my yam 200 pro v

[jagmanpete]

Hi everyone,took my Phantom 20 out yesterday to try and nail down why it broke down in october.I thought it was electrical but yesterday I discovered that the problem disappears once the motor is running quite hard,if I can get the boat up on the plane over 2500rpm approx it goes great.idling is very erratic and keeps stalling when you put it in gear.I have checked the carbs(clean as the day they were made),fuel pumps,tank,filter is new,fuel is fresh,primer bulb pumps up hard.
Could this possibly be a reed valve problem?
Also when idling in gear if you flick the choke switch before it stalls the motor
instantly clears for a few seconds then starts to fail again.
Looking forward to some good ideas.

[rodbolt17]

you still have a carb issue.
by tagging the choke you force the carbs rich bypassing all normal circuits.
if it was a mechanical issue,reeds,crank seal rings or piston issue tagging the choke would have no effect.

[jagmanpete]

thanks rodbolt17,
As the carbs seem in such good condition inside and out i was thinking that if the reeds were not closing properly their would be insufficient vacuum to draw the fuel through the carbs,closing the choke flaps would then increase the vacuum momentarily even if the reeds were a problem,hence the sudden improvement,what do you think?

[rodbolt17]

nope
think very very hard on what that reed does.
if it doesnt seal when the piston is coming down,pressurizing the crankcase, it blows the A/F mixture back out of the carb under crankcase pressure.
its easy to check, with the engine running and the airbox off.
hook up a timing light and use the light to look at each cylinders carb throat.
if you dont see fuel being ejected from the carb throat that reed is sealing.
a small amount of spit back is normal,its why the airbox drain goes to the intake manifold/crankcase.

[jagmanpete]

hi rodbolt,
yes i agree with that,think i'm going to have remove and strip the carbs.
thanks for your help.

[jb123]

also with a reed issue you should see and hear blowback fron crankcase