1987 merc i/o question

[alex254]

Hi everyone i'm new at this whole boat motor stuff. I just got my 1st boat its a 21' 1987 glastron. It has a 4cyl 165hp merc i/o. when i slow it down all the way it shuts off. Today when i was pulling into the dock it shut off again but this time when i started the motor the rpm meter was at 20 and was reving up really loud. So when i put it in forward drive it jerked very hard then the rpms went back down to 10 but was still moving pretty quick for the 1st gear. And still when i start the motor rpms are very high. Before It was nice and quiet at the rpm meter was at 10. Why do you think the rpms is so high? What can i do?

 

[SS MAYFLOAT]

Re: 1987 merc i/o question

First of all I wouldn't put it into gear @ 2000 rpm (you call it 20) This can cause major big buck breakage. It can strip the gears, bust the gear cases, and sometimes cause the universal joints to fail. <br />For troubleshooting your problem, I would first check the compression on all four cylinders. They should be within 10% of each other. If you have a bad cylinder this could mean numerous things. Broken Rings, burnt valve, cracked head, hole in piston etc. If the compression is okay, then check your timing to make sure it is set to your models specs. If it is set to the specs, I would question the carb to have a restricted idle circuit. If this is clogged, you will not idle under 1800 rpm. I had this problem with my old V20 Stingray. I rebuilt the carb and everything has been good since then.

 

[alex254]

Re: 1987 merc i/o question

ok i'll do that <br /><br />thanks,<br /><br />just to as some more info it seems to be fineat idle when warming the engine up but when the engine is already warm then the rpms stay above normal at idle.