Pontoon Boat & Deck Boat Forum

My pontoon with it's 70 hp Johnson 2-stroke has been running great. However, this past weekend an issue has shown up. I took it out on Saturday and it started fine, but had no power. Even at highest RPM's, it would only push the pontoon at 5 - 10 mph. After about 10 minutes of running, the issue seemed to go away and started to run fine and could maintain it's usual top speed. It ran fine the rest of the day. The next day we took it out again and once again there was no power. Even after 10 - 15 minutes of running, there was very low power. We anchored and went swimming for about an hour. When it was time to go back, the motor started and idled fine, but as soon as I put it into forward or reverse, the motor would die. This continued for at least 20 minutes, it would idle and rev fine but would stall when ever "dropped into gear". Finally after playing with it for a long time, it would keep from stalling and we were able to bring it back to the slip.

We didn't try running it after that. Does anyone have any idea what the issue could be? It is a 2 stroke motor, could it be that it just needs an unusually long time to warm up? It has new plugs this Spring and have verified that both the gas and oil pump are working fine.

I would appreciate any guidance anyone can give.

Thanks

Craig

could be several things, sort of sounds like the carb or fuel pump but it could be a ing issue to

Any idea on how old the fuel lines and primer bulb are? It sounds fuel related and these 2 items are not only easy to replace they are subject to collapse, deterioration passing junk to the carbs, cracks and sucking air etc...

Thanks for the suggestions. The fuel line and primer bulb were replaced this Spring, so they are new. Did not rebuild or clean the carbs, so gunk could certainly have gotten in. Would you suggest running some carb cleaner through it?

Seafoam. If that doesn't help you'll have to clean the carbs.

[quote="Craigld"]Thanks for the suggestions. The fuel line and primer bulb were replaced this Spring, so they are new. Did not rebuild or clean the carbs, so gunk could certainly have gotten in. Would you suggest running some carb cleaner through it?[/quote]

Try draining and refilling the carbs several times, there should be a drain on the bottom of each bowl. While Seafoam does not fix everything it does manage to work wonders sometimes. I might even drain & refill the carbs with it and let set for a spell it may help...

When was the last time you changed the fuel filter?

[quote]When was the last time you changed the fuel filter?[/quote]

The fuel filter was changed at same time as the fuel line and primer bulb.

ALL things mentioned are very possible, however on an older motor I would do a quick compression test on the engine to eliminate an internal problem. testers are pretty cheap and very handy to have. Remove all three spark plugs and test each cylinder one at a time, open your throttle all the way, crank the engine for several revolutions until you get the highest reading. should be around 100 psi or so, maybe higher, the big thing your looking for is a vast difference between any the cylinders. you can rent one for free from autozone if you don't want to buy it. http://www.autozone.com/loan-a-tools/co ... ster-gauge

[quote] on an older motor I would do a quick compression test[/quote]

As part of the engine work that was done this Spring, a compression check was also performed. The compression in all three cylinders was pretty consistent at about 120 psi. Only a small variation between them.

If my issue was fuel related, either dirty carbs or fuel lines, wouldn't it also run bad when in neutral? The motor would start fine and run smoothly until I attempted to put it into either forward or reverse. It seems like the big difference is I then have placed a load on the motor.

The pontoon and motor are down at Lake Anna in VA now and I am back up in Northen VA. I hope to do more testing this coming weekend.

Reed valves haven't been mentioned. A two stroke uses a reed valve (like a one way valve) to keep air from escaping back into the carb on the down stroke pushing it into the cylinder. If these are not closing that could possibly cause what you are describing. Runs fine at idle because enough is getting into the cylinder but as soon as it is given a load it dies.

I'm no 2 stroke mechanic but that is how I understand the workings.

http://www.cycleworld.com/2015/04/06/tw ... in-cameron

Maybe one of the new plugs is bad and works after it warms up. Have you tried pulling a plug wire off one at a time and see if it runs any different?

Is your fuel tank properly vented?

If the vent isn't open, it could do what you're experiencing.

If you have a portable fuel tank, it's usually in the cap.

If you have a permanent tank, the vent can be in a variety of places, usually near the filler cap.

[quote="JLester273"]Reed valves haven't been mentioned. A two stroke uses a reed valve (like a one way valve) to keep air from escaping back into the carb on the down stroke pushing it into the cylinder. If these are not closing that could possibly cause what you are describing. Runs fine at idle because enough is getting into the cylinder but as soon as it is given a load it dies.

I'm no 2 stroke mechanic but that is how I understand the workings.

http://www.cycleworld.com/2015/04/06/tw ... in-cameron[/quote]

In the older 2 stroke carb'd motors, a broken reed was usually accompanied by what is referred to as the engine "sneezing" usually at idle it would sneeze and spit fuel back out from the carb throat, because as you said, it was letting compression back out through the carb.

[quote="FLOUNDERPOUNDER225"][quote="JLester273"]Reed valves haven't been mentioned. A two stroke uses a reed valve (like a one way valve) to keep air from escaping back into the carb on the down stroke pushing it into the cylinder. If these are not closing that could possibly cause what you are describing. Runs fine at idle because enough is getting into the cylinder but as soon as it is given a load it dies.

I'm no 2 stroke mechanic but that is how I understand the workings.

http://www.cycleworld.com/2015/04/06/tw ... in-cameron[/quote]

In the older 2 stroke carb'd motors, a broken reed was usually accompanied by what is referred to as the engine "sneezing" usually at idle it would sneeze and spit fuel back out from the carb throat, because as you said, it was letting compression back out through the carb.[/quote]

Thanks for the clarification. not sure if that is what was happening or what I just figured it would seem similar. The no power etc.

Worth a check I guess. Maybe they are just not sealing but not totally broken?

As always check the easy stuff first. Plugs are easy. etc