Yamaha 50tlr 2 stroke fouling plugs immediately

[Sourdsul]

Hello, I have a Yamaha 50tlr 2006. 3 carb 3 cyl engine. Motor sat for 4 years, first thing I did was pull the carbs and full carb clean with new gaskets/floats/needles.
New pump bulb.
New fuel pump.
Engine seemingly runs good for all of 15-30 seconds, before fouling cylinder 2 spark plug and starting to run noticeably crappier (misfiring) and eventually dying out. Assuming there is a still a fuel flow issue somewhere, maybe causing that cylinder to lean out? I've been through 3 plugs experimenting. Cylinder 1 and 3 are running fine, plugs stay looking clean. Cylinder 2 plug turns black very quick. I should mention I am just running a scepter portable vented gas tank.
Tried tightening air fuel mixture screws all the way in and than back out 1.5 turns like recommended. Any ideas?

[robert graham]

Sounds like a bad fuel pump diaphragm, but you mentioned a new pump.... How old is your gas?....old/contaminated fuel can cause fouling.....

[Sourdsul]

New gas no ethanol. New pump

[99yam40]

did you check the prime start system to make sure the system is functioning properly and that diaphragm is also good?

regular fuel pump runs off of the pulses from #3 crankcase, so that should not affect #2 plug,
but the prime start diaphragm may run off of #2 crankcase.

also are you sure the PS system switch is set to the automatic position?

if everything else is in spec, check timing to make sure it is doing what it should and in spec

[ausnoelm]

Check spark on that cylinder.

[Sourdsul]

did you check the prime start system to make sure the system is functioning properly and that diaphragm is also good?

regular fuel pump runs off of the pulses from #3 crankcase, so that should not affect #2 plug,
but the prime start diaphragm may run off of #2 crankcase.

also are you sure the PS system switch is set to the automatic position?

if everything else is in spec, check timing to make sure it is doing what it should and in spec

Haven't messed with the prime start, it is set to auto. Don't know much about it, didn't think it would effect much other than startup. Engine starts right up, just continues to foul plug #2 very quickly. Thought it was fuel pump,replaced that still same issue. Even pulled the carbs again checked the floats.. Everything looked good. I should add that I didn't replace the mixture screws.. Although they looked fine.

[Sourdsul]

Check spark on that cylinder.

All plugs have spark

[brian3006]

Haven't messed with the prime start, it is set to auto. Don't know much about it, didn't think it would effect much other than startup. Engine starts right up, just continues to foul plug #2 very quickly. Thought it was fuel pump,replaced that still same issue. Even pulled the carbs again checked the floats.. Everything looked good. I should add that I didn't replace the mixture screws.. Although they looked fine.

I believe what he is referring to is that the primestart is located on the #2 carb. if the diaphragm on it is torn, it could be dumping fuel into the #2 cylinder much like a bad fuel pump diaphragm would do to the #3 cylinder. If you turn the prime start to the off position, I believe this will close the fuel path from the diaphram to the carb... I would try that and see if there is a difference.

[Sourdsul]

I believe what he is referring to is that the primestart is located on the #2 carb. if the diaphragm on it is torn, it could be dumping fuel into the #2 cylinder much like a bad fuel pump diaphragm would do to the #3 cylinder. If you turn the prime start to the off position, I believe this will close the fuel path from the diaphram to the carb... I would try that and see if there is a difference.

Yeah the prime start is off the middle carb I'll give it a try

[99yam40]

actually , Looking at a diagram I drew years ago on my C40,
it looks like if the prime start system diaphragm gets a hole in it,
turning off the red lever will not stop fuel from being sucked into the crankcase thru the pulse port.
and I think that port is on #2 crankcase.

I would take apart the system and inspect the diaphragm

[brian3006]

actually , Looking at a diagram I drew years ago on my C40,
it looks like if the prime start system diaphragm gets a hole in it,
turning off the red lever will not stop fuel from being sucked into the crankcase thru the pulse port.
and I think that port is on #2 crankcase.

I would take apart the system and inspect the diaphragm

Hmm. good to know... I thought the red lever would cut the flow off all together..

[99yam40]

Hmm. good to know... I thought the red lever would cut the flow off all together..

it will thru the PS, but not the pump on it.
just like the main fuel pump and the carbs it feeds, the extra fuel before it gets to the carbs is still dumped into the crankcase without the help of the carbs con*****ing it

[ausnoelm]

It will take a few minutes to check the spark on that cylinder, you just don't know.

[Sourdsul]

actually , Looking at a diagram I drew years ago on my C40,
it looks like if the prime start system diaphragm gets a hole in it,
turning off the red lever will not stop fuel from being sucked into the crankcase thru the pulse port.
and I think that port is on #2 crankcase.

I would take apart the system and inspect the diaphragm

Switched to lever to closed and the motor seemed to run beautifully. Only got to run it for about a minute or two, all of a sudden it didn't want to pee. The muffs I have are kinda shitty and spraying water out the sides going to order a new pair and see if it starts pulling water... I replaced the impeller a week ago. Thanks to you and the other guy who suggested prime start. Problem solved

[brian3006]

Glad you found a temp fix, you should still look into the primestart unit though. sounds like something might be in need of repair. If you go to start your boat on a cold day, you might very well wish you had it working.
I had some issues with mine this winter, but it was the opposite of yours, mine wasn't supplying enough fuel when cold. I took the solenoid off and adjusted the plunger a little and it works much better now. I use this motor to duck hunt with, so I need it to start up on 20-degree mornings.

Check out youtube. several good videos on there explaining the whole primestart system as well as how to bench test and adjust the solenoid/plunger if needed. Dangar marine is one that comes to mind.