@help starboard engine not reaching max rpms

[jcsmith77]

@HELP maiden voyage today and the starboard engine won't get over 6500 rpm while the port gets over 8000. Anyone?

 

[Scottintexas]

when was the last time you were able to get full rpm's ?
any unusual sounds or vibrations that could be cavitation?

I would start with plugs, it usually solves about 90% of peoples problems.

 

[latitudeadjuster]

Plugs if not changed. Is plug clean out in properly?

 

[mark_m]

Check to be sure all connections complete / each plug. This happened to me on first launch this year.

 

[Scottintexas]

when you said maiden voyage I was thinking first one this year, is this the first time ever out in your new boat?

if so, did you take it for a test ride before buying?

 

[jcsmith77]

First time this year, it ran fine last fall. I fogged and blew out but didn't do a plug change. I checked and reseated the clean out plug and checked for debris. No change.

 

[latitudeadjuster]

Change plugs....most likely the problem. Change just in engine with issue aND see...but go ahead and change plugs in both. Fogging causes more issues imo ....I have never fogged.

 

[Zarrella]

I'm betting on fouled plugs.

 

[jcsmith77]

Are the plugs for these readily available or a special order type item?

 

[latitudeadjuster]

Dealers have them, amazon has them, Adance auto can get then next day if they don't have them in store. I order mine amazon 2 days.

 

[jcsmith77]

Does anyone know offhand the part number or link on amazon. Hard to research from my phone. Much appreciated.

 

[itsdgm]

Does anyone know offhand the part number or link on amazon. Hard to research from my phone. Much appreciated.

NGK CR9EB (6955) available at O'Reilys and most auto parts stores.

 

[latitudeadjuster]

https://www.amazon.com/dp/B001RM8JSK/ref=cm_sw_r_sms_apa_pTmxxbGA6MY68

 

[itsdgm]

Don't forget to use anti-seize on the threads and do not over tighten. Over tightening can snap it off in the head. I can't remember the exact torque specs, buts it's in the "inch pounds" not "foot pounds". It's common practice to just spin the plug by hand until the gasket touches, then tighten 1/4 turn.

 

[Scottintexas]

From our faq
https://jetboaters.net/faq/how-do-i-change-the-spark-plugs-in-my-yamaha-jet-boat.7/

 

[latitudeadjuster]

Yup X2 anti-seize
https://www.amazon.com/dp/B0002UEOLO/ref=cm_sw_r_sms_apa_ZanxxbQ1VK1HG

 

[txav8r]

They got you covered on the spark plugs. And low RPM is a spark, fuel, or air related issue, inside the engine, so spark plugs are the cheapest and quickest way to start that. Low RPM can also be a saturated air filter, but generally you will be rough running or won't even start easily. Cavitation or any introduction of air into the pump won't decrease RPM, unless the pump is jammed, and that will have other symptoms with it, like noise and bad vibration. Also, not only will cavitation not decrease RPM, but the engine will rev to high RPM unrestricted, without load on the engine...just like it will when your running on the hose or not on the hose out of the water. If the impeller has air in it, then it isn't pulling water in and pushing water out...and the pump is turning without "load". So the RPM will race upward with the slightest throttle increase, all the way to top RPM if you push the throttle that far. So when you see reduced RPM, it is generally a fuel burn related issue, where the engine isn't producing horsepower to get it that high. And that means one of the three things required for combustion is reduced. And as history shows, spark plugs are the most common culprit on these engines. That said, the 1.8L is much less sensitive to our historic spark plug issues we had on the MR-1 engine, both from a fouling standpoint, and from a seizing standpoint. But I would recommend fogging any one of these engines routinely, according to Yamaha tech bulletins, as well as using anti-seize on the threads of the spark plugs. I would also not use a torque wrench on the spark plugs for the average home mechanic. Because anti-seize changes torque, torque wrenches are not calibrated correctly, not being familiar with them, and there isn't a need. The best way to tighten (and know you can remove) spark plugs on any of these engines, is to tighten to the gasket without wrench, just turning the plug with the socket and extension by hand as far as you can, then only 1/4 turn more. That will be less than the torque wrench recommendation, but more than is needed to seat the plug securely.

 

[jcsmith77]

Solved, so sparkplugs it was. Found a Napa close by and they had 4 so I went and got them this morning and changed them out and everything was right with the world again. Thanks to everyone for the assistance.

 

[jcsmith77]

I will be getting 4 more to bring back with me for the other engine next weekend.

 

[itsdgm]

I will be getting 4 more to bring back with me for the other engine next weekend.

It's not a bad idea to keep a spare set onboard too for the ..... Dare I say it ...... Next time. It's pretty common for the plugs to "foul/go bad" on our vintage of yamahas.

Ps. Glad you got it fixed