2004 225 Yamaha 4-Stroke has backfire problems on the top two cylinders.

[Fish & Chix's]

2004 225 Yamaha 4-Stroke has backfire problems on the top two cylinders, when I go above idle. I believe it's a timing problem but not sure on how to check. Does anyone know what would cause this?

 

[99yam40]

back fire to me on a 4 stroke is poppping back thru the intake.
is this what is happening?

 

[robert graham]

Has any work or changes been done to the motor that may have caused this backfiring?......like a timing belt?....

 

[Fish & Chix's]

99Yam40 and Robert

First..... Thanks for responding to my post........... 99Yam40 you are correct it's popping through intake, which only happens on the top cylinder on both sides. I also have 135psi compression on those two cylinder in all others I have 150. Robert, I bought the boat knowing that the fuel system needed to be cleaned and it had been sitting for a year. I cleaned or replaced all injectors/filters and fuel pumps in the fuel system. I have lower compression in the same two cylinder that it popping through and no problems with the others, I'm not sure what would cause this...... Any and all help is much appreciated

Eric

 

[99yam40]

popping back to the intake means intake valves are not closing, or have a leak due to burnt valves.
or timing of spark is off. timing light should show that

a leak down test might be in order to see what it says

 

[Fish & Chix's]

99Yam40

I was leaning towards a timing problem, Do you know what the timing should be on a 2004 225 4 stroke fuel injected?? The drop in compression in the cylinders that are popping is what throwing me off, do you think the 130 psi just means the valves need to be cleaned to get a better seat ie... some carbon build up on those cylinders. The rest are 150 psi.... Do you know how of any way to clean those valve without tearing down the engine?

Thanks

Eric

 

[99yam40]

do a leak down test on all of the cylinders to see what it tells you

 

[boscoe99]

How is it known that it is the top two cylinders are the ones that are backfiring?

The timing is computer controlled. No adjustment is available.

 

[99yam40]

what is someone swapped plug wires.
Just a thought of how spark could be at the wrong time