1975 Johnson 25hp won't idle

[Jason6586]

Hello everyone,

I have a 75 Johnson 25hp (Model - 25R75B), the engine starts good but won't let me idle it down to shift. I will be rebuilding the carb as soon as my kit comes but was wondering if there could be something else I need to adjust or address. It idles down but just not slow enough to where my arrow is pointing to the shift location, it will die before it gets to that low of rpm or location on the handle. Any info is greatly appreciated. Also can anyone tell me what the carb settings should be set at after rebuild.

Thanks Again

 

[nphilbro]

No Title

I was just rebuilding a '76 25hp this week and got it to finally fire and start today. It's a bit older than I normally work with but their are a ton of adjustments on this motor. On the outside of the port side there should be an idle adjustment screw you can turn in or out to set the low idle timing plate stop point.
I also noticed on this motor that the shift stops on the starboard side, visible just below the flywheel, can get out of sync. Whereas, with the motor off, you need to put it in gear, turn to WOT then back to lowest speed setting and shift to neutral. This will make sure the shift safety stop arm is on the correct side of the stop after bracket.

Regarding the carb sync, I'm getting mine dialed in little by little. It has point/capacitor ignition, which I don't like, so you have to first make sure the spark is good enough to reliably fire on each cycle. Make sure they aren't fouled. I've had to clean mine 3 times this afternoon but they are coming out cleaner each time and the steady idle is getting lower. While waking this old motor back up I've had to adjust the inside carb throat armature to be what I assume is slightly open at the lowest timing position to get it to run steady, but higher than I like (but still burning the cylinders back to clean).

Also, make sure you have spark on both plugs- it will start and run on a single cylinder, but not very well.

If you still have issues, pop the flywheel off and check the points. The gap is .020. Mine are quite new but still had to clean them really well with lacquer thinner several times before finally getting spark to each plug.

Hopefully you didn't also blow out an entire beehive when you first started, I still have honeycomb floating in the tank!

 

[hardwater fisherman]

Dont worry too much about what is written on the tiller handle. None of mine are very accurate. There is an idle adjustment screw, it is kind of hidden. Follow the tiller arm around the back, there is a long plastic screw with a spring that butts up against the gear. But as previous has said check to see if you have good spark as well. I have a 40hp with the same low tension magneto system and I found that those points need to be clean. If dirty it is hard to get it dialed in for idle. As for the carb 1 1/2 turns out from gently seated is a starting point for the slow speed needle.

 

[nphilbro]

On mine today, I gradually got the carbon burned out and took the RPMs up (in the tank) in intervals of 1-3 minutes based on how it sounded. I was able to readjust the throttle armature back to closed at low timing as it should be. It now idles really low while in the tank and in gear and will go all the way back up. You can see my thread from yesterday with more detail. I didn't have a tiller arm on mine so had to adapt one to fit. I also took a torch to the plastic idle adjustment on the outside since it was seized and drilled it out to thread a long 1/4 stainless steel bolt through - it works just fine.