1989 mercury 9.9 need help.

[Codessa]

Hi all. Ive got a 1989 merc 9.9 with supposed 15 kit..motor that ran great when i got it year bfor last. Last summer we ran it hard for a week. During that week i ran a can of seafoam thru it. Last day of trip it starts running rough and dying. I rebuilt carb/cleaned, changed plugs, gas, gas lines, u name it. As of now it will fire up on choke. As long as i stay on the choke it will idle but as soon as i put in gear n go it dogs out n dies then wont start for few min then do same thing over n over. I talked with a local boat repair guy and he suggested to much carbon build up that the exhaust cant exit and chokes it out.. Any suggestions..or a way to clean the exhaust out without taking power head off. Thanks in advance for any and all help!! Be safe out there.

 

[flyingscott]

What is the low speed screw adjusted out to. If you have carbon build up try powertune or engine tune. Also is it firing on 2 cylinders spark test and compression test. Pretty doubtful your motor has a 15 hp kit on it they did not share blocks in 1989.

 

[Codessa]

Its set to spec. 1 1/4i beleive...got spark and good compression.. I am getting bit of left over oil on plugs. But it doesnt smoke. The main exhaust port barely has compression to the feel.

 

[flyingscott]

Try adjusting the low speed idle out more. Why would you feel compression out the exhaust port? What is good compression? Does the spark jump a 7/16" gap

 

[Codessa]

That ill have to measure i culdnt find that spec in repair manual. I know i over looked it tho. Ill get back to u on that.

 

[Codessa]

Ive done everything i know possible to this motor. Many many hrs spent foolin around. But im just a backyard mechanic. All the normal overlooked things have been addressed. Will return with measurement tho. Thanks.