violent shaking on mercrusier 120 i/o

nightsniper1 · May 11, 2009

the engine shakes about 6 inches at all rpms, inculding idle. all compression is good, we changed the coil, distributer cap, points and condeser, there all brand new. theres a new carb on it and still the same thing. i think its a 1970. any ideas of what could be wrong. thanks.

HT32BSX115 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Check the firing order and make sure the the spark plug wires are in the correct order.

This wouldn't be the first time a couple of plug wires got reversed

Cheers,

Rick

Bt Doctur · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Firing order correct? front to back 1-3-4-2

rocket350 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Check timing and dwell too. Dwell is VERY important. If your ganna keep the boat, buy a dwell meter. Feeler guages just are not as precise as a dwell meter.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

HT32BSX115 said:
Check the firing order and make sure the the spark plug wires are in the correct order.

This wouldn't be the first time a couple of plug wires got reversed

Cheers,

Rick

yep there in the correct order.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Bt Doctur said:
Firing order correct? front to back 1-3-4-2

there correct.

Don S · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Are you sure you are going the right direction on the distributor cap? Note direction of rotor rotation in drawing below.
Also be sure #1 plug wire is where it actually is, it may not be as the picture shows.

Bondo · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

there correct.

Ayuh,.... If everything were Correct,... It wouldn't be Skipping,+ Shaking Violently....

Did you try removing the plug wires, 1 by 1, to see which is the offending cylinder,..??

APPALOOSA2 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

If that motor is shaking 6" from misfire I would also check the motor mounts. The 120 is a transom mount engine.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

ok a little more about the boat, ran out of time before. we were out fishing all day and no problems, we left it out over night and the problem started the next day. so we changed all of that stuff after the shaking started. we had problems with the distribter cap before, because it keep moving but, it has been doing that for years and it ran fine. ill check the cap tommorow and double check to make sure its right.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Bond-o said:
Ayuh,.... If everything were Correct,... It wouldn't be Skipping,+ Shaking Violently....

Did you try removing the plug wires, 1 by 1, to see which is the offending cylinder,..??

no i havent tried pulling one by one yet. i might be getting it out tommorow to try and if i can ill video a short clip of it so you guys can get an even better idea of it.

Don S · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Have you ever used this boat before? Do you give it some throttle when starting? Tell me you aren't trying to start it by just turning the key to start and hopeing.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Don S said:
Have you ever used this boat before? Do you give it some throttle when starting? Tell me you aren't trying to start it by just turning the key to start and hopeing.

ya we've had it for 15 years.

Commissionpoint · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

nightsniper1 said:
ill video a short clip of it so you guys can get an even better idea of it.

Yeh, post a vid, I'll have a look. Shaking around 6" like you say is kinda scary for the mount set-up on this engine. Almost certainly a misfire situation to make it move about as much as you say.

JustJason · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

If your going to pull the wires 1 by 1 off of the cap do yourself a favor and buy some plastic or insulating plug wire pliers.

So your saying that the boat ran fine for an amount of time and with nothing changing it starting bucking that bad? Did you happen to hit anything in the water? Any damage to the drive unit?

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Commissionpoint said:
Yeh, post a vid, I'll have a look. Shaking around 6" like you say is kinda scary for the mount set-up on this engine. Almost certainly a misfire situation to make it move about as much as you say.

ok i will as soon as i can. ya the whole boat shakes when it does that too.

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

JustJason said:
If your going to pull the wires 1 by 1 off of the cap do yourself a favor and buy some plastic or insulating plug wire pliers.

So your saying that the boat ran fine for an amount of time and with nothing changing it starting bucking that bad? Did you happen to hit anything in the water? Any damage to the drive unit?

i have some of those pliers. ya it ran fine and it just didnt work right the next day, we didnt change anything untill after it started. no we didnt hit anything, the lower unit is new.

Commissionpoint · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

nightsniper1 said:
ya the whole boat shakes when it does that too.

I'll bet it does.......

Lookin' forward to the vid.....

Bt Doctur · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

pull the plugs and see if #4 is rusty or wet.may have popped a hole in the riser killing #4 cylinder

nightsniper1 · May 11, 2009

Re: violent shaking on mercrusier 120 i/o

Bt Doctur said:
pull the plugs and see if #4 is rusty or wet.may have popped a hole in the riser killing #4 cylinder

ok ill take a look in the morning. i talked to a friend awhile ago and he said there might be a hole in the manifold.

violent shaking on mercrusier 120 i/o

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