Yamaha 90 won't get high RPM

[Alumahollic]

2004 yamaha 90 that will start right up and idle perfectly, but whenever I gas it more than a slow idle it just kind of shakes and never kicks in. I can push the throttle all the way forward and it just sounds like its trying really hard, thinks start shaking etc, but it never goes up at all in RPM. It has happened random times after I kill the engine and then start it back up. Just recently, it did it from the moment i cranked up and never got better.

 

[wellsc1]

Re: Yamaha 90 won't get high RPM

Sounds like carbs need cleaning. My 90 ran fine until WOT attempted, but had no power to pull onto a plane. High-speed jets were clogged. Mechanic told me to run carbs dry when storing it. Gas blends today are terrible.

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

Well, it has sat up for a while. I did a quick glance at the carbs through the intake and they look spotless, the engine is still basically brand new. I sprayed some carb cleaner and let it run for a while, still won't hit high RPM. Anyway to clean the high speed jets without a mechanic or having to take everything apart?

 

[robert graham]

Re: Yamaha 90 won't get high RPM

You can drain each carb, spray carb cleaner into float chamber through drain hole, pump primer bulb to flush float chamber and float needle valves. That might help, but you're probably going to have to clean carbs by disassembly/carb kit. A boat dealer can do it for about $150. After this, use Stabil Marine and install a fuel/water separator to prevent this hassle and expense. Good Luck!

 

[99yam40]

Re: Yamaha 90 won't get high RPM

Looking into the carb that way will not tell you anything, because the plugging is in the jets and passages.Spraying carb cleaner into a carb still mounted on a motor will not do anything but put chemicals into the motor which is not good for it.
If you are sure the compression and spark is good then You need to disassemble the carbs and clean. It is not that hard to do, but I recomend getting a Yamaha manual for your motor and read up on it and how to adjust after. Complete Carb kits are normally not needed just a few orings /gaskets.

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

The weird thing is that it doesn't die or anything. It just starts vibrating real weird. It does sound like its struggling for gas, but i just figured it would die after i pushed the throttle all the way through.

Basic question, do all 3 cylinders fire at all RPM ranges? I assumed they all do, and that the high speed jets just take over at higher RPM's (power band), but could one bad spark plug be the problem? I'll check the plugs later.

 

[woodjm]

Re: Yamaha 90 won't get high RPM

Mine did the exact same thing a couple months ago. Needed to clean the carbs. I suspect it was due to ethanol gas and letting it sit in the bowls of the carbs. I took them all out and and found that one of the carbs had its needle stuck in the seat so gas would not flow in the carb. To clean these you will first need to take the carb off of the engine and disassemble it. For help on dissasembly you could look at the parts diagram on boats.net. Make sure you take off any rubber or plastic before you spray it with carb cleaner because it will dissolve anything. Then spray jets and any holes you can find with carb cleaner. I would just take one apart at a time to get familiar with it and if you forget where a part goes you can refer to the other carbs. To prevent this problem in the future disconnect the fuel line from engine and run the carbs dry. Good luck and take your time with it if you decide to do it yourself.

 

[rodbolt]

Re: Yamaha 90 won't get high RPM

DO NOT run the carbs dry, it will still leave enough fuel in the bowl to make nasties.
wont hurt but it wont help because you simply CANNOT run them dry.
each bowl has a drain,simply loosen the drain screws a few turns,wait 10 min and retighten them.
what your describing could be a clogged carb but it could be an alarm is triggered.
have you tested the audible alarm?

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

Hmm, I'm not sure how to test the alarm. I've never heard any noises or beeps or anything. Could you explain what I need to do?

thanks for the responses, alot of good advice.

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

Another weird thing, I have been using a water/fuel separator filter that I bought from Academy. It's supposed to deal with the ethanol problems I was told.

 

[woodjm]

Re: Yamaha 90 won't get high RPM

water separators are good to have but don't completely eliminate the problem from what i hear ( I have one as well). I was told if you hit a wave the water in the separator can splash up and get sucked back into the line and go to your engine. Know that the separator only separates water, not ethanol. So ethanol gas will still be in the carbs and can cause problems because it deteriorates very quickly. The best thing I think would be to pay a bit more for regular gas without ethanol if you can find it. You can google gas stations that sell ethanol free gas. I keep my tank full so that water wont form from condensation on the sides of the tank. that helps a lot.

 

[boben2830]

Re: Yamaha 90 won't get high RPM

Hey would be a good idea to have you coils checked also..Good luck !!!!!!

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

checking the coils, that kind of goes along with my last question:

Are all 3 spark plugs firing the entire time the motor is running? Or, are do additional one/two fire whenever the RPM's are increased? It's a basic internal combustion engine question i guess but its got me thinking...

 

[Alumahollic]

Re: Yamaha 90 won't get high RPM

(refferring to my last question/post):

Basically, I'm wondering if its even possible for it to be a spark/electrical problem. Since the boat will run, and travel up to 15mph or so, does that eliminate spark problems?

If all cylinders receive gas and spark at all times, it seems unlikely that this could be the problem or it wouldn't run at all.

However, if one/two of the cylinders only receive gas/spark at higher RPM's then it would make since that this is a territory to explore.

 

[papaterk]

Re: Yamaha 90 won't get high RPM

I think it is time to do the carbs! I have a three cylinder that started:redface: great and idles perfect, but had bad loss of power under full throttle. The carbs have different circuits in them. The idle circuit seems to be the least effected by trash or varnish. The reason the high speed gets clogged up is because it pulls fuel off the very bottom of the float bowl. I did my carbs twice before I found the problems. Clogged passage. I wish there was an easier way, but I am afaid there is not.

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