Cuts off at idle (video of offending motor included)

Blue_Runner

Blue_Runner

Administrator
Staff member
Finally got off my @ss and cleaned/rebuilt the carbs on my 2 stroke yamaha 150. Did not replace floats. By cleaning, I mean carb cleaner and compressed air. Anyhow, she's still misbehaving. Before and after carb work the motor runs strong entire spectrum. Problem is it cuts off frequently at idle. Any help is appreciated on what to look for.

https://photos.google.com/share/AF1QipNj73X2nkBgKuBJcwsiHQ6ieaJHt1XVeqPAunaG5Kac1kOoqJ1Lqc7KiuKhcHuijw/photo/AF1QipOOCyp6seF2Cv68yJlu-1c_Brl8NkxFLuurJbmC?key=V0Q3b3VkN1RvN2hWNzV3X1RXLTRTTmMyanVWQmN3
 
Carb cleaner and compressed air isnt going to remove heavy varnish. You need something to soak them in that will completely clean them.
 
Thanks Ferm. Carbs didn't look very dirty to my untrained eye. Could fuel pump cause this symptom? I had a bad fuel pump when the motor was only a few years old, but that impacted my ability to get up to max rpm, not idle. I've seen at least one instance online (must be true!!) where a motor was doing similar to mine at idle and it was confirmed to be fuel pump(s)
 
Sometimes it will cough and manage to keep running. The particular time in the vid it had done it maybe 20 seconds earlier, then once I got it on video it was ready to quit.
 
on my carbed merc, when the fuek pump was getting weak, i would notice it when trolling. the motor would start dying. i could run back and pump the ball a few times and it would pick up and be ok for a while. next time it starts to stumble, try pumping ball.

like skunk said, video sounds like u cut the switch off
 
When the pump fails they normally stop pumping, leak fuel into the crankcase from a ruptured diaphram, or leak externally. If it was a weak pump, you'd have to go back and pump the primer bulb to restart it.
 
I agree, not the best video. Just before I started filming it really showed it's @ss. I do have to sometimes squeeze the ball to get it going again. I think I'm gonna replace the fuel pumps ($100) and see what happens. I've paid more than that for a diagnostic fee before :hi: Appreciate the replies, will keep you guys posted on the outcome.
 
Have you tried pumping the primer bulb while its running? This would basically be using you/the primer as the fuel pump. I just rewatched the video and it sure sounds like a lean sneeze to me that shuts it off.
 
Ferm, I have tried squeezing the bulb, but it has been a while and best I can remember I had mixed reviews about it helping to keep the motor running. Can try again and report back

Let's say I ruled out fuel pumps and suspect lean sneeze. What would the remediation steps for such symptoms?
 
Ok, good news and bad news. Good news first - I installed brand new fuel pumps! Bad news - No change in my issue. What do I soak the carbs in? Some KnockerLoose? :beer:

For those keeping score:
Motor - 2
BlueRunner - 0
 
Not sure what is up with the vid. Step imagine the motor purring at idle, then suddenly a sneeze and poof she cuts off. I'm going to take the carbs off and get them apart and follow Ferm's advice then go from there. :beer:
 
I used to use evinrude engine tuner in my ultra sonic cleaner for cleaning up carb parts. We can't get good cleaners anymore, so you have to make due with what we can get anymore.
 
Well, finally some good news to report! I took the carbs (80's technology lol) off again. Did the same routine as before with carb cleaner, compressed air and using a wire to make sure passages were not blocked. I did not completely soak the carbs, however I filled the holes where the needles seat and the holes on the other side with carb cleaner and tilted the carbs so that would soak in overnight. Before that, at one point I was poking my wire and felt some resistance, which cleared. So I don't know exactly what the smoking gun was. The bottom carb seemed to be the culprit as it did look dirtier than the other two - cleaned them all the same nonetheless. My guess is gravity and the fact that more gas sits in the bottom carb. I drained out the carb cleaner and blew out the rest with compressed air. Put em back together and fired it up on the hose. 1st I notice it is idling WAY too high. Like 1800 rpms or something like that. Hmmm. Adjusted the throttle arm and still 1200 rpm and running a bit rough similar to before. So I backed out the carb adjustment screw quarter turn - improvement. Another quarter turn and she's at 700 rpms, no coughing/sneezing, and no cutting off.

I think after the carbs were cleaned it was idling too high because when carbs were dirty I had increased idle because it was too low.

So next will be to drop it in the lake and put it through its paces. Thanks to Ferm for making me take it apart again! I am cautiously optimistic :sun:
 
Be prepared to redo all those adjustments once you put it in the water. High idle on the hose is normal and expected on a carbed 2 stroke. You never make adjustments unless it's in the water, or the foot is in a barrel of water submerging it to where it would be in the water.
 
You must log in or register to reply here.
Back
Top