68' Johnson 9.5 Outboard weird RPM issue.

[Shawn244]

I have a 1968 Johnson 9.5 outboard that i've been working on. Done a bunch of cleanup on it to get it back on the water including the following for future reference:

Carb clean, new fuel pump, new fuel lines, new Impeller, Gearcase oil, new points, new condensers, cleaned and filed stator points of contact, new throttle link arm, new shifter link, cleaned plugs and tested spark (good spark) .... theres probably more but i can't think of it all off hand

Note: I have not tested compression, i don't have a reader but i've seafoamed to clean up as much carbon as possible to ensure i'm not losing compression due to that. The motor ran better in a barrel at home than on the water under load.

So, to get to the issue,,,, Motor starts up quick and easy, first or second pull and idles well (i noticed it idles with or without the choke) when I put it into gear it will allow me to putt along just fine at low speeds, when i give it too much throttle it seems to spike the RPMS and then completely lose RPM before choking itself out and dying. Generally speaking i've been able to start it back up right away after. It seems to run the same with or without the hood on, i don't suspect a exhaust leak but it's on my list for diagnostic.

The butterfly plate in the carb opens up at high speeds, as well as the high speed fuel jet seems to be pretty clear (I may check it again just out of crossing all my possibilities off)

Anyone have any suggestions as to what else I could start looking at or back-tracking towards if need be.

Thanks in advance! Tight lines and safe boating!

 

[boobie]

Do a cylinder drop test on it.

 

[racerone]

Does spark jump a gap of 5/16" on an open air spark test device ?----Is front mount on engine block in good repair.-----Plug wires are known to crack where the come out of the magneto plate.

 

[F_R]

"Pretty clear" doesn't get it. It must be absolutely, positively squeaky CLEAN. But don't be jamming wires and drills and such through it.

Will it keep running if you pump the squeezer bulb when it starts to cut out?

 

[tomhath]

When you cleaned the carb, did you take it completely apart, including the welch plugs and ensure the low speed circuit is clear? Falling on it's face when you open the throttle can be sign it isn't getting fuel through those holes.

 

[Shawn244]

Thank you for the responses, as for the carb I had it all apart and cleaned with an air compressor, carb cleaner, and wires. Other than not being physically able to see inside jets it was all as clear as i could get it. (I'm human tho I wont claim to be perfect, I will still likely give it a second pass for good measure and appreciate the thoughts on it greatly!)

The primer bulb stays firm through my troubleshooting and priming it doesn't seem to affect the run condition so thats why I've been leaning more towards the cylinders or spark. (which should be an easy fix if its spark as it's all new or tested components)

Front mount and wires are in good condition, especially for its age and theres no damage or corrosion on the wires,

As for the plugs, I re-tested tonight and started increasing gap to which I was able to get one to fail much before the other (i don't have the measurement as to which it failed, just that they were both set at the same gap) , so I have replaced that plug and am seeing better spark now, i'll cry if this is seriously all it was.... (I'll have to wait until the morning to test it again either on the water or in a bin)

Kinda frustrated i didn't catch that earlier as prior to initial testing in tubs or on the water it had spark on both and looked alright to me but i wasn't putting a lot of focus on it.

 

[Crosbyman]

odd… my last 9.5 was acting the same way I've revived 4-5 of these 9.5's all came out OK with around 65psi but this last one drove me crazy ..I ended with no cure late sept. before I put it away :blue:

did you redo the plug wires ?? did you inspect the coils (hidden cracks maybe) wires do break internally see pict.

these 2 wires were both broken in the bend

if you find a cure could you send me a PM in case I loose track of your post :encouragement:

 

[oldboat1]

Does spark jump a gap of 5/16" on an open air spark test device ?

Tester like this:

The object is to verify/measure the strength of the magneto output.

 

[Shawn244]

The object is to verify/measure the strength of the magneto output.

