1988 merc 90 3cyl bogging above 3000rpm.

[electricjohn]

This one has me baffled. Good fuel pressure, clean filter. Carbs are clean. Electrical readings are good on the ignition system at least up to 2000 rpm. Starts and runs fine up to 3000 r's. Any ideas?

 

[racerone]

Checked cylinder sleeves for being out of position ?

 

[Faztbullet]

What it do at 3000???

 

[electricjohn]

Starts hesitating or bogging like it's looking for more gas. Best it will give me is 4000rpm, where normally 5500 easy. Can't find anything wrong with fuel delivery, wondering if its electrical? Perhaps a coil acting up with higher voltage above 3000 rpm?

 

[racerone]

Hook up a timing light one cylinder at a time.-----Go for a spin and observe the light at 3000 rpm.-----Checked the flywheel key ?---Compression test has been done I hope.------Should not be hard to find what is wrong on this motor.

 

[Sirrobin53]

My trigger had swelled causing it to stick on the race. Timing was nailed at 11°. Would start and run but having no advance it was sluggish and never wot. With the help of all the members I was able to get mine going. I removed the throttle linkage and activated the throttle by hand and found the stuck trigger. I scraped just enough plastic off it so it would turn freely. Wa La. Ran it last weekend

 

[electricjohn]

Hook up a timing light one cylinder at a time.-----Go for a spin and observe the light at 3000 rpm.-----Checked the flywheel key ?---Compression test has been done I hope.------Should not be hard to find what is wrong on this motor.

Agreed, I could not get a boat driver last fall so I could spend some time back at the engine with a DVA, timing light, or pressure gauge. Hopefully in the spring. Compression was 115 in all 3.

 

[electricjohn]

My trigger had swelled causing it to stick on the race. Timing was nailed at 11°. Would start and run but having no advance it was sluggish and never wot. With the help of all the members I was able to get mine going. I removed the throttle linkage and activated the throttle by hand and found the stuck trigger. I scraped just enough plastic off it so it would turn freely. Wa La. Ran it last weekend

I will check for full movement later. Did not notice anything out of the ordinary when checking link and sync.

 

[racerone]

You do not need an assistant to use a timing light to trouble shoot the spark.-----You lay the light on a seat and observe the behavior of the light as you throttle up.-----Repeat with # 2 and 3 cylinders.

 

[wn6ngp]

You do not need an assistant to use a timing light to trouble shoot the spark.-----You lay the light on a seat and observe the behavior of the light as you throttle up.-----Repeat with # 2 and 3 cylinders.

That could be a case of distracted driving.

 

[electricjohn]

My trigger had swelled causing it to stick on the race. Timing was nailed at 11°. Would start and run but having no advance it was sluggish and never wot. With the help of all the members I was able to get mine going. I removed the throttle linkage and activated the throttle by hand and found the stuck trigger. I scraped just enough plastic off it so it would turn freely. Wa La. Ran it last weekend

Checked it out yesterday, and sure enough trigger was not advancing to the max timing stop. Coming up about an 1/8 to a 1/4 inch short. Could move it by hand, so I have something to look at this spring after the ice is out. Good call, thanks.

 

[quicktach]

advance sticking?

 

[electricjohn]

advance sticking?

Yup, guessing I will have to pull flywheel, ect. It will go to max with help but not on its own by the internal spring tension in the throttle arm.

 

[Sirrobin53]

In above reply I mentioned that the trigger swelled up. That I scraped just enough to get it free and ran it. WELL,.... here it is. I was just checking the timing and removed the throttle linkage and there it was, stuck. Again. I don't know why this happened but the thing swelled even more. I have replaced it with a new one. I really was surprised to find it also scraped the paint on the flywheel.
Outboards...... gotta love em.:lol: