old johnson idles too fast, 9.5 HP

[kjohnson47108]

I have two late 60 to early 70s Johnson 9.5HP engines. One idles fine but will not RPM up to a resonable speed under load. I asume that one is low compression. The other one is the question. I can not get it to go lower in idle than about 1500 to 2000 RPM. When you slam it in gear it goes. How do I get it to a lower idle? I have changed out carbs and they both run the same as before. Not a carb issue.

 

[bktheking]

Re: old johnson idles too fast, 9.5 HP

I have two late 60 to early 70s Johnson 9.5HP engines. One idles fine but will not RPM up to a resonable speed under load. I asume that one is low compression. The other one is the question. I can not get it to go lower in idle than about 1500 to 2000 RPM. When you slam it in gear it goes. How do I get it to a lower idle? I have changed out carbs and they both run the same as before. Not a carb issue.

The one that will not get to RPM either is running on 1 cylinder or the high speed jet is clogged in the carb.

The second one sounds like it needs to be synched, when it's at idle is the butterfly in the carb half way open?

 

[kjohnson47108]

Re: old johnson idles too fast, 9.5 HP

The one that will not get to RPM either is running on 1 cylinder or the high speed jet is clogged in the carb.

The second one sounds like it needs to be synched, when it's at idle is the butterfly in the carb half way open?

The one that will not gain RPM is running on both cyclinders or at least I have spark on both. I change the carb to the one that was running high idle and it still ran the same. I have wrote it off as low compression other wise it runs great.

The second one with high Idle, the butterfly is close to closed, how do i sinc it? I do not see any adjustment. It seems to be plate steel linages. I think it does need to be synched.

 

[bktheking]

Re: old johnson idles too fast, 9.5 HP

The one that will not gain RPM is running on both cyclinders or at least I have spark on both. I change the carb to the one that was running high idle and it still ran the same. I have wrote it off as low compression other wise it runs great.

The second one with high Idle, the butterfly is close to closed, how do i sinc it? I do not see any adjustment. It seems to be plate steel linages. I think it does need to be synched.

Well usually a motor with low compression is a nightmare to start. If you suspect a compression issue test it and report back. Have you checked the point adjustment to make sure it's bang on, bad timing will equate to no rpm.

There is a sync setup for this motor but can't paste it as i'd break the rules. The butterfly needs to be completely closed at idle, there are throttle cam marks and so on and so forth that have to be in time with the twist grip, it sounds like at idle the butterfly is somewhat open.

 

[ezeke]

Re: old johnson idles too fast, 9.5 HP

At the base of the tiller handle there is an idle adjustment knob on all but the earliest 9.5 models. Turn that to set the idle speed.

 

[bktheking]

Re: old johnson idles too fast, 9.5 HP

At the base of the tiller handle there is an idle adjustment knob on all but the earliest 9.5 models. Turn that to set the idle speed.

Ya glad you posted that EZEKE, my 65 doens't have it.

 

[kbait]

Re: old johnson idles too fast, 9.5 HP

Ezeke's right, and on '65, '66? it was an plastic adjuster (Idle stop setting) just aft of the flywheel (plug side) that adjusted the stop on the arm.plate. It has a thumb screw on it for easy adjustment, but you need to pull the hood off..

 

[ezeke]

Re: old johnson idles too fast, 9.5 HP

Ezeke's right, and on '65, '66? it was an plastic adjuster (Idle stop setting) just aft of the flywheel (plug side) that adjusted the stop on the arm.plate. It has a thumb screw on it for easy adjustment, but you need to pull the hood off..

Right, I've circled it in the thumbnail to get it in this thread. That's on 1964-1966.

 

[kjohnson47108]

Re: old johnson idles too fast, 9.5 HP

Thanks guys, I did not even see that adjustment knob. I am sure that is what it is because it runs great just will not go down to idle. I will try it when it quits raining. At least its not snowing, Summerfield florida, lake weir.

I saw a posting that there is a high speed needle in the bottom of the float bowl. I need to look at it in the one that runs slow because I did not switch that part out. I did clean it but i did not know there was a port in that part so I did not take the time to check it well.

Thanks all, I will let you know.

 

[bktheking]

Re: old johnson idles too fast, 9.5 HP

Don't think it's a needle like the old motors, more likely a fixed jet behind the screw in the bowl assembly.

 

[ezeke]

Re: old johnson idles too fast, 9.5 HP

All of the 9.5's came with fixed high speed orifices - not needles.

There were high altitude kits for the 6HP that allowed you to convert to needles, so maybe someone came up with something for the 9.5. - ?