Yamaha 28hp going roughly

[Bjornis]

Hi!<br />I have an 28hp yamaha late 1970 year. When driving it goes well on full speed but when it gets down to half trottle one cylinder dies. As soon the trottle goes past half trottle it fires up again. Let the dealer have a look on it but they cant find the problem.<br /><br />anyone that has an idea what the problemcan be?<br /><br />Regards<br />Bjornis

 

[Bjornis]

Re: Yamaha 28hp going roughly

No ideas?

 

[rodbolt]

Re: Yamaha 28hp going roughly

has your dealer isolated it to ign or fuel. when it drops a cyl does it quit sparking or is that cyl starving? I have no service literature for a model that old as theye were not imported here. but like every other articulated rod internal combustion engine it has to suck, squeeze, bang and blow.

 

[Bjornis]

Re: Yamaha 28hp going roughly

Dealer thinks its electrical but not sure. I have rebuilt carb and changed gaskets on the intake side. Reeds lok fine. Dont think it is fuel problem, doesnt "feel" like that.<br /><br />Tried it today, goes rough until about half trottle, then it kicks in and runs like new.<br /><br />Checked compression on both cylinders and they are fine.<br /><br />Gona check with timing light if it fires on both cylinders on low rpm.<br /><br />Any more ideas?