1973 Johnson 50hp Will not get Full Throttle

[nickfranch330]

I recently purchased a 1972 Wellcraft 15ft runabout with a 73 Johnson 50 Hp outboard for an absolute steal. The motor and boat are in fantastic condition. Upon purchasing the boat, I changed spark plugs, cleaned the carbs, and put fresh gas in it. The motor starts instantly, runs very well up until about 1/4 throttle. This motor will not reach full throttle, and I have determined that it is an issue with the adjustment of the linkage or throttle cable.

Image 1: Linkage with no throttle, in neutral.

Image 2: Linkage at full throttle.

Image 3: Throttle Plate at full throttle.


As you can see in the photos, the throttle stop is almost all of the way turned out. Is there something simple that is hooked up incorrectly? I am very mechanically inclined and very good with two strokes, but this one is throwing me for a complete loop. The boat will only pull about 15mph at WOT, whenever I believe it should be able to pull well above 30, possibly even into the 40 range. Please let me hear all of your ideas.

 

[oldboat1]

Unhook the remote cables at the motor, and check the motor linkages. If correct, would reattach the cables to match the motor linkages/settings, adjusting cables with the plastic wheels. Possible the cables are an incorrect length, but more likely badly adjusted.

 

[nickfranch330]

Unhook the remote cables at the motor, and check the motor linkages. If correct, would reattach the cables to match the motor linkages/settings, adjusting cables with the plastic wheels. Possible the cables are an incorrect length, but more likely badly adjusted.

Thank you for the reply. Do you really think it could be the cables? I will look into it further when I get off today, but the thing that really confuses me is that the linkage hits it's physical stop which leads me to believe it has nothing to do with the cables themselves.

 

[racerone]

So with control box in full forward and maximum throttle the throttle plates are not fully open ?----How did it run for you last season ?------When / how did this happen ?

 

[nickfranch330]

So with control box in full forward and maximum throttle the throttle plates are not fully open ?----How did it run for you last season ?------When / how did this happen ?

Correct. Same with reverse and the warmup lever. I am not sure how this happened, just bought this boat a few weeks ago. This is not my first boat or first outboard by any means. I have had it out on the water once, that is when I noticed the throttle issue. Motor idles perfect and starts right up every time, and even ran good at this "Full Throttle." This really has me pretty confused on how it could possibly happen.

 

[racerone]

You can not go full throttle with the warm up lever.-----Disconnect throttle lever at the motor.---Can you then get full the throttle plates fully open by moving the lever.

 

[nickfranch330]

You can not go full throttle with the warm up lever.-----Disconnect throttle lever at the motor.---Can you then get full the throttle plates fully open by moving the lever.

I actually just managed to adjust the linkage and cable so that the motor can now hit full throttle. Another issue has came from this however, now the timing is so far off that the motor will not start. Is there a way to adjust the timing by hand close enough to get it running so I can use a timing light?

 

[racerone]

The ignition timing is FIXED / SET at the factory.----It does not go out of adjustment by itself.-----Something is not right here.-----Best to look things over very carefully before you damage this motor.----Yesterday I coached a novice boat owner and said " make sure you hook red to battery positive terminal "-----About 10 seconds later the smoke suddenly appeared.----Sure enough he still hooked it up backwards.----So stop adjusting things until you determine where the fault is !!

 

[nickfranch330]

The ignition timing is FIXED / SET at the factory.----It does not go out of adjustment by itself.-----Something is not right here.-----Best to look things over very carefully before you damage this motor.----Yesterday I coached a novice boat owner and said " make sure you hook red to battery positive terminal "-----About 10 seconds later the smoke suddenly appeared.----Sure enough he still hooked it up backwards.----So stop adjusting things until you determine where the fault is !!

I would normally agree, but someone had to have adjusted this linkage at some point and then apparently messed with the timing. It will spit and sputter but not run at idle now, and the only thing that would make sense to me was the timing. I had to adjust the linkage arms, and the timing moves with the linkage so the timing is not the same as it was before. The service manual has a very detailed section on the timing adjustment, so I believe that it is a safe spot to start.

 

[racerone]

Follow the manual to get back to factory settings.----Do NOT deviate from factory maximum timing advance.

 

[nickfranch330]

Well I figured it was time for an update. I spent most of my day yesterday messing with the linkage and the timing on that motor. I finally got it running perfect, will rev up to full throttle and everything. Factory timing specs call for 3 Degrees at idle and 18 at max advance, and the motor is now set to that. Thank you for your help, cannot wait to have this thing out on the water.

 

[Mblender]

It’s going to go out on you again. It’s one of two things, your control box has something malfunctioning in it.”is it hard to shift between forward,neutral and reverse” or it could be you need to lube your cables. Your timing probably wasn’t out of sink,
Racerone is right, you shouldn’t mess with factory settings. You might have just masked What’s really wrong. Sticky cables will throw you timing all out of whack. It happened to me a month ago, where my butterflies were wide open with the control arm full throtype and bogged at about the same as yours. 6mph I did a little test and as soon as it started bogging down I pressed the choke on and off rapidly. Took off like a bat out of hell flying across the lake full speed.