Yamaha 150 CDI & Control Unit

[yuddenise]

Symptoms: 1985 Yamaha 150 HP starts fine, idles fine, revs out of gear fine and runs underway under 2000 rpm fine. Underway, won't go over 2000 rpm. Note - no alarms. Green light only on my dash.<br /><br />Tests:<br />*Compression on all cylinders: OK<br />*Ignition coils: OK<br />*Fuel pumps - suspect might have problem (I installed a suction pressure gauge while idling at 2000 rpm - got no suction pressure (0 in Hg) Diaphrams have no holes, but I can blow air past the check valves in the wrong direction.<br />*Pulsar coil, charge/lighting coils OK.<br />*Resistance tests per manual on rectifier - NOT to spec.<br />*Resistance test per manual on CDI - NOT to spec.<br />*Resistance test per manual on Control Unit - NOT to spec. <br /><br />Any Help Greatly Appreciated:<br />I plan to replace fuel pumps but am leary of my resistance test (done w/ digital meter). If these units all bad, would engine still run OK in neutral as described? Engine is old, so I'm scared to spend money for new CDI assembly.<br /><br />Thanks.

 

[Ray Neudecker]

Re: Yamaha 150 CDI & Control Unit

Very unlikely to be electrics. Very likely to be fuel restriction. Replace thse pumps as a starting place.

 

[ianyoung77]

Re: Yamaha 150 CDI & Control Unit

Yud,<br /><br />I had some similar problems and it turned out to be the primer bulb! For twenty bucks it was the cheapest fix ever but for some reason I found it difficult to diagnose.<br /><br />I also changed my loose tank connector at the same time and the system is now sweet.<br /><br />Good luck, Ian

 

[yuddenise]

Re: Yamaha 150 CDI & Control Unit

Problem was fuel related. Thanks for the advice. I did replace the fuel pumps. Waited a week for parts, then got it to the water to test again - no joy. Same problem. I disassembled each of the carburetors and did find some gunk in the bottom where high speed fuel jets sit. Cleaned them well, installed new gaskets - and worked well. <br /><br />I do still have a problem with my fuel bulb. After running at high speed for some time, I again lost fuel - but problem was obvious. The fuel bulb was caved in from suction. I assume I have a defective bulb, or a bulb that is not meant to let as much fuel as I need get past. I'm looking into that now.

 

[easygo0]

Re: Yamaha 150 CDI & Control Unit

ck tank vent also

 

[MSST8DOG]

Re: Yamaha 150 CDI & Control Unit

Problem was fuel related. Thanks for the advice. I did replace the fuel pumps. Waited a week for parts, then got it to the water to test again - no joy. Same problem. I disassembled each of the carburetors and did find some gunk in the bottom where high speed fuel jets sit. Cleaned them well, installed new gaskets - and worked well. <br /><br />I do still have a problem with my fuel bulb. After running at high speed for some time, I again lost fuel - but problem was obvious. The fuel bulb was caved in from suction. I assume I have a defective bulb, or a bulb that is not meant to let as much fuel as I need get past. I'm looking into that now.

I had a bulb collapse and the problem was two-fold. 1, the bulb was breaking down and was too flimsy. 2, the tank cap vent didn't work and I unscrewed the cap a bit and it worked fine from then on. I have since replaced the bulb and all lines and installed a new vented cap.