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454 wont idle below 1500 RPMs

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454 wont idle below 1500 RPMs

Old 11-08-2020, 05:05 PM
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Default 454 wont idle below 1500 RPMs

1993 454 that will start up and run, but only at 1500 rpms or higher. The motor stalls at anything below that. I have tried adjusting the electric choke and mixture screws with no luck, and the float levels appear to be ok. The carburetor is a holley. Does this sound like a rich/lean problem with the carb or do I have something else going on?
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Old 11-08-2020, 06:56 PM
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Sounds like a vac leak
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Old 11-09-2020, 04:59 AM
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Originally Posted by liberator221 View Post
Sounds like a vac leak
Would this be from a way to lean mixture? I usually associate a vacuum leak to a high idle with the throttle in the nuetral position. I need throttle to get the motor running and I cant bring my throttle to the neutral position without it stalling.
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Old 11-09-2020, 07:27 AM
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Would this be from a way to lean mixture?
If the carb is clean inside and idle jets are not clogged, then No
It would be from things like the intake gasket, carb gasket, or other place on the intake. Take some WD40 and spray around the gaskets while motor is running. If the spray changes the motor rpm, then you found the place
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Old 11-09-2020, 07:45 AM
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I think I mispoke, I didnt mean was the vac leak caused by a lean mixture. What I meant to say is, would the vacuum leak cause a serious lean condition enough to make the motor not idle?

I will be pulling a plug tonight to get a reading and then I will check for vacuum leaks.
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Old 11-09-2020, 07:57 AM
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A vacuum leak does lean out the fuel mix.
Again if the idle circuits in the carb are clogged then there is not enough fuel being supplied so the motor idle at lower rpm. Increasing the idle speed gets it past the dile circuit (so to speak) and lets it use the main jets to get fuel

Either can cause the issue

Is this a new to you boat, or just a new issue?
Has the fuel filter contents been looked at?
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Old 11-09-2020, 08:06 AM
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This is a new to me boat. Motor supposedly has 40 hours on a rebuild, and this summer all new ignition components were put on and carb was rebuilt.
I have not checked the fuel filter yet, but I can hook up my fuel pressure gauge. In my head though if fuel pressure was an issue I would be having problems in the higher RPM range, not idle issues.
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Old 11-09-2020, 08:28 AM
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Have you tried to adjust timing, it might be way off? Or try adjusting timing to see if it can be idled down

Checking the fuel filter contents was just a thought that if it had water and crud in it, then it may be clogging the crab idle circuits. Carb being rebuilt is good if it was done correctly
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Old 11-09-2020, 08:33 AM
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Timing is in my list of things to check but I wanted to see if I could get it idling in more like the 1000 RPM range before doing that. Probably not a bad idea though to adjust it slightly and see if it makes a difference or not.
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Old 11-09-2020, 08:35 AM
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Did it do this on the sea trial ?
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