Help with '79 XS400 main air jet

brockd · Apr 16, 2015

Hey all - was supposed to pick up the bike tomorrow, but the mechanics found out I'm missing a pair of jets... :doh:

They tell me they're part number 52 on the attached exploded view. Yammy discontinued them aeons ago and I'm now trying to figure out replacements.

I was speaking with one carb guy in Ohio and he said they may have been taken out and left out to lean out the mixture. The mechanics think they should be there. I have very little experience in carbs, haven't seen these parts, and haven't seen the hole where they belong.

I've checked out a block of sites and wondered if someone with experience in this could point me in the right direction:
1) http://www.mikesxs.net/products-74.html#products
2) http://www.dimecitycycles.com/motor...retor-parts.html?cat=1727&motorcycle_make=164
3) http://www.bikebandit.com/aftermark...carb-kits-parts-accessories-universal/pb91sg0
4) http://www.z1enterprises.com/ShopBy...ion=Used+on+Mikuni+CV+carbs&category=01043801
5) http://www.pjmotorsports.com/mikuni-jets.html

Tx! :bike:

xschris · Apr 16, 2015

pjmotorsports has them. They are B42/55 air jets. #170

brockd · Apr 16, 2015

Thanks for the reply, Chris. Can anyone else confirm this - just so I can have 2 opinions...? Want to make sure I'm getting the right thing.

Tx!

brockd · Apr 17, 2015

Yay! I think I've found what I'm looking for.

MikesXS has a Canadian distributor counterpart in Stratford at xs650direct.com and they have almost all the jets you could imagine right here: http://www.xs650direct.com/products-38.html

My mechanic was confused in the hunt as these are all fuel jets but reading the fine print it states they're also used as main air jets on Mikuni BS34s :bike:

Despite all the trouble this ride is causing me, I'm learning more about bikes than I expected to before even hitting the road.

brockd · Apr 17, 2015

Now here's a question - the original parts breakout calls for a #170 jet, which the distributor doesn't seem to have. If I went down a size to a 160 d'you think we could adjust the fuel jet to correspond and run ok?

Tx!

xschris · Apr 17, 2015

Those are not the same jets. Trust me I have bought them before. http://www.pjmotorsports.com/mikuni-jets.html B42/55 jets are what you need!! The one on the left is what you need. They where used in the 77-79 xs400. The one on the right is the type used in the 80-82 xs400 and the 80-84 xs650.

brockd · Apr 17, 2015

Hey Chris - I'm talking about the jet on the airbox side of the carb, not the fuel jet. I've also checked the manual that came with the machine and it shows that the carbs used are BS34s. What do you think of the description found here - http://www.xs650direct.com/products-38.html - under Main Jet - Small round type where they mention this also fits as the air jet on the BS34s.
Not trying to say you aren't right - just going off what my manual tells me.
Cheers!

brockd · Apr 17, 2015

Also - is it possible that the BS34s in the '79 XS400 and the BS34s in the '80 XS650 differ at all?

Cheers!

JARichmond · Apr 17, 2015

Just an FYI, the part you're looking for is not a main jet. They will be different as the part you've listed sit in the carburetor bowl. Note that the threads are different. Chris is a seasoned veteran regarding his XS and has got some pretty insightful advice regarding getting yours to run perfectly. I'm not saying he's a demigod but....

brockd · Apr 17, 2015

Hey JARichmond
Sorry - I meant I'm after the air jet that sits on the airbox side, not in the bowl.
I wish I could sound like I know what I'm talking about but the bike is still 300km away from me. Can't just nip out to take a photo. Will try to get the shop guys to send me one.

xschris · Apr 18, 2015

brockd said:
Also - is it possible that the BS34s in the '79 XS400 and the BS34s in the '80 XS650 differ at all?

Cheers!

Yes. The 77-79 bs34 used in the xs400 is not the same as the 80-84 xs650 bs34 in many ways. The 77-79 have exposed idle mix screws, screw in float valves, different size and shape air screws, different diaphragm/slide size, different needles and needle jets and the outer covers for the butterfly seals are fixed metal washers. First pic is 77-79 xs400 and the second is 80-82 xs400 (with a few mods).

xschris · Apr 18, 2015

First pic shows the jet I am talking about. Second shows the the 80-82 carb (left) and the 77-79 (right)

brockd · Apr 18, 2015

xschris said:
First pic shows the jet I am talking about. Second shows the the 80-82 carb (left) and the 77-79 (right)

Interesting! I love forums - learn so much.
Thanks very much for the info. I'm gonna have the mechanics send me a pic and will report back.

brockd · Apr 19, 2015

Now here's a question - in the interest of saving time - might anyone here in Ontario have a spare pair of these jets (for the '79) kicking around that I could buy? Looks like my only two sources are in Oregon and California and I'd really love to be able to get this thing on the road by next weekend.
Cheers!

brockd · Apr 20, 2015

Woof - both PJs and Jets R Us DO NOT like canadian credit cards...
I've managed to place an order with Niche Cycle out of FL and they seem to have no problem with my money.
Will be popping the jets in this week and will report back with the findings

brockd · Apr 21, 2015

Finally got a pic from the shop... and it's a perfect match to yours, Chris.
The jets are in the mail and should plop right into those holes.

OleDoc · Apr 21, 2015

Yes listen to Chris.he knows these bikes like the back of his hand

iamunique127 · Apr 21, 2015

Ditto what OleDoc said.

When I first came on this forum I read somewhere "I should just listen to you guys the first time, it would save me a lot of time".

I have found that to be true.

brockd · Apr 22, 2015

Yer all very right. I also hang out over at a guitar forum and should have known to trust the masters. I only just realized XSChris falls into that category with his 6k+ posts in here.... :yikes:

So please humbly accept my newb-ish badgering

xschris · Apr 22, 2015

It is always a good idea to ask questions about a purchase

Saving money is a good thing.

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