1989 Murcury 100 hp rough idle but fine at WOT

J

Jbny

Recruit
Joined
May 28, 2012
Messages
4
After a tune up this year all was well. New plugs, clean/sync of carbs, fuel diaphrams, needles, and seats. Over the weekend i developed a rough idle condition. Enough to cause the motor to stall when placing into gear. I was able to get going again and there was no issue throughout the throttle range. Once back to the dock, stall.... The roughness sounded like lack of fuel but the bulb was good to go. Plugs? Wires? Thoughts?
 
D

Dave1027

Lieutenant Junior Grade
Joined
May 25, 2010
Messages
1,083
Re: 1989 Murcury 100 hp rough idle but fine at WOT

What RPM is it idling? You said, "roughness sounded like lack of fuel but the bulb was good to go". How does roughness sound like lack of fuel? Describe the roughness in more detail.

Plugs? You have new plugs.
Wires? Doubt it. Not much can go wrong with solid cores.
 
J

Jbny

Recruit
Joined
May 28, 2012
Messages
4
Re: 1989 Murcury 100 hp rough idle but fine at WOT

RPM at idle is 1000 with not much more room to go in the adjustment. When first put into gear the RPM drop enough to make the engine stall. If it does not stall right away the RPM fluctuates between 500-900 roughly before it quits. The only way to keep the engine from stalling when placing into gear is to quickly move to quarter throttle. If you just engage it will not run smoothly as it did before. It seemed to be starving for fuel or lack of spark but once beyond 1800RPM everything is kosher.
 
D

Dave1027

Lieutenant Junior Grade
Joined
May 25, 2010
Messages
1,083
Re: 1989 Murcury 100 hp rough idle but fine at WOT

Could be something went bad like a float sunk. First thing to confirm would be the link/sync.
 
J

Jbny

Recruit
Joined
May 28, 2012
Messages
4
Re: 1989 Murcury 100 hp rough idle but fine at WOT

Thanks for the tip. All the links were tight and in position. I spent a few bucks on carb cleaner today and went to town on the note of a "float". A few hours later and it is getting better. The response in neutral from idle up to 3000 rpm is close to normal again. Maybe one more round of cleaning and I'll be set. It seems even the most scientific fuel additive (k100) doesnt save you anymore these days. Lack of use during the week doesnt help my situation either. ;)
 
O

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: 1989 Murcury 100 hp rough idle but fine at WOT

The ethenol gas today that one buys is recon havic on some older 2 stroke motors. A search for Pure Gas .org will get you a list of gas stations near you that have gas without ethenol in it. Ethenol gas has been eating up old fuel lines and pump diaframs, not made to handle the new ethenol gas, and cause the rubber to plug up filters and carbs quickly. other option is to replace fuel lines and all rubber parts with new ethenol restant parts. JMO
Oldman570
 
J

Jbny

Recruit
Joined
May 28, 2012
Messages
4
Re: 1989 Murcury 100 hp rough idle but fine at WOT

i'll give it a shot. I suppose fuel lines are next. Thanks again.
 
O

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: 1989 Murcury 100 hp rough idle but fine at WOT

Not sure about your motor, but some newer 4 cylender motors only run on 2 cylenders when at idle and pick up the others as the motor speeds up. A compression check of the motor will show if everything is good to go. You might also have a plug or wire that is not fireing as it should (carbon build up on plug). JMO
Oldman570
 
You must log in or register to reply here.
Top