See full version: Yamaha 50hp outboard only running on 2 cylinders
LIT-18616-01-79 Service Repair Manual Application: 1998-2005 Yamaha Marine Outboard 4HP (4-HP) 4-Stroke Engines F4X (F4-X, F-4X) 1999, 2000, 2001, 2002, 2003, 2004 & 2005. This manual covers all 4HP 4-Stroke models world wide including F4MSHX, F4MLHX, F4AMH, USA CANADA.
See Starting & Charging System Troubleshooting in Service Manual. [links]
LIT-18616-01-28 Service Repair Manual Application: 1995, 1996, 1997 (95, 96, 97) Yamaha Marine Outboard E48T (E48-T) C55T (C55-T) 48HP & 55HP 2-Stroke. Item Model Names: E48T, C55T, E48C, E48MH, E55C, 55BM, C55ER, 55BE, 55BEM, C55TR, 55BET.
LIT-18616-02-66 Service Repair Manual Application: 2004 2005 2006 Yamaha Marine Outboard 70HP (70-HP) 2-Stroke Engines. Model name 70BETO, USA and Canada name 70TR 70C (70-C).
Throttle is “rolled back” or closed, thereby actuating idle cable roll-off (disengage) switch.
FUEL SYSTEM TROUBLESHOOTING
I wouldn’t be surprised if it was the inner exhaust plate. Salt water motor? Not flushed after use?
Getting closer I will post pics 2 morrow once they go to the icloud. 2 screw heads were missing on the top cylinder reed valves closest to the rod the 3rd and only screw left was barely holding the reeds and back stop on the screw being bent kept it from unscrewing. My bet is the rod knocked the screw heads off. Here is an auction on ebay right now for a used reed valve assy for that motor notice how the middle screw has been getting hit by the rod. http://www.ebay.com/itm/381402128198?_t … EBIDX%3AIT leads me to think it is a problem with these motors especially when compression is over 170 on each cylinder. [links]
I put a used rod on the upper cylinder when I rebuilt it due to cost of new one which was in specs with a new big rod bearing assy. It is possible when it threw the rod it loosened those screws since the rod cap bolts had loosened causing the engine failure and they unscrewed and the rod hit them I didn’t notice that when I had it apart. I felt the rod with my finger where the two halves of rod come together it still feels tight. I decided to roll the dice and fixed the reed assy best I could and added new screws and lock washers re-installed it and the motor ran a lot better almost getting to WOT. I am going to pull them back out 2 morrow and see if the rod has pecked on the new screws if so the motor will have to come back apart and I haven’t wasted my new head gasket that is coming if not I will look for some good used reeds assy.
Post by nccatfisher » 04 Feb 2020, 16:40 here
Post by Riverdog » 04 Feb 2020, 20:00 here
I'm looking at a 98 Johnson 50 hp SPL 2 cylinder outboard motor ,my plan was to put a jet pump on it .
I have no experience with this motor so any info would be greatly appreciated .
I have a factory 40/30 yamaha jet on a 1448 MV Lowe currently am I better off with the Yamaha motor instead of the Johnson ?
thanks folks
Post by nccatfisher » 04 Feb 2020, 23:24 [links]
2013 1752 Blazer SS Mercury 60/40 here
Modern fuel systems on outboard engines are complex. In the old days, fuel was delivered to the engine in a gravity-feed system, but that is no longer the case. [links]
Yamaha outboards are also quieter than most other brands, again in particular comparison to Honda. Outboards are loud, period, but Yamaha’s 40 is will be easier to hold a conversation over. here
Several models of the 4-stroke 40 using carburetors from before 2010 had particular difficulty gumming up, and the design made it difficult to clean them. Replacing them was the only option, and the difficulty in this design-led to most of the 4-stroke 40s going to fuel injection. [links]
This makes it a little bit easier to deal with maintenance. more