emulsion tube

P

perkinja

XS650 Addict
Messages
128
Reaction score
7
Points
18
Location
Munster, Indiana
I've rebuilt my carbs (bs38's), gone through all ranges of jets from stock to lowest andI'm 95% sure my rich problem is coming from the damn oring that goes around the emulsion tube. I've ordered the viton mccar master orings everyone suggests, when I went to put them on and put the tube in it just doesn't hold or seal the tube off. I've find 4x1.2's too big and I'm wondering the seats for my tubes has worn itself bigger if that's at all possible.
 
man.. idk... I put m4x1 on my tubes, and they still wiggle quite a bit. But they do seal.
Once the bowl is on, Iguesse they seal up tight, ive had no issues. But a few years ago, I put mikes O-rings on, they were tight, but now since I actually own the bike, I wanted something better, good thing too. Mike's rings were rotted after only 4 years, and that was without running.
 
As Angus said, the float bowl pushes the tube in completing the seal. You said the tube doesn't "hold." The float bowl holds it in.
Why do you think you have a rich problem, what are your symptoms?
 
DogBunny said:
As Angus said, the float bowl pushes the tube in completing the seal. You said the tube doesn't "hold." The float bowl holds it in.
Why do you think you have a rich problem, what are your symptoms?
Click to expand...

I started off my carbs with the stock 27.5 pilot 135 main 2 1/4 turns out, with pods on the carbs and no baffles on the exhaust. I figured since the increase in air i would have to go up in jet sizes, but at idle i get a brown plug, riding around in first/second gear at an 1/8 to maybe quarter throttle i still get brown, but when i hit anything past that quarter throttle ( 3rd, 4th, 5th gear) my spark plugs are just dark as night. Correct me if i'm wrong but a little past a quarter throttle the main and needle come into play i thought?

Sooooo, with what i assumed i thought that my main was too high, so from 135 i went down to 130, still rich, took my needle all the way to the top and i'm still rich. I just put in the 125 mains today and have yet to ride it around and test it but my assumption being that that oring isn't sealing anything off it's not going to matter what main i have in there because gas is just dumping into the carb.
 
Your needle jet (the emulsion tube) should be a Z-2. Please verify.

I base the Z-2 needle jet on the stock jetting and air mix screw setting that you specified, which indicate that you have a 78-79 carb set. Can you verify that? I.E., do you know how to tell a 78-79 set from earlier years?
 
Yes they are stock carbs from a 2f which came with bs38's unless i read this owners manual wrong. this book i got along with an original yamaha guide not a clymer to work on the bike says bs38's (SU) x2

I do have the Z2 needle jet (thought it was called an emulsion tube) and the 502 slide needle.
 
Last edited:
You did not answer if the emulsion tube is a Z-2. The Z-2 tube does not "pop out" nor does it need to be held in with the float bowl the way that the 1977 and earlier tubes do. So, if the tube "doesn't hold" as you wrote in your original post, it may be because you have the wrong tube, or the wrong carb, but I can't tell if you wont verify what tube and needle you have.

As for determining what year your carb set is, look at the intake bell, if there is an oval opening at the top and two small round openings on each side, then you have a 78-79 carb set (assuming that you have BS38 and not BS34 carbs). Otherwise, you don't. Go to mikesxs.net, click on the model I.D. chart, go to the bottom, and identify your carbs.

If you don't have the right slide needle and tube, or if you are jetting for a wrong year carb, that could be the cause of your problems.
 
Okay, if your emulsion tube is really loose, maybe that's your problem. With o-ring (4 x 1 is correct), it should stay in place (without the float bowl holding it). Maybe someone damaged the hole in the carb body trying to remove it.

Your main jetting numbers are way off. If the bike is stock, stock jetting and needle clip position should be right or very close to right, unless you have a damaged carb, which maybe you do. If you really think that your carb is properly cleaned, and everything else is working right, you could try using a "gasket maker" type flexible rubber silicone sealant in conjunction with the 4 x 1 o-ring to seal the tube and see what happens.
 
Even with getting rid of the stock airbox (i've got pod filters on it) and not having the baffles on the exhaust (they were cut off, hardtailed the frame so they would no longer fit) the stock jetting should be correct? Ill look around for some gas resistant sealant and possibly go that route. Thank you for the replies dog.
 
I forgot about your pods and pipes. For your set-up, one up on pilot to 30.0, four up on main jets to 145, and raising (leaning) the clip one slot from third from top to second from top should run very well if the carbs are working right. So, the jetting you've been describing indicates something wrong.

The only other things I can think of are correct float height and good diaphragm rubbers, but I don't think either of those would give you your symptoms. Have you done a diaphragm drop test?
 
The needle jet itself can be bad. It can be "worn" on the inside, the metering orifice now larger than when it was new. This isn't usually a wear thing, the needle rubbing the the jet bigger. That can be a problem for some bikes and their carbs but I've not seen it with this bike. What I have seen here and with other bikes is a badly gummed up carb having the gas residue eat away at the inside of the needle jet, enlarging it and making it richer. If you're at your wit's end and ready to throw in the towel, I would suggest replacing the needle jets.
 
Just throwin' it out there, a bandaid solution. A job for a caliper and Xacto knife. Measure the ID of the hole, and OD of the fitted o-ring, to get the mis-fit value. Then cut some thin fuel-resistant tape, perhaps 0.025" wide, and wrap enough winds of that tape in the groove of the needle jet to make up the missing diameter...
 
I'll try your bandaid twomany and test it from there tomorrow and see if that fixes anything. if it does maybe my emulsion tube is worn and ill try ordering new ones. If not ill go 5twins route and replace the needle jets. either way i'll post back with my results once i get them. Thanks again guys for the help.
 
So I tried the bandaid fix with yellow Teflon tape, 30 pilot 140 main. At idle and an 1/8th throttle (under load 1st and 2nd only) the spark plugs were fine. When I tried to give it anything past an eighth tho I could tell it was just starting to foul out from too much gas (would give it a quarter and it would bog down but once I hit about 3/8ths it would power through). I switched my main back to a 125 with the needle notch all the way up and test road it around and it had great response up to 3/8ths and a little more. I didn't try to take it to half throttle but when I pulled the plugs they were a little fouled but not nearly as bad as before the bandaid fix.

I'm gonna assume that its my emulsion tube at this point not sealing correctly.
 

Similar threads

B
My dead XS650
2
Replies
21
Views
1K
650Skull
650Skull
M
Float Height for Mike's/Aftermarket Floats
Replies
8
Views
854
5twins
5twins
V
A first time builders journey
Replies
11
Views
809
Kevin Werner
Kevin Werner
Cafe Murdock
Freshly rebuilt xs650 to face fireing squad
Replies
12
Views
1K
Cafe Murdock
Cafe Murdock
K
Right Carb Running Rich
Replies
18
Views
2K
5twins
5twins
Back
Top