Won't idle but will run with high throttle


Old 06-11-04, 11:16 AM
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Won't idle but will run with high throttle

1989 Marathon powered by a 3.0 liter mercrusier. 2bbl rochester. The enigne does not idle in neutral, but with throttle raised enough to engage the prop it will run. I've replaced the fuel pump, rebuilt the carubartor, fuel line and vacume line is clear. The ignition sytsem meets book specs. Timing appears to be right on the mark. I was told if the automatic choke moves at all it is working. I was considering changing the choke to a manual one to test it. Does anyone have any ideas I haven't tried?
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Old 06-11-04, 08:45 PM
Nautical Nature
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May be a vacuum leak. Excess air in the intake air system leans out the fuel mixture which produces lean low speed running conditions and or problems like those you mentioned, etc.

Another condition may be still with the carb. Low speed fuel circuit in the carbs unable to supply enough fuel at idle. Main fuel supply to carbs may be okay but not within the carb.

Idle speed fuel adjustment may be too lean. If carb has adjustment screw(s) be sure they are adjusted correctly.

Off idle lean running conditions may be either of the two possible causes mentioned above. Spark (ignition) advance still may be yet another.

Choke not likely the cause unless it has to be partially closed to keep engine running. Which means fuel suuply is too lean. But than engine would need it closed at all times to run. Which is not the case here as you described.
Old 06-25-04, 09:09 PM
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I've been told old gas may be the culprit. I have no way of knowing how long this boat sat in the boat yard before I bought it. Judging from the mess in the float area of the carb, (oatmeal like corrsion in the carb when I rebuilt it), I would say it was corroding for quite awhile. I can't seem to find anyone to take the old gas and I am planning to try to run it out. Then I'll go back to the engine components. Does this sound sensible?
Old 06-26-04, 08:10 AM
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Hello: Tank

After rebuilding the two barrel carb and running the engine with the same stall fuel in the tank, chances are excellent the entire fuel system is fouled up once again. Including the newly rebuilt carb.

Which means the carb rebuild and entire fuel system has to or is very likely to have to be redone over again. Not a pleasant thought, granted. But very likely.

If the carb had slug in it upon the first rebuild, the tank should have been totally removed, flushed out at a boat repair shop, and reinstalled. A clean fresh start with fresh fuel would likely not have receated the same problem over again.

Stale fuel is safely disposed of at boat repair facilities same as any auto dealers, etc. They have the legal means and equipement to do so. Inquire at the local shops. Likely take the fuel you have. May be a small disposal fee.

Your thoughts are very sensible. Follow the plan to restart over all new. I do not see any other way to accomplish the end result. A fresh start over again.

I highly doubt (IMO) attempting to run the existing fuel out will help. May or is very likely to create more problems inside the engine, etc.

Regards, Good Luck & Safe Boating. Sharp Advice.
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