I've tested and inspected the magnetos (had them fully out and used a multimeter because that's the method i had known before this issue) as well as filed the contacts and put a hair of dielectric grease on the pins where they plug in. I have dealt with fouled stators before and based on past experiences I'm more or less leaning against them being the issue at this time.

I am however putting new plugs in today, by inspecting them a bit closer and trying other plugs in the boots i believe that I may have had one plug running much weaker than the other. If it were just running primarily on one cylinder due to a plug failing I can certainly see this being my issue. I had tested the plugs a few weeks ago when i was trying to address no-spark and the visual of them giving spark was my test but I didn't really put too much focus on them because it seemed like they were going and there was other issues at hand rather than the plugs.

I will update today once i've gotten new plugs in and can test in a barrel. Fingers crossed on a super simple fix!

 

[Shawn244]

odd… my last 9.5 was acting the same way I've revived 4-5 of these 9.5's all came out OK with around 65psi but this last one drove me crazy ..I ended with no cure late sept. before I put it away :blue:

did you redo the plug wires ?? did you inspect the coils (hidden cracks maybe) wires do break internally see pict.

these 2 wires were both broken in the bend

if you find a cure could you send me a PM in case I loose track of your post :encouragement:

I have a buddy that runs a outboard repair shop, one thing he cautioned me of was a seal between the motor and leg that can go and cause this very same issue while chatting with him over the phone last night. He also cautioned of anything less than 80 psi on these motors specifically to just walk away (but i'm stubborn and don't like the idea of walking away so i created this post for some brainstorming)

I sincerely hope that my issue here is that I neglected giving the plugs enough attention lol

 

[racerone]

But the sparkplug only provides a gap for the voltage coming from the coil.---------------Answer this ? , Does spark jump a gap of 5/16" with a snap you can hear , yes or no ?------Or run with a timing light hooked up to # 1 and see how spark behaves.---Repeat on #2 cylinder.---Or bring the motor over as I have 8 or 10 of these for parts.----Be an easy fix.

 

[oldboat1]

Maybe the problem here is terminology. "Magneto" refers to the ignition system, including but not limited to the coils. If you get a strong 5/16" spark with an open air adjustable tester, you can assume that the ignition is operating properly. The only caveat would be a situation where sparking stops, usually while underway. The cause is often overheating of ignition parts (like coils), and the timing light test is used to determine whether spark is "dropping out" at some point. Troubleshooting would follow.

Even if you've found that (say) fouled plugs are the likely problem, you would still be well advised to do the magneto testing described.

 

[racerone]

A stuck open thermostat ( very common ) can be a reason for a cold looking sparkplug too.----A simple process needs to be followed to find the issue with this motor.------Compression values vary quite a bit depending on gauge used and operator " pull " on the recoil.-----It should NOT idle with choke pulled out.-----I believe that should be looked into.

 

[Crosbyman]

''

I have a buddy that runs a outboard repair shop, one thing he cautioned me of was a seal between the motor and leg that can go and cause this very same issue while chatting with him over the phone last night. He also cautioned of anything less than 80 psi on these motors specifically to just walk away (but i'm stubborn and don't like the idea of walking away so i created this post for some brainstorming) ​

''

I guess opinions differ… I am not a outboard mechanic but I have enjoyed the oldies hobby for several years now and my prized turtle was a solid lock up cleared with TLC soaking wood peg and a hammer. I have fixed up several of these E&J turtles none of which exceeded 80 psi . It seems that it is an accepted fact that these 9.5 have low compression numbers and work fine with 65-70 (Leroy's mentions it in his MQ write up) I would never walk away from one with 65 psi

From Leroy's rambling on MQ's

Compression :

Compression on these motors may seem lower than some of the others. Displacement of the these 9.5 hp motors is 15.2 Cubic Inches with a Wide Open Throttle of 4500 RPMs. Where the later 9.9/15 HP motors utilized 13.2 CI at 5000/6000 RPM, where higher RPM increases the HP. A normal compression reading of 65# to 75# appears to be fine for this motor. ​

.

