Rough idle to 3000 rpm

[scoutfisher]

So I finally got he new prop on the boat I got a month ago. Take it to the lake and it start great. Little rough idle bit smooths out after about 10 seconds. Put it in gear and it is really rough. Put it in neutral and rev it and it's the same up to 3000 rpm. Go ahead and run it awhile and it literally shakes the bolts out of the alternator bracket.. Put it back together and check again and it appears that the roughness is there even when not in gear. When I got this boat I had to install the intake And manifolds. Do u think the roughness is a put together problem or internal problem??

 

[Don S]

Re: Rough idle to 3000 rpm

Do a compression test per this Merc service bulletin http://www.boatfix.com/merc/Bullet/97/97_25.pdf
Report back with your findings..

PS Read the full bulletin before you do the test, and understand what you are doing.

 

[scoutfisher]

Re: Rough idle to 3000 rpm

Guess I should tell ya the boat... 1993 seaswirl with 5.0 Eco. Omc obviously. Thanks

 

[Don S]

Re: Rough idle to 3000 rpm

Doesn't matter what the engine, that is how you do a compression test so it means something. That may be a Merc bulletin, but Volvo had an identical one, and OMC probably would have to, except they were too busy going out of buisness.

 

[scoutfisher]

Re: Rough idle to 3000 rpm

Will do when get home. Supposedly it was done before I bought it that's why I had to put the manifolds and intake back on. Thanks for the input.

 

[scoutfisher]

Re: Rough idle to 3000 rpm

OK. Got home and did the spark test first. all wires firing and doesnt seem to have any change in idle when plugs are unhooked one at a time. all plugs look really good and no fouling at all. NOW FOR THE COMPRESSION TEST.. #1 100#, 2- 105#, 3- 110#, 4- 110#, 5- 110#, 6- 110#, 7- 105#, 8- 105#.... thanks.......... just out of curiosity, what if one or two of the plugs were not totally tight? 5,6,7,8 were all very easy to remove. would think that they would have vibrated out tho...

question #2... with the system in neutral what is turning in the out drive??? again this is a new boat and only the second time out after re-assembly and smacking the prop... maybe its drive related?

 

[Idlespeedonly]

Re: Rough idle to 3000 rpm

The compression is low. Did you do it warm and with the throttle wide open?

 

[scoutfisher]

Re: Rough idle to 3000 rpm

i followed the instructions on the bulletin that Don S provided.......I'm at almost 6000 feet so maybe that's why numbers are a little low I'm told.