While doing the work on the carburetors I saw two of the butterfly shafts had bad threads for the 3mm screw holding the butterfly valve.

The one on the photo below looks like it has a previous repair using some sort of insert, not sure but it looks bad.

Click on the images for detailed view

The procedure below is a much better way to do the repair. Since the shaft is made of brass a new piece of brass can easily be soldered into the bad area.

 

Drill down about 1,5 mm using a 6mm drill bit.

  

Continue down to 2,5mm using an end mill. ( not all the way through )

 

The piece of brass has been soldered

 

 

Use a lathe to turn turn off the brass piece until the shaft looks smooth and nice.

 

Use the second hole as alignment to get the right angle before you drill out the new part using a 2,5mm drill bit.

 

Make new 3mm threads and you are done. Good luck 🙂

 

Mounted back into the carburetor

The assembly process are very much the same for all three.Please see the previous posts for the left and right carb. Do the same for the center one except from the bracket at the end.

As always, click on the images for detailed view.

Step 1

Add some grease on the both ends of the shaft.

Very much the same assembly as on the right carb ( see the post Right butterfly vavle assembly )

 

Step 2

Insert the seal with the lips facing outwards. Two seals, one for each end.

 

Step 3

Insert the shaft and the butterfly valve. Secure the screws with loctite. Use new screws if they are worn.

Note, the text on the valve facing upwards (red arrow on the picture )

Make sure the valve sits well and is the correct position. If not you will get trouble later on doing the synchronization ( balancing ) of the carbs.

 

Step 4

 

Step 5

Most of the parts got some seconds or minutes on the polishing machine before mounting, the spring as well. Looks so much better.

 

Step 6

 

Step 7

 

Step 8

DONE !

 

Butterfly valve assembly on the right carburetor

Click on the picture for close up view.

Picures shows the order how to assembly. The valve can also be mounted as order number 2. Don’t mount screws with damages. The screws in pictures 10 will be replaced.