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deathtrapmfg
03-20-2010, 6:41 PM
so i just picked a mint condition 81 xs 650 special.the dude i purchased from told me it need a new diaphram in the right side carb.i just dropped a new batterie in and got it to run for a few before it died out ,but it was pissin gas out the left side of the airbox ,my questions are woould gas come flowing out the left side air intake becuse of a bad diaphram(im thinking he was just wrong a bout what side the bad one was on).also when i replace the diaphram do all the gaskets and rubber rings need to be replaced or can they go back in if not damaged.also if im gonna run v stacks or pod filters and straight pipes will i have to rejet the carbs if so wich jets and how much bigger or smaller would they have to be.sorry for all the questions. sorry for all the question i just dont know shit about carbs.

revmike
03-20-2010, 9:58 PM
I just cleaned a set out today too. If you free up the air flow you need more gas as well, or you'll run hot and burn holes in things that shouldn't have them. I have my filters off and have to run about 1/3 choke just to keep it going, but you don't want a blow torch in there.

I have Mikuni CV carbs. There isn't much on them rubber wise or o ring wise to replace besides the diaphram. Have you pulled them apart, or are you wondering before you jump in there what you will need to do?

You can tear them apart pretty well without hurting too much that isn't already going, I would think. I know I just stripped 2 down and totally cleaned them out and reassembled and the bike started immediately which I don't think it had done for years. No replacements though...

Do you know which carbs you have?

~Rev Mike

deathtrapmfg
03-21-2010, 7:55 AM
thnaks for the advice revmike,from what i gather ive got the mikuni bs34 cv carbs.so ill most likey have to put bigger jets in the carbsif i free up the air flow going into nad out of the motor,but wich ones the main or the pilots jets and how much bigger would they need to be.do you think that a bad diaphram would make the gass come pissin out like that or is it maybe just dirty and plugged up inside. and no they havent come off the bike yet im tryin to figure out what i gotta do first the whole thing is getting tore down soon though i just wanted to fire it up and make sure it was gonna run before i riped it apart.

revmike
03-21-2010, 8:43 AM
The diaphrams are pretty easy to check. They sit beneath the dome on top. You could take the four screws out that hold the dome on and slide the diaphram and throttle out, or just look at the diaphram. That's pretty easy, but I wouldn't do it with them in the bike.

A hole in the diaphram would definitely and critically mess up the flow of air and gas through the carb. I don't know that it would let gas go out the intake side, but stranger things have happened.

As far as jetting goes. I don't know what would get you there. Mostly because I'm not that smart. But you also have the issues of current jet size, elevation, air filter and exhaust flow, etc.

Your best first bet would be to get it running, even if it is rough, with the current set up and start adjusting from there. If you have to replace the diaphram it wouldn't affect the jets.

As far as which jets go, I'm trying to figure that out too.

Hope that helps a bit.

~Rev Mike

deathtrapmfg
03-21-2010, 12:09 PM
thanks bro i really apperciate the insight .it helps alot .

BrettMavriK
03-21-2010, 3:48 PM
I'm rebuilding my carbs on my '81 XS build right now and am going through the same process as you.

I found these adjustable aftermarket needles on ebay from a guy named XS John:
http://cgi.ebay.com/ebaymotors/XSJOHNS-XS650-HI-PERFORMANCE-BS34-CARB-JET-NEEDLES_W0QQcmdZViewItemQQhashZitem439e1faff4QQite mZ290415685620QQptZMotorcyclesQ5fPartsQ5fAccessori es#ht_500wt_1182

http://i90.photobucket.com/albums/k276/brettmavrik/Private%20Stuff/XS650%20Project/My%20XS650/IMG00467.jpg

I've heard these needles are a Godsend for BS carbs, and John has been very helpful via email. He says stock, I should have 132.5 main jets. I found someone had switched them to 130's, which was my lean condition culprit. John recommends 135 "large round" main jets with his needles. These engines are very sensitive to air filter, header, and muffler changes, so these needles should really help to dial it all in. His kit comes with different spacers, and a bit for drilling out the pilot jet to 46 from a 42.5 which he recommends for better idle and cruise. John and I are actually emailing each other back and forth right now. Cool guy.....

Here's a link for the 135 large round main jets:
http://cgi.ebay.com/ebaymotors/Mikuni-Main-Jet-Tuning-Jetting-RS-HS-N100-604-135_W0QQcmdZViewItemQQhashZitem2305d31d5bQQitemZ15 0421577051QQptZMotorcyclesQ5fPartsQ5fAccessories#h t_2256wt_939
Don't get the hex jets as they aren't the right ones for us.
HTH

revmike
03-21-2010, 9:49 PM
The stock needles should be adjustable too 5 positions I think, although you really only get one richer setting without changing jets.... The needle should affect about 1/2 the range from 1/4 throttle to 3/4 throttle. I didn't think about that, but Brett's right, that is one way to approach the mix without changing jets.

