Spark plugs

[Liveto99]

50 hours is what I’m getting then my rpm’s only go to 73 or 7400. Change the plugs and it is back at 8,000. Anyone else?

 

[anmut]

You're saying you have a new boat with 50 hours and new plugs caused a 600rpm gain? Single / dual engine? Have you owned it since new? Carbon fouling on the old plugs? Gas treatment? Winterization? Elevation?

 

[Grassman]

No idea why but yes same here. 120 hours and im on my third set of plugs

 

[Liveto99]

2018 I bought it new. They looked ok but gain back my rpm when changed. I have 145 on it now and Back to 7300 I’ll change then when I get back to Fl next month. Just went 175 miles in it yesterday.
Dual engine, use rec 90 no ethanol, marine stable to a full tank every month when I go away for 3 or 4 weeks. Sea level Fl keys. But same happened in NY at sea level with no stable.

 

[Liveto99]

No winterization I bring it to the Fl Keys for the winter.

 

[jtwrace]

Do you idle speed a lot? It's a bit of a secretive issue that they foul plugs at extended periods of time. It's important to run them at WOT for a bit afterwards to help "clean" the plugs. And I have found that 70 - 80 hrs hrs is about the best time to change them.

 

[Liveto99]

I don’t idle normally and I run at full speed a few times a day. I figure it is a jet ski engine and should run full out a bit. I do run full out for extended times when I’m on my way home and it is getting late. Some times a half hour or so. Other wise 7200 rpm is a Great cruise or 6900.
63 or 6400 when it is rough out.

 

[jtwrace]

Yep, that should be enough for sure. You're using the right heat range plug?

 

[Liveto99]

Dealer did it. I have new stock plugs in it, to change it this time.
@Grassman has the same thing I think.
This is the new ? TR-1 HO engine. Somaybe it has something to do with it.
@Foobar how many hours do you have on your FSH? Did you do plugs yet?

 

[jtwrace]

I had an odd fuel injector issue that Yamaha said was fine so that's a possibility. Also, make sure your TPS is getting full voltage at WOT.

 

[Foobar]

Dealer did it. I have new stock plugs in it, to change it this time.
@Grassman has the same thing I think.
This is the new ? TR-1 HO engine. Somaybe it has something to do with it.
@Foobar how many hours do you have on your FSH? Did you do plugs yet?

I just did mine this year as I did not use my boat last year. I have less than 50 hours. I have old gas in the tank, so my boat isn't running as fast as usual. I will know more once the weather warms up a bit.

 

[Grassman]

I've spoken with other owners of Yamaha jet boats that have the same issue including the 24 foot models. They just claim ""new plugs do wonders for these boats". But no idea what exactly is going on. I just replace them when it bothers me.