1984 90hp problems

[Steve1122]

My engine has developed a weird habit of starting/running fine but will drop a cylinder (or 2) after a load is put on it. Yesterday I covered about 4 miles at near WOT before this happened. I replaced all 3 coils this morning but as usual, it started and ran fine for a bit and then lost one and then another cylinder.
I haven't replaced the spark plugs yet but this doesn't seem symptomatic of bad plugs.
Any ideas?

[Ken]

Steve,
If it has been at least a year since new plugs, replace them.
Good luck,
Ken K

[Steve1122]

I just replaced the plugs and no better...pulled the plugs and only the bottom showed any sign of firing - pulled the drain plugs on the top 2 carbs and there was no fuel - got to looking around and the fuel supply hose to the fuel pump was pinched. In the process of trying to straighten it out I broke the nipple off the fuel pump. No biggie, I probably could use a new fuel pump anyway, along with new fuel hoses. I pick up those items tomorrow and see how it goes..

[Ken]

Dang, Steve, sounds like my luck - but this is how you learn this stuff. Since it looks like you are going to be taking care of your own service on that 90 Yammie, get yourself a Yamaha shop manual - it will pay for itself many times over.
Good luck,
Ken K

[Steve1122]

Well I took it out today and it's no better. Starts & runs fine for maybe a mile near WOT but then slows down, comes off plane and runs on 2 cylinders...this is frustrating!
Has anyone ever had problems with the CDI box? I'm thinking this may be something to check.

I have 2 separate fuel systems and it runs the same with either of them - I was thinking maybe I had a clogged fuel tank vent but that's not the case..

I'm taking it down to Mexico this Saturday for a week at LA Bay - sure would be nice if it was running good!

[jb123]

steve, does your key switch buzzer work correctly when you start up??

[Ken]

Steve,
Your 90 HP may be going into rpm reduction mode - but your alarm should be going off also. There should be at least one thermo switch mounted in the head assy - find it and disconnect the two wires that come to it from the ignition control (should be bullet type connectors). With the ignition on, short the two wires together (the pair that leads back to the ignition control). This should immediately sound the alarm. If it does not, then the alarm system needs to be worked on. Also, remove the thermo switch and test it per the shop manual. It should close at around 185 degrees to sound the alarm and put the motor in rpm reduction.
Good luck,
Ken K

[Steve1122]

Good info Ken & jb...I'll check those issues out after work today.
I'm going to install a new fuel pump today and remove & clean the carbs.
Thanks for the assistance guys!

[Steve1122]

Yep, alarm works...

I pulled the carbs and believe I found the problem - the carbs were totally crudded up with fuel varnish particles - some near 1/8" in dia! Looks like I've solved this issue - I'm headed to the lake tomorrow to do some "hot laps".

BTW - even though the engine ran like crap yesterday, the fishing was excellent - caught at least 20 calico bass while I was "field" testing the engine...

[Ken]

Steve,
The fishing gods have blessed you!!!
Now, if you can just get those carbs cleaned up...
Are you going to install carb kits, or just clean them out?
Good luck,
Ken K

[Steve1122]

I just cleaned them out with carb cleaner - removed the jets, float assy, etc...They look like new now. The engine fired right up and seems to run excellent. I'll do a run to the lake tomorrow and then it's off to Baja for a week of real fishing.

[Steve1122]

UPDATE:

The engine now runs excellent and I'm on my way to Mex for a weeklong fishing expedition.

Thanks to everyone for their suggestions - I really appreciated the support!

[Ken]

Steve,
Glad you got your Yammie running good - what do you think was the reason the carbs were gummed up? Did you let it sit for a long time without running. I try to run mine in the off season at least every two weeks - preferably every week.
Good luck fishing in Mexico - PM me with a fishing report!
Ken K

[Steve1122]

Ken:

Yes it sat for pretty much the whole winter. We had an abnormally wet winter and I never made it out with the boat. I usually fish in the winter so this gelling of the fuel is new to me.

I'll send you a link to our trip pics when I return.