Max Pilot size on BS38 Carbs?

[warrenlevihursh]

1978 XS650, Really short dual exhaust, Mike's POD filters, BS 38 carbs, stock ignition/points/advance.

Hey guys!,

I got my chopper project running, charging and riding, so I took it to a buddy's shop for them to check the timing with a light (bc I don't have one) and jet the carbs. They were all stock (27.5 pilot). I figured they would have them in stock so it would be easier than me ordering a bunch of sets and waiting. Anyway, I probably should have just did it myself. They went up 2 sizes first, then had to order 3 sizes up, and now are saying it still seems like it needs more fuel. They are trying pilots in the 40's range at the moment. I don't think that this can be possible. Has anyone seen a need for a pilot so big or is something else wrong, like the advance sticking etc? Thanks.

 

[retiredgentleman]

1978 XS650, Really short dual exhaust, Mike's POD filters, BS 38 carbs, stock ignition/points/advance.

Hey guys!,

I got my chopper project running, charging and riding, so I took it to a buddy's shop for them to check the timing with a light (bc I don't have one) and jet the carbs. They were all stock (27.5 pilot). I figured they would have them in stock so it would be easier than me ordering a bunch of sets and waiting. Anyway, I probably should have just did it myself. They went up 2 sizes first, then had to order 3 sizes up, and now are saying it still seems like it needs more fuel. They are trying pilots in the 40's range at the moment. I don't think that this can be possible. Has anyone seen a need for a pilot so big or is something else wrong, like the advance sticking etc? Thanks.

Have the carbs been fully inspected inside? Have the float levels been set properly? Is the rubber O-ring for the needle jet in good condition?

I'd say your buddies don't know a lot about XS650 carbs. A #32.5 or #35 should be in the right area. Most unlikely to be a larger pilot jet than that.

Yes, you should learn to do this work yourself. I use the dead cylinder method to adjust my mixture screws. If you find you have to set the mixture screw at 3 turns or more, it means you need to go up one size with the pilot jet.

 

[5twins]

Pilots in the 40s should be way too big for your particular carb set. As RG said, 30 to 35 should do it but 35 is probably too large as well. On the several '78-'79 carb sets I've tinkered with, it has been. A 30 or 32.5 did the trick. Make sure the shop is using the proper style of pilot jet. This carb set uses the VM22/210 type pilot, not the BS30/96. If they're using the wrong style, it won't flow correctly and that may explain why they think it needs to be so much bigger.

Also make sure they are starting with the mix screws open enough. On many carbs, the setting is around 1.5 turns out to start. This carb set is different and requires a 2.25 turns out initial setting. If they're setting the screws in too much, even slightly larger and possibly correct pilots might seem too small. They're cutting too much of the flow off with that lean screw setting.

The style of pod filter you've fitted may be adding to the tuning problems. The pleated K&N style pods don't work right on a CV carb. You'll never get them tuned perfectly with that filter style. UNI foam pods work best.

 

[warrenlevihursh]

Thanks guys, you confirmed what I thought about being way to big. The frustrating thing is I can do the work, especially with the forum help. I sort of wanted to give them some winter business and I am pretty busy.

I bought the UNI foam filters for my Café and swapped theses filter to the hardtail because I wasn't overly concerned with "performance".

Ill give them a call later and see about getting the bike back. At least at home I can swap filters and try different things. I don't think they have much more then an hour in labor so It isn't really a huge deal.

 

[warrenlevihursh]

Hey 5twins, talked to my buddy on Friday. He confirmed they did order the wrong (BS30/96) pilots. I mentioned about him double checking after your suggestion. I'm not sure how he got the wrong ones. He said that is what was in the carbs when they were taken apart, but I'm not so sure. It had the stock sizes in (Im pretty sure they were original). The bike ran very good other then needing the choke on slightly. I can't believe the 27.5 were the wrong style. Anyhow, the new pilots should be here today. So a 32.5-35 should do the trick. Thanks for the help!

 

[retiredgentleman]

With pilot jets being so inexpensive, maybe try a #30 pilot jet first, then if it does not tune well, go to the #32.5, and then to a #35 if needed. Its best to just go step by step.

 

[warrenlevihursh]

With pilot jets being so inexpensive, maybe try a #30 pilot jet first, then if it does not tune well, go to the #32.5, and then to a #35 if needed. Its best to just go step by step.

Good call. It seemed surprising close with the stock jetting. It doesn't seem to need much. I'll be happy to be able to ride it around.

 

[5twins]

If your pilots were the originals, then the shop could have been easily confused. The originals were a no-hole style of the VM22/210. They had no air bleed holes down the sides. I think Yamaha had them made up special because I've never seen them available from Mikuni. The only similar looking pilot they list is the N151.067. It has no air bleed holes down the sides but is actually a no-hole version of the BS30/96. Maybe that's what they ended up with.

 

[retiredgentleman]

If your pilots were the originals, then the shop could have been easily confused. The originals were a no-hole style of the VM22/210. They had no air bleed holes down the sides. I think Yamaha had them made up special because I've never seen them available from Mikuni. The only similar looking pilot they list is the N151.067. It has no air bleed holes down the sides but is actually a no-hole version of the BS30/96. Maybe that's what they ended up with.

Yes, my bike had the original VM22/210, with no holes, and they have the Mikuni stamp of the square inside a square. Mikuni knew that holes were not required for these carb sets, so they saved money by not drilling the holes in the large production runs.

However the aftermarket guys, who are too lazy to do the research, did not know the holes could be omitted. So the aftermarket lads spent extra money drilling holes that aren't needed.

My present VM22/210, aftermarket # 30 pilot jets have side holes, and yet they work quite well, so no harm no foul.

 

[warrenlevihursh]

Good to know. Man, you guys know everything! I'll have to let my buddy know this so he doesn't freak out when he gets the replacements and they still don't match the original pilots lol!

 

[warrenlevihursh]

I got the bike back the other day. The correct jets obviously fixed the problems. They decided on 2 up on main, 37.5 on pilot at 2 turns and 2nd from the top on needle. It was popping pretty good on decal, with a slight hesitation right off idle if you slowly opened the throttle lugging the motor. I played with the mixture screws and decided 3 turns was the best. 1.5 really made it pop, 3.5 ran poor. 3 seems pretty decent.

I believe the pleated pods may be causing the slight hesitation. It's pretty good though, I am just being really picky. I know the 37.5 seems jetted really big, but the plugs look a tad lean if anything, definitely not black or wet or sooty. Here is a picture of the exhaust. I don't know if I explained just how short they are. Thanks for the help once again.