Yamaha Knocking...pls help.

[TwinAceMarty]

I went out with the family for a nice relaxing day on the water. On the way back i noticed that the engine started idling up and down by itself. It would go up to 3500 rpms and drop to 2800 rpms by itself without me touching the controller. When we were turning in to the marina i noticed a knocking sound from the engine which progressively got louder. I took off the engine cover and it sounds like its comming from the powerhead!!! Any ideas what this could be?? It has new filters and plenty of oil & new spark plugs so i dont know what the prob could be!!! thx, Marty

 

[AlanR]

Re: Yamaha Knocking...pls help.

Does the knocking get louder the more revs you give it?

 

[Triton II]

Re: Yamaha Knocking...pls help.

Any ideas what this could be??

Marty, it would help guys like Rodbolt and the other engine gurus on here if you posted the model and year of your Yamaha!

TII

 

[TwinAceMarty]

Re: Yamaha Knocking...pls help.

The motor Is a 2004 Yamaha 200hp HPDI. It had major problems with fuel cause I hadn't moved it in about a year or so! Thx to Rodbolt and the rest of you guys I was able to recognize the problem and change the fuel pump in the VST tank, all the filters and the spark plugs and it has been running great for 3 months now! Yesterday however I started having the erratic revs and the noise! The noise was getting louder with higher revs! Thx

 

[rodbolt]

Re: Yamaha Knocking...pls help.

sounds like your back to the fuel buggers on the surging.
the knocking is a bit tougher as I cant hear it.
but mechanical knocking on a two stoke is never good.

 

[TwinAceMarty]

Re: Yamaha Knocking...pls help.

sounds like your back to the fuel buggers on the surging.
the knocking is a bit tougher as I cant hear it.
but mechanical knocking on a two stoke is never good.

Yea, I figured the knocking was bad! I just don't understand how it can just up and break down like that!! Rodbolt, if you had to venture s guess what would you think the knocking is on my model? Piston Rod??

 

[TwinAceMarty]

Re: Yamaha Knocking...pls help.

I just found out that poor grade gas could be the culprit? I have always filled with 93 grade from Shell but this particular time I drove in another direction so I filled up with 87 grade from a cheap gas station! Could this be a problem??

 

[TwinAceMarty]

Re: Yamaha Knocking...pls help.

Today i made a compression check on the engine. Results were 112-120 on all cylinders. I then started the engine and no noise. Even at higher RPMS...still no noise. I figure it must be a gas/oil thing? any further suggestions??

 

[robert graham]

Re: Yamaha Knocking...pls help.

Seems if knocking comes and goes, then most likely not mechanical, could be fuel related, but I've always run regular gas(87 octane) and never any knocking. Is your knocking coming from the powerhead area or the lower unit, like drive shaft or gear noise?

 

[rodbolt]

Re: Yamaha Knocking...pls help.

that engine is designed to run on 87 octane fuels.
dunno.
fuel buggers will cause it to run lean which willcause detonation and sound like its knocking.

 

[robert graham]

Re: Yamaha Knocking...pls help.

Well if it was knocking due to detonation caused by a lean fuel condition then better get it fixed before a piston fries. Wonder how low the fuel octane would have to be to cause a knock and what would cause it to be low? I've just never heard a 2 stroke detonation knock but I expect if it came on all of a sudden at say 4000RPM's it might just fry something right quick? That knocking would really worry me until I got it fixed. Good Luck!

 

[robert graham]

Re: Yamaha Knocking...pls help.

One other item that might cause detonation/knocking might be carbon deposits in the combustion chamber creating hot spots? Maybe run a de-carbon dose of Ringfree through the motor to try and eliminate that as a possibility.