1996 2-stroke rpm's dropped during ride

[Bigfoot100]

Hello - We have a 1996 Johnson 2-stroke outboard, Model Number J90ELEDR. It was running fine and we were out for a ride and had been riding for 20 minutes or more. Then it just started slowing down (RPMs dropped). It idled fine, but we couldn't get it to rev back up. I tried pumping the fuel bulb while it was running, and that helped, but after a few tries doing that, the bulb just wouldn't fill back up. So, I was squeezing an already squeezed bulb, just trying to get something out of it. That helped just a little, so we just putt-putted back slowly and called it a day. Again, it started and idled just fine. Just wouldn't rev up. It seems to me that it was starved for gas. I'm no expert though, which is why I am here.

Any thoughts on troubleshooting steps?

I did buy a new fuel filter and will put that in, as I don't recall doing that in quite a while.

Thanks!

 

[Droid]

If the bulb squeezed & didn't expand back up, there is a restriction before the bulb. Check for tank not venting, plugged pick up tube, plugged anti-syphon valve (built in tank), plugged fuel line especially the cheap gray crap lines.

Fuel filter is after the bulb, actually inside the engine cowl. That won't stop bulb from expanding back up.

 

[racerone]

Running with VRO in service or 50:1 mix?----Did it perhaps go into S.L.O.W. mode?

 

[Bigfoot100]

Finally got back to this. I pulled the priming bulb and then compared the sound of it as I pumped it to a new one, and the old one was definitely not working right, based on the sound alone. I'm guessing the little one way valve inside died. So I installed the new bulb, pumped it, started the engine, and the engine ran smoothly, as good as ever, for a nice cruising speed. So that problem is solved.

HOWEVER, at some point I decided to rev it up to go fast. At first it was fine, but after a few seconds the RPMs dropped. At that point, I could not maintain the faster speed, as the RPMs would go up and down sporadically. Once I dropped back down to a more moderage cruising speed, it ran fine. At this point I looked at the bulb, and it was flat! I tried this sequence twice, and both times after the "starvation" at high RPMs I could see that the bulb was being sucked flat.

So, this makes me think that I have some sort of obstruction in the fuel line or gas tank that is limiting the flow of gas. Does that sound right?

This is on a Grumman deck boat, and getting to the gas tank is a major project as far as I can tell, so I am thinking of just running a new fuel line to a separate gas tank as a test to see if I can go fast in that configuration. This would either point the finger directly at the tank/line or rule it out as the problem. Make sense?

If it's the tank/line, then for this season at least, I may just use a separate marine gas tank (<$100), and worry about resolving the issue with the built-in tank and/or line when the season is over.

 

[Droid]

Yes, you have an upstream restriction like I said in post #2 above.
As for your boat, I have no idea how or where the tank is installed but I can't believe there isn't some access hatch or panel for the hose & sending unit access/repair.

 

[louc]

I used this for testing my I/O last year, I had the same issue, the engine would not plane out the boat, it turned out to be the fuel in the main tank. Never had fuel go bad on me before, but that's what it was. After running this test where the engine had all of its normal power back and pulled right up to 4800 rpm, I pulled out the anti-siphon valve and the fuel pick up tube. Tested both with a vacuum gauge and both seemed fine but replaced with new anyway. Had 30 gallons of bad gas pumped out and it's back to its normal behavior.
If you wind up doing this be careful with the anti siphon valve (if you have one, might just be a regular barb) and the pick up tube. My boat has an old aluminum tank and they both came apart thankfully.

lol
nothing wrong with the old ones.
Lesson Learned
before rebuilding carbs, changing points, etc
run it on the separate outboard tank with fresh gas!
I did put a shut off valve on the line from the outboard tank just in case.....