BAD MISS.. thought it was the gearcase!!!

[bob johnson]

so we learn as we go...and we become experts at the stuff we solved, but are newbies when we encounter stuff unseen before.

I had what I was thinking was water in the gas...but since I had hit my SS prop on my 1995 Johnson ocean runner 115 twice in the previous week...I thought... I MIGHT have damaged the gears...and I told myself a few years ago...NO MORE SS PROPS!...but I chewed up all my aluminum props and on went the SS.. and it just stayed because I procrastinated....so now I am here with this miss...tried switch gas tanks..it s worked for a little while then the miss came back...Next time out I put in dry gas!!!...still the miss happened...and the miss was so strong I lunged forward from my standing position a little when it happened... it was like a hit something under water a few times!!! I thought...that has to be a broken gear floating around getting caught now and then inside the LOWER UNIT.... so I eventually got a rebuilt unit and installed it.....we sure enough...the miss came back... and it was as sporatic as usual. now I am thinking, IT MIGHT HAVE been the water or an electrical miss I have never experienced before....soooooooooo

the question is with misses...either the water in the gas or a bad -clogged carb..... or an electrical misfire...or short.... would either one of them cause such a horrendous miss...that it gives the boat a jolt...like it hit something....ie the people standing in the boat fall forward a little....

I went out sat about 2 miles at 3500...smooth as a whistle....just hummed along...sweet... I thought..."its nice to have the rebuilt LU on"... then while putzing around..the miss showed up.. and it missed often up to 2500 rpm/..... it has never shut me off... and the motor starts very easily, even ay 20 degrees!!...

so what shoud I concentrate on...water in the tank? or carb rebuilds< or Electrical checks???

thanks

bob

 

[racerone]

Run with a timing light hooked up.-----One cylinder at a time.----Lay the light so you can observe ignition behaviour when the " miss " happens.

 

[sutor623]

Man I am sorry to hear this Bob!!! Fresh lower unit and more issues to surface............ It certainly would be great to have a test prop so that you could hook a DVA to your power pack leads and run the motor at the RPM where the issues is to see if it is electrical. Have you checked timing at higher rpms?

 

[F_R]

The absolute LAST thing I would suspect would be the fuel or carburetors. Other than that, it might be electrical. But my money is on the lower unit. Clutch dog and forward gear to be specific. How do you know you didn't buy one with the same problem as yours? On the other hand, you say it was a rebuilt unit. So, who knows. Hard to diagnose from a distance.

 

[bob johnson]

I rebuilt the lower unit myself as a spare a few years ago...and then last year traded it to the guy at the parts store-shop, for a long shaft midsection.... and a lower unit and cash... since I thought my LU was going.... I called him and he still had it, so I bought it back!!...it has nice gears and a new prop shaft... all new seals.... its clean and good!!

I am convinced now...my other LU may actually still be good... the miss was so abrupt...I went quickly to . GEARCASE!!!....but in retrospect...I am thinking bad gas or electrical..

its tough to get a buddy to go hunting during the winter out on the salt water...much less JUST to tag along and help troubleshoot!!!!!!!!!!.... the shop I use... they just shum work these days...its all prep for winter... then store, then prep for spring and unwrap... and maybe sell new motors here and there...he doesnt want to repair motors anymore!!! most of the other shops are closed for the winter... to run the timing light, you need someone to hold it!!!!!!!

that would be a good test..... if the light didn't miss a beat when the miss happened..it would have to be fuel related.......\



bob

 

[dingbat]

I had the exact same problem with my 200 HP when I bought it.

I swore it was the lower unit, nope. Rebuilt carbs, nope. Replaced a couple of coils that where suspect. Finally gave up and took it to the shop.

They put it on the dyno with a spark "tree" attached. Long story short, they replaced the flywheel. Problem solved

 

[bob johnson]

I had the exact same problem with my 200 HP when I bought it.

I swore it was the lower unit, nope. Rebuilt carbs, nope. Replaced a couple of coils that where suspect. Finally gave up and took it to the shop.

They put it on the dyno with a spark "tree" attached. Long story short, they replaced the flywheel. Problem solved

well...this motor and yours have totally different flywheels....so my fingers are crossed...IT ISNT the flywheel!!!

I have a ton of spare parts...so I can throw a bunch of electrical parts at it...if need be

bob

 

[F_R]

It would be hard to convince you because your mind is made up, but a hard jolt that shakes the whole boat like you hit something is the classic symptom of a clutch dog & gear. Outboard mechanics that do this stuff for a living hear the same old story over and over again. Sorry 'bout that. Let us know what you find so we'll all know.

