no go fast

Can anyone maybe offer some direction?? I just took possession of a boat with a 1999 johnson 40hp 2 cyl. motor. The motor starts and runs nicely, with no missing that I can hear, again, it runs very smoothely, BUT, at full throttle, I move along at maybe 5 knots. I have changed plugs, gas tanks, gas, added fuel stabilizer, etc. still, no speed. The boat, used to go along pretty good, but sat in my brothers yard since last summer. He did start it on occassion, but, has not had it in the water since last year. Also, at full throttle, it runs at about 3000 rpm's. Any ideas?
Rob

 

I heard of something similar once, the mechanic eventually found the entire boat trailer still strapped to the underside of the hull. I'm assuming that's not your problem
How's the cooling water flow? A Johnson 40 (two stroke, i presume?) should spit a fairly powerful, steady stream out the back starboard corner of the powerhead after about three seconds of running. They also spray a lot of water out the exhaust bypass (centre back of the shaft) at speeds above a dead idle, once the engine heats up. The S.L.O.W. system will kick in and limit the RPM if the engine gets too warm, ie. if the cooling flow is backed up. If the engine was run on dry land without a proper cooling water line, the water pump impeller will be completely shot, which will certainly trip the S.L.O.W. switch.

 

Lol!!! Yeah, the trailer is not still attatched to the hull...
Ummm, the water flow you speak of is occuring in both places, on the shaft rear as well as the hose it comes out of after circulation, both seem to be flowing pretty solidly

 

Hi,
Did you check your Primer Bulb at fuel line, are the valves clean?
Have nice boating
Amador

 

Make sure the choke is not sticking closed. If it is it won't let in enough air to run it very fast. I have this same motor in a 50 hp and it has been trouble free.

 

I'm not sure of your engine's particular configuration, but it sounds like you have a timing advance issue. The manufacture can do this a few different ways. I could be a high speed trigger, a function of the stator or other method to advance the timing. What is your normal (or what it's supposed to be) RPM at WOT? What is you current RPM at WOT? If you're hitting your RPM at WOT then you have a boat problem (trim, drag, etc.) If you're not hitting your target RPM at WOT then you have an engine/prop issue.

 

how heavy is your boat?

 

Some propellors have a rubber hunk in the hub to prevent damage on hitting junk.

Put the engine in gear (stopped) and see if you can turn the prop by hand.

If you can , try a different prop.

FAST FRED