Mister ED
05-29-2006, 11:52 PM
Having issues with my 70 hp Yamaha. I've done a bunch of trouble shooting ... but I'm running out of options. It will start fine and idle all day long (in or out of gear). However, when I give it some throttle it will bog right down and eventually stall (warm or cold does not make a diff). When this happens there is no roughness ... as in one cylinder missing etc, it just looses RPM until it dies or the throttle is backed off. Hit the key and it will fire right back up. Here is a run down on what I have checked out so far:
Rebuilt the carbs over the winter (before the issue arrose) and it was running very well afterwards.
Tried aux tank, hose & primer bulb ... same issue.
Replaced fuel pump and all hoses from fuel connector to carbs, was going to do this anyway, and still have issue.
By-passed fuel filter ... thought maybe plastic housing could be leaking and allowing air into system.
Pulled all 3 carbs back down and checked mains and float height ... all look good.
Warm comperssion is 118, 121, & 118
Checked Ohms on Crank sensor and Pulasar coil ... both were within the range in the Yamaha shop manual.
Idle mixture screws are set right on factory specs.
Bolts on coils are tight, had one loosen once which created a miss and rough running ... completely diff symptoms now.I probably looked at more that I can't think of right now. At this point I'm thinking spark advance & CDI box (the advance is controled by the CDI on this motor). Unless anyone has any other thoughts, I'll probably be hauling it into the Yamaha service dept as they should be able to check the CDI.
Thanks
Rebuilt the carbs over the winter (before the issue arrose) and it was running very well afterwards.
Tried aux tank, hose & primer bulb ... same issue.
Replaced fuel pump and all hoses from fuel connector to carbs, was going to do this anyway, and still have issue.
By-passed fuel filter ... thought maybe plastic housing could be leaking and allowing air into system.
Pulled all 3 carbs back down and checked mains and float height ... all look good.
Warm comperssion is 118, 121, & 118
Checked Ohms on Crank sensor and Pulasar coil ... both were within the range in the Yamaha shop manual.
Idle mixture screws are set right on factory specs.
Bolts on coils are tight, had one loosen once which created a miss and rough running ... completely diff symptoms now.I probably looked at more that I can't think of right now. At this point I'm thinking spark advance & CDI box (the advance is controled by the CDI on this motor). Unless anyone has any other thoughts, I'll probably be hauling it into the Yamaha service dept as they should be able to check the CDI.
Thanks