Rough idle and up to 1500RPM

[82RAYSONCRAFT]

I have an 82 225 merc that is running rough at idle & throttle up to say 1500 RPM's. Run's great from 1500rpm to full throttle (5800rpm). Figured the carbs needed cleaning since I recently purchased this boat (82 19' Rayson Craft). Last night I removed carb's and disassebled each only to find them spotless! Every crack and passageway looked like new. Proceeded to spray out all passageways with carb cleaner and blow out with comp air. Going to reassemble with new gaskets, float needle & seat tonight.<br /><br />I really don't fill this was the problem as it looked like they had just been rebuilt very recently. Is there any other items I should check prior to reinstalling the carb's. Iv'e heard that a broken reed valve may cause this also.<br /><br />I haven't checked comp on the cylinders and will do that next. <br /><br />Should I do a decarb prior to checking compression?

 

[82RAYSONCRAFT]

Re: Rough idle and up to 1500RPM

Noticed missing vent jets!<br /><br />Just finished my carb's and noticed that the fuel bowl vent jets are missing! <br />Would this have any impact on the rough idle problem I'm having.<br /><br /><br />I wouldn't think so since it is only a vent to the bowl. <br /><br />But why would merc put it ther to start with. <br /><br />There is reason for everything. <br />Or was it just a engiener trying to justify his position at merc . <br /><br />Any thought's?

 

[andy6374]

Re: Rough idle and up to 1500RPM

Keep those vent jets outta there. There purpose is to increase fuel efficiency at the midrange. But they can do if your carbs are the least bit gummed up is cause you to run lean, which is very bad.<br /><br />I had rough idle before and even though I the carbs looked like I could eat off them they were apparently dirty. I soaked em in the liquid carb cleaner and tons of crap spit out of them. Blew out with compressed air and reassembled with new gaskets. And she purred.<br /><br />You might check to make sure that while you are in idle the throttle shutters in the carb throats are completely closed. This will surely cause a rough idle if they aren't.<br /><br />-andy

 

[dakk1]

Re: Rough idle and up to 1500RPM

You should be able to see the reeds with the carbs off. Not a good look, but a look. You could pull the reed block housing and inspect the reeds if you really thought that could be the problem. I would do a compression test first then decarb, and another compression test. See if there's a difference.<br /><br />Dave..

 

[82RAYSONCRAFT]

Re: Rough idle and up to 1500RPM

Andy, I' ll leave the jets out since I don't have them on hand. Soaked carbs and blew out with copmressed air. Reassembled with new gaskets, float needle & seat.<br /><br />Dave, Visually inspected reeds with a flexable bore scope light. What I could see looked fine. No signs of cracks with all reeds sitting in their seated positions. I'll do a comp test, decard, then test again.<br /><br />Thanks for all of your help. I'll post the outcome.