switching my 72 bs38's for 76 bs38's and jetting???

[thrashin]

So my 72 xs650 has PAmco ign, banshee chargin system mod, mini batery, mikes xs standard coil, ngk's, cut stock pipes, and the rest of the motor is stock as far as I know.

I live in so. Indiana and it gets sticky hot, no altitude.

I could use some help on rejetting the carbs. This was pretty much a basket case when I got it. Did some work and now have it "running". Actually fires up on the first kick and idles, but after that it's done. I try to give it throttle and it pops through the tail pipes. Then I noticed that fuel is running from the float over flows.

Another thing I noticed is that the petcock on one side of the oem tank is not working as well as the other. The tank is going to be swapped out to another with 1/4" manual petcocks.

I've done a lot of research, but haven't found my answer yet. please help

1. 72' bs38's come stock with 130 mains/ 42.5 pilots
76' bs38's come stock with 122.5 mains/ 25 pilots

If I want to jet up a bit should I jet according to the year of the engine or the year of the carbs?

2. What kind of air filter would you suggest? I'm leaning towards uni cheapo's

 

[thrashin]

the reason I ditched the 72 carbs is due to the poor shape of the needles, o rings are gone and the diaphram was shot on one side. Picked up a pair of 76's on the forum and they need jets.

Can I just swap out the jets from the 72 into the 76 and try that?
Is there anyway to tell if the jets are worn?

 

[weekendrider]

I would jet for the carbs not the year of the motor.

 

[5twins]

Yes, base your jetting on the year of the carbs, not the motor. None of the jets from the '72 carbs will work in the '76 set except maybe the mains. However, the 130 mains may not be quite big enough. I jetted a set of '76-'77 carbs for my bike with pipes and pods and they needed a 132.5 main.

 

[thrashin]

how about:
132.5 mains
30 pilots
and straight pipes with pods

 

[5twins]

Original pilot was a #25 so a #27.5 may be all you need. Also, the '76 carbs use the VM22/210 type pilots - make sure you get that kind. Your '72 carbs use the other kind, the BS30/96 type. The 2 look identical on the outside but are different on the inside and do not interchange.

You will also want to drop your needles a step to lean the midrange because of the larger mains. The larger mains are also going to richen the midrange making it too rich, in fact. You lower the needle to compensate for this. There are 3 circuits in your carbs. Changing one affects the one next to it as well. You have to consider this when re-jetting. A change of the mains may require some midrange adjustments. Midrange changes may require some pilot and main circuit adjustment.