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QD16 Issues diagnosing a miss??

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seahorse10

New member
I have a 1955 Johnson Seahorse 10hp (QD16) and this is my first boat and first motor and I am having trouble with an intermittent miss. Last spring I rebuilt carbs and the entire ignition system:
2 new coils, new points, new condensers, new wires, new connections to spark plugs and new Champion spark plugs (as recommended). Everything is gapped as well as I can make it with my knowledge – points at .020, coils matched to the plate with a straight edge, etc.

I had it running pretty well last year (though I was only able to use the boat a few weekends) but near the end of the summer I was getting an erratic miss every once in a while under ¾ to WOT throttle while in gear.

When I started it up this year I initially thought that I was good to go as it started on the second pull…then I realized it wasn’t cooling properly. Since we had an extremely cold winter I erred on the side of caution and replaced the impeller, impeller plate, & o-ring on the shaft. I put it back together and we were back in business...so I thought.

I started getting a miss the miss on occasion, so I started adjusting slow and high needles to see if I could get it to settle down. It seemed to smooth out and ran well in idle and when in gear so I figured I just needed to tweak my fuel mixtures and keep an eye on things. Then I came back the next day and the miss was much worse and was happening in idle but was very bad when in gear. At this point I took off the flywheel to inspect the ignition set up. I immediately noticed that both coil ground wires were rubbing on the center of the flywheel and had caused a short as the wire was rubbed down to copper. At this point I was rather frustrated, I pulled out a meter and tested continuity for the coils – primary and secondary seem to be okay so I used RTV silicone to cover the exposed wire and to hold the ground wires in place closer to the coil so that it would not get caught by the fly wheel again. I reinstalled and reset all gaps.

Seems to now run fine, at times for a minute or so, and not at other times. I will start the motor and get only a few light misses and I will shut it down and restart and then it sounds like one cylinder is dead and it is missing heavily and constantly. I have two new coils on order but I wanted to reach out to all of you to see if you have any other ideas – if you don’t think it is the coils then please let me know and I will not install them and save (or invest) the money somewhere else if need be.

I appreciate any and all help.

Thanks,
Chris
 
Run with a timing light to see which coil might be causing the issue.---Then again it could be jumping out of gear too.
 
the decision almost always comes down to fuel or fire after a compression check is made....a 40 buck inductive timing light is a good investment for anyone that takes care and trouble shoots boat engine and lawnmowers etc...we see a hell of a lot of money wasted by people that replace parts as a diagnostic tool....everything from stators (300 bucks) to power packs(100+) or you name it....the timing light and a good multimeter(under 100) is the way to go....of course the compression gauge is a must...
 
Thank you both for your responses. Here is where I show my inexperience - but how do I tell which coil is bad when testing with a timing light? What would I be looking for that would distinguish between the coil firing on the top cylinder vs the bottom cylinder being good or bad?

Chris
 
Well, each cylinder has a coil / condenser / points and a sparkplug.---So hook the timing light to top cylinder and oserve the light.--Then try the bottom.
 
racerone said:
Well, each cylinder has a coil / condenser / points and a sparkplug.---So hook the timing light to top cylinder and oserve the light.--Then try the bottom.
Click to expand...

Wow...that was something that was very obvious and I should have put together myself. Thanks!

I'll report back with what I found out when I get to work on it this weekend.
 
Okay so yesterday I had some more time to work on the motor and dial in the timing using a timing fixture and set the coils using a ring and it fired right up and sat at an idle nicely for about a minute then gave one little spit (all of this while in neutral). I then put it into gear and after a few seconds it was acting like it was before...only I think I may have misdiagnosed the issue as a miss. After doing some more reading it sounds like it may be jumping gear? While in gear the motor feels like it hits a log. It then gets worse and is repetitively "popping" and at times sounds metallic like an engine knock in an automobile. Does this sound like a gearing issue or could it still be a "miss"? I only doubt the gearing issue because I got one little spit while in neutral, no gears right so why would it happen there as well?

I wanted to reach out to all of you before I start putting more money and time into the motor - also I have never had a lower unit apart before and am not really sure what I should be looking for and how to diagnose what does need replaced once I get in there.

As always any help is much appreciated.
 
kimcrwbr1 said:
http://www.leeroysramblings.com/johnson_QD.htm
maybe you can find somthing here?
Click to expand...

Thank you for your response. I have actually been utilizing his site as a reference for a while - it's actually how I found this forum ;)

I was planning on using his instructions as a basic guideline to do the physical work but wanted to consult all of you prior to opening up the lower unit, if you thought it was something still with ignition and not the lower unit I was going to try and rule out any ignition issues prior to starting in on another part of the motor.
 
Ok so I had the boat up and running last weekend and it seemed to be working well. Compression was even on both cylinders but was at 60lbs..that seems low but I have had a hard time finding what compression should be, does anyone know? I got home and pulled the plugs and the top cylinder is burning perfect but the bottom was oil covered and wet. Any thoughts? No longer missing once warmed up bit did miss for a few seconds upon start up. Could I be running on just one cylinder. Top speed was about 13mph in a 14ft deep V fishing boat. Thanks everyone! At least I was out fishing :)
 
seahorse10 said:
Ok so I had the boat up and running last weekend and it seemed to be working well. Compression was even on both cylinders but was at 60lbs..that seems low but I have had a hard time finding what compression should be, does anyone know? I got home and pulled the plugs and the top cylinder is burning perfect but the bottom was oil covered and wet. Any thoughts? No longer missing once warmed up bit did miss for a few seconds upon start up. Could I be running on just one cylinder. Top speed was about 13mph in a 14ft deep V fishing boat. Thanks everyone! At least I was out fishing :)
Click to expand...

What did you do to get it running?
Bill
 
I just recently got a QD16 as well and despite assurance from the previous owner it has been giving me some grief. It starts after just a couple of pulls but takes forever to get to the point where I can shut the choke off and then what seems to be WOT is at some odd halfway point on the range of the throttle. It also will do the sort of clunk-and-miss thing for a while and generally only in neutral.
The other issue is putting it into gear. I move the lever into the proper position but often times in doesn't always engage the prop right away and does so with a clunk. If I turn the handle all the way back to SHIFT to shift it it will stall so I move it a bit off and then it will go.

I haven't replaced anything yet and was hoping to give it a once over myself before taking it to the mechanic. It certainly needs some love and I'm sensing that it's worth the effort based on what I've read here so far.
Any warnings or obvious red flags before I break out the wrenches?

thanks

Ben
 
Last edited:
Sorry about that. I'll put it where it belongs. Thanks for the heads up. I had read up on the aforementioned site (and anywhere else I could find on the web) but didn't find the answers I was looking for.

Ben
 
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