Loss of power at full throttle

[Tuffy Boat Guy]

I have an 89 Suzuki DT55. It will run fine for awhile then at full throttle it will drop down to about half the rpm's. I have had it in to get looked at and tested and everything tests out fine. But, once it is back on the lake it will do the same thing. After it loses power it does it for the rest of the day. runs great at low RPMs and starts right away, but I can't get it to go over about half throttle. Any suggestions are welcome.

[Valv]

There are a couple questions to answer.

Does motor sounds "bogged" down like it would like to go but cannot push enough (propeller pitch too high).

When you toke it to check what did they look for ?

[Tuffy Boat Guy]

It runs a little rough, but not bogged down. It is almost like one of the cylinders shuts off. It runs at a really steady rpm, it is just that it is about half what it should be. They ran it through a bunch of tests and put it on the dyno. I took it in 2 or 3 times. One time they replaced the hub and prop because they thought it was a spun hub. It didn't do a thing.

[efgh]

Sounds to me like you have a colasped hose somewhere on your feed line from the tank to the motor, the inside neopreme of a hose will squash together and limit the flow of fuel to a trickle, might not be the answer, but easy to check out.

[Tuffy Boat Guy]

I forgot to mention that one time when it was in the shop they replace the water flow sensor thinking that it was faulty so it thought it was overheating and limiting the rpms. Didn't do a thing.

[gunflint]

I agree with efgh. It sounds to me like it's somewhere between the bottom of the fuel tank and the carb.

[DTro]

Sure sounds like it's going into limp mode to me. When it starts to happen, have you let it sit for an extended time (cool down) before trying again?

[Tuffy Boat Guy]

I haven't let it sit for a long time. Every once in awhile it will go full throttle right after restarting, but it doesn't last very long.

[PierBridge]

Could be a stator problem.

[Valv]

Ok, since it was in the shop I assume the following are not an issue:

- Compression , good all cylinders

- Water cooling, good no overheating

- Fuel filter, clean no clogging

I would agree with weak spark under load or more toward fuel inlet issues. Your fuel tank has a small pickup screen, I never see one plugged (even after many years sitting) but it cannot be taken out of consideration.

Also check the fuel hose bulb, check valves can be bad and not letting much thorugh.

You can do a test while on water, take cowl (hood) off and run motor, you should be able to see fuel lines if they get empty or not (filter, lines, etc.) while at full throttle.

Sorry for all these questions and ideas, but a diagnose without a physical inspection (just by small description) is very, very tough.

[Tuffy Boat Guy]

Thanks for the ideas. I will look into them once I get it out of storage.

[castindad]

valv 50-1 oil for a 1976 20 hp johnson? what spark plugs would you use if it where yours? allso do you know where i can pick up the johnson logo that snaps on the motor cover castindad [email protected]

[BarryG]

I have an 89 Mariner and it was doing close to the same thing, it would run fine then you would be going down the lake WOT and it would bog down. Like running on 1/2 throttle, I had a few things done to it and it didn't help. Finally had it torn down and top piston was coming apart and had to have it rebuilt. Runs Great now!

[john.wells]

It could very easily be a coil. When coils go "half" bad, they can short out when warm and act normal when cold. You would get intermittent/no spark. One of the other posters noted the stator- same potential problem. It can be a little tricky to test. If you get a good in line spark tester, you can check it yourself on the water with someone you trust at the helm . Just put the tester in line (at every plug) when you know it is running well and see what it looks like and then do it again when it starts to dump out. You would see it best at night, but dusk or dawn would be better for safety reasons. Better yet, have your dealer run the test in a tank so you can be sure you won't be taking an unwanted dip.

[MossBoss95]

Tuffy guy you better get that thing fixed or you will be fishing from the dock on opener. Shoot me a call later, thinking of a little ice fishing on Sat, maby go after some northerns?

[Muskieguy]

Yeah, tuffy guy...get that thing fixed....no more room in my boat at Crane..

Just talked to MossBoss and I might be able to sneak away on saturday to do some fishing with you guys..as long as it is not too cold.

Later.

Jason.(aka Muskieguy)

[Tuffy Boat Guy]

Mossboss and Muskieguy, Saturday should work for me. You guys name the place.

I will have the Tuffy ready to go to crane. Luckily Mossboss is giving me a hand.

This posting gave me some good ides.

[steve schmidt]

I had the same thing and as some other posts have said...it was a "cracked hose" in my gas tank. It was sucking gas at low pressure, but sucked gas and too much air at higher demand.. It only cost me a $100 to find that out.