High speed miss, Yahama pwc

[Johnny-Mike]

I have a yahama 701T engine installed on a Zodiac Jet.
I have a high speed miss that starts in the 4000 rpm range. new plugs (2) installed..
Any clues where to start? I don't know wether it's fuel or iginition?
Thanks----from sunny Florida, Jon

 

[Jeff Walkowiak]

Re: High speed miss, Yahama pwc

it may be fuel starvation, if the carbs haven't been rebuilt in a few years they probably need new diaphragms and the internal filters cleaned at a minimum, it may be a bad fuel selector switch, or bad plug leads from the coils.

 

[Johnny-Mike]

Re: High speed miss, Yahama pwc

it may be fuel starvation, if the carbs haven't been rebuilt in a few years they probably need new diaphragms and the internal filters cleaned at a minimum, it may be a bad fuel selector switch, or bad plug leads from the coils.

 

[Johnny-Mike]

Re: High speed miss, Yahama pwc

Hi Jeff- Thanks for your reply! New carbs installed 4 months ago, new fuel selector valve installed. It was so rough, on the water, that I didn't or could not take one hand off the steering wheel to try the choke knob.... I have installed a new alternator kit and one of those mini tach's that wrap around a plug wire. I have changed almost all electrical componets except the coils - but it ran great without hesitation until recent. This is a new boat for me----just don't have it all figured out. The spark plugs want to foul out on starting. The spark seems weak. I exected to see a brilliant white spark to the plug - going to ground. It was almost yellow in color. (maybe not a good ground for the spark plug) As an old 2 cycle mechanic I never had a plug foul out from too much fuel,on starting.
Bye for now.... Jon

 

[JUSTINTIME]

Re: High speed miss, Yahama pwc

sounds like bad spark or not adjusted carbs

 

[Jeff Walkowiak]

Re: High speed miss, Yahama pwc

sounds like you know what you are doing,, check all ground wires and remove the plug caps from the wires, take a pair of needle nose and pull on the wire core, if wire pulls out the plug wires are bad, I have had this happen on older plug wires many times.

 

[Johnny-Mike]

Re: High speed miss, Yahama pwc

Thanks Jeff, I'll give this a try.... By the way this is a 2000 boat and motor. I am having a problem with water getting into the hull when launched. it appears to be coming thru the 2 thru-hull fittings. I'm stating this only because I did not use a water-proof sealant on the new flywheel housing gasket. maybe moisture is entering the flywheel housing and causing a problem with the iginition.
Thanks for your input....Jon

 

[Jeff Walkowiak]

Re: High speed miss, Yahama pwc

well obviously you will need to look at that and seal the fittings, I nearly lost a ski over a lousy screw for a rear step that was leaking , . water in the hull can get slung in to the air and ingested in to the air box then pulled in to the engine and can eat a piston,, I had a sea doo blow a piston from just that problem when a flush fitting leaked.
once water gets in to the combustion chamber it removes aluminum from the piston and deposits it on the cylinder walls,it also washes the oil off the cylinder walls. so eliminate the water in the hull