And again...carb settings..

[voelser]

I know there are hundreds of threads about this and I have read quite a few and I have also gone though a lot of the steps in them. But to no avail....

Let me set the scene: '78 XS650E, modified to have pod filters and straight through pipes. I am using the stock carbs (BS38...however going by the internals this is a '77...more about that later). Top half of the engine rebuilt, rebored to second oversize. Carbs cleaned, new gaskets, floats set, stock pilot jet #25 VM22/210, stock needle jet z-8, new needles on third slot, main jet from the stock 122.5 to 135 (on Heiden Tunings recommendation), but now back down to 130.

Now here is my problem: whatever I do the engine is running too rich. Way too rich. Sooting up the plugs very quick, puffing smoke on revving and running rough. I have changed the main jets (as above), tried the needles in several positions and even put in new ones, changed from pleated filters to foam filters. But none of that seems to make any difference.

I'm not quite sure what else to try. The only thing I can think of is even smaller main jets (maybe back to stock) or maybe smaller pilot jets?

I'd love your thoughts and input.

Cheers!

 

[Motocue]

U may need new piston and rings and a valve seat job. U may or them carbs r junk. First try a leaner pilot . The main and needle is not going to help at idel just the pilot and a little from the air screw.

 

[voelser]

Cheers for your reply. I forgot to mention that of course with the rebore came new pistons and rings! Had this done by an expert, so Inwould assume that's all in order. But then again stranger things have happened!

But yiu agree I should try smaller pilot jets then. Any idea about size?

 

[Motocue]

U have 25's try 22.5 see if it gets better than ride it and if it feels a bit rich in the mid range lean the needle clip one by going up on the clip bringing the needle down into the carb more. If u got down to a 20 and it pops when u let off its two lean.

 

[650Skull]

Internals won't tell you what year BS88's you have. need to identify them by the externals before setting up your jets.

There are plenty of threads that show the year of the carbs and the set up needed.

You need to read the carb guide, (Tech menu, Carbs), that has all the answers in it.

Google search.........BS38
http://www.xs650.com/forum/searchgoogle.php?cx=partner-pub-9696397702584771%3A6nvbm3frz9z&cof=FORID%3A9&ie=ISO-8859-1&q=bs38%27s&siteurl=www.xs650.com%2Fforum%2Fshowthread.php%3Ft%3D11980%26page%3D8&ref=www.xs650.com%2Fforum%2Fforumdisplay.php%3Fs%3D2647dafb19484fa5a058fb786b2412ec%26f%3D2&ss=14328j60447422j8

Threads
http://www.xs650.com/forum/showthread.php?t=23881

http://www.xs650.com/forum/showthread.php?t=21807

 

[voelser]

Cheers. I was pretty sure I have a '77 BS38 and after checking that thread I'm even more convinced.

I've read the carb guide and as said went through quite a few of forum posts. What strikes me is that with the changes I did (open air filters and open pipes), I should be running lean and need bigger pilot and main jet, which makes sense to me: more air, more petrol needed! But all the signs I am getting are that I'm running rich. Hence me turning to the forum..

So my main jet has gone from 122.5 to 135 and back to 130. Pilot jet is 25, but now thiking of making that smaller as well...odd?

 

[Motocue]

Yeah u should not have to go any leaner on the pilot. Mains sound close... U could have weak spark bad plugs... So many things. But I raced pro motocross all my life and lean pops rich runs gurgly loads up. Good luck ... All else fails by beer and push it to the back of the garage and forget about it for the night.

 

[XSLeo]

Some when in 78 they changed the carbs. The early 78 carbs were the 76/77 carb set, the later carbs were the 78/79 carb set.
So having the early set is ok. Your stock brass being a 122.5 main, 25 pilot, 4M1 needle, Z8 needle jet indicate this.
Where did you get the new needles? If they came in a kit they are probably not the right needle. If you still have the original needles try putting them back in the carbs.
Check the markings on the new needles. If they don't have the 4M1 on it they are wrong.
You might have Y22 needles from the kit. They may be too short as well as the wrong taper. Even with the clip in the top slot the needle won't go far enough down into the needle jet.
Leo

 

[5twins]

Yes, the notorious Y22 generic needles. They are 5mm shorter than the 4M1 needles that came stock in the '76-'77 carbs. The clip slots on Mikuni needles change the height by 1mm so the Y22 would be like 5 steps richer. Even at its lowest setting, it would still be 3 steps richer.

 

[voelser]

I got mine from Heiden tuning:

http://www.heidentuning.com/p/28/2390/mo74-cg|25=4/%2348-0657-slide-%28jet%29-needle-4m1

Seems to be the right one. I've been away fro the weekend, but now I can dive into this issue again. They are in the third (middle slot). Maybe drop them one?

Some when in 78 they changed the carbs. The early 78 carbs were the 76/77 carb set, the later carbs were the 78/79 carb set.
So having the early set is ok. Your stock brass being a 122.5 main, 25 pilot, 4M1 needle, Z8 needle jet indicate this.
Where did you get the new needles? If they came in a kit they are probably not the right needle. If you still have the original needles try putting them back in the carbs.
Check the markings on the new needles. If they don't have the 4M1 on it they are wrong.
You might have Y22 needles from the kit. They may be too short as well as the wrong taper. Even with the clip in the top slot the needle won't go far enough down into the needle jet.
Leo