Johnson LT39

Outboard Related Only
Posts: 2
Joined: Mon Jun 25, 2018 10:27 pm

Johnson LT39

Postby biagidm » Wed Aug 08, 2018 10:25 pm

Hi All,

Got a few questions on my LT39 (s/n 337653)

Here is what currently has been done:
- Bright and strong spark after coil checkout, points cleaned and set, and replacement of plugs, high tension leads, and condenser
- Compression after 4 pulls is as follows: 65psi on the top cylinder, and 63psi on the bottom cylinder. Was not able to find a compression range in the manuals to confirm if this was an acceptable value.
- Carb removed and was squeaky clean. Unit was shutdown using the fuel shutoff valve to prevent varnish during long term storage.
- New carb gaskets made, float checked for operation, new leather primer seals installed per instructions from Lloyd Lautner ensuring that the smooth side of the leather seals were in the proper orientation and the brass washers were also in the proper orientation. Brass sleeve required to be remove via a 1/2 tap per the manual.
- Check valve and screen were the only items on the carb that could not be removed. The aluminum screw head of the check valve was very unhappy with the steel screwdriver being used. I stopped before too much damage was done but was not able to break it loose from the carb body even with valve grinding compound on the screwdriver head and enunciated French language that accompanied the process.
- Tank and all fuel lines cleaned with high and low speed needle valves set per the manual.
- John Deere corn head grease in the lower unit.
- 16:1 mixture using straight gas (no ethanol mix) and marine synthetic 2-stroke oil.

Unit runs as smooth as a sewing machine, however, it take approximately 20 pulls before one of the cylinders will fire. Primer is depressed 4-5 times on every 2-3 pulls until started. After one of the cylinders fire, then it take an additional 2-3 pulls before the motor will stay running.

Water pump appears to be functioning fine, however, I was not able to find where the water discharge is at in the manual. I am pumping water out of a weep hole on an elbow at the top of the lower unit that is piped to the powerhead, and also spitting out water at 2 holes at the drivershaft casing near the quadrant. Where should the water discharge be on this motor? Motor did not appear to be running hot as the powerhead felt fairly cool with the warmest part of the motor being the driveshaft casing below the 2 weep holes that were spitting out water.

Biggest concern is the hard starting. The brass sleeve was reinstalled after removal and cleaning, and as stated previously, the brass sleeve had to be removed with a 1/2 tap per the manual. I am questioning if scoring of the sleeve from the tap could be causing air leakage, and therefore, and inability to prime. The other item is the check valve and screen that failed to become dislodged despite some "spirited" conversation.

Has anyone experienced this before? The brass sleeve and the check valve/screen removal are the only items that I can think of from my review of the manuals that would cause this issue.

Thank you kindly for your efforts and assistance!

Kind Regards,

User avatar
Posts: 3254
Joined: Mon Mar 09, 2015 9:34 pm

Re: Johnson LT39

Postby Buccaneer » Thu Aug 09, 2018 8:54 am

It seems to me, that on my LT10, TD's, HD's, etc., with the
same carb set-up, that you can feel and hear
if the primer is working, if the low speed
needle is opened far enough. If it's closed all
the way, no primer fuel can get to the engine.
Not sure where your low speed carb needle is set, but it seems
like mine end up 1/2 to 3/4 turns open after

Posts: 2
Joined: Mon Jun 25, 2018 10:27 pm

Re: Johnson LT39

Postby biagidm » Thu Aug 09, 2018 9:43 pm

Thanks for your comment Buccaneer! Per the manual, the slow speed needle was closed, and then set at 3/4 off of the fully seated position. The unit idled really well after starting so that led me to believe the slow speed needle was in the optimal position. I did adjust it while at idle, but the best position was at 3/4 turn from fully closed.


Lloyd Lautner
Posts: 28
Joined: Sun May 07, 2017 4:30 pm

Re: Johnson LT39

Postby Lloyd Lautner » Fri Aug 24, 2018 8:08 pm

Don't worry about the tap scoring in the brass sleeve. 65 and 63 PSI is not great but should run OK but with less than ideal slow idle speed. 70 -75 PSI is ideal. Sounds like the one way valve and or it's screen may be your problem. Or the line up to the idle mixture orifice may be plugged. Watch the small hole on the front of the crankcase while pushing down on the primer. You should see fuel spray out of the hole when you push the primer. If not, get that one way valve out and clean it and the line. Impact driver or large blade screwdriver should get it off. More good info at or call me and I will walk you through it. If the spray is good when you push the primer, then you have some other problem like compression or ignition.

Return to “Ask A Member”

Who is online

Users browsing this forum: OLCAH, outboardnut and 10 guests