Re: Help on adjusting idle on 340 Six Pack
[Re: Imrare]
#1974106
12/21/15 10:36 PM
12/21/15 10:36 PM
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Joined: Jul 2013
Posts: 1,272 Northern Calyfornua
Sxrxrnr
pro stock
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pro stock
Joined: Jul 2013
Posts: 1,272
Northern Calyfornua
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Are you certain that throttle butterflies on any of the carbs are not hanging up in a bore? No gasket leaks at intake or carb mating to intake, causing vacuum leak,,,fast idle is often a sign, particularly when mixture screws have no effect. Also if throttle butterfly is hanging up in bore you are likely in transition circuit which would cause ineffective mixture screws and fast idle.
How are mixture screw set in outboard carbs?
15 inch vacuum sounds ok, perhaps a little low for 900 rpm, depending on camshaft. Again possible vacuum leak.
Is 6 btc normal for this engine? Sounds a bit low,,,,again causing you to adjust throttle butterflies to be off idle circuit and on transition circuit,,,making all bets to be off
Just throwing thoughts agn the wall. I have six pack on a big block. Runs very well.
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Re: Help on adjusting idle on 340 Six Pack
[Re: Sxrxrnr]
#1974133
12/21/15 11:10 PM
12/21/15 11:10 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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what cam? Try bumping the initial up to 15 or 18 (I'm running 18 on a bone stock 83 318) & see if that will let you slow it down.
live every 24 hour block of time like it's your last day on earth
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Re: Help on adjusting idle on 340 Six Pack
[Re: Imrare]
#1974848
12/22/15 11:21 PM
12/22/15 11:21 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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RapidRobert - 6 BTC is a bit advanced actually, the book calls for 2 1/2 BTC. The cam is a stock cam as defined in the specifications section of the service manual for a 340. If I advance the timing more, the engine will run faster not slower. I can reduce the idle by retarding the timing but that doesn't make the engine "happy". Actually what I was thinking was to bump the timing up which yes will speed it up THEN slow the idle with the idle speed screws. then recheck the timing & set it back to 15 or 18 if it is (now) below that after you have (1) bumped the timing up and (2) slowed the idle speed. I wouldn't be afraid of 15 or 18 & yes that'll demand that the slots get shortened but one thing at a time & it might solve the idle speed prob. Are you on ported or manifold?. keep us posted.
live every 24 hour block of time like it's your last day on earth
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Re: Help on adjusting idle on 340 Six Pack
[Re: Imrare]
#1975683
12/24/15 02:59 PM
12/24/15 02:59 PM
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Joined: Jan 2003
Posts: 5,789 Hamilton, Ontario Canada
Magnum
master
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master
Joined: Jan 2003
Posts: 5,789
Hamilton, Ontario Canada
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You definately need all the air to supply the engine from the center carb. If the mixture screws are having no effect on idle, you are correct, the blades are closed all the way.
Air is coming in from somewhere else. I'd block the air horn on the end carbs and if that has no effect, start looking for a vacuum leak.
69 Super Bee, 93 Mustang LX, 04 Allure Super
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