1988 yammaha150 kicks back or backfires at idle

[nelson]

i have a 1988 yam 150 with ab

i have a 1988 yam 150 with about 325 hrs. i got boat this year at idle it seams to kick or backfire out the exust about once or twice 5-15 sec. then it stall's but i can start right up i removed the carb's cleaned them out and changed the fuel pump put it back it seemed to work ok for a little wile (an hour) but it's back the engine works fine above 12-1300 rpm's i just cant get it to idle i don? think its the timing? But i can use some help on this

Thanks
Nelson

 

[bubba]

" Could have a reed stuck open

" Could have a reed stuck open or even damaged. First I would link/sync and set idle ignition timing. This is important as Yamahas idle with the throttle plates open. If your igintion timing is too retarded, you would make up for the loss of idle speed by twisting on the idle adj. screw on the middle carburetor, thereby opening the throttle plates even more, making the motor idle lean - causing a "sneeze". Timing can be set staticly on most Japanese outboards. Look up the timing specs on your outboard, set everything where it belongs, and if the problem persists, remove the carbs and peek at the reed assemblies with a flashlight. If the motor makes full power smoothly, your fuel pumps and fuel supply system are probably OK. If you need specs or more datailed instructions on set-up procedure, leave a posting. "

 

[nelson]

" thanks for the quick reply,

" thanks for the quick reply,
yes, it's like sneeze's but not from the carburetors it' from the exhaust side
i moved the magneto control lever to see it would afect it but it was the same
i i did have to advance the idel rpm to 950 so i can use the boat
i will try to staticly time the motor i have the seloc book for the spec's unless you have a better way. if this does not work should i change the reed'S
thanks "

 

[sparky]

First and foremost do a compr

First and foremost do a compression test. It is the only way to quickly determine the condition of pistons and rings.Check to see that each cylinder is getting a strong spark ( better than 3/8" ") . Crankcase compression is a little more involved and some yamahas have reed blocks with a rubber coating that cracks with time and exposure to fuel and alcohol.Remove the reed blocks and replace them if faulty (they are not cheap). Shining a flashlight into the carburetors while the engine is running can also give you valuable clues as to the operation of the carburetors. If the engine is not pulling the correct amount of air thru one of the carburetor throats then that carburetor can not do its job.Is the flywheel nut tight and the key in good shape? this affects ignition timing.

 

[tonyob]

" Nelson,

I think Sparky is

" Nelson,

I think Sparky is on the right track here.

Backfiring out the exhaust is generally either worn rings or a timing problem.

Tony "