1975 Johnson 6hp (6RL75R) — idle timing off due to play in throttle shaft, need diagram of shaft/socket coupling

[meser300]

Hi folks,
I'm newbie in the Johnson motors and met the next problem:
Working through a full rebuild on this motor — carb rebuilt, fuel pump rebuilt, points gapped at .020, spark good on both cylinders. Motor starts and runs fine at FAST but won't hold a stable idle; throttle plate barely opens at SLOW/START positions.

Traced it to the armature plate not reaching its correct SLOW/START position — it reaches full advance fine (hits the mechanical stop at FAST), but on the low end there's roughly 1-1.5" of travel missing at the plate's edge.

Found two contributing sources of play in the throttle shaft (the vertical shaft connecting the tiller twist-grip's bevel gear down to the linkage that turns the armature plate):

• ~0.65mm gap in the keyway (shimmed this already)
• Additional radial play of the shaft inside its socket, independent of the key

With the plate held stationary, the shaft/linkage still has noticeable wobble in the socket — so the missing travel isn't in the plate itself, it's upstream in this shaft-to-socket joint.

I can't find any parts diagram anywhere (Crowley, marineengine, boats.net) that shows this shaft/socket assembly — it doesn't appear to be listed under Magneto, Carburetor, or Powerhead sections, possibly because it was never sold as a separate serviceable part.

Has anyone dealt with this specific joint before, or knows where to find an exploded diagram of it? Trying to figure out the correct fix — shimming the socket bore, or if there's a proper replacement bushing/shaft part number I'm missing.


Photos of the joint and the remaining gap attached.

photo-1 gap in the START handle posittion
photo-2 gap in the SLOW handle position
photo-3 joint

 

[racerone]

Picture of the tip of the slow speed mixture needle?

 

[meser300]

Picture of the tip of the slow speed mixture needle?

Photo-2. The gap is about 1" for slow and 0.5" for start

 

[racerone]

I do not see a picture of the tip of the slow speed needle !-----Look under EXHAUST HOUSING for the parts.

 

[meser300]

Which number you mean?

 

[meser300]

Did you mean the carb idle needle?

 

[racerone]

Correct.-----Nothing wrong with the needle.-----Does spark jump a gap of 5/16" on both leads ?-----Post actual compression values here.----I have more than 1 of these wonderful 6 HP motors.-----I can not see or touch yours.----You have to answer questions.

 

[Crosbyman]

the cam under the mag plate has a mark (bar) it must lineup with the cam follower on the carb when the throttle is at START

adjust the side throttle meshing gears on the handle to have the mag plate rotate properly so the cam can be positioned properly to line up the mark and cam follower

 

[meser300]

Correct.-----Nothing wrong with the needle.-----Does spark jump a gap of 5/16" on both leads ?-----Post actual compression values here.----I have more than 1 of these wonderful 6 HP motors.-----I can not see or touch yours.----You have to answer questions.

The compression is around 80 on both cylinders. The spark plugs are brand new Champion J6C. The gap is about 0.30.

 

[meser300]

the cam under the mag plate has a mark (bar) it must lineup with the cam follower on the carb when the throttle is at START

adjust the side throttle meshing gears on the handle to have the mag plate rotate properly so the cam can be positioned properly to line up the mark and cam follower

That is exactly the problem. When the handle is at the 'start' point, there is a 0.5" gap between the cam and the follower (see photo 1). I ordered a throttle control gear (part no. 0324512) to reduce the gap, but this was not enough. How do I adjust the meshing gear on the handle?

 

[Crosbyman]

if you disconnect the vertical post and the mag cam can travel..rotate ok to aling cam mark and follower then just adjust the meshing of gears .

the engine came with the correct parts no need to buy new parts.... the are great kickers

 

[racerone]

The question is ---Does spark jump a gap of 5/16"?----Sparkplugs are not mentioned.----Sparkplugs are not involved in this test.----The parts books seem to show a roller on the follower.----Perhaps the carburetor is not original.

 

[meser300]

if you disconnect the vertical post and the mag cam can travel..rotate ok to aling cam mark and follower then just adjust the meshing of gears .

the engine came with the correct parts no need to buy new parts.... the are great kickers

Do you mean that if I remove the clamp collar holding the shaft, I'll be able to disconnect it from the lever? (photo-7)

Quick clarification — when you say 'the cam under the mag plate has a mark', do you mean the mark is on the breaker/armature plate itself, or on the curved cam piece (the one with the part number cast into it)? I've checked the cam piece closely and the only marking on it is the part number — no separate index mark. So if the mark is supposed to be on the breaker plate, what does it actually look like, and what is it meant to line up with?
But here's what's confusing me — no matter what position I put the handle in, that mark only lines up with the follower when the throttle is at maximum (fully open), not at START. The cam only mounts one way, so there's no way to re-index it differently. Is this the mark you meant, or am I looking at the wrong thing? (photo-5,6)

 

[meser300]

The question is ---Does spark jump a gap of 5/16"?----Sparkplugs are not mentioned.----Sparkplugs are not involved in this test.----The parts books seem to show a roller on the follower.----Perhaps the carburetor is not original.

Sorry for the confusion — English isn't my first language, and I initially misread your question as being about the spark plug gap rather than a separate spark-gap tester test. I understand now that you're asking whether the spark can jump a 5/16" air gap on a tester, independent of the plugs.

I don't have a spark gap tester on hand — could you point me to what tool/setup is typically used for this test? I'll get the actual reading and post it here.

Also, regarding the follower roller — I checked the parts diagrams for my exact model (6RL75R) and they don't show a roller on the follower, just a direct pin/lever contact with the cam. The carburetor matches the parts list for this model as well, so I don't think it's a substitution from another engine — but let me know if there's a specific detail that made you suspect otherwise.

 

[tphoyt]

I haven’t work on one of these in a very long time and can’t remember what it should look
like but the cam follower looks to be pretty well worn.

 

[Crosbyman]

disconnect clip #33 from the vertical post this allow mag to rotate fully

https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1975&hp=6&model=6R75R&manufacturer=Johnson&section=MAGNETO

 

[meser300]

Disconnect clip #33 from the vertical post to allow the magazine to rotate fully.
https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1975&hp=6&model=6R75R&manufacturer=Johnson§ion=MAGNETO

Thank you very much, sir! You helped me disassemble and remove the shaft. It wobbled slightly, probably due to the lack of a bushing, which would have created a gap with the follower. However, how can I adjust the gear throttle (#73) or break the hard link to turn the magneto without using the handle? Simply disconnecting the vertical shaft does not solve the problem.