# Yamaha 90 2-stroke, bogging WOT with video.



## Guest (Oct 14, 2019)

Sounds like she is going in to rpm reduction. You need to verify absolute/actual engine temp. Also need to check the oiling system. There are and have been cases where faulty horn and or improper wiring under the console have caused this as well. Some will yell you I am crazy on that last bit but trust me, I am not! If you are competent with a multi meter I can walk you through some diagnostics. I don’t say this often but you may be better off taking it to a competent shop and let them do the work as you could be chasing a gremlin and I know the bite is about to turn on.


----------



## RABillstein (Jan 10, 2019)

@Boatbrains . Is it typical for the RPM reduction to be an intermittent blipping of the throttle to a lower RPM? I have never experienced RPM reduction mode on another boat before but I assumed it instantly dropped you to a lower RPM and limited going above, until the alarm condition was remedied.


----------



## Guest (Oct 15, 2019)

What rpm does it drop to when it blips down? If you hold it there does it keep doing it? The motor sounds to me like it is going in to rpm reduction.


----------



## RABillstein (Jan 10, 2019)

@Boatbrains . At WOT (roughly 4500) it cuts down (and bounces back up) to about 3600. In the video it demonstrates it around the 17 second mark.


----------



## Guest (Oct 15, 2019)

I am still leaning towards rpm reduction. Does the warning horn work? You can test by removing the cowling, find the pink wire on the cyl head, turn key on, now ground the pink wire. Your horn should sound constantly until you remove the pink wire from ground. You can eliminate boat wiring by starting the motor then disconnecting the canon plug at the motor and running the boat. If you do this you will have no emergency kill and you will have to plug it back in to shut the motor off.


----------



## Smackdaddy53 (Dec 31, 2012)

I thought RPM reduction on these Yamahas is 2500 when there is an issue? I’m not near my service manual.


----------



## Guest (Oct 15, 2019)

Smackdaddy53 said:


> I thought RPM reduction on these Yamahas is 2500 when there is an issue? I’m not near my service manual.


It is, but they act goofy at times


----------



## RABillstein (Jan 10, 2019)

I did everything I could to rule out a fuel tank vent blockage. I ran the boat today and still had the issue despite the gas cap being unscrewed. I did notice that if I squeeze the primer bulb while experiencing the issue, it resolves and returns to WOT. Does this mean the issue can be narrowed down to somewhere between the bulb and the engine (rather than between the fuel tank and bulb)? Should I be thinking fuel pump maybe?

Also to note: I made sure to note WOT RPM at ideal trim (the aforementioned 4500 was without any trim). My WOT was closer to 5300 with speeds in the upper 30s.


----------



## Smackdaddy53 (Dec 31, 2012)

A fuel pump for that motor is about $38 and a Yamaha fuel hose with primer bulb and fittings is about $60. If your fuel hose is old I’d replace it and be done and the fuel pump can’t hurt. I put things like this into perspective: how much is my fishing time worth? Your primer bulb could have a bad check too.


----------



## MariettaMike (Jun 14, 2012)

RABillstein said:


> .... Should I be thinking fuel pump maybe?


Your problem is fuel related as proven by your pumping the bulb observation. It’s obvious the bulb works so it might be the fuel pump. I recall there being an easy test for checking the fuel diaphragm integrity. Maybe Google that.

However it has been my experience with that engine running rough that all the problems were carburetor related. I highly recommend you solve this problem quickly before you burn the rings out of a cylinder that may be running lean at WOT due to a carburetor problem. (That’s the one cylinder cutting out at WOT.)

It’s not that hard to remove and clean the carbs on that engine without replacing anything. Just take pictures or video of your process for putting it back together.


----------



## State fish rob (Jan 25, 2017)

Ethanol


----------



## CaptDanS (Oct 26, 2017)

Clean the carbs not a difficult job. Soak the low ideal jets and high idle jets in carb cleaner an hour or so then blow out with air. Gotta love ethanol.


----------



## State fish rob (Jan 25, 2017)

Ive had 50/50 success w startron enzymatic cleaner. Flooding carbs overnite in place.


----------



## Elusive Porpi (Jan 24, 2018)

With the venting ruled out. i would say high speed jets are plugged or the fuel path to the carb is plugged. Slowing down lets the fuel fill back up in the carb.