 

[Shawn244]

So a bit of an update, was misfiring on the top cylinder, the points were off by just a hair, adjusted and tested much stronger but still dying off at higher speeds. During my last test I WAS able to get it to keep running by pumping the primer bulb and I believe that the issue may be due to the fuel pump I installed. So I've tried rebuilding the original fuel pump with new membranes gaskets and springs. The housing was a bit different on the new pump and I was concerned if it would react the same, could be possible right?

I pulled the thermostat yesterday and tested in the house in some boiling water, it's working as it should.

I understand magneto, re-read and yes i was talking without explaining my thoughts lol,,, the only part that I didn't replace was the stator coils, thats why my thoughts were mostly surrounding that.

I will try to barrel test today if it warms up a bit more (-8 C here right now)

 

[Shawn244]

I'm going to try to re-explain the issue at hand with a bit more detail in case this fuel pump doesn't do the trick for me:

Upon running it starts up quick first or second pull
It quiets up quite a bit as soon as I remove the choke and runs with very little vibration (I could put my coffee on the cowl)
Idles okay but unless I hold the handle it wants to drop throttle and die
Shift into forward and runs okay at low speed, still very little vibration or variation in RPMS (this comes into play in the next point)
As I start to increase throttle, about half way, the RPMS will spike huge without me adding throttle and then die right off right away. If I drop to low throttle on the control arm I am able to save it from dying, but if I don't adjust it will die.

As of a couple days ago I wasn't able to save it or stabilize the RPMS by pumping the bulb on the tank, however yesterday I have now gotten it to the point where this will save it now! (happy improvement, i feel like this was a multi-issue run condition)

Hope this helps!

 

[racerone]

Remember that this magneto was in production for nearly 40 years.---Installed on everything from 1-1/2 HP to 40 HP-----It is a very well engineered unit.----It is in fact 2 independent systems and motor can run on one cylinder.-----I have seen countless coils with a hole burned through the coil where it is near the magneto plate.-----It will show spark on the plug laying against the block, but will not fire the plug when installed in the cylinder.-----Perhaps your " online purchased ? " fuel pump was a dud.-----Simple testing will find the fault with your motor.

 

[tomhath]

As I start to increase throttle, about half way, the RPMS will spike huge without me adding throttle and then die right off right away. If I drop to low throttle on the control arm I am able to save it from dying, but if I don't adjust it will die.

Sounds like its starving for fuel, maybe the pump, maybe a restriction somewhere. RPMs will increase when it runs lean just before it dies. If you take the fuel line off the carb and spin the motor you should get spurts of gas coming from the pump.

 

[Crosbyman]

back to basics…

as per racerone comment coils can go bad …. so just to clarify… did you or not remove & inspect coils for burn marks, airline cracks etc..?

did you or not …. replace 7mm plug wires with metallic core wires ?

did you adj. timing using the "tool" or the V.O.M. method

did you clean the carb under the dime size plugs ??

btw no "stator" on these 9.5 just standard magneto coils


you mention replacing pump parts then mention a new pump... did you do a blow test on either ??
air flow in to out no air out to in these pumps are tricky to rebuild and the air test is mandatory !

 

[oldboat1]

Also in the way of basics, you don't want to rev the motor while running in a barrel. I wonder if you have enough water. If the prop is uncovered/partially uncovered, you will get the revs -- possibly stalling if the prop bites again. I use a large plastic trash barrel for testing, with the water level half way up the shaft -- and leave the hose running while testing. Additionally, exhaust can rise up and stall the motor. You can run with a box fan to blow away exhaust, or make sure the powerhead isn't directly over the rising exhaust. I use a stand for testing, and move the "barrel" underneath the leg, then fill and test.

Not exactly a pro setup, but works for my purposes.

(And---measure the spark with an adjustable tester!)