Jetting issues after head rebuild

[vorhese]

Jetting issues after head rebuild / and mixture screw issues

I have a 1980 XS650 with pods and BUB exhaust (welded in baffles). After rebuilding the head, my bike seems to be running really rich and sputtering. It currently has 145 mains (that seems big) and 45 pilot. Stock is 132.5 and 42.5. Before the head rebuild I had some no baffle cones on and it ran good for 8 years, the mixture screw was 3 turns out. Then I put the BUB exhaust on and it ran good.

After the head rebuild it started up strong (2nd oversize pistons). After a few torques and valve adjustments, everything is set. The bike sputters from about 1/4 throttle on, black smoke, and will stall after a minute. I had to screw the mixture screw in until 1 turn out to have it run well.

Any idea what the heck is going on?

 

[vorhese]

Is the main affecting this? Technically it should be 137.5 (2 sizes up) with pods, correct? Even at 1 turn out on the mxcture, I get stutter at about 1/2-3/4ish throttle.

 

[vorhese]

I found this on this link
http://www.xs650.com/forum/showthread.php?t=1650


"Bub pipes require jetting changes to the stock Mikuni carbs. We found that K&N R-135/2 air filters (they replace the airbox) are quieter and cheaper than the OEM-type K&N replacement filters. After fitting the Bub pipes and K&N filters, the main jets
should be replaced with No. 145 jets, the needle should be dropped to its lowest
position (remember, lower the needle not the clip), and the plastic caps removed
from the idle mixture screws. Adjust the mixture screws for fastest idle, keeping the
idle speed down to less than 1200 with the idle-speed screw. The idle-mixture screws
should be set so that turning them a quarter-turn in either direction will cause the
idle speed to fall slightly."

should lowering the needle fix this problem?

I guess this is taken from here
http://www.biker.net/650/betterxs2.html

 

[vorhese]

I could use a little help figuring out if it's the needle that's affecting this, and what to do about it. I see there are various ways to make the needle adjustable, but I'm not sure what route to take.

 

[ippytattoo]

If you have the bs34's that should be stock on your bike then the needles are not adjustable (other than shimming which will raise the needle) unless they have been changed over to the Canadian needles and needle jets. may want to check float height and verify what carbs you have on there.

 

[weekendrider]

^ +1 Try a 140 main.

 

[5twins]

The article you quoted from is the old Minton Mods one. They were working with a '78 Special which had BS38 carbs, so their jetting recommendations aren't going to apply to you and your BS34s. Try a 137.5 or 140 main. I'm not really sure why the 145 worked in the first place. It's very big. Your needle isn't adjustable but it came set lean from the factory. The slightly larger mains and pilots should work fine without needing to lean the needle further. But 142.5s or 145s may need a leaner needle setting. That's why you were getting the break-up probably.

 

[vorhese]

Thanks everyone.

Well, I decided to check the free stuff first and thought about my floats. I had set mine to 25mm according to the manual... but reading here the 1980 should be set at 22mm+/-1mm. I was hoping that was the culprit, but thinking about it that should have made it a lean condition. I also threw in 142.5 mains while I was in there (the smallest I had). I'm still sputtering 1/4 throttle on and don't feel comfortable doing highway. Black smoke on throttle blips. I guess before I worry about adjustable needles I should try a 137.5 and 140 mains? Do the mains have a lot of affect in the 1/4-3/4 throttle?? Perhaps I should also get a 42.5 pilot (back to stock) even though I have pods?

EDIT:
Wait a sec... According to this chart 1980 (G model) should be 27.5mm float??? That should lean it out, right? They are all over the place with the settings!!!

 

[5twins]

Yes, if you have 1980 carbs with brass floats, the setting is around 27mm. Yes, that will make it leaner than a 25mm or 22mm setting. The manuals didn't keep up with the hardware changes. The floats were changed but the manuals still listed the old setting specs. It took a bit of research to find all that info when I put that chart together.

