'88 50hp knocks/taps/misses on downthrottle

[jomishx]

Got a 1988 Force 50 hp recently. Motor is on a stand and has been ran on muffs and in a tank. Starts, idles and revs good. Problem comes when you downthrottle. There is a very noticeable knocking sound...maybe like a hard miss even? The engine shakes and takes a few seconds to return to idle. There is a video of it below. I noticed other Forces doing what seemed to be a similar shake and knock on youtube vids. The comp ran 120 on both. This is my 1st and maybe last Force. Is this "normal' for these engines? Any suggestions

http://www.youtube.com/watch?v=Wz3tKY63pXU

 

[Frank Acampora]

Re: '88 50hp knocks/taps/misses on downthrottle

That's quite normal when you mistreat an engine on a test stand by throttling up to a high RPM, then down with no load. On a boat under load it should perform well.

Why are you so dissatisfied that this may be your first and last Force? The engine seems to run well.

 

[Josh P]

Re: '88 50hp knocks/taps/misses on downthrottle

Yes no load is causing that. Take any other 2 cycle engine and take the load of it and it will do the same thing. BUT also like frank said its miss treating the engine and is not good for it.

 

[capri1600]

Re: '88 50hp knocks/taps/misses on downthrottle

Let me pile on.....don't run the engine like that! Get it on a boat and go run it. I think it'll be fine. You'll ruin it the way you are trying to play with it.

 

[jason32038]

Re: '88 50hp knocks/taps/misses on downthrottle

I actually seen a couple of videos after yours on youtube and they were doing the same thing. Looks normal

 

[jomishx]

Re: '88 50hp knocks/taps/misses on downthrottle

Wow, i feel dirty AND ashamed. Didn't realize the rpm's were that high. I appreciate the feedback. I thought it may be a problem as i have never seen this with any of my Johnson or Evinrudes.

What should be the max rpm in neutral. It was way below the stop that it has built in. Does it make a difference when on muffs or in barrel? I've never ran it in gear above idle. By the way, this vid was taken with the lower submerged.

 

[Josh P]

Re: '88 50hp knocks/taps/misses on downthrottle

I actually seen a couple of videos after yours on youtube and they were doing the same thing. Looks normal

Just because you saw it on youtube doesn't mean its right.

 

[jomishx]

Re: '88 50hp knocks/taps/misses on downthrottle

Josh, that's what i was saying. I don't want to go thru the time and expense of removing the 30 hp Johnson and mounting this to my boat if it is not going to run right. Maybe I will have to take it to the local marina for assurance. Thanks for your help

 

[dkonrai]

Re: '88 50hp knocks/taps/misses on downthrottle

hey if you really dont want that crappy motor...... i can help you take it off your hands
yeah that motor runs really bad, i think its a bad rod knocking....should get rid of that thing right away!!

 

[Josh P]

Re: '88 50hp knocks/taps/misses on downthrottle

Josh, that's what i was saying. I don't want to go thru the time and expense of removing the 30 hp Johnson and mounting this to my boat if it is not going to run right. Maybe I will have to take it to the local marina for assurance. Thanks for your help

No i was talking about running it at crazy rpm levels with no load. I revved mine up once to make sure i fixed my ignition problem it scared me because i didnt think it was going to idle down, it sounded the same way, i would rig it up and test it out thats the only way your gonna know if its good.

 

[jason32038]

Re: '88 50hp knocks/taps/misses on downthrottle

I took a second look at the video and it looked like you had to force the throttle lever back to fix it. Check the wires on the trigger to see if they're binding on anything when you throttle down. Also the trigger might have to be greased. Lube up all the moving parts of the throttle and timing linkages. Or maybe there wasnt enough back pressure on the exhaust. You'll never know until you test it on the water.