getting my Johnson MD-39 running again

[Hugh Davis]

Hello!

I am cleaning up my MD-39 and trying to get her running. Do you have a forum that is specific to the MD-39’s?

Luckily, the last time it ran was back in the early ’70’s so it has never been exposed to unleaded gas or ethanol. The cleaning process is going well and she has spark and compression.

I have several questions to ask, can you tell me the appropriate format to ask them? do I ask here or do I go to a specific location on AOMCI website?

thanks!

Hugh

[stanley]

Yes,ask here.

[Hugh Davis]

Thanks Stanley!!

There is what appears to be a freeze plug on the top side of the carb (looks like brass) How can I remove it to clean out the channel tube?

Is there a gasket for the top of the carb bowl? the top is held on by spring clip and I would think will slosh out gas when we eventually are out jumping waves on the lake.

what is factory setting for HS needle valve?

I plan on using leaded gas only in this engine, what octane is appropriate? Racing fuel is available here, should I use racing fuel?

what is proper compression on an engine of this age? If I don’t have to take the head apart, I won’t need a gasket that I probably will have to have made or have to replace rings if needed???( if I can find them!)

Water intake mechanism is befuddling me. I’m not sure how it works so I’m hesitant to take it apart, only to find irreparable parts. Does it need to be serviced? I won’t know it’s sucking up water until I start cranking in it and she starts sucking.

what weight oil should I put in the foot?

I found a MS-38 for sale, I am pondering purchase so I can have a source of parts but I don’t know if MS-38 and MD-39 parts are interchangeable. Are they?

If I can get her running, I think my OCD will kick in and I’ll want to paint and decal her for posterity and my son/future scion. Not sure where to look for that information.

Thank you in advance!!

Have a great weekend!

Hugh

 

[Mike M]

I would start by cleaning gas tank and carb.. don’t remove freeze.. set needle 3/4 turn and go from there..get a spark plug tester and see if it has spark. I wouldn’t tear it down yet

When she starts you will know right away if the water pump is working

use non ethanol gas  16:1 mix .. use John Deere corn head grease for lower unit

I bet after you clean the tank and carb and verify it has spark she will fire up.. good luck and post a picture.. this is only what I would do to start off..your at the right place for info

 

 

 

[Hugh Davis]

gas tank, carbs and lines cleaned in sonic vibratory spa.

she does have spark, have not verified strength/power/voltage of spark. I need to figure out what spark plug I need

I have a bunch of pics but the format is not the right one.

thanks Mike!

[Tubs]

First, if the MS -38 is complete, with a decent gas
tank, and has the spark plug cover at an affordable
price, you should grab it. It is way more desirable
than your motor. Just the spark plug cover, in good
condition, has more value than your motor complete.
Same for the gas tank. I have no experience with
the power head, however I would suggest you change
your approach to repair as needed rather than taking
something apart before you find a need to. I do have
some experience with the lower unit though from
having other models. A piston works off a cam on
the prop shaft. You should clean out any grease
remaining in the gear case and inspect the check
valves to insure they are clean and operate freely
before refilling. Hopefully your motor was put up
without any water remaining in the gear case.
Tubs

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

[opposedtwin]

No gasket on top of carb bowl. At 1.1 hp you won’t be doing any wave jumping. 🤣

 

The MD-38 and MD-39 are essentially the same motor. It’s the deluxe version with the cowling and the recoil starter. The MS-38 and MS-39 are essentially the same motor and lack the cowling and auto recoil but they have the horse shoe or “sausage” gas tank which is very unique.  I believe all 4 have the same powerhead, hp, etc.

I agree with the Boat House, if the MS-38 is complete and in decent shape it’s worth 150-350 depending on mechanical and cosmetic condition. Even if it’s a parts motor you should still buy it if the price is reasonable. Those parts are typically in higher demand than much other stuff.

Welcome aboard and have fun!
Scott

[Hugh Davis]

Thank you Mike, Boat House and opposed twin!!

it’s all back together and I can get spark at the plug gap but I can’t determine if its sparking at TDC, nor the power of the spark.

I am going to replace the spark plug wire as its rather brittle. but I don’t know if points, condenser and coils are functioning properly or need to be replaced. if they need to be replaced, do you know any sources of new, used or remanufactured parts for a 1939 MD-39? do you know what spark plug I should have in there? I have not been able to find that information

gas is flowing thru, as the spark plug is wet after cranking her over.

I’m not sure if the factory painted under the flywheel the black you see or that was somebodies work in the ’40’s or ’50’s. should I clean up the electronics and reconnect or am I at risk of breaking it rather than fixing it!

I just purchased the MD-38, but it will be days before it arrives(if it does!)

[Mike M]

Spark plug is a champion J8J

if you are seeing spark then your coil and condenser should be good..

 

[Hugh Davis]

thanks Mike!

We gapped the points to 20 thousandth, she’s running!!!!

the plug I got in there right now is an HO8A

[Author]

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