* If your fuel lines are from 2007, you should cut into the end and see oi the liner has crumbled apart due to ethanol. (its usually a gray hose that has the liner in it.) this happened to me
* Then i would check any external fuel filters
* Internal fuel filters
* Fuel pump as mention above
*Could also be a little bit of water in the carb
* Fuel Bulb could be worn out not allowing enough flow


----------



## RABillstein (Jan 10, 2019)

PROBLEM RESOLVED. Replaced fuel pump and engine runs WOT for as long as I demand; no hesitation.


----------



## Smackdaddy53 (Dec 31, 2012)

RABillstein said:


> PROBLEM RESOLVED. Replaced fuel pump and engine runs WOT for as long as I demand; no hesitation.


Good deal, they are cheap enough to carry a spare and very easy to swap if you are in a pinch!


----------



## Marsh Pirate (Sep 15, 2016)

Don't you love it when you can find and fix it!


----------



## RABillstein (Jan 10, 2019)

When I ran it a few days ago after the new fuel pump, I really put it through its paces with a few hours on the water -- perfect performance. Yesterday, it suspiciously developed a new issue it had never demonstrated prior. It would bog, then surge intermittently. Very suspicious because it had never done anything like that before in the dozens of hours I ran it before replacing the fuel pump. I got home and checked the pump to see if it had failed, and it appeared to be fine. Seems very likely that it could somehow be related to me fixing the fuel pump (I have no idea how). Why else would this issue mysteriously pop up after running her often, filling her with REC 90 gas, and giving her new parts? If it was carb, fuel line, filter, etc. related I would have expected to see it behaving poorly this whole time. I don't know. I'll get to tinkering, and if I get stuck maybe I'll start a new thread.


----------



## Smackdaddy53 (Dec 31, 2012)

That’s why I was saying to replace the fuel hose and primer bulb too. Eliminate from the water separator to the carbs at least.


----------



## BobGee (Apr 10, 2019)

RABillstein said:


> When I ran it a few days ago after the new fuel pump, I really put it through its paces with a few hours on the water -- perfect performance. Yesterday, it suspiciously developed a new issue it had never demonstrated prior. It would bog, then surge intermittently. Very suspicious because it had never done anything like that before in the dozens of hours I ran it before replacing the fuel pump. I got home and checked the pump to see if it had failed, and it appeared to be fine. Seems very likely that it could somehow be related to me fixing the fuel pump (I have no idea how). Why else would this issue mysteriously pop up after running her often, filling her with REC 90 gas, and giving her new parts? If it was carb, fuel line, filter, etc. related I would have expected to see it behaving poorly this whole time. I don't know. I'll get to tinkering, and if I get stuck maybe I'll start a new thread.


Is there a fuel filter that’s clogged?


----------



## RABillstein (Jan 10, 2019)

The small fuel filter under the cowling isn't clogged, checked it yesterday. The fuel water separator (I have not checked if it is clogged) was replaced in June, I believe, when the previous owner had a Yamaha mechanic do a major overhaul of the fuel system.


----------



## RABillstein (Jan 10, 2019)

If anyone cares, I believe I fixed it. I found that the bracket that houses the regulator/rectifier, ignition coils, spark plug wires, etc. had worked itself loose from the bolt and was bouncing around. It might have only been giving intermittent power to those components. Also, while I was under there, I rag-choked each carb, while giving it throttle, to pull anything out of the jets that might have been clogging them. Ran it yesterday on the water, with the express purpose of trying to make it fail; ran perfectly for a couple hours.


----------



## Guest (Oct 31, 2019)

RABillstein said:


> If anyone cares, I believe I fixed it. I found that the bracket that houses the regulator/rectifier, ignition coils, spark plug wires, etc. had worked itself loose from the bolt and was bouncing around. It might have only been giving intermittent power to those components. Also, while I was under there, I rag-choked each carb, while giving it throttle, to pull anything out of the jets that might have been clogging them. Ran it yesterday on the water, with the express purpose of trying to make it fail; ran perfectly for a couple hours.


This goes more along the lines of what I was hearing in your video than a fuel issue. I’d almost bet you found it now!


----------



## No Bait / Lures Only (Apr 10, 2011)

State fish rob said:


> Ethanol


Never!


----------



## Marsh Pirate (Sep 15, 2016)

Good deal! Way to stay after it.


----------

