90HP Yamaha 2 Stroke Won't Rev Past 4K Under Load
#1

First time posting after lurking for a number of years. This is a great board and I have learned a lot and been able to keep my boats runing well due to you guys so thanks. I can't find what I am looking for so I'll ask for some assistance please.
I have a 2009 CS 178 DLV with a same year 90 HP Yamaha 2 stroke (TLR) on it. Took it out 3 weeks ago and it ran great for 40 min with full range of throttle up to near 6000 RPMs. On the way back, I dropped speed in a no wake zone and upon coming off of the other side I throttled up again and the engine wouldn’t rev up past 4200 RPM and the boat wouldn't get on a plane. Once hitting 4200, further throttle produces no additional results.
This is higher than the 2000 RPM limp mode and there were no warning lights or buzzers so I don’t believe it is an issue with the oil level sensor (plenty of oil) or temp sensor (water is flowing full stream through the engine) – both of which would send it into limp. The boat would rev higher in neutral, but not under load. (I know that these are 2 different operating conditions, but just making the observation) Seemed like a fuel issue. Since the boat is newer to me and I had no baseline of repair history to work from, I did the following:
Am I dropping a cylinder? Maybe not getting spark somewhere? I would think that I wouldn't be able to rev it up in neutral either if that was the case. What should I be looking at next?
I have a 2009 CS 178 DLV with a same year 90 HP Yamaha 2 stroke (TLR) on it. Took it out 3 weeks ago and it ran great for 40 min with full range of throttle up to near 6000 RPMs. On the way back, I dropped speed in a no wake zone and upon coming off of the other side I throttled up again and the engine wouldn’t rev up past 4200 RPM and the boat wouldn't get on a plane. Once hitting 4200, further throttle produces no additional results.
This is higher than the 2000 RPM limp mode and there were no warning lights or buzzers so I don’t believe it is an issue with the oil level sensor (plenty of oil) or temp sensor (water is flowing full stream through the engine) – both of which would send it into limp. The boat would rev higher in neutral, but not under load. (I know that these are 2 different operating conditions, but just making the observation) Seemed like a fuel issue. Since the boat is newer to me and I had no baseline of repair history to work from, I did the following:
- Replaced the fuel filter
- Replaced fuel water separator (no water in the old one when checked),
- Replaced spark plugs
- Cleaned and rebuilt all 3 carbs with new kits.
Am I dropping a cylinder? Maybe not getting spark somewhere? I would think that I wouldn't be able to rev it up in neutral either if that was the case. What should I be looking at next?
Last edited by vbskiff; 10-24-2020 at 04:23 PM.
#2
Senior Member

First off, revving it in neutral is no test, forget doing that, check spark on all cylinders when it's playing up, all cylinders, not just one the 3 cylinder Yamaha has a unique ignition system! if you have dirty fuel and you clean the carbs, and run the boat, the carbs can get "dirty" very quick, clean them properly again and run off a remote tank complete with fresh fuel and hose.
#4
Senior Member

That's nice, stabiliser will not "fix" your issue.
#5
Admirals Club 


I have same engine. I would also check spark for all 3 cylinders. Seems like an intermittent issue and those can be hard. Good luck. Tighten all your connections and ground.
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#7

Sometimes stabilizers and additives with scrub a dirty fuel tank clean. I have a 3 cylinder Yamaha that sat unused before I bought it and I had to clean the carbs twice when whatever crud in the tank dislodged and made it’s way to my carbs.
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#9
Senior Member

Yeah you can do that....but will it help if spark is not the issue? Trouble shoot, fix the issue, don't root around with "stuff"
#10

Agreed. I haven't touched anything since it started acting up again today. Going to take it out again tomorrow with someone else behind the wheel so I can pull the plug boots while under load.
#14
Member
#16
Member

The other thing to recommend is to make sure your battery uses clamps or nuts and not wingnuts. Clean all the connections from battery to engine as well after you diagnose the regulator and stator. Those high resistance connections or dropped connections at the battery can kill your electronics.
#17

The other thing to recommend is to make sure your battery uses clamps or nuts and not wingnuts. Clean all the connections from battery to engine as well after you diagnose the regulator and stator. Those high resistance connections or dropped connections at the battery can kill your electronics.