RD runs rich

[ADAM GIBB]

I am supposed to be working on the model A Johnson in my project thread but got distracted.

A few weeks ago I was cleaning up the shop and looked at a cowl and though "hmm, that’s a bit too nice to repaint." So what does any responsible outboarder do when they have a nice original cowl, but no motor…..dig through the parts bins. After rounding up the appropriate parts, I assembled this RD 17.

The Powerhead was assembled from good used parts, bores honed and new rings. All seals replaced

Today I put it in the tank for a run. It starts and runs well. It seems to run rich. It was running best with the low speed open 1-1/4 turns and the high speed was only open 3/8 to 1/2 a turn. It seems to me that most of my other motor take about 3/4 to 1 turn out on the high speed. The needles on this one are good. After about 15 minutes of running. The plugs came out very wet. It also seems sensitive to throttling up, and sometimes has to be leaned out and then richened or it will drop a cylinder.

I was testing in a cold garage (5 Celsius) and the water was also quite cold, but what puzzle me is how much fuel it is getting with the high speed almost closed. The carb does not overflow, and it pumps up and holds pressure against the tank primer.

What would you check first?

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Attachments:

[William Jatzek]

Did you have a fan blowing away the exhaust smoke from the engine when it was running? Or was it running in a heavy layer of exhaust? I just had a nice discussion on another topic here. Title RDE-18 power head to exhaust plate/ gasket. We discussed changes also made to the 1955 25 HP. regarding enlarging a hole in engine pan to 2” hole. Check it out. Maybe your engine just needs this hole enlarged and a fan blowing away the oil fumes as it runs. Bill,

[chris-p]

What plugs are you running? I personally find many of my RDS end up around 1/2 turn out from seated on the high speed needle.

Obviously spark is a bright blue and will jump a good gap?

[garry-in-michigan]

Those engines do not have a 302984 high speed jet gasket like the smaller motors because it was thought the amount of fuel bypassing the adjustment orifice would not be enough to prevent a proper adjustment. If you are disturbed by having a less than ¾ of a turn for a proper adjustment, put in the gasket (even though the factory doesn’t think it necessary as long as the motor slows at the leaner setting). . . 😉

[frankr]

I consider somewhere around 1/2 turn open to be normal. That’s because of the very blunt end on the high speed needle. That’s the way it’s made, and it ain’t broke so it doesn’t need fixing.

[chinewalker]

Don’t worry about it until you can run it on a boat. Very hard to dial it in in a tank.

[fleetwin]

quote Chinewalker:

Don’t worry about it until you can run it on a boat. Very hard to dial it in in a tank.

good advice for sure

[ADAM GIBB]

Thanks everyone.
I tested the motor without the cowl, but it does have the modified air intake hole in the lower pan. I keep a pedestal type fan near the test tank to keep the exhaust away, both the motor and I enjoy the fresh air 🙂
I will set it aside for now and come back to it when the water softens up.

Adam

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