99 C150 bogging issues at WOT

[ThanksandGigem]

I've been discussing this topic on another fishing forum hear Yamaha c150 bogging/surging - Page 3 - 2CoolFishing

I'm hoping to get some input regarding my issues. I understand how a 2 stroke motor works and am fairly mechanically included however my experience in diagnosing issues is limited in this area.

For the past few of times I've taken my boat out I have been getting a surging issue with the motor when I run above 4k. It started after I changed from pennzoil to supertech oil I also added a can of seafoam and filled the tank probably around 14 gallons of 93 with pennzoil and 20 gallons with supertech. The first day I ran the boat was only about an hour to test the new prop and trim tabs. Everything went great and didn't have any issues with the motor. Then I stored the boat after flushing it and didn't get a chance to get out for a few weeks. I ran out and had no problems until I burned about half a tank down so I figured it was probably just old gas and was finished for the day any way and topped off the tank before I went out last time. 3 weeks ago I took a buddy and his stepson out and same thing happened only this time at around 2/3 tank we were almost done for the day so we headed back. I got home and checked the fuel filter and pickup screen in the tank everything seemed more or less clean so I did the decarb with seafoam 80% filled in the filter blew out the fuel lines with air and ran the motor for about 20 minutes and it smoked like hell went from white to yellow to white and then pretty much gone. I did a compression test and everything was within spec for the maint manual. I changed the spark plugs. then topped off the tank and stored the boat. Today I finally had a chance to run out in east bay and it ran amazing until I got to half a tank and the surging started all over again.

What I mean by surging is that if I'm over 4k i can make it up to WOT for sometimes 5 min sometimes 15-20. Then the motor starts surging then bogs down and if I don't change the throttle to 2k or less the motor will die. i've tried pumping the primer bulb and if I squeeze it while the motor is over 2-3k it will stay relatively flat but below that it eventually pops up. staying at around 4k I have no issues.

Because the primer bulb stays flat I assume that means the fuel pump has enough suction. I have checked the vent and it seems to be venting even tried opening the tank and it made no difference. Originally I though it was **** in the fuel tank which I will check if need be but will have to empty the other half tank and get it out from under the center console to inspect.

I was thinking of doing a carb job but am not sure that is what the problem is since it started so suddenly and the boat only sat for a short period of time.

I have gone ahead and run a new fuel line inspected the old, installed a new bulb and tightened all of the crimps. I also siphoned 95% of the fuel out and there was hardly any particle/trash. I checked the pickup screen and and it was clear the anti siphon valve seemed to function fine so i blew out the tube with air and snipped about an inch off the line because it was longer than the depth of the tank. Last night I pulled the fuel pumps and the Diaphragm looked to be in fine shape no visible tears at least. I went ahead and ordered new pumps because the cost difference of the pumps vs the rebuild kit was roughly 10 per but shipping was free on the pumps. I'll install those friday.

One person mentioned to run my fingers along the spark plug wires to feel for a shock in case there was a pinhole in them I did that last night and wasn't shocked.

Last time I was out I also took the cowl off the motor and watched the fuel filter since its clear I could see the fuel level and it always stays roughly a half inch from the top. This is at idle and WOT when the bogging does eventually start the fuel level never changes then either.

Any ideas?

Thanks ahead of time

[99yam40]

Bulb staying flat sounds like a restriction.
In my opinion Motor dieing unless you back off throttle means the motor is running out of gas.

Tee in a vacuum gauge at different places to see what restrictions you have after you replace the pumps. Use a clear piece of tubing in the line while doing this to see if any air bubbles are shown

[ThanksandGigem]

Thanks I'm gonna do a carb job this weekend to so I'll test run and reply back with results

[rodbolt17]

carb job wont hurt.
most likely wont help either.
find and fix the restriction between the primer and the liquid in the tank.

[ThanksandGigem]

carb job wont hurt.
most likely wont help either.
find and fix the restriction between the primer and the liquid in the tank.

