Bogging down under load

[Banjo]

I have a 50 yamaha with 150 hrs on it. When I put it I the water, and put it in gear, I can't get over 1400 rpms. Now if I just use the cold start lever it revs right up. There is a little red lever under air silencer. If I move that lever to open/ emergency position it idles rough, but will roughly eventually get up on a plain. So far I have rebuilt all carbs, changed the diaphragms in the case with that little red lever, and the solenoid on top of that case. Replaced hose and tank. The fuel filter has been removed and inspected. Timing has been checked. The last time ( yesterday ) I put her in the water, the first time I tried it seemed like nothing was wrong. It got right up to 4700 5000 and ran good until I throttled down to idle and problem persisted. After that run is when I changed hose and tank. Then took the boat out today and it was doin the same thing. Every time I put it in gear it wouldn't get past 1000 to 1400 rpm before it bog down and kill.

- banjo

[99yam40]

I would have to say it definitely sounds fuel related if switching to open helped.
Did you check the fuel pump and does it help to pump the primer bulb while problem is happening?
Did you check the timing while the problem was happening to be sure it was not retarded like in safe/alarm condition?

I believe you need to pull and clean the carbs again, would not be the first time trash from the lines or pump plugged up some newly cleaned carbs

[Banjo]

Pumped ball

Yes the fuel pump should be fine because the ball gets hard as a rock. and I did try pumping ball while accelerating. The timing adjustment bumpers however is not maxed out or bottomed out when the problem happens. It happens right around 1400 rpms. As far as the carbs go: What gets me though is that the problem exsited before I took the carbs down. When I did inspect the carbs and rebuilt them they were crystal clean before I touched them, and were def clean when I put the back on with new jets and rings, and the problem did not change. When I changed the diaphragms in that fuel switch( the red switch) ,she seemed to idle a lil better, but the Main Overall prob is still definatley there. I will pull fuel pump and dissect it, because until now I relied on hard ball to tell me fuel pump is fine. I guess I can't be too sure.

-banjo

[99yam40]

Testing with a fuel pressure/vacuum gauge is always a good idea to make sure it will pump properly and there are no restrictions in the supply system.

Have you checked the compression on all cylinders and tested spark with a spark tester?

Does your alarms system function properly, can you hear the horn when you test it?

Over temp or low oil level if it is self oiling motor will sound the horn and change the timing electronically to limit the RPMs.
So checking timing with a timing light is a must as you will not see the linkage move.

[Banjo]

Not temp or oil switch

Remember that when I flip switch to open... It goes so it's not an oil lvl or temp prob right? I have to test fuel pump out. I will post as soon as I put her back in water. By the way I have a question ... What is that red switch exactly ? Is it a manual choke? Fuel line on off switch ?

[99yam40]

From what I under stand It is a bypass around the prime start system to add more fuel when the pilot/idle passages go bad you can get it cranked and limp back to port .
You know I just talked myself into thinking you need to pull and clean the carbs

[Banjo]

Okie dokie

I will pull fuel pump and carbs and cross my fingers
I will post with results

Thanks for the input!

-banjo

[Banjo]

Fuel pump

Ok so I pulled the fuel pump and one of the metal diaphragm / valves is not seating correctly. I will getthe fuel pump replaced and test her out. I'm almost positive that will solve the prob. I will post if it does.

- banjo

[rodbolt17]

when you flip that lever to open you manually force the fuel mixture rich, bypassing the carbs and adding fuel directly to the intake manifold.
if its an oil injected model this can cause piston or rod bearing failure.
would be better to actually fix your fuel system issue .

[Banjo]

I changed the fuel pump with no luck, but I then changed the tank full of pre mixed fuel with the oil tank on engine still connected also full of oil, but to my surprise there was not an excess of smoke... AT ALL. This leads me to believe the oil Injection system is malfunctioning. Now to add to the confusion after I put the tank on I am able to gun it and with a very slight hesitation she gets up and goes everytime. Once I'm on a plain I can throttle down slowly all the way to an idle with no problems, however I cannot come from an idle at a slow pace without it killing at around 12 to 1300 rpms. She runs like a clock otherwise. I am goig to go get a gallon of carb cleaner and soak carbs for 24 hrs a piece, and clean them with the spray and q-tips and air compressor afterwards. Now these carbs were rebuild as soon as problem started and they were clean as a whistle to begin with, but all the guts were replaced anyway. The problem persisted. So hopefully by some kind o crazy luck a piece of trash managed to get in there because if I take them down clean again and the prob is still there...... I'm all out of answers. I took video of me testing engine today if someone has an email they would like me to send it to. Btw thanks again for reading

- banjo

[99yam40]

remember you need to do the sync and link like the Yamaha service manual states, every time you pull and reinstall carbs

[Banjo]

Hmm gave up on me

My grandpaw gave the motor to a mechanic. Mechanic says the timing was way off and the linkage had to be set. We supposed to take it on the water tomorrow. He did not want me to do anything tothe carbs. I am going to be surprised if the prob was fixed because I check timing. And before I touched timing the prob existed. All it did was run better since I have been working on it. Guess we will see. If the motor does happen to run without a problem I will call the mechanic myself to see exactly what he did because I'm sure the main problem was not the timing.

-banjo

[99yam40]

What was the timing when you checked it and what did you change it to?

Did you follow the service manuals procedures and specs?

[Banjo]

Service Manual / Service Ticket

Yes I followed service manual to the T when adjusting the timing. FYI it was not that off when I checked it the first time, but it was off none the less. Well it gets into focus now. My grandpa seems like he wanted to justify his 480 dollars, because I looked at the service ticket and did not see anything about timing or linkage, but I did see carb rebuild and new fuel line....go figure. I was on the right track. I will call the Mechanice personally, but Im willing to bet one of the low speed jets was clogged. I know for sure his hose was bad because when i used my hose and my tank, the boat was able to get up out the water only if i gunned it to 'bypass' low speed jet. So I would chalk this up for anyone troubleshooting this problem as the fuel hose and tank needed changing and the carbs cleaned out. The carbs must have gotten some trash even after a total carb rebuild, so you were right there yam.....thanks for all the help/input.....like I said I will call mechanic too and see what I can get out of him.

-banjo

[Boggeddown]

Bogs down under load

I am having the exact same problem with my Father-in-law's Yamaha 50. What was the final decision on the problems Banjo had in 2011? Blocked jets? Sync and Link? Air leak? Bad fuel? Thanks.