Johnson HD-20 Won’t start

[gjonz]

While you may have spark…have you checked the magnets to be sure they have a good, strong pull? If not they may need recharged. Spark may not be the only indicator they need charged.

You also might put a drill on the flywheel nut and turn it over until she fires and perhaps while adjusting the carb at the same time.

Greg.

[jsonova99]

How can I get the magnet recharged?

My other question would be a good explanation of the priming system. Does it only prime the low speed Venturi? If the seals are bad will it just leak or cause fuel flow issues? I know mine can pump fuel to the low speed venturi, but it does leak. I’m wondering if that could prevent a steady stream of fuel to the low speed venturi. I’m in the process of getting new leather seals for it now.

[jsonova99]

I’m trying to understand the check valve, if you suck on it air should pas thru which should be equivalent to fuel being pumped through it toward the low speed venturi, but if it allows flow in the reverse direction would you have a fuel delivery problem? Is there something inside of the passage? I’m pretty sure my passes air in both directions.

[jsonova99]

Sure enough when I checked the two check valves, the current one passed air in both directions and the new one only in one direction. Swapped in the spare and saw mild improvement. starts easier now (in that it catches on most pulls even though it stalls quickly), but still only runs for 3 or 4 seconds tops. I went through the carburetor in pretty good detail again and I can’t find anything that I missed, fuel delivery should be fine. Will check compression again and re-check the point and plug gaps.

[jsonova99]

It runs…. with a catch. I got it to run dry, and I got it to run in water with no prop so that I had cooling. starts right up, but with a propeller, it just can’t get going.

[jsonova99]

When it’s running, I notice that’s it’s a bit unstable, initially races up to high rpm with throttle seat in start position, then calms down a bit. If I accelerate it responds ok, but going the other way it wants to die out unless I start playing with high speed adjustment. Again, this is with no load on it. Runs with a lot of smoke, expected to an extent with the 16:1, but seems worse than some of the ones I watched on YouTube, since that’s the only comparison I have. Defitinetly doesn’t want to run at low rpm. My fear is that this is a power head issue, but I’m still not 100% convinced of that.

[jsonova99]

Just rechecked compression:

Top: 70 lbs
Bottom: 75 lbs

That should be pretty good for this motor from what I’ve seen

[kevinf]

Compression sounds ok. Is it delivering fuel through the low speed carb? Having to use the high speed needle as it decelerates sound like the low speed isn’t running properly.

[jsonova99]

As far as I can tell, once running, when the rpms settle down and it appears stable, it’s very sensitive to adjusting the low speed needle. I can hear the engine sucking air in at the low speed Venturi as well.

I replaced the low speed packing, but not sure if I did it right, is it just one small gasket?

I tried starting up dry again today after poking through the high speed jet with some fine wire, that was the only passage I had initially missed. Not sure why that would have done anything, based on the fact that the issue seems to be low speed related but I shot some carb cleaner up through the high speed access on the bottom and watched it shoot out of the jet so that passage is clear. I also verified fuel through here by adjusting the high speed needle and watching fuel drip out or stream out when opening the high speed needle. The carb itself seems to be fine at this point other than the leaky primer washers.

Anyway, it now starts on the first pull cold with both needles set at 3/4 of a turn out. I did notice though that this time once the carb filled and I had primed it, there was fuel dripping from the high speed jet. Other than the leaky primer, I’ve had no leaks.

Once running though it again wanted to race up to high rpm before settling down. I

Going back to the low speed, will these engines run with the high speed needle closed completely? Trying to think of a way to really isolate the low speed.

[jsonova99]

Got it running this afternoon in water. Similar behavior though, the throttle is hard to control, not very responsive to the throttle lever. Wants to rev up when started then settle some, moving the throttle lever produces a delayed reaction in the motor.

Not sure if this could be something related to the magneto or could it be something like a leaky gasket where the carb attaches to the block causing the air/fuel ratio to be unstable.

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