Commando Carb Sync With Nails

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Big_Jim59

Big_Jim59

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It became evident that the carburetors, in my '74 Commando, were out of sync. It was the cause of the popping and protest from the left side as the right side was pulling up ahead of it. I used the nail method to adjust the sync. I have not seen this discussed so I will lay it out.

You need two large nails. Remove the air cleaner (mine is the K&N unit type so it was easy) and insert the nails under the slide on each carb. Make sure the nails are balanced with the heaviest side outboard of the carb. You don't want it slipping down the hatch by accident. Twist the throttle slightly and watch the nails. You will discover which side is pulling up first because you will see that nail dip first. I adjusted my bike accordingly and it runs great and pulls up even now.

I will probably put the carb sticks on it at a later date to see how close I really am but it is a whole lot better than it was.
 
I use this method except I use cut down wooden kebab skewers - works really well in my opinion.
 
Big_Jim59 said:
It became evident that the carburetors, in my '74 Commando, were out of sync. It was the cause of the popping and protest from the left side as the right side was pulling up ahead of it. I used the nail method to adjust the sync. I have not seen this discussed so I will lay it out.

You need two large nails. Remove the air cleaner (mine is the K&N unit type so it was easy) and insert the nails under the slide on each carb. Make sure the nails are balanced with the heaviest side outboard of the carb. You don't want it slipping down the hatch by accident. Twist the throttle slightly and watch the nails. You will discover which side is pulling up first because you will see that nail dip first. I adjusted my bike accordingly and it runs great and pulls up even now.

I will probably put the carb sticks on it at a later date to see how close I really am but it is a whole lot better than it was.
Click to expand...
The only drawback with this method is it doesn't take into account carburettor wear being different from one side to another
A set of vacuum gauges will solve this
Also it's best to micro adjust the point at which the slides lift off the idle adjustment screws
 
Big_Jim59 said:
I used the nail method to adjust the sync. I have not seen this discussed so I will lay it out.
Click to expand...

It has been discussed a few times before often with a link to the Bushman's tuning webpage :)...
... but using drill bits, rods, etc.

baz said:
The only drawback with this method is it doesn't take into account carburettor wear being different from one side to another
A set of vacuum gauges will solve this
Click to expand...

Yes, although I've used the rods/drill bits method I generally balance the carbs with (Morgan Carbtune) vacuum gauges.
Replacing the balance tube afterwards doesn't seem to alter the settings.
 
L.A.B. said:
It has been discussed a few times before often with a link to the Bushman's tuning webpage :)...
... but using drill bits, rods, etc.



Yes, although I've used the rods/drill bits method I generally balance the carbs with (Morgan Carbtune) vacuum gauges.
Replacing the balance tube afterwards doesn't seem to alter the settings.
Click to expand...
I'm a big fan of the Morgan Carbtune....good price compared to other types out there. Can be had in 2 or 4 cylinder versions:

 
L.A.B. said:
It has been discussed a few times before often with a link to the Bushman's tuning webpage :)...
... but using drill bits, rods, etc.



Yes, although I've used the rods/drill bits method I generally balance the carbs with (Morgan Carbtune) vacuum gauges.
Replacing the balance tube afterwards doesn't seem to alter the settings.
Click to expand...
I forgot about the drill bits! I am pretty sure that my vacuum gauge will get it closer and I will give that a go but it was so far out of sync is was just tragic.
 
If you wind the throttle so the slide cutaways are just disappearing at the tops of the chokes, you can usually get them equal visually, with the cable adjusters. But if you cannot get in a position to see down the chokes, you cannot get them equal. If you do it at the bottom of the travel, you need to make sure the stop screws are backed off. Syncing with a vacuum gauge is OK, if your two inlet valves are seating properly.
 
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acotrel said:
If you wind the throttle so the slide cutaways are just disappearing at the tops of the chokes, you can usually get them equal visually, with the cable adjusters. But if you cannot get in a position to see down the chokes, you cannot get them equal. If you do it at the bottom of the travel, you need to make sure the stop screws are backed off. Syncing with a vacuum gauge is OK, if your two inlet valves are seating properly.
Click to expand...
We also used to stick our fingers in the mouth of the carb and feel the slide. You can get them pretty close this way.
 
acotrel said:
If you wind the throttle so the slide cutaways are just disappearing at the tops of the chokes, you can usually get them equal visually, with the cable adjusters. But if you cannot get in a position to see down the chokes, you cannot get them equal. If you do it at the bottom of the travel, you need to make sure the stop screws are backed off. Syncing with a vacuum gauge is OK, if your two inlet valves are seating properly.
Click to expand...
Be careful as the depth of the groove the slide drops into in can vary quite a lot. I imagine that's why the round bar method is the norm.
I always use the 2 bars method as it was all I had as whippersnapper. Over the years I've invested in vac gauges and even a Morgan Carbtune and for twins 99% of the time found the old bars were spot on. I set the tick over using my fingers, the slide that moves first is the lowest.
 
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