 

[vorhese]

they are black plastic floats. ??

EDIT I checked my serial
4N9-004454
That looks like a
XS-H SPECIAL II 80-81 4N9 4N9- 000101

so I guess it's an H model? So 22mm is correct float?

 

[5twins]

Then someone "upgraded" them to the newer ones. That can work but there are some shit repros out there that don't work too well. How do they fit on the pivot pin? Loose? The originals had a sleeve insert in the hinge that made for a nice snug fit on the pivot pin. Some of the repros don't have that insert and are loose as hell, metering fuel like shit because of it. You will need to use the 22mm setting for those plastic floats.

My buddy went through this with his 1980 BS34s. He finally gave up on the shit repro plastic floats he had, bit the bullet, and bought genuine Yamaha replacements (brass, just like the originals). Problem solved.

 

[vorhese]

I edited my above reply

The float pins are really tight, I can't even tap them out it seems. At least, not easily like a lot of carbs I've had.


I feel like all I have left as an option is the main jet.

 

[weekendrider]

The 34's float pins are very tight to begin with.
Careful or you will break a pin tower.

 

[5twins]

Yes, those pins have a splined end and that fits very tightly in the post. That's not the tight part I was talking about though. I meant the float's fit on the pin. Those bad aftermarket ones are very loose and sloppy on the float pin. That causes them to meter imprecisely. Sometimes they do OK, then other times the carbs will just start belching fuel. They're junk. They just don't meter consistently.

 

[vorhese]

UPDATE:
So I'm now running 137.5 (2 up from stock) mains and still running 45 pilots (1 up from stock) and the mixture screw is about 2.5 turns out. Carbs were bench sync'd. I've narrowed it down to getting a fouling plug on the left side. It will idle ok, but any throttle will cause it start to sputter and stall. Left pipe shoots a cloud of smoke on throttle blips. I switched plugs, and it repeats to fouling on the left side. My floats were set at 25mm originally, now 22mm since a few days ago... but they are the only thing I can think of that would cause the fouling. I set them having the carbs at 45 degrees and the tang just touching the float needle, measured both floats in both carbs. I am baffled.

EDIT: BTW I'm getting 140 compression on the left side.

 

[TwoManyXS1Bs]

Some info here: http://www.xs650.com/forum/showthread.php?t=32330

 

[vorhese]

Ok I took the carbs again and took the float bowl off the left carb, hooked up gas, and I pushed up the float until just as it stopped dripping. I did it multiple times. It always read 22mm. But that's assuming that is the correct measurement for these floats. Here's a picture of the floats, not sure if they are aftermarket or not. The tang looks unusually pushed down compared to other floats I've dealt with. I might try setting them to 25/26mm like before and see if that helps.

these are my carbs

 

[5twins]

Those look like original floats. I can see the sleeve insert in the pivot in your pic. 22mm would be the setting for them. Where are you measuring to? You should measure to the top of the round part of the float "bulb", not the flat area up by the hinge, like so .....

This one is set at about 21mm. Are the o-rings on the float needle seat and mix screws in good shape? Do you have the rubber plugs over the pilot jets? Any of this stuff being bad or missing could cause a rich condition.

 

[vorhese]

Measuring correctly. O-rings look good. Rubber plugs over pilots.

My one mix screw is very difficult to screw in and out, the one on the fouling side. I swapped it from the other side carb to see if it was the carb's threading, and it's as difficult to screw in on either carb. It looks fine, even the threads, so I didn't understand why it was so tough. Maybe I'll try replacing it now. It needs to be done anyway. How many different types of carbs use this mix screw? Maybe I have a spare.

 

[5twins]

Only the BS34s have that exact style of mix screw. It would be the same from any year BS34 but none of the BS38 mix screws would fit. When you switched the mix screws side to side, did the rich condition follow? Did you examine the screw tip? Maybe it's bent?