I figure the restriction must be cleared at this point since I've replaced everything from the tank to the outboard except the anti siphon valve. In cleaning the carbs do you soak the whole bowls then remove the plugs and blow them out withou removing any of the jets? I saw in another thread you mentioned not remove the pilot jets unless the motor sank which it hasn't.

[rodbolt17]

typically unless its nessasary I don't remove the pilot fuel or air jets.
they break easily.
I also don't typically remove the two large brass plugs on the top.
nothing there to see.

[ThanksandGigem]

typically unless its nessasary I don't remove the pilot fuel or air jets.
they break easily.
I also don't typically remove the two large brass plugs on the top.
nothing there to see.

Roger that and thanks. I've never rebuilt carbs especially from an outboard so I want to make I don't create a new problem

[rodbolt17]

but saying I replaced everything BUT.
that's kinda like saying"I am feeling much better. I think I will take a walk.

[ThanksandGigem]

but saying I replaced everything BUT.
that's kinda like saying"I am feeling much better. I think I will take a walk.

True if it still has the bogging I believe at least fuel related that could be the only left over problem. Or maybe... I should just go ahead and put a new one of those in just in case. Then I won't feel like I did a whole bunch of extra work and found out it was just one fitting.

[99yam40]

Testing things is better than throwing parts at it and hoping.
Carbs will not have any affect on the bulb collapsing or motor running out of fuel and dieing

to make the motor die all of the carbs would have to have the same problem(run out of gas) at the same time

My thoughts are that if you jack with anything that you do not need to there is always a chance you could cause a problem

[ThanksandGigem]

I agree that throwing parts at the problem isn't really what I should be doing from a T/S point of view. I intended to identify the root cause which is why i replaced the fuel line and bulb. The pumps where really just a thought that maybe they simply were sticking because about 50% of the time at WOT I have no issues. and maybe 10% of the time the motor will surge up in down almost feels like hitting a speed bump. The final 40% is the bogging down.

The carbs haven't been run through in 8 years so I figure that's a good idea to do just for preventative maintenance. As far as I know I don't believe the fuel pumps have ever been replaced.

I would prefer to test one thing at a time but i'm 1.5 hr from the nearest boat slip so I feel inclined at this point at least to do as much as possible to ensure it is fixed.

Is it typical that something like this happens so suddenly if it is simply the bulb or a loose hose clamp. When I changed the fuel line I pressed it with 7 psi and couldn't find any leaks.

[ThanksandGigem]

Also shouldn't I expect the fuel level in the filter(right before the pumps) to change if the motor is being starved of fuel? The level did not change when I observed the bogging down.

Just to clarify the bulb doesn't go flat on its own just stays relatively flat after I squeeze it while at WOT. If i do this it doesn't make any impact to the way the motor is running either way it still dies unless I decrease the throttle.

[boscoe99]

If the primer ball gets flattened in use, and the anti-siphon valve has not been replaced but everything else has, then I would bet on the valve as contributing to the problem.

The primer ball should pop right back to its normal ovaled shape as soon as you stop squeezing it. If it doesn't, something upstream from the ball is creating a problem. Guess what is upstream from the ball? The anti-siphon valve.

Get rid of the valve. It serves no real purpose. Not required in a boat that has an outboard motor for propulsion.

[ThanksandGigem]

I thought about removing the valve as I had read and other posts it's recomended however the tank is under the center console and the bulb is below the top of the tank at the rear of the boat so I figured I should leave it in. Plus so far most input I've gotten was that this doesn't sound like a anti siphon valve issue. Is there a way to simply punch out the ball or should i get a new fitting?

[boscoe99]

I would simply remove it and replace it with a 90 fitting.

Now what you can do for a test is to remove the fuel line from the valve. Connect the fuel line end to a three or six gallon gasoline tank and run the motor. If the problem goes away then it looks like it might be the valve.