Going from BS38 Non-Linked to Linked Carbs... ???

[OakBehringer]

I got a set of linked BS38s to me in the mail to replace my unlinked carbs (main reason to go to single cable throttle). Few questions:

- Will the jets from my unlinked fit in the linked carbs?

- Should I plan on using the same size jets, or are there internal differences in the carbs that would suggest different jet sizes without otherwise different conditions? Reason I ask: stock jet sizes were smaller in later year BS38s, but I realize this could be a result of exhaust and air filter changes, etc.

- Do the same intake rubbers work?

Thanks all I can think of for now, thanks!

 

[OakBehringer]

It looks like the pilot jets are not interchangeable. My follow up question:

Should I expect to change the jets in the linked 38s, from a 76-77 model, to match those of my unlinked 38s, '73 model? Or will the smaller jets in those of the later model work fine?

I'm assuming all other things being the same, I should expect the former. Just not sure if there are changes in the 38s that would necessitate different jet sizes.

THANKS!

 

[retiredgentleman]

Click on "Tech"...............go down to Carbs section. 5twins has made up a chart that shows the correct jets, needles etc. for the different years. Its not wise to mix jets etc. that do not match his chart.

 

[OakBehringer]

Yes, but I'm putting the 76 carbs on my 73.

The stock jetting for these years are different. They both use BS38 carbs. The 76 BS38s are linked and use a single throttle cable, vs the unlinked, dual cable setup on the 73. What is unclear to me is if there are internal changes in the different BS38s, or if the changes are all external, dealing with the throttle linkage.

Lets say my 1973 bike runs well with the stock jetting for the stock 1973 BS38 carbs.

What happens when I put the 1976 BS38 carbs on, with stock 1976 jetting, which is different than that of 1973?

 

[5twins]

Jet the carbs based on the carb set year, not the motor year. So, no, the '73 sizes won't be right for the '76-'77 carb set. Also, the 2 sets use different types of pilot jets and needle jets - they won't interchange. Well, they might physically interchange but they won't work right. Here's the chart RG mentioned .....

Yes, there are internal changes as well as the linkage on the outside. That's partly responsible for the jetting changes. Carb jetting specs are worked out as a complete package. The 3 circuits (main, midrange, and idle) influence the ones next to them so must be jetted to work with them. You'll notice from the chart that larger mains require smaller needle jets (midrange). Your current carbs can use 130 mains because they have a Z-6 needle jet. Your new set switched to a richer Z-8 needle jet and needed smaller mains as a result.

 

[5twins]

You will also need different new style manifolds. They angle different than your current ones. The newer carbs may not mate up with the original airbox due to this.

 

[OakBehringer]

Awesome, thanks for the response!!!