Missing at idle

[Wonbigfish]

I have a 1997 90 hp Force. It has been a great running out board. The last time out I noticed it was missing @ idle and lower RPMs. It seems to clean up when I get boat on plane. This sympton just started last trip out. Can someone point me in a direction for diagnosis. I guess every repair has a starting point.
Thanks ahead of time
Wonbigfish

 

[jerryjerry05]

Re: Missing at idle

Water in the gas?
Do a compression test.

 

[foodfisher]

Re: Missing at idle

Clean sparkplugs?

 

[Jiggz]

Re: Missing at idle

I'll start with compression test and visual inspection of the spark plugs. Sometimes when an engine is only missing on one cylinder people tend to think the misfiring goes away at high RPM when in reality it is only masked by the louder noise generated.

 

[Wonbigfish]

Re: Missing at idle

Compression test has 150 on all three cylinders. Replaced plugs & water separator filter. It ran great when I started it then after it warmed up it went into a rough idle or missing mode but never died. Any ideals what to look at next. It sure seems like it's something simple but I have had simple things erupt into bigger problems.

Thanks in Advance
Wonbigfish

 

[Jiggz]

Re: Missing at idle

Do the following troubleshooting:
As soon as the misfiring or rough idling starts, try squeezing the fuel bulb and see if it gets better. If it does it is fuel related. If not continue on next step.
Using a timing light, watch the constancy of the firing (strobe from the timing light) from each wire plug to see if misfiring is caused electrically. If it is you will need to visually check on the trigger and the stator by removing the flywheel and do resistance checks as well. Also check all wiring make sure none has cracked insulation.

 

[Wonbigfish]

Re: Missing at idle

Thanks Jiggz
I will try this tonight

 

[Wonbigfish]

Re: Missing at idle

Due to recent algea bloom & truck repairs I am just getting back around to my boat. I changed plugs & thought that was it. NOT. Took it out & it was the same. I ran it at home & put my timing light on all 3 cylinder wires. They all seem to fire consistantly. I then noticed the water from pisser seem to spit or sputter with a little air in it. I then did another compression check. 140 120 140. Is it possible to have a had gasket starting to go. I couldn't help but notice #2 plug looked gray as if water was getting to it. When I get into upper RPMs it runs strong without miss. How can I diagnoise a head gasket. Is there something else to check?
Wonbigfish

 

[jerryjerry05]

Re: Missing at idle

Pics of the plugs?
20# doesn't seem like a lot but it is.
Look for water.
Spray some oil in and do another test.If there is water in there it will turn it milky/gray etc.
I had a head gasket go bad. The comp was 145# all three.But the middle hole the gasket was leaking water.
Maybe pull the head?
Be real careful when removing.Tey were only put on with 20# of tourqe.So if they don't go easy, you can break them off.

 

[Wonbigfish]

Re: Missing at idle

Thanks JJ
I think I will tear down head. Gaskets are fairly easy to do but, just as easy to screw up. This motor has had little salt time. 2 gaskets can't be that asking to much for a hunch?

 

[Jiggz]

Re: Missing at idle

Or you might want to re-verify all head bolts for torques and then try again. If it doesn't improve, then it is time to open and inspect the gasket.

 

[Wonbigfish]

Re: Missing at idle

Or you might want to re-verify all head bolts for torques and then try again. If it doesn't improve, then it is time to open and inspect the gasket.

Thanks Jiggz
I will check torques first.

 

[jerryjerry05]

Re: Missing at idle

Your not too far away.If you can't finger it out bring it on down?

 

[Wonbigfish]

Re: Missing at idle

Tore into it today Head gasket is the problem. What is the torque spec for head bolts on 1997 90hp force?

 

[jerryjerry05]

Re: Missing at idle

I think 20# is the tourqe.
Some say to re-tourqe after a short time,some don't.
I've never found it necessary.

 

[Wonbigfish]

Re: Missing at idle

I think 20# is the tourqe.
Some say to re-tourqe after a short time,some don't.
I've never found it necessary.

120 inch #s plus 1/4 turn as works out. Repair is complete & ready for Mosquito Lagoon
Thanks for all the help