Prime Start / Cold Start Question/Issue

[233mako]

I have a 2007 Yamaha F20 with remote controls (not a tiller model). I do have the Service manual and I'm pretty good at spinning wrenches. When the motor is dead cold and I crank it .. it starts but then sputters and dies. If I push in on the rubber button on the throttle and advance the RPM's it will stay running. I have to let it warm up sometimes for 20 min plus to allow the throttle to be moved back to neutral/idle. I have removed and checked the OHM value of the prime start assembly and measured the length of the needle/piston valve with a micrometer at both cold and hot (12V applied) and it is working/moving. My question is : should there be voltage on the 2 blue wires on the prime start assembly with the key on? I measured it with key on but saw no voltage when connected or disconnected to the harness. When I connected the prime start by itself to an external 12v battery i of course had voltage and the primestart got slightly warm too. I am assuming I should see 12volts on the leads when it is connected to the wiring harness at "key on" position. If I don't have voltage where can i check for the source of the 12v and then move forward through the harness?

 

[99yam40]

voltage should come from the motor running not just key on

 

[233mako]

Just came in from checking voltage with motor running. I pushed the leads from my multimeter into the rubber boots and cranked it up. No voltage. The motor will run for 6 to 10 seconds at high idle and then slowly sputter out. If i put the gearshift/remote into neutral and give it more gas it will keep running indefinitely at the higher rpm. Once this motor warms up it runs ok. It seems to idle up for 10 sec .. then down .. then up again. The way I understand it is the prime start plunger is retracted (pulled back) to let more fuel in during warm up and then slowly closes off the orifice tube with its needle. Logic would indicate that it should start and warm up just fine but stay on high idle if the prime start wasn't working at all (no voltage) and not the opposite of having trouble while cold.

I will hard wire the prime start assembly to the battery and see if that smooths things out. Then diagnose why I'm not getting 12 volts at the prime start leads while running.

 

[99yam40]

I know nothing about your F20 motor or its prime start system.
but my 1999 C40 has one that when cold opens the needle to let more fuel in and as it warms up it closes off.
A wax pellet inside the unit is heated up from the electrical flow thru the heater unit and the wax expands and pushes the needle down
if it is not getting any voltage then it will never close off and run too rich when motor has warmed up

does your motor have a red lever to turn the enrichment to auto, off and closed manually?
If so make sure it is in the normal(auto) position

 

[233mako]

I talked to a buddy who is a professional outboard mechanic and he told me the voltage from the stator/lightning coil is A/C not DC. That might be why i didnt see 12 V DC from the wiring harness at the prime start leads. I have pulled the carb and and doing the right thing .. cleaning all jets, using Merc Powertune carb cleaner. Will re-assemble tomorrow with fresh gaskets and provide an update.