92 Mariah Carb Adjustments

I am having a devil of a time with cold starts and idle settings. I realize there are only 4 adjustments, but I'm frustrated and would like some guidance. I rebuilt the stock 4160 last winter and setup/tuning in the driveway went well, but once in the water it struggles to idle unless I give it enough fuel to get the idle up above 1000 rpm. I have to warm it up to about 140* before i can put it in gear without it dieing. I can slam it in gear and goose it to get moving, but the rpm must be kept higher than normal to keep it running. When putting it in gear after its warm the rpm drop can get really low and it may die or it may be fine. Increasing the idle speed screw helps this. Then there is the choke. No idea where to set this to help. It accelerates and runs so much better after the rebuild, but the idle issues have me scratching my head, especially when its Jekyll and Hyde between the driveway and the lake. I think I should start over with initial settings. Any help?

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Originally Posted by JSPulliam21

I am having a devil of a time with cold starts and idle settings. I realize there are only 4 adjustments, but I'm frustrated and would like some guidance. I rebuilt the stock 4160 last winter and setup/tuning in the driveway went well, but once in the water it struggles to idle unless I give it enough fuel to get the idle up above 1000 rpm. I have to warm it up to about 140* before i can put it in gear without it dieing. I can slam it in gear and goose it to get moving, but the rpm must be kept higher than normal to keep it running. When putting it in gear after its warm the rpm drop can get really low and it may die or it may be fine. Increasing the idle speed screw helps this. Then there is the choke. No idea where to set this to help. It accelerates and runs so much better after the rebuild, but the idle issues have me scratching my head, especially when its Jekyll and Hyde between the driveway and the lake. I think I should start over with initial settings. Any help?

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99% of the time when you have to idle an engine up too keep it running, you have a vacuum leak somewhere. Are you sure you installed the correct base gasket under the carb? You can also spray carb cleaner around the carb when the engine is running to see if you can locate the leak.

I used the new gasket that came with the Holley rebuilt kit. I will try checking for a vacuum leak. Saw some stuff about a bad PCV valve causing headaches, so I'm going to replace it as well. It's just odd to me that it is ONLY troublesome in the water. Driveway is fine.

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Originally Posted by JSPulliam21

I used the new gasket that came with the Holley rebuilt kit. I will try checking for a vacuum leak. Saw some stuff about a bad PCV valve causing headaches, so I'm going to replace it as well. It's just odd to me that it is ONLY troublesome in the water. Driveway is fine.

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I'm thinking you may have it really leaned out on both of the mixture screws, but the choke keeps it running until you warm it up and then it goes into a lean condition. I would let it get to full temp in the driveway (145-160 degrees depending on your thermostat) then adjust the mixture screws. The choke should be set the next day per when it completely cools down. Remember, you don't need a lot of choke since your not running in sub-zero weather like an automobile.
Start with a small amount of tension on the choke spring. You can always increase it in small increments when you take it out.

Sounds like a base plate leak. Mine did the same. While running, spray starting fluid at the throttle linkage hole where the throttle shaft goes into the baseplate. If you get a few extra revs, you're leaking.

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Which direction is less choke? Rotate the housing clockwise or counter clockwise?
If the throttle shaft hole is worn and leaking what's the fix? New carb? Bushing?

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Quote:

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Originally Posted by JSPulliam21

Which direction is less choke? Rotate the housing clockwise or counter clockwise?
If the throttle shaft hole is worn and leaking what's the fix? New carb? Bushing?

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Generally counterclockwise reduces the tension on the spring. If you loosen the (3) screws on the choke housing, you should be able to rotate clockwise and counterclockwise and see the choke butterfly moving. Only do this when the engine is completely cold. You could have clearance around the throttle shaft, but if thats the case, then you have a LOT of hours on your engine or there was excessive pressure or misalignment on the throttle linkage. Have you run the engine and sprayed card cleaner around it yet?

I have not tried the ether yet. The engine has 1000 hours on it.

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JS Pulliam

I have a 1992 Supra Mariah and I have the same problem..... What did you do to fix it.

I live in oregon and I can call you or you can call me,

Thanks

Chris

541 NINE FOUR EIGHT 6440

Ideas

https://forum.supraboats.com/showthr...ear-quot/page2