1989 johnson 40hp missing on bottom cylinder

[Tubes66]

so here's the run down on the motor . I just bought it recently and wasn't running very good at all . so I rebuilt both carbs , replaced fuel lines , new impeller . It had 110 psi on both cylinders when I bought it using a buddy's compression tester and I checked it the other day and my compression tester said 90psi in both.
(I believe my buddy's compression tester more then mine because it gets used way more and is a nicer tester).... it has great spark on both cylinders jumping a 1/2gap. so then I checked the reeds and they looked fine. I know the bottom cylinder is getting plenty of fuel and I have changed the plugs and wires. so I have a feeling its the timing or the timer base. any suggestions , the attached link is a video of it running .... https://www.youtube.com/watch?v=pI8WYk5VG1s

 

[Bosunsmate]

Spray fuel mix into the bottom culinder and see if that helps, it may be lower crank seal

 

[Tubes66]

Spraying starting fluid in bottom carb does nothing

 

[gm280]

Spraying starting fluid in bottom carb does nothing

Sure sounds like it has a miss. Are you sure when you cleaned the carbs that the float levels were set correctly? It could have a bad coil and still jump the 1/2" gap but not all the time. Have you tried to swap the coils to see if the miss changed to a different cylinder? Do you presently know which cylinder is missing? And have you changed the plugs? Just some ideas. JMHO

 

[Tubes66]

Set the floats the exact same , it's the bottom cylinder , I'll try switching the coil around . And I have cleaned and switched plugs around .

 

[gm280]

Set the floats the exact same , it's the bottom cylinder , I'll try switching the coil around . And I have cleaned and switched plugs around .

Okay, that sounds like a good plan. If you switch the coils around, and the miss follows the suspect coil, you have found your problem. You surely have to post back here to let us all know what you find. :thumb:

 

[oldboat1]

Dunk the l.u. deep in a barrel or in the lake. See first what back pressure does, given compression. Don't rev it either in a barrel or on muffs.

If it runs with some back pressure, pull off plug boots and see if it makes a difference -- should stall or stumble, or give you an rpm change. If no effect, that cylinder is not firing.

With less exhaust noise, you might be able to hear a little clearer what you have. Might be able to correct with slight adjustment to the slow speed carb needle.

 

[Tubes66]

So I checked timing , checked the timer base , and switched coils and nothing changed. So then the thought ran threw my head that it was running lean .... so when I rebuilt the carbs I set the idle mix screws at 1.5 turns like was suggested by many posts so I did that . Well I turned the bottom carb out a full turn and bam she started firing consistently . So I guess it was "lean pop" it was running great but idling slow so I started to adjust the idle mix screws a little (i know I really have to do it in the water but I wanted to get it close )... then the alarm started sounding on the controls and I shut it down I then felt the head and it was hot as hell. It has a new impeller and is pumping water great so I'm thinking thermostat is stuck .... where is that located ? And is there an idle adjustment somewhere?

 

[Bosunsmate]

well thats weird as you said spraying fuel in lower carb did nothing

 

[Tubes66]

Ik but idk maybe something I did helped too , definitely weird as hell .

 

[oldboat1]

Not weird at all. The motor will run lean on muffs, and can easily overheat if revving. You can't test the water pump operation or cooling function on muffs, nor tune the motor.

Air mix settings that you find in your manual are initial settings to get the motor running, and you dial it in from there -- idling in the water with the engine warmed up and in gear. (Initial settings for your '89, by the way, may be more than 1 1/2 turns open -- as you may have found by trial and error.)

 

[Bosunsmate]

Why would it run lean on muffs? Is that something to do with backpressure and why would that not affect the top cylinder as much?

 

[oldboat1]

pulls through less fuel for the same rpms, compared to operating under load. Will mask a problem with a weaker cylinder.

 

[Tubes66]

I was watching some YouTube videos , should I do a carb sync/balance ?

 

[gm280]

If you cleaned and rebuilt the carb(S), maybe you needed to open up the top carb idle needle as well. It could have been running but still on the lean side and heating up. But that is just a wild guess not being there to see. JMHO

As for the sync/balance, absolutely. I mean you did remove the carbs, so I would thing they would have to be resynced now.

 

[Stumpalump]

I just set a 91 48spl yesterday on muffs. Also owed a 1985 60hp. All the same motor. Would not run at 1.5 out so I opened them up. Got it running smooth by just bumping screews in and out. Killed motor and counted turns. One was out 3 and one was out 2. Set them both at 2.5. Some books and some VRO versions call for 2.5 coincidently. I adjusted further but wound up at 2.5. It runs perect and fires up without the choke during the warm day. In the water I'll tweek it but it will be close to right. On muffs go in until it revs then back out just until it smooths on both carbs. The little 2 cly are so responsive to tweeks that all a synconizer does is creat a hassle. You can hear and feel exactly when it's right on these little gems. Best motor of all time and the same poweheads are still raced today in the stock SST45 class. Find a set of the bigger carbs from a 48,50 or 60 if you need a more power. That is the only difference.

 

[Tubes66]

Thanks for all the help guys . I tried taking out the big plastic plug that the thermostat is behind and is cracking and won't budge any suggestions on getting it out?