Home › Forum › Ask A Member › 1970-ish Yamaha Mariner 8 runs erratic. Can you tell me why?
- This topic has 10 replies, 7 voices, and was last updated 7 years, 7 months ago by
billw.
-
AuthorPosts
-
September 22, 2016 at 10:13 pm #5336
I am trying to repair this motor as it runs at high speed for a short period of time, then just dies out (unless you pull the choke). I have cleaned the carb and filters. I find no leaks in the fuel lines. I thought it might be the fuel tank or the fuel line so I took my OMC tank and put the connector for the Yamaha on the OMC tank but got the same issue.
The video below shows what I mean. It starts right up with no problems. I can idle this motor all day long. At higher RPMs, after a short while the motor will start to die out. If I briefly add choke to it, it will stay running. If I put the choke on you can see that it will stay running (not very well, but it will stay running).
I am stumped here and was hoping for your help with this one.
Thank you
BillSeptember 22, 2016 at 10:39 pm #44553Running on one cylinder ?
September 22, 2016 at 11:11 pm #44557fuel pump diaphram, still OK at low speed but can’t handle the increased volume of high speed. Years ago I had a friends similar motor the same way, after I did the fuel pump it ran like a raped ape.
September 23, 2016 at 1:35 am #44569The owner said he replaced the fuel pump diaphragm. Wonder if I should replace it again?
September 23, 2016 at 9:43 am #44581If it is the fuel pump or something like that, you should be able to pump the primer bulb and have it run well again. Usually when Yamaha pumps go bad, they idle poorly because gas goes into the crankcase. If you pump the bulb and it doesn’t help, I would revisit the carb, particularly the area between the fuel inlet nipple and the float valve.
If THE OWNER HIMSELF replaced the diaphragm, then, yeah, I would suspect he messed something up….
(You’re sure it’s not overheating, right?)
Long live American manufacturing!
September 23, 2016 at 12:25 pm #44590This certainly seems like a fuel delivery problem of some sort. I’d try pumping the bulb when it starts to stall out first, as was mentioned before. If that makes it take off again the fuel pump is suspect.
If it ends up not being the fuel pump, I’d check out the carburetor. Maybe the high speed circuit is partially blocked, maybe the float leve.is set too low, maybe both, maybe there is a partial blockage in the path between the output of the pump and the float valve in the carb.
Question: is it my imagination or does the tiller grip twist clockwise on this motor to throttle up? I’d have a rough time getting used to that.
-Ben
OldJohnnyRude on YouTube
September 23, 2016 at 3:24 pm #44599I had that unexplainable dying problem with a friend’s 8 Mariner. On that one it was the connector on the motor-end of the gasline. The small metal part that clicks into the groove on the pointed anchor pin on the motor needed bending inward slightly so the fuel line connector was anchored slightly farther onto the motor. Sounds too simple but it worked! Of course, you can try just replacing the whole connector instead. This may not be your problem, but it’s an easy fix to try.
DaveSeptember 23, 2016 at 4:18 pm #44601I recently used a fuel pressure gauge placed in between the fuel pump and carb. I had the factory info on what PSI at what rpm the pump should put out, it removed any doubt as to the pump output.
"Some people want to know how a watch works, others just want to know what time it is"
Robbie RobertsonSeptember 23, 2016 at 11:19 pm #44622A while back someone I know had a dying out problem, after checking about everything we could think of, it turned out to be nothing more than the Oring in the fuel connector to the motor!!
September 25, 2016 at 10:42 pm #44710I tried putting the motor in the test tank and when it started to bog down and quit, I would squeeze the bulb in an effort to force fuel in. It made no difference and the motor would die out. The only way to keep it running is to briefly pull the choke.
Any other suggestions?
-
AuthorPosts
- You must be logged in to reply to this topic.