ALTHOUGH, as Brett says here, Yamaha made the carbs WAY lean with 130 main jets. Prob to help get through emissions requirements.

But again, who knows what is in there after this much time.... I'm still just trying to get mine running before I can get fancy and make it actually run RIGHT...

Thanks for the info Brett... keep us posted...

~Rev Mike

BrettMavriK
03-21-2010, 10:11 PM
The stock BS needles aren't adjustable.
Grit, contaminants, and varnish build up can screw with the precision instrument of black magic known as the carburetor. You could have a leaky ballast in a float, a torn or dented float needle tip, or a bad rubber seal somewhere. Did you have them apart as of yet? did you replace a float bowl gasket? I've heard some replacement gaskets are a missing a necessary hole punch for a passage...
You're going to have to disassemble your carbs and go through them to figure out the problem anyways. Get Johns needles, the 135 main jets, and then get the Carb rebuild kit from Mike's XS. Then go to the parts store and get the gallon carb cleaner with the drop in parts pail inside. Methodically disassemble and reassemble them one at a time after you clean the components thoroughly; replacing anything that needs it.

Do it.
Until then, keep guessin'.... = ]'

deathtrapmfg
03-22-2010, 3:41 AM
thanks for the advice brett im gonna do that. i prob wont get to it til the weekend to tear em apart but ill try and keep you guys posted .

XS2rat
03-22-2010, 5:31 PM
i had gas spitting out at me from my 72' after completely rebuilding with kits and new diaphragms and i found it to be a leaking float. same thing can happen with a stuck needle. floats may not leak right away after sitting. just had the same thing happen this week with a cb350 ive been riding. took the better part of the week for the corrosion buildup on the old float to wear off, make a pinhole and start filling the float with gas.

also check out how healthy the throttle shaft seals are. i couldn't tune my 72 carbs right because of vacuum leaks at the shafts. i could push with my thumbs on the ends of the shafts and drop the idle speed. my carbs were 38s i think so your carbs are a little different but these are two things you can easily check that sometimes get overlooked.

i ended up buying a pair of later carbs but haven't run them yet. the adjustable needles look like a good idea. i plan on running some kind of pod or stack and long straight pipes so i'll have to jet up as well. ive heard some say to go for a bigger main and pilot first before changing needle settings.

revmike
03-22-2010, 11:19 PM
Brett: I haven't done it, but if you take the needle apart from the slider, you'll see that it is adjustable once you get it out of the holder. If you look on Mike's they sell the stock replacements which are adjustable. As I said, I haven't done it, just saw the reference in my service manuals. I wouldn't be surprised either way.

Stock BS 38 Needle: http://www.mikesxs.net/parts/img250/48-0653.jpg

Mike's Needles (http://www.mikesxs.net/products-37.html#products)

BrettMavriK
03-23-2010, 12:04 PM
All '80 up BS34 needles have only one slot and are tapered differently than pre years from that.

http://i90.photobucket.com/albums/k276/brettmavrik/Private%20Stuff/XS650%20Project/My%20XS650/IMG00471.jpg

John's needles are made specific for specific carb types and have multiple slots. John also provides different spacers to dial in the fuel map curve. He also recommends drilling the pilot jet out to 46 from 42.5 for better idle, cruise, and cold starting, using his supplied wire bit. You can get 45 or 47 pilot jets from Mike's XS. There really isn't that much difference in performance from a 34mm to a 38mm BS carb. It's all in the needles and the fuel map set up on a stock engine with changes in exhaust and air filters. I was going to go with different carbs, but John showed me I can get great performance from my BS34's. I'll know when I kick my bike to life for the first time since the chop next week.

