Your thoughts on Merc. 3.7 idle problem.

[boltonranger]

1988- 3.7 Merccruiser I-4<br /><br />Got it running well except at idle. It will idle well at first but after 3-5 minutes it will slowly wind down and stall.<br />Plugs are new; points are gapped. Cleaned spark screen; which was filthy. It has one screw for speed one for mixture. I assume fixed high jet.<br /><br />Does this sound like sticky float or something else;<br />Motor performs well otherwise.<br />Your thoughts?<br />-br

 

[MrBill]

Re: Your thoughts on Merc. 3.7 idle problem.

A few things quickly come to mind:<br />1 Choke - could be that after warming up choke opens and engine runs lean, then stalls. Make adjustments to idle and mixture after engine is warm, then adjust choke fast idle when cold.<br />2 Timing - check for advance, s/b 4 BTDC at idle and not go beyond 32 at WOT RPM.<br />3 Points - check with dwell meter, just gapping is good enough to get the engine running, but you could be off by 10+ degrees.<br /><br />I'm ready for a carb rebuild on my 3.7 - 165 and have a (open) float issue, just causes a slight flooding problem, runs a little rich but will fix at season end...this should not cause the problem you describe. Let us know how you make out.

 

[boltonranger]

Re: Your thoughts on Merc. 3.7 idle problem.

Thanks Bill;<br />Gosh it's been decades since I set a dwell.. Not sure I remember how. <br />I'll check it this evening.<br />-br

 

[metwrench]

Re: Your thoughts on Merc. 3.7 idle problem.

Does it have Idle/Mix Screws ? base of the Carburetor ?? Might be 1 or 2 ?? Try taking them out, Blowing Carb Cleaner in the holes they came out and Re-install them. Fully seat them and then Back them both out 3-4 Turns. Start the motor and see where the idle is at. Adjust for best and Highest Idle.<br /><br />try that ?

 

[Bob_VT]

Re: Your thoughts on Merc. 3.7 idle problem.

Additionally to the dwell you need to clean the carb sounds as if the idle circuit is clogged and the passages are tiny. The smallest piece of grit will kill the idle.<br /><br />If it is the carb you should consider an inline fuel filter to prevent future problems.<br /><br />Bob