yamaha 3.5 air cooled OB

[santelmo]

I recently came into possesion of an old yamaha 3.5 air cooled OB that I was hoping to use to tide me over till I can get something better. There have been a few issues to sort out including rust in the tank. The main problem now is that it will not run without the start/ choke out and only then for about 3 or so seconds then dies. It wont start at all without choke out. I have striped the carb 3 times the last time I soaked the jets overnight in carb cleaner. Its got fresh fuel.a new fuel filter. a new spark plug and I have checked that there is a spark there and the filler cap vent is clear. This fault came on suddenly. any help appreciated.

 

[NickRobinson]

Resurrected 2S outboards can get some of those symptoms if the crank seals have gone too-

 

[VicS]

I recently came into possesion of an old yamaha 3.5 air cooled OB that I was hoping to use to tide me over till I can get something better. There have been a few issues to sort out including rust in the tank. The main problem now is that it will not run without the start/ choke out and only then for about 3 or so seconds then dies. It wont start at all without choke out. I have striped the carb 3 times the last time I soaked the jets overnight in carb cleaner. Its got fresh fuel.a new fuel filter. a new spark plug and I have checked that there is a spark there and the filler cap vent is clear. This fault came on suddenly. any help appreciated.

Have another look at the carb.. If its the same as this Mariner one http://www.boats.net/parts/search/Merc2/Mariner/3.5/642-23740 AND BELOW/CARBURETOR/parts.html pay particular attenetion to the idle jet #25 and the jet pipe #26. Poke a soft copper wire through them .

 

[RIBW]

Have another look at the carb.

+1 with Vic.
I've resurrected 5 of these engines (the Mariner variant was made by Yamaha - so some googling based on Mariner is valid) and it took a while to learn the carb has three paths:-
Starter, slow and main. (somewhere in the depths of my archive I have coloured drawings of these but they would require time to find).

Also, the points can be troublesome.

When I was having similar difficulty on one of the engines someone suggested it might be the reeds but eventually the carb was the problem.

Good luck
Bob

 

[santelmo]

Yes I think that I have seen the drawing that you refer to here its post #8 on this thread in a different form
http://www.yamahaoutboardparts.com/forum2/3-5-hp-coil-pt-no-f6t-405-a-th16541.html
Thanks for the ideas I will look at them all