How to balance carbs with no vacuum ports?

[Redstern]

I have a 2000 Johnson 40hp 2 stroke. It has 2 carburetors. I need to clean and then balance the carbs. I have a vacuum gauge, but the carbs don't have any vacuum ports. How do I balance them without vacuum ports? I included a diagram of one of my carbs with this post.

 

[gm280]

You could use a tach and see how the idle mixtures work. Adjust one for best RPM and then the other. But don't just go for the highest RPM, usually you adjust one until the RPM peaks and then back off until it starts to flutter. Then set that mid-way and go to the other. I would do that a few times between the two carbs to verify it is running properly. If there are high speed adjustments as well you will have to load the engine to accomplish that. JMHO!

 

[Redstern]

You could use a tach and see how the idle mixtures work. Adjust one for best RPM and then the other. But don't just go for the highest RPM, usually you adjust one until the RPM peaks and then back off until it starts to flutter. Then set that mid-way and go to the other. I would do that a few times between the two carbs to verify it is running properly. If there are high speed adjustments as well you will have to load the engine to accomplish that. JMHO!

I tried that a few years ago, and it didn't work well. It ended up that it idled better but I had totally messed up the high end. It is also hard to tune by ear when 2 strokes always idle rough. My carbs also only have one mix screw for high and low end. My guess is that I got a higher idle, but it wasn't balanced well, so the high end was bad. Is there any other way to balance them?

 

[racerone]

Using a vacuum gauge may not apply to you 2 stroke motor.

 

[ondarvr]

I have never used a vacuum gauge on one of those motors and I was always able to get them to run great. The screw you can turn should only affect the idle, or slightly above, it should have no affect on how it runs other than that.

 

[Faztbullet]

My carbs also only have one mix screw for high and low end.

High speed is fixed jet the mix screw only adjusts low end idle mixture...

 

[grid]

To balance the carbs, remove the connecting rod between the two carbs, right side of the engine. Loosen the screw on the plate where the rod clips in (only 1 carb should have that screw I identified). Make certain the throttle advance cam is not touching the throttle roller. Snap both throttle plates open and make sure they snap closed. The 40/50 2-stroke will "unbalance" faster than you'd believe, so start the engine, make sure it idles okay with nothing opening the throttle plates, then attach the connecting rod, THEN snug the connecting rod screw down. If it starts idling poorly, loosen the screw again and when it smooths out, hold the linkage TIGHTLY and tighten the screw. It should idle okay at that point. Then push the throttle roller back against the cam and align it with the line on the cam, and you're back in business..

 

[flyingscott]

You do not need to balance the carbs on a 2 strk do the link and sync as prescribed in the maunual. Did the motor not run well before or is this something you think you have to do. If you put the carb adjustments back where they were and cleaned the carbs correctly you should have no issues no need to make more work for yourself.