Brain buster!

[hondakillrsx]

Hey Guys,
Alright guys so i've got a problem that I'm hoping someone has seen because it doesn't seem normal. What happens is after running my 91' 2 stroke 50 horse for a little time (varies), I'll go to throttle up on plain and the motor will sound a bit different and it not have much power at all, I'll have the throttle pretty much all the way down and it won't even be on plain and just after I realize that the motor overheats! But after a couple minutes of letting the motor cool down it will run fine and be back to normal. Has this happened to anyone? I just replaced the Impeller because I thought thats what I needed but now I'm thinking its overheating because of whatever is making it loose all that power. I check the compression and it is perfect in both cylinders just under 150. please help!

 

[jerryjerry05]

Re: Brain buster!

Does the motor loose power or just not get up on plane.Is it reving up?
Change the thermostat,it could be opening to let a little water not enough to cool. Just for GP. Then check the timing.Then check the fuel pump diaphram.J

 

[hondakillrsx]

Re: Brain buster!

it seems to be loosing power. It's not at the proper RPM it should be for being full throttle. It's really hard to explain the tone it makes but its not the same as if it were running fine. It's more of a throatier sound.... I'll check all of those but I would think if any of them were bad then the boat would just not run right out of the gate but it will run fine for a long while with no problems, then out of the blue, I'll start it up to leave a fishing spot, give her some throttle and then see the problem. Then i'll let it sit for a minute, start her back up and it will be fine again... (most of the time) Thats why I think its going to be hard to troubleshoot this one. thanks again for any further comments.

 

[Frank Acampora]

Re: Brain buster!

Well, Here's a "Hail Mary" thing to check. I have seen it on larger engines but never on a 50 size.

Remove the prop and check the end play of the prop shaft. When you grab it you should be able to pull it out and push it in a small amount (about .005 inch). If it has a ball bearing on the prop end of the shaft, it may be a bit tight and difficult to move but you still should be able to move it (I think--if it is similar to the Chrysler lower units). If the lower has been repaired in the past, it may have the incorrect shim between the prop shaft and the forward gear.

If the lower unit is set up too tight, it actually heats up some and "hardens" to a stop. The engine sounds different, like it is working harder, and indeed it is. This may cause the overheating. Since the lower unit is in the water which is an excellent heat sink, it cools almost immediately and the engine can be immediately restarted, just as if nothing is wrong.

 

[hondakillrsx]

Re: Brain buster!

you know, I was thinking something like because just before it happened this last time I hit the prop on the bottom. And it just seems like it would be something in the lower unit. I will look at this and check back in, thanks a lot!

 

[BuzzStPoint]

Re: Brain buster!

I'll throw my 2 cents in..

Cavitation?

I think that was my issue last night.. While running at WOT the sound of the engine completely changed. Just didn't normal. I backed off the throttle to an almost stop and went back up. Sound was normal..

Only reason I say it was cavitation, We had a little heavier load so I adjusted the motor pin outwards. We crossed another boats wake when this happened.

 

[hondakillrsx]

Re: Brain buster!

fairly new to boats what is cavitation?

 

[milehighboater]

Re: Brain buster!

it is when the prop is trying to pull water from turbulent water or is sucking in air. It most commonly happens when a person trims the motor up too far, but it can also be caused by improper motor placement/height amongst other things.