BBK Jetting

[BowlingSS]

I am putting my 750 kit in my Tracker that I am working on. I still have a lot to do but wanted some info on jetting my 1981 XS650SH carbs. I did a search but did not find exactly what info I wanted. I have two into one pipes and will be running K&N filters. I did not do anything to the crankshaft. I am not going to drill out my jets, so I wanted advice on what jets I should start with. I am probably too early on asking this advice but the early worm .......
Thanks.

 

[5twins]

Having the 750 kit shouldn't change the jetting requirements much, if any, over what would be needed for a modified 650. If you look at the carb jetting specs for the old TX750 twin Yamaha produced in '73 and '74, they were virtually the same as the 650 specs at the time. Both used pretty much identical BS38 carbs.

So, that being said, typically the BS34s need one up on the pilots and 2 to 3 up on the mains. You can also reduce the air jets a size to make the idle circuit a little richer, but not as rich as going up another pilot jet size would do. But, just be aware that 2-1's can be difficult to tune for sometimes, and the K&N style pleated filters don't work well on CV carbs. Using those two components may make getting a perfect state of tune difficult. For pods, the UNI foam ones are a better choice. For an exhaust, your basic 2 into 2 works better.

 

[BowlingSS]

Where do you get the best pods at?

 

[BowlingSS]

When I bought the bike it had a two into one.

 

[5twins]

The UNI pods are available from many places online. For your BS34's, you would want the UP4229 or UP4229ST (dual layer). You'll often find them on Amazon for a good price, or eBay. They usually sell for between $15 and $20 each.

 

[BowlingSS]

The 81 has BS38’s , don’t they?

 

[BowlingSS]

What size should I get? Double layer or single?

 

[5twins]

Well, stock an '81 would have BS34 carbs, but parts get swapped around so much (and easily) on these bikes, who knows. But, you will need to figure out for sure which you have because they take different size (intake diameter) pods. That 4229 number I gave you is for the BS34s. The BS38s take a UP4200 or UP4200ST. I don't feel the dual layer version is needed unless maybe you live and ride in a very dusty area. I do have them on my '83 but only because I got a good deal on them from a local guy who bought them for his bobber. They wouldn't fit because of his hardtail frame .....

On my other 650 I just have the plain ones .....

The dual layer version is nothing more than the above plain filter with a foam "sock" on it. Take that off and you're left with the plain filter .....

So, I guess it's up to you which version you get. You could run the dual layer either way, with or without the extra foam sock. But the dual layer costs a few dollars more than the plain one usually.

 

[BowlingSS]

I have two other XS650's (72-73) that use the BS38. Sorry about that. Thanks for the info.

 

[BowlingSS]

Are the 4229 straight or angled?

 

[5twins]

They are straight, but they do make an angled version too. Here's a page with all the UNI pods listed .....

https://unifilter.com/online-catalog/clamp-on-air-filters/

 

[BowlingSS]

Got the UNI filters. Now I just need to finished up everything else.

 

[5twins]

I don't think I mentioned it, but the pic above shows it. Don't use the special foam filter oil on these, it's too thick and can clog them. Use a 50-50 mix of gas and motor oil. As shown above, I simply "paint" the filters with the oil mix then let them sit 10 or 15 minutes so the excess can drain off.

 

[BowlingSS]

I don't think I mentioned it, but the pic above shows it. Don't use the special foam filter oil on these, it's too thick and can clog them. Use a 50-50 mix of gas and motor oil. As shown above, I simply "paint" the filters with the oil mix then let them sit 10 or 15 minutes so the excess can drain off.

I already bought the oil kit.