The rest of my carb rebuild parts will be here tomorrow from Mike's,
I'm covering my carb rebuild on my thread if you'd like to follow.

http://www.chopcult.com/forum/showthread.php?t=3169&page=6

deathtrapmfg
03-27-2010, 8:03 PM
so i pulled the carbs apart it looks to me that the diaphrams are fine no visable holes or anything funky looking .but i did find the carb on the choke knob side (the one that was leaking gas out of the intake) the main jet was plugged up to were you couldnt see through the hole.would that cause the gas to fill up the bottom of the carb and drain out through the intake?also the other carb the float seemed to be kinda gummed up and not as responsive as the other im thinking that could be the problem the previous owner thought was the diaphram that caused the bike to bogg down when given throttle.im not sure im right any insight is well apperciated.

revmike
03-28-2010, 1:12 AM
so i pulled the carbs apart it looks to me that the diaphrams are fine no visable holes or anything funky looking .but i did find the carb on the choke knob side (the one that was leaking gas out of the intake) the main jet was plugged up to were you couldnt see through the hole.would that cause the gas to fill up the bottom of the carb and drain out through the intake?also the other carb the float seemed to be kinda gummed up and not as responsive as the other im thinking that could be the problem the previous owner thought was the diaphram that caused the bike to bogg down when given throttle.im not sure im right any insight is well apperciated.

If they are gummed, the diaphragm can't suck up the carb slide, which would be LIKE not having a good diaphragm and bad (no) response. run the carb cleaner with the little straw attachment through all those little holes and openings. Some you have to spray for a while to get them to loosen up. They should fo somewhere, so if it doesn't flow out when you spray it, keep spraying until it breaks free. There are one or two that go no where, just to fuck with you... take off the big parts and clean them and take apart the choke with the brass nuts and spray/wipe those out. Wear eye protection because some of those holes will send the carb cleaner off in odd directions - usually where ever your eyes are. reassemble like any gasketed part - go around and slowly tighten the opposite nuts and then don't tighten down too far. The diaphragm wants to pop out of the little rim a few times but it will settle down eventually and you can bolt er down.

Of course, by now, you're already done and drinking beer while she purrs in the background.

I got my wife's going, only to find the leaking seals.... oh well, that's one way to trouble shoot...

~Rev Mike

BrettMavriK
03-28-2010, 11:46 AM
Best $19 you ever spend on rebuilding your carburetors...

http://i90.photobucket.com/albums/k276/brettmavrik/Private%20Stuff/XS650%20Project/My%20XS650/IMG00537.jpg

Autozone, Napa, Advance...they all have it.
Get a rebuild kit, 135 main jets, and XS John's Needles. You'll be glad you did if you want performance. This bucket comes with a parts dunking pail. Completely disassemble the carbs and submerge the entire carb bodies, float bowls and related parts for 15-20 minutes and watch the visible varnish disappear. Do not put anything rubber in there or it will be eaten.
Do it once, do it right......and fugetaboutit'... = ]'

http://i90.photobucket.com/albums/k276/brettmavrik/Private%20Stuff/XS650%20Project/My%20XS650/IMG00491.jpg

deathtrapmfg
03-28-2010, 6:33 PM
i actually stopped at pep boys today looking for that carb cleaner kit but no luck gonna try advanced.how do u get the pins that hold the floats in out.

1fughit
03-28-2010, 7:52 PM
Before you dip them make sure to remove the air screw on top of the carb,
there is a little o-ring in there that you will need. If the screw is stuck you can
cut the tower down and notch the screw with a dremel. http://i93.photobucket.com/albums/l75/nkolas/DSC01140.jpg[IMG

1fughit
03-28-2010, 7:58 PM
Also Mikesxs has a generic setup for the 34's.
I run a #145 main #45 pilot and 127.5 air jet 2 1/4 turns out on air screw.
for what it is worth. http://i93.photobucket.com/albums/l75/nkolas/DSC01139.jpg

Robhall
06-16-2010, 12:50 PM
Old thread, but you might want to look at the petcocks. XS's are known for these things leaking gas when they are old. And if your BS34s are anything like the BS38s on my 79, there is no bowl overflow, so it will flood the carb, piss out of the air filter, and also leak into the cylinder, past the rings and into the oil. Might want to check your oil for fuel contamination.

tobiism
06-16-2010, 6:26 PM
You should NOT be dipping those carb bodies in that carb cleaner! The pivot shaft for the butterfly has 1 quad ring on each end. Those quad rings will dry out and not seal on the shaft and can cause really annoying vacuum leaks that can be a serious pain in the ass!

Robhall
06-16-2010, 7:24 PM
You should NOT be dipping those carb bodies in that carb cleaner! The pivot shaft for the butterfly has 1 quad ring on each end. Those quad rings will dry out and not seal on the shaft and can cause really annoying vacuum leaks that can be a serious pain in the ass!

It's funny you mention that. I came across this thread searching about butterfly shaft seal leaks. I never did this with mine though, they're just old and worn out. Mikes XS sells new seals for 5 bones a pair: http://www.mikesxs.net/products-75.html#products It's near the bottom of the page.