TOPIC: Shaking and vibrating underway

Took the 85hp '78 Evinrude out again and the torque steer problem is solved but there still is a slight shaking/vibration that goes through the entire boat at no wake speed. Might be at higher speeds but engine noise and water conditions make it hard to tell.
Doesn't seem to be any missing in the motor, idles and accelerates very good. I changed the prop and didn't make any difference. There is some very slight play in the prop which I could shim out but I don't think that is the problem. Bent prop shaft?? how can I check for that. Any other suggestions are welcome.
Cal

Turn the prop slowly while watching the center machining dimple for wobble.

Jim, did what you suggested, no wobble or spiral at all. I changed the LU lube last week and have since had it on the water and rechecked the oil again today, still clear as a bell and that was after running at idle and WOT so I think that rules out a bad/loose seal. I did have to put a shim on the prop shaft between the prop and unit and torqued it down, any number on ft lbs for that prop nut?. That took care of the loose feeling.
Darn,,,,I'll just have to go back out on the water again
Anyone think a low idle under load would cause a firing miss? Very hard to tell. I put in new plugs two days ago also. Bosh surface fire. I've always had the best luck/performance out of those. Never a big fan of Champions. What ever is causing it sorta shakes the entire boat at slow speed. I haven't check the motor mounts yet.

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Two hours later. Could it be as simple as this?
I was moving the motor trying to check the rubber mounts, all seemed tight but I noticed some slack in the steering knuckle(s), I thought it was just loose. I removed the connection by the motor and it seems the brass bushing, ss sleeve and bolt are sorta egged out, almost enough to cause any motor vibration to amplify and pop back and forth to the steering system. I could really feel the vibration in the steering wheel. Hope it's as easy fix as this.

Yeah that could be it Cal unless the timing belt is a tooth off. Does it start easy?

Bob

Bob, starts easy, runs almost too good. Prolly get back out on Monday to check it out again.

Waterwings wrote:

Yeah that could be it Cal unless the timing belt is a tooth off. Does it start easy?

Bob

No timing belt on these motors Bob.... You're thinking too old!

Cal, I don't trust rebuilt props - especially ones that you don't know the history of the damage.

Motor mounts deteriorated or broke?

Doh sorry Jim should have read that closer.

Bob

Whoops! This got by me too! YES! Replace!

"I was moving the motor trying to check the rubber mounts, all seemed tight but I noticed some slack in the steering knuckle(s), I thought it was just loose. I removed the connection by the motor and it seems the brass bushing, ss sleeve and bolt are sorta egged out, almost enough to cause any motor vibration to amplify and pop back and forth to the steering system. I could really feel the vibration in the steering wheel. Hope it's as easy fix as this."

For now I just put in a brass shim. If that works I will plan on replacing the entire motor end this winter. I do not believe this is the proper fitting for a trim/tilt motor because there is no swivel on the motor end and any trim or lifting on the motor is putting stress on the bushing.

I do have a swivel end replacement that would be proper but I will have to shorten the motor connecting shaft and thread the end.

Was out this evening and most of the vibrations is gone but another question. Would a bad coil cause a cylinder to miss at slow speed but not be a problem WOT? Maybe I just need to clean and adjust the carbs.

A weak coil could be the cause and it typically will get worse over time, especially when they get warm, they begin to fail and then go dead. Carbs may also be an issue at idle. You can also try a can of Sea Foam to clean out your fuel system. Then go run it and get some time to reevaluate your situation.

All secondary ignition circuit (plugs, wires, cap & rotor if used, and coils) problems will first show up under a load, not at idle. Like when you drive your car through water and it starts missing out when you try to accelerate but runs fine when you let off the gas. This is because there is much more resistance to jump a spark across a plug when the cylinder is packed with a dense fuel mixture and higher pressure. So, the electricity will take the path of least resistance across a wet distributor cap, or through the crack in a coil.
Most likely, if you have a miss at idle, it's because the idle jet in the carb is plugged. Which is pretty common because it's such a small orifice to begin with, when left over the winter (or longer) without draining, they are the first to gum up.

When a coil was failing on my 73 65hp Evinrude it gave the same sympton (really bad at low speed but pretty good above 4,000 rpm. New coil solved it (also, got worse as motor got warmer).

Run on a hose after dark - should be able to see halo/arcing from the bad coil.

Boy, the neighbors would love that
Very possible the carb since the boat was last registered in 2012 but runs like a champ otherwise. I did run a tank of seafoam, smoke and all. Has a good hole shot without any sputter and top end is good without issues. Guess it just needs some carb tweaking.

Surface gap plugs were intended to keep people from blowing holes into pistons - but they can cause firing problems in some cases - especially on motors that are run "leisurely" They are best used on engines that will be run hard and fast. For "everyday" use a lot of people changed over to standard gap plugs on those engines.



Here is a list of plugs to consider

www.maxrules.com/OMCplugchart.html


Maybe look at the NGK BZ7HS-10 or BR7HS

HI:
I took the standard plugs back out of my 1973 Evinrude 65HP and went to NGK 2522 (BUHX) surface gap plugs. These plugs run cleaner, and solved all issues for me. They will not foul wether I run slow or fast, can idle forever without a sputter or stall.

I recommend you give them a try.

Bruce, I respect all your advice but I guess it's the ongoing discussion about what works best for the individual. I'm a fan of surface gappers also. Always had trouble with Champions and AC's, seems they always have a tendency to foul on me, even on my chainsaws and blowers. I changed the plugs the day I started having issues.
Gradually working out the problems one step at a time. The good news is that it's still a running, working motor doing what it's intended for....see insert taken last Tuesday

I'm not saying that the plugs are the problem. In certain cases they can be the cause of misfires. I also like gapless plugs, and I have nothing against them. It is just that in some cases the gapless plugs cause problems. So if you completely run out of things to try and are still having the problem, this is one more thing to look at. You also may have a carb with a bit of "crud" stuck in a low speed bleed hole / orifice. Could be one of the coils is taking a dump. It may not even be a misfire. Just throwing out possibilities -

I worked in a bike shop for many years. And the 2-strokes were, of course, hardest on plugs and the bad brands would show their heads pretty consistently, especially from the guys who raced. 9 times out of 10, if a two stroke bike came in that wouldn't run, it was because someone had put Champion plugs in it! Never understood how those plugs got such a name for themselves... marketing I guess. They wouldn't last 2 hours if a bike was a little too rich. Throw a set of NGK's in them and never see them again! I've seen regular, non-platinum, nothing special NGK's in cars with over 75,000 miles... both electrodes worn to a point... and still not missing a lick!!! It's all I've used for over 25 years and only change them when I'm afraid they may be seizing in the heads... and I always use anti-seize on them.

I put the NGK in my Jeep several years ago, hasn't missed a beat. My 11 year old Chrysler mini had issues with occasional coughing. Had to replace the EGR again and sure glad I used never seize on the previous one. Still had some sputtering issues and put in a set of Bosh platinum. Problems solved.