 

[Frank Acampora]

Bob: Don't know your engine exactly but I have worked on a few OMC so here are a couple of hints. They are worth what you paid for them though.

If the miss is sporadic and yet strong enough to lurch the hull, then it is not a misfire on one cylinder. If your engine has VRO there may be an electrical circuit to stop ignition or slow it in the event of oil failure. If an intermittent short here the oil alarm may not sound Again, ignition may have a safety to retard timing and again, a short might cause the problem. You might even have a salt short within the ignition switch.

If it were my engine I would get a manual with complete wiring diagrams and inspect ALL ignition wiring including the cable up to and including the ignition switch

 

[bob johnson]

It would be hard to convince you because your mind is made up, but a hard jolt that shakes the whole boat like you hit something is the classic symptom of a clutch dog & gear. Outboard mechanics that do this stuff for a living hear the same old story over and over again. Sorry 'bout that. Let us know what you find so we'll all know.

well this weekend, ill tear down the first LU... and if there isn't a broken gear...I don't have to open up the rebuilt unit...
and Ill concentrate on the electrical side... if the main harness shorted.... would the motor restart itself?... is the stop circuit shorted....could it re start itself in a half second under speed???

I had a short when I first got this motor and harness... and it was a nightmare...eventually in the harness under the floor, I cut open the factory sheathing and found a broken shorted wire!!!!!!!! and that killed the motor....but it would not restart until enough "contact" was made on the broken wire....twice I got back in eventually..

bob

 

[F_R]

You are not looking for a broken gear. You are looking for worn faces where the clutch dog engages the forward gear. They must be absolutely flat and not chipped or rounded over. You would be surprised to learn how little it takes to make it jump.

 

[Faztbullet]

Hey Bob...does it do it at high RPM? When it misses is there a "Knock"? Run the engine till it shows up and hold it there for several minutes then turn off key don't reduce throttle just turn it off.Pull plugs and inspect for water dropplets or steam cleaned plug. If so the glue line is leaking in block if not swap the pack and eye.

 

[bob johnson]

Hey Bob...does it do it at high RPM? When it misses is there a "Knock"? Run the engine till it shows up and hold it there for several minutes then turn off key don't reduce throttle just turn it off.Pull plugs and inspect for water dropplets or steam cleaned plug. If so the glue line is leaking in block if not swap the pack and eye.

I never really tried to diagnose it on the water...we are on the way to a place and time is important... with the new LU on I have only made one trip so far and the morning run out was 3500 rpms for 15 minutes and then we slowed and set decoys..... the miss didn't show up till later when we moved around a little and it was at intermittent rpms if I remember....I never took it up past 3000 the rest of the day .... if I remember right, I was running 2500 or less ...actually when I replaced the LU I removed the plugs and they were pretty oily and dark.... I cleaned them up and reinstalled...

ill try that test next time out...shut off under power after a minute of issues...pull the plugs.

BOB

 

[sutor623]

You could always hook up a DVA meter to the pack leads in the driveway once the motor gets good and warm. Sometimes a small drop in DVA will be apparent at idle that is undetectable to the naked eye/ear.

 

[bob johnson]

so I took a short video coming in from a hunt this past Saturday......it was blowing 20 mph... and even though we were going with the wind, I didn't want to stop the motor and do the test that Faztbullet suggested in the dark in the wind!!... but I did film this segment... the motor didn't skip a beat on the trip out (20 minutes)...

.View My Video

bob

 

[sutor623]

I think you are getting water into the combustion chamber. BUT, I have had a trigger failure on an old mercury that displayed similar symptoms. It would fire a cylinder multiple times per revolution, and sometimes the wrong cylinder. Anyway could you get a timing light on it and index the flywheel for your next trip out? This will isolate which cylinder (if any) is acting up.

Hopefully next time out you can perform a high speed shutdown like Fazt suggested.

 

[bob johnson]

I wish there was a place you could dispose of gas and I could dry out my tanks and start with clean known fresh fuel... and give it another run....but I don't know of anylace that will take gasoline!!

bob

 

[F_R]

Nah, that is not a clutch dog.

 

[oldboat1]

Albany. Lot's of gas storage there.hwell:

Might try a heavy dose of drigas, and run out what you have. Maybe some Techron, or similar too. Should clear out any condensation, anyway.

 

[bob johnson]

I pout a bottle of dry gas in each tank( 9 gallons tanks) two trips ago....I didn't use that much gas though... at lower speeds the miss is more dramatic....and the boat reacts more ... to motion than it does at 3000 rpm!!!