1986 90 HP Yamaha surging

[AquaPatio]

This outboard was running fine the other day.
I pulled in, shut down, refueled, and topped off the oil reservoir. Two days later, I started it up and it was surging at anything above an idle. I thought it might be some bad fuel, so I switched to another tank with the same results. I idled around for over an hour and pulled back in. I changed spark plugs, pulled and cleaned the fuel filter, which was not dirty, and checked spark. The indicator light shows the oil reservoir is full. It is still surging at anything over an idle.
Any ideas would be extremely appreciated.

 

[Ray Neudecker]

Re: 1986 90 HP Yamaha surging

The surge is either from a fuel restriction or a CDI problem. Check the firing when it does it. If firing correctly, then check the compression. if it is good, you are back to a fuel restriction.

 

[AquaPatio]

Re: 1986 90 HP Yamaha surging

Sorry it took me so long to get back. Firing on all 3 cylinders. Compression at 140-143 on all cylinders. Replaced fuel line. Checked spark advance linkage.
Idles very good, but try to increase RPMs and it starts surging.

 

[Marc III]

Re: 1986 90 HP Yamaha surging

You may need to remove and clean the carbs. They're relatively easy. The idle circuit is on top of each, the mids and high speed jets are accessed from the float bowls.

I did the ones on my 1988 90 hp a few weeks back. I ground the shoulders off a good mid-sized flat head screwdriver to remove the jets. Blow them out with carb cleaner and compressed air. I reassembled mine w/o needing new gaskets or anything.

 

[AquaPatio]

Re: 1986 90 HP Yamaha surging

I appreciate the response. It will be a few days before I can get back to the boat. I will pull and clean the carbs and post the results.