New Old Stock carb

[robotmark]

Hi crew! Today I got a “new” old stock carburetor for my ’71 40 hp Johnson. It was in its original box and very clean, but it’s still be sitting around for 40+ years. Are there any recommended steps before putting on my engine and firing it up? Thanks!

[aquasonic]

The original cork floats were coated with shellac which is not very resistant to ethanol. The newer floats are made of ethanol resistant plastic.

The original black main gasket has been updated to a tan nitrile gasket in the OMC kits. Not sure about the ethanol resistance comparison. Sometimes the black gaskets are degraded and cracking.

It seems like the nozzle gasket is now made out of nitrile. The original ones tended to crumble.

If you plan to use the motor on a regular basis, a new OMC carburetor kit would be a good upgrade. Avoid the cheap aftermarket kits they have a host of problems.

[frankr]

Yeah, go back old enough and they did have shellac coated cork floats.  But 1971 should have what looks like shellac coated floats but are alcohol resistant.

[robotmark]

It’s interesting. I’ve had good luck with the cork floats, as opposed to the black plastic ones that come in the new kits. The cork ones I have haven’t really degraded and seem to fit a little better. Now that I’ve got two carbs, maybe I can do an A / B test to see what kinds of differences I see. After digging around it seems that the carb assembly was from 1983.

[robotmark]

OK – so I cleaned the carb, installed it, and seated the needles at the recommended amount of turns. I took it out on the reservoir today and it fired up immediately. However, as you can see in the video I linked, at WOT I only went about 6 mph (on a good day I can hit 28 mph with this thing). Any thoughts on where I should look first to figure out why I’m bogged down at WOT?

https://youtube.com/shorts/yOpxjmY5EnM

[aquasonic]

I can’t watch the video because it’s “private” and the viewer needs to sign in.

Anyway, did you adjust the high and low speed needles on the boat? Are you getting spark to both cylinders? Are you sure that the NOS carburetor is correct for your motor?

[robotmark]

Try this link (it hadn’t finished publishing yet) https://www.youtube.com/shorts/yOpxjmY5EnM

So yes, I adjusted both needles on the engine while under power. It was idling beautifully and when I adjusted the high speed it sounded like it was going fast but the boat was going relatively slow. I can run by spark plug tester today, but I’m pretty sure they were both firing. And finally, the NOS carb is identical to the one that was previously on there (OMC model 384919). 

 

Thanks!

[Buccaneer]

If the cables are adjusted to let the throttle open all the way,
then back to the basics.

Prepare to be boarded!

[bob-d]

Double check the plugs to see if it’s firing. Those big twins can idle very nicely on one cylinder. Had same problem this summer, one brand new Champion was bad.

Bob D

[aquasonic]

I watched the video, and the motor does not sound like it’s getting up to the proper RPM. It may well be running on one cylinder as bob-d mentioned. The symptoms fit.

[Author]

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