yamaha 50TLR can't get past 4200RPM

[srantheman]

Just to give everybody an update on what I found out.

Took the boat back out two weekends ago. Boat run better but still not great. Took it home and talked to the mechanic about the history of the boat. He pulled the carbs off it to make sure they were set correctly (since previous owner said he did them). We found out that the previous owner used the old gasket instead of new ones and a diaphragm was also damaged. We have ordered an entire gasket set and are going do the proper yamaha carb sync when he installs them again. I'm hoping this will solve all of it's issues and we can get back to boating at full speed again. We are hoping to do another water test at the lake either this week or weekend. I'll post back the final results once that is complete.

 

[srantheman]

So here is where we are now. New gasket set was ordered and installed. We put it all back together it didn't run any better. Talked to the mechanic, and he is saying it's not getting enough fuel. It doesn't change if I squeeze the bulb so we are now thinking it might be the fuel pump. The bulbs in the carbs are filling up but it's struggling to rev up. Below is everything that we have done in a list. My thought is it only cost ~5K for me to purchase a refurbished motor so I don't want to spend a fortune trying to fix this when I can just purchase a newer one. At this point, I honestly don't know what else it could be. We will finally figure it but right now i'm scratching my head on this one.

Compression test - All cylinders are 110 (little lower than I like but all three are the same)
New Carb gasket set and carb sync run on all 3 carbs.
New Fuel Tank
New Primer Bulb
New fittings on tank and motor
New Spark Plugs
New Fuel Filter

 

[JimS123]

Your "mechanic's" diagnosis of stuck choke still bothers me. If it were me I'd search the internet for a certified master mechanic and have him look at it. I realize it might be a wait longer than you want, but a new(er) motor might not be a better approach.

 

[mphelle8vld]

Reading through your thread it might just be a failed diaphragm in the fuel pump which would allow extra fuel to be drawn into the bottom cylinder. Easy to check, loosen the 2 mounting bolts and pull the pump away from the crankcase. Pump the primer bulb, if fuel dribbles out the back of the fuel pump it needs to be rebuilt or replaced.

 

[rejesterd]

So those spark plugs in the pictures were brand new at the beginning of this season? I'm talking about the first set of pics you posted, not the second set. I would say those definitely needed to be replaced, and the fouling is certainly consistent with your observation that it seems to be running rich. I know it's a 2-stroke, but the plugs shouldn't foul that quickly on a 2010 imo.

Also, if your mechanic mentioned anything about a choke, stop going to him. You don't have a choke, you have Prime Start only. And if you flipped the switch to OFF and there was no change, then it's probably not related to the enrichment system (unless that switch itself is broken, which is highly unlikely).

"It doesn't change if I squeeze the bulb so we are now thinking it might be the fuel pump."

I would think it's the opposite.. if pumping the bulb helped, then that would indicate your fuel pump is bad. No change, to me, means that the pump is doing the same thing your hand is doing with the bulb.

I would get a clear piece of plastic tubing (3/8 and 5/16), and see if there are any air bubbles in the fuel being drawn up from the tank. Then do the same test for each component from the tank all the way to the on-engine fuel filter. Bubbles means you have a leak around that area.

Given what your plugs look like though, it really seems more related to the carbs or the linkage being incorrect.

 

[srantheman]

Good afternoon,
I paid to have all carbs rebuilt and the boat is now running somewhat better but not totally correct. I was doing some testing at my house and noticed that the motor was backfiring at idle. I grabbed a can of starting fluid and starting looking for a vacuum leak around the carbs. I found the vacuum leak at the intake gasket. By the Yamaha manual it has a gasket on each side of the manifold plate. They will be here first half of this week from my Yamaha dealer. My question for you guys, since I’m doing this myself and the carbs have to be taken off, can anybody tell me where I can purchase a repair manual for torque settings and also the sync procedure for the carbs. I have all of the other information off the Yamaha schematic for the intake off the Yamaha site.
After all of this I’m hoping to be back on the water and running smooth.

 

[rejesterd]

Edited: didn't see OP's latest update.

 

[Sea Rider]

Sync-up multi carbs it's a nightmare procedure, doesn't matter if having an oustending high quality musician ear to sync a multi carbed motor. If with no previous experience bad music, it's something that can't be learned reading a service manual for first time as proven experience is what really counts..

If at idle all carbs are not well synched doesn't mean that the motor will work lousy at higher rpm past idle setting, the carbs will work on their fixed jets which are non adjustable.

Happy Boating

 

[srantheman]

Sea Rider I don't totally understand what you are saying. I'm by no means an expert on anything. Are you saying that you can't sync them without proper tools or are you saying if you get it close at idle it will be okay at WOT?

I'm not saying that was my oringinal issue. I have only had this boat since the spring and have already fixed several issues that the previous owner "fixed" This intake gasket I'm hoping is my last problem before I'm able to get back on the water. I won't have to adjust the carbs but they do have to be removed to install the gasket. That is why I asked about the sync procedure. I'll do my best and if I run into other problems, I'll have to find a new mechanic to work on them. We only have one dealer within 100 miles of me and told me it would be winter before they are able to look at it. It's a crazy time now with all the new COVID boat owners.

 

[rejesterd]

yamahapubs.com is where I got my service manual. Not cheap, but has definitely paid for itself by now. It will have the basic link/sync procedure and all the torque settings. I think Dangar Marine channel on YouTube also has an advanced syncing video.

 

[Sea Rider]

If you remove the carbs to change carb gaskets won't need to synch them again provided that are put back in same position and motor was previously running at idle as a swiss clock, take pics while removing what needs to be removed. If the idle setting from each carb is not well snych between the number of carbs the motor works with will idle uneven and limp, but at higher throttle setting past idle won't be an issue.

Happy Boating

 

[Faztbullet]

That motor should have the fixed armature plate ..Make sure the sync and link to CDI is correct as that controls the timing.

 

[srantheman]

Good morning,
So I got the boat put back together. It now runs a lot smoother now on the idle. TBH better than it ever has. I now have a new problem. It will idle at 1400RPM in neutral and around 1100 RPM in gear. If I try to accelerate in gear the motor will die. It will rev up if I leave it in neutral. I have checked to make sure that the timing advance does move when you hit the throttle but I don't know what else to check. Is there anything simple I should check before I try and take it to a shop? Thanks to all of the help from you guys I'm slowing getting this thing to run like it should.

 

[tblshur]

i would get some pre mixed fuel in a spray bottle get it to 4200 rpms then spray a little fuel in each carb see if it changes

 

[tblshur]

sorry i posted before i saw 3 pages of post hope you get it fixed soon and thanks for updating your post