes water until I put in a powervalve that opened at 8 inches of vacuum. I think if you talk to a good engine tuner that knows Holley carbs and how they work they'll back me up on this.
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Old 07-30-2007, 06:06 AM
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I agree power valves have nothing to do with idle mixture when working right, but if the diaphram is ruptured it will leak fuel through the vacume port in the baseplate all the time and yes definately at idle. It'll be pig rich.
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Old 07-30-2007, 06:12 AM
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Quote:
Originally Posted by ernkazern
I'm sorry but you're wrong about the power valve not affecting performance at idle. The power valve on a Holley is designed to open as engine vacuum drops. For example the valve may be designed to open at 12 inches of vacuum, if you have a radical enough cam you'll have 10 inches or less of vacuum at idle and the power valve will allow fuel to flow. I had that problem on a built up Chevy engine. The exhaust from the tailpipes would make your eyes water until I put in a powervalve that opened at 8 inches of vacuum. I think if you talk to a good engine tuner that knows Holley carbs and how they work they'll back me up on this.
No. Sorry but you're wrong. It doesn't matter if you have the right powervalve or not the valve will not affect idle quality if it isn't ruptured. The idle circuit does not get it's fuel supply through the enrichment circuit and fuel doesn't flow through the boosters at idle. The only thing the power valve does is add fuel to the boosters when vacume drops-it does nothing for the idle circuit. The only way the powervalve will affect the idle is if it's leaking where is flows gas through the vacume port in the baseplate. Mainjet also has no effect on idle quality.
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Old 07-30-2007, 11:21 AM
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idle

Quote:
Originally Posted by ernkazern
I'm sorry but you're wrong about the power valve not affecting performance at idle. The power valve on a Holley is designed to open as engine vacuum drops. For example the valve may be designed to open at 12 inches of vacuum, if you have a radical enough cam you'll have 10 inches or less of vacuum at idle and the power valve will allow fuel to flow. I had that problem on a built up Chevy engine. The exhaust from the tailpipes would make your eyes water until I put in a powervalve that opened at 8 inches of vacuum. I think if you talk to a good engine tuner that knows Holley carbs and how they work they'll back me up on this.

This has been discussed on here many times before... If you take a meetering block and trace the PV circut you will very clearly see that it feeds the main well and not the idle circut. In the bottom of the main well is a small idle feed orfice that feeds the idle circut with fuel. No matter how much fuel you put into the main well only the meetered amount will pass into the idle circut.
POWER VALVES (that are not ruptured) do not effect the idle circut period...

I have had many people fight me over this... It's real simple just look at the meetering block and you will see what i am talking about. I have been tuning holleys for 20 years.
Keith
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Old 07-30-2007, 11:50 AM
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idle

I know what the tuners around here tell me and how rich my car was at idle until I changed the power valve. I guess we'll agree to disagree.
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Old 07-30-2007, 11:55 AM
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idle

Maybe my power valve was punctured and the two tuners I spoke to around here were wrong. I put in a different number power valve and the car idled and ran much better, but maybe it was punctured all along and didn't realize it.
Party on!
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Old 07-30-2007, 12:06 PM
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Idle

Just out of curiosity, where does the fuel that flows through the power valve go at idle? Assuming that the vacuum in the engine is too low for the power valve and it's open at idle.
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Old 07-30-2007, 12:53 PM
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idle

I'm going to have to find a Holley and pull it apart. What I don't understand is how the path through the power valve that the fuel follows is different when the diaphragm is ruptured and when it opens in the normal way.
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