Browse Category: Suzuki GT 750

Carburetor synchronizing

Sorry for a long time of doing nothing on my blog. Hope to do better in 2022….

I come to mind I did a upload some years ago on YouTube showing an alternative way of synchronizing the carburetors, but I never posted the link on my blog. So, here it is:

The service manual explain how to balance the carburetors, but it can be hard to get it right, and annoying surging will occur at low rpm. Some adjust the butterfly valve looking at the air/light gap holding the carbs up agains a light source, but again, not an easy task.

In the video I pour methylated spirit ( petrol smells too much) into the carburetors and get the time of the drainage. Adjusting the carbs to about the same speed of drainage and the surging is gone at low rpm.
I learned this from Steve in Melbourne, Australia when I visited his sister Donna Ann 5 years ago.

Anti-surge jets

I bought a new carburetor kit last summer and mounted it for a couple of weeks ago. Interesting to compare with the old one I had. The first test run was promising. After a longer ride I got more and more annoyed about the surging at low rpm. Pretty sure it’s more surging compare to the old one. The fuel consumption is better and the color on the spark plugs looks also better while using this kit. If I can get rid of the surging I will keep them on the bike.
The new carb kit has no anti-surge jets mounted. The previous owner said they are all tapped and ready to be fitted with jets.
I don’t have a new jet-kit, but I have a lathe and milling machine. Let’s make a set of three 0,8mm jets.

Bulletins no 36 explain how it’s mounted :http://www.ozebook.com/compendium/techbuls/index.htm

Jet fitted:

Please read the application note no 36 and follow the procedure how use the 4mm tap.

Test ride:

Very pleased with the test run. The annoying surging issue was gone. 🙂

GT750 startup 2020

As usual, instant start on the GT. First ride this season. The spring has been horrible cold so far. Was snowing for a couple of days ago. Will enjoy the short MC season on the GT750 this year and hopefully the GT380 will be on the road the next year.

Tank

My GT750 A tank is back from repair and has got a new paint. My nephew Thomas has once again done a fabulous work on this. I’m so pleased with his work.

On my ride to the classic Suzuki rally in Denmark last summer i had an accident and got an annoying dent in the tank. Now it’s all gone 🙂

🙂 🙂

A new look :)

Had to put the tank back on and take some pictures with the new GT wheels mounted.

Looks nice with original wheels on 🙂

 

 

The video on the PC below shows the bike with the old GS wheels mounted

Butterfly shaft repair

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

Left butterfly valve assembly

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 !