how to tune dual carb outboard johnson

[tonyscj5]

I have a 19 foot boat with dual johnson 50s on it. I have been working on it lately and want to properly adjust the low idle jet on the carbs. I am unsure of how to adjust the dual carb set up. I am aware of how to adjust the mix on a single carb set up but I cant figure out the dual carb.<br /><br />The motor idles fair know, but dies everyonce in a while. I borrowed a set of carb synchs to get the air flow the same, then I figure I should turn the jets in all the way then out 1.5 turns and go from their. I just dont see how the adjustments will work, do you make any adjustments to both carbs or one at a time.<br /><br />If some could tell me the proper procedure it would be great.<br /><br />thanks<br />TOny

 

[WillyBWright]

Re: how to tune dual carb outboard johnson

Both carbs should be set the same. If you try to tune them individually, you end up with one lean and one rich to compensate. On older 50s (pre VRO) the needles should be about 1 1/2 turns out. On the newer ones with VRO (most) it'll be between 2 1/2 and 3 1/2. The pre and post VRO reference is a ballpark figure. I doubt the carbs actually changed like that with the introduction of VRO, but it's close. Both motors will end up with the same or nearly the same adjustments, as long as they're both healthy.

 

[Joe Reeves]

Re: how to tune dual carb outboard johnson

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)<br />(J. Reeves)<br /><br />Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.<br /> <br />Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.<br /> <br />Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting. <br /> <br />Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor.<br /><br />It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing the above final adjustment due to the fact that one of the valves may be set ever so slightly lean.<br /><br />When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[tonyscj5]

Re: how to tune dual carb outboard johnson

A buddy of mine loaned me a set of carburator synchronizers that he had for tunning a vw motor. They are just vacum meters to ensure that the carbs are sucking equal amounts of air. Is this nessecary on an outboard. It seems like it would help? Do I need to do this before tunning?<br /><br />Also my motors are VRO motors but the VRO set has been removed, so which initial set up should I use? 1 1/2 or 2 1/2?<br /><br />thanks<br />tony

 

[tonyscj5]

Re: how to tune dual carb outboard johnson

Okay- I thought I had it figured out and headed down to the marina to tune the carbs. The SS mix screw it on the front face, the surface where the air box mounts, of each carb, right?<br /><br />Anyway if those little brass plug looking things are the jets, then I was adjusting the jets and.... All of them were fully seated, turned completly to the right. Ind if I backed them out and started the motor they would vibrate back to closed?<br /><br />WHta am I doing wrong? Are these even the ss jets?<br /><br />Tony

 

[Joe Reeves]

Re: how to tune dual carb outboard johnson

Brass Plugs? Judging by your initial post, we assumed that you had a older engine that had adjustable needle valves. If those "plugs" incorporate a standard screwdriver slot and have a small hole in them..... they are fixed jets and should be tightly secured, in which case there is no adjustment.<br /><br />What is the model number of the engine?

 

[tonyscj5]

Re: how to tune dual carb outboard johnson

the motor is a 1989 johnson 50 hp outboard, it had the VRO but the the previous owner removed it. <br /><br />The "brass plugs I am reffering to are screwed into the carbs on the surface that the air mounts to. They are slightly above and to the right of the carb throat. It makes sense that they are fixed jets, because when I try to adjust them they just rattle out.<br /><br />So my next question is if those are the fixed where are the slow speed adjustable jets? I figured that those were them, because with them out the motor only will run at idle if I prime the **** out of it continually and runs fine at high RPM?<br /><br />WHats that mean, how do I adjust the low idle mix?<br /><br />thanks<br />tony

 

[tonyscj5]

Re: how to tune dual carb outboard johnson

the motor is a 1989 johnson 50 hp outboard, it had the VRO but the the previous owner removed it. <br /><br />The "brass plugs I am reffering to are screwed into the carbs on the surface that the air mounts to. They are slightly above and to the right of the carb throat. It makes sense that they are fixed jets, because when I try to adjust them they just rattle out.<br /><br />So my next question is if those are the fixed where are the slow speed adjustable jets? I figured that those were them, because with them out the motor only will run at idle if I prime the **** out of it continually and runs fine at high RPM?<br /><br />WHats that mean, how do I adjust the low idle mix?<br /><br />thanks<br />tony

 

[Joe Reeves]

Re: how to tune dual carb outboard johnson

On that model, the slow speed adjustable needle valves (if your engine incorporates them), would be on the starboard side of the carburetor about 3/4 of the way back.