115 Yamaha Saltwater Series Experts (2-Stroke) - Engine Bogs Out Under Load

[115SWS_2STK]

Hey guys, I have a late 90s 115 HP Yamaha Saltwater Series 2-Stroke that is having issues under load.

The motor starts up fine, idles real well, and can be reved in neutral as well.

The issues is that when it is put under load and I try to get past a certain mid-range rpm, the engine starts bogging out. The issue can be remedied by engaging the choke and it will get past that point. Besides that mid-rpm issue (where it feels like the engine isn't getting enough fuel), the engine runs great in all other RPM ranges.

Fixes that were done so far:
1. New fuel lines
2. New fuel pump
3. New fuel filter
4. Carburetor has been taken out and cleaned through a sonic cleaner machine
5. Typical 300 hour maintenance (water pump, thermostat, gaskets, spark plugs etc)
6. Spark plugs were tested for power and they seem fine.
7. Checked compression and it was good.
8. Fuel/air mixture adjusted and runs well on that

Future testing procedures I will do:
1. Run it again on spare tank
2. Try seafoam in spare tank
3. Check if bulb stays hard during engine running

Do you guys have any advice on what it may be?

Thanks

[brian3006]

Sounds like it is not getting enough fuel when under heavy load. once you get it past this point, the boat probably plains out and is under less load and thus requires less fuel. When you took the carbs off to clean them, did you perhaps check the float levels on them?

[Jason2tpa]

Agree it's likely a fuel system issue, specifically the carb jets. When you pulled the carbs to clean did you also pull the jets and verify orifices were completely clear? The smallest bit of debris clogged in the jet will result in a performance issue under load. And in my experience, no amount of seafoam or likewise fuel treatment will remedy a clogged jet.

[99yam40]

it is not just the jets, it is also the passageways drilled thru the carb all over that need to be clean

[115SWS_2STK]

**Update**

Had seafoam ran through the engine and it runs much better now. Still some hesitation so there may still be some gunk in there. Will try to run a couple more cycles of seafoam or chemtool through the system to see if it can get the rest out.

99yam40 - How do you close up the drilled passage ways once you're done cleaning? There seems to be a ball or some sort of thing that keeps it closed.

Jason2tpa - The jets are clear. I think its the internal passageways.

[99yam40]

heated sonic cleaner more than once may be needed

some carb kits have discs to put back in or lead balls to seal off openings if you have to drill and pull to clean, but that is not normal an these Yamahas

I have had some good results from shock treatments of Yamaha rind free.
2 oz per gallon of fuel in small 2 stroke motors

make sure you follow the link and sync procedures when putting carbs back on every time you reinstall THEM

[115SWS_2STK]

Ran it at the ramp for about 15 minutes with one gallon gas and 8 oz sea foam (maybe I should've used more). Engine sounds like it runs better and I got it to maybe 50-65% throttle before I was worried the boat might run into the car from the trailer. Will do a water test this weekend after letting that seafoam from the mixture soak in the carbs a bit longer.

[115SWS_2STK]

So ran it today on the water after the seafoam treatment. It ran really well for the first 30 minutes. No hesitation all the way from idle to 4000-5000rpm.

On the way back to the dock, I ran it at full throttle just to see if everything else is well. While slowing down to the no wake zone, the engine sounded like it was running on two cylinders or starving of gas and eventually died. This was going at 5-10mph.

After that, it was hard to start and would only start if I revved the engine in neutral and pulled the choke. The fuel bulb stayed hard all throughout even when the engine was dying.

It did seem like the seafoam helped a bit since I was able to run the engine normally for 30 or so minutes...

Any thought guys? Maybe bad fuel or electrical spark plug coil issues? I did put 50 gallons of non ethanol into the tank.

[99yam40]

cleaning out everything and then something plugging it back up is always a problem in these things
I have found stuff that looked like small clear sheets of plastic that I assume came out of the lines or pumps inside the carbs that caused problems after cleaning several times.
run often and do not let that stuff build up from drying fuel in carbs and lines

and it is always a good idea to change plugs after running a cleaner

[TownsendsFJR1300]

Might try and drain the carbs with the drain plug at the bowl of the carb(s).

I'd catch what comes out to check for debris. Wouldn't hurt to "flush" the carbs, drain out, prime the primer bulb.

If that doesn't help, open up the carb(s) again..

.

[115SWS_2STK]

I will try to clear out the fuel in the carbs and run it on a spare tank again. I suspect it might be fuel inside my gas tank. The tank is almost 40 years old and sometimes has water swishing around the fuel tank cavity (can’t drain).

Possibly the water had time to settle when I turned my engine off prior to driving back to the dock yesterday. Seems like once the problem starts, all RPMs are messed up and hard to start the engine.

[115SWS_2STK]

Pulled the Racor fuel/water separator and checked if there was water in fuel. Doesn't seem like there was any water when I put it in the jar. The jar did however showed a bit of floating debris in the fuel. I wonder if it was from the fuel/separator housing.

[TownsendsFJR1300]

Pulled the Racor fuel/water separator and checked if there was water in fuel. Doesn't seem like there was any water when I put it in the jar. The jar did however showed a bit of floating debris in the fuel. I wonder if it was from the fuel/separator housing.

Fuel line internally breaking down is more likely.

Did you check the under hood fuel filter?

Floating debris, once in the carb(s) can/will cause major running issues as well.

.

[115SWS_2STK]

So I pulled the in-line engine fuel filter and found A LOT of crud in it. Also dumped the fuel/water separator twice and found TWICE a lot of debris in it. I think I may have found the issue... Should I pay $800 for another carb clean to see if this is in fact the issue......? I imagine running it on my spare tank didn't do any good because the carbs are clogged again....

[TownsendsFJR1300]

So I pulled the in-line engine fuel filter and found A LOT of crud in it. Also dumped the fuel/water separator twice and found TWICE a lot of debris in it. I think I may have found the issue... Should I pay $800 for another carb clean to see if this is in fact the issue......? I imagine running it on my spare tank didn't do any good because the carbs are clogged again....

As of right now you don't need a carb. From your post above, there's crap further up past the fuel water separator/fuel tank/BEFORE the separator..

You do need to at least drain the carbs looking for any debris that made it past.


Might want to try a clean, portable fuel tank with known good lines, plumbed into your engine (carbs at east drained) with clean fuel.


* A new carb with crap in it won't run correctly either*..

.