Johnson HD-20 Won’t start

[marvk]

quote jsonova99:

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.

I have a HA-15 with the same carb setup. Yes, you should be able to start and run with the high speed needle completely closed. To start, low speed should be 3/4 to 1turn open. It should start at the low to mid spark advance setting. Mid to high setting you will need to start opening the high speed needle. My high speed setting runs best about 1/2 open. After it’s running, low speed setting is about 3/4 open. Remember also, the low speed adjusts the air flow, not fuel flow. Turning it in, will richen the mixture.

[garry-in-michigan]

I believe the low speed needle valve adjusts the fuel. If you screw it all the way in, the primal won’t work.

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[marvk]

Hmmm…. Now I’m confused. 😕 I was under the assumption that because the the fuel line and the low speed needle were on opposite sides of the rotary intake port, that the fuel doesn’t actually flow through the needle itself like in later carbs, that the low speed needle controlled the air flow.

Studying the cutaway illustrations more closely, I think I see how it works now.

Wouldn’t be the first time I was wrong. 😉

[aquasonic]

Thanks to Garry for posting this service information. I think he posts this a couple of times a year, and every time it seems I learn something new. Reading through this, you can get a good sense of just how important it is to have a properly functioning check valve, otherwise the low speed circuit won’t work well at all.

These check valves have a tendency to get gummed up and stuck from long periods of non-use. I’ve had good results freeing them by soaking in acetone overnight, then gently tapping them on the bench, blow out with compressed air, and repeat as necessary. An ultrasound would be helpful with this also.

[garry-in-michigan]

A good functioning primer can develop enough pressure to frequently unseat those sticky valves. But then they may remain open, starving the idle circuit for fuel. The 1934-’35 Evinrude Sportsman had the same problem. The check valve is necessarily at a low point in the fuel circuit. So it has a high likelihood of retaining fuel. Removing it to drain the line sometimes results in the sealing disk being lost. I know of several cheap trade in motors that would not idle that were "cured" by installing this (then) five cent part.
. . . 😀

[jsonova99]

That’s a great reference, I need to go through it in some more detail. I tried starting the motor with the high speed needle shut and the low speed open 3/4 turn the magneto lever set in the start position. It will start, but it immediately races up to high RPM, even with just the low speed needle. It then settles down, and I can get it to run with the magneto lever somewhat below the start position and the low speed needle opened to about 1 full turn.

I need to play with it more, but it’s doing the same thing I saw this weekend where it would race up to high speed right after starting and it doesn’t immediately respond to adjusting the lever down.

Not sure if I mentioned it in the beginning, but I’m running J6C spark plugs in it gapped to 30 mil.

[jsonova99]

Replaced the carb to block gasket, no change.

The motor runs pretty well at high speed, but basically doesn’t want to run with the magneto set below the start setting. Anything below that and it dies out.

Runs fine at high speed, tuned the high speed needle to about 1/2 turn to peak up the revs. Seems like a low speed issue only. One interesting thing I noticed was that I could start it with the high speed needle closed, then start backing out the low speed needle and the revs were coming up pretty high, well into a region that should have required the high speed portion of the carb. It also starts easier if I set the magneto to full speed rather than start. I’m wondering if the low speed venturi is damaged from somebody screwing in the needle too far as mentioned in the manual above. Don’t know what else it could be at this point unless there could be something with the ignition. Still some hesitation in the throttle sometimes, I’m sure it’s related to my low speed issue.

I winterized it after playing with it today, I need a break from it, I need to source a few small parts for it to complete it, but otherwise I’m going to move onto something else until spring.

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