Carb Tuning lessons learned.

[dbeardslee]

Ivan - Cobia may be on to something with the pilots. I just jumped up a size on my pilots (although I also went a size up on the mains). I like to test my low end out on a very steep hill near my house. I go down there and see how low an rpm I can pull it with. Even with the 750 FD Betsy will walk up the hill at less than 1500K.

DGXSER just turned me on to to this yesterday. Seems to be some pretty good info on CV carbs.

[Ivan]

I have been using the factory pro guide for quite some time. I even have it bookmarked, and several print outss laying around my garage.

I have a set of 50 pilots ordered. I cant seem to adjust my idle rich enough, then at off idle its way rich. I dropped my floats to the point that they only opened about 1/8 inch more than closed. Low end pulls likee a tractor this way, but is flat on the top end. I imagine I can raise the floats if I get a leaner needle setting. Thee problem is that 81 needles arent height adjustable. I guess I could remove the little plastic spacer and use some thin washers. I would definately like to keep it so changing back to stock is easy. I have a set of early carbs that have adjustable needles, so I may try a swap on those. If that doesnt work, I will order a set from Mikes XS.

Trial and error. gotta love it. I can pull carbs in two minutes, adjust in another three and have them back on in another three and a half.

[dbeardslee]

Ivan - I got a set of kits from carbkitscapital last fall that included the needles. They didn't look identical to stock, but Betsy sure seems to like them. 'Course those were for 78/79 carbs - don't know about the 80/81's.

[Ivan]

well, tonight, I swapped some identical washers in for the little plastic spaced on the needles. I would say the washers are about half the thickness of the spaced, which would lower the needle about 1/16 of an inch. The difference was not very noticeable. I put the floats back up to about 2 mm lower than stock, so maybe it helped. maybe not.

Tomorrow, I am going to try swapping the needles from teh set of old style carbs, if it is even possible. I'll see what happens then. Hopefully my pilot jets are in and I can swap them as well.

[Ivan]

Well, today I got the 50 idle jets in and they are way too much. I went form a 45 to a 50 and it got much worse. So I went back to the 42.5 jets and they are much better. Still a bit fat in the low end, but much better.

The problem is that the idle needles are almost worthless at idle. I had to tune them at about 2000 rpm with the throttle locked to get a good feel for the idle. At idle speed, they are either closed and not running or even just 1/8 turn ope is the same as 5 turns open. At a higher idle speed, then I can get the normal peak and settle like it should be.

If it stops raining I will try and lower the floats down a bit. I wish I could post some measurements, but the kids ran off to school with my carb scale.

[DGXSER]

Ivan,Sorry I do not remember what year your bike is. I know you are a top rate mechanic, so take this with a grain of whatever makes it sound best.

Your problem sounds a whole lot like mine to some extent. My bike would start great and idle fine. But if I left it idle for long or rode for long at all at lower RPMS, no 1 would soot up BAD and foul out to the point of missing! All other three looked great no problems. I could turn that no 1 mixture screw form 1/2 turn out to 5-6 turns out and hear no change in how she idled or how sooty it got.

I finally just last week got the bright idea to check my needles. I found that no 2 needle would turn easily and no 1 would not budge, it was MUCH tighter. So I opened it up and could see no reason, so I checked the fiche and concluded I assembled it in the wrong order. I had the spring on bottome which raised the needle ever so slightly and cause all of this trouble. If you've been in your carbs, might want to make sure.
HTH

[Ivan]

Yeah, I have thought that might be a common problem. My 81 has the spacer, the clip and then a washer and a spring on top. The older carbs have the spring on the bottom, and an adjustable needle position. My 81 only has one groove for the clip. I have had the needles out a few times putting different washers in various positions, to no avail. Finally went back to stock.

I think the bike needs to be lean just above idle and the pilot jets are what controls that, but it needs to be a tad richer at idle, and with narrow jets, the idle screws can only lessen an already lean mix, so they are either very insensitive or all together useless in this case.

As it sits now, I have the 42.5 idle jets, the floats about 2mm down from stock and 117.5 mains. It starts easy, idles smooth enough even at 600-700 rpm. The hesitation is nearly gone, but still there. I was idling in 5th gear and rolled on the throttle and she pulled all the way through from 15 mph on up. Not spectacular acceleration, of course, but she did it. I could not have done that before. I think I am going to try the 120 mains, I still get a squishy feel on the top end. Almost like backing off the throttle a bit makes it pull harder.

I am getting closer, and thanks for the suggestion. At some point, I will probably make that very mistake.....

[Ivan]

I have since went to the 120s on the main jets. This helped with the top end. I am guessing I could open it up another size.

Tonight I got sick of waiting for several different shops to get some pilot air jets for me, so I bought a set of smaller jets and drilled them out with a drill a size bigger than would fit through the stock 185s. This helped a bit. I am hoping this will let me get my low rpm to pull without lowering my floats so far. Tomorrow I will pull some drills from work that should closely correspond to the sizes in the jets, and work my way up.

[Crazcnuk]

http://www.xs650direct.com/products-37.html

part #48-0663

This is the adjustable needles I am using right now, with the matching emulsion tubes.

Mike's XS recommends this combo over the stock needle/tube combo installed orignally in the BS34 carbs.

I have also been all over the spectrum trying different things. Right now I am running 120 mains from 110 stock), 42.5 pilots (45 stock), the above needles and floats down 2mm.

With this combo my bike will idle (cold) w/o choke at 600rpm, smoothly, and 1000rpm when warm. The bottom end is good, no bog, or hesitation. Mid range is good, but the high end is a little flat above 7000rpm.

I am using the stock airbox w/ K&N washable element and 4 into 2 turnouts.
I am getting 45mpg(imp) with this combo, so far.

Like you the bottom end issues bothered me, more than the top end, but I wouldn't have thought I should be looking at going over 120 mains.

[petejw]

Hey Craz,
What position have you got the needle in?
Are there part numbers on the needle and tube?
am asking cause our 'sports' bike (81)similar to the US special
came out with adjustable needles.
The part number for the needle is 5GIZ30 and the tube number
is 37351X2.

[Crazcnuk]

I have them in the middle position (stock) right now. Our Canadian model 80 carbs came with 5 position adjustable needles stock.

You can see the needle comparisons here:

http://www.xs11.com/forum/showthread...nd+cure&page=8

Some people have good results dropping the needles a notch, whereas others have success dropping the floats. Both may be doing the same thing, ie; compensating for wear in the needle/tube assys, or changes in the relative density of our modern fuel vs 1970's reg gas, or a combination of both.

The needles have 51X11 on them and the tubes 336-Y0

[yamahansolo]

hey what pods do you have....i have used the emgo's in the past and they seemed to always stumble at low rpm's.i have the mikes xs pods on my 11 and there is no stumble at all. the emgos throat diameter blocks the airjet....

[madmax-im]

With pod filters you have to be careful because some brands have a lip on the inside diameter of the mounting ring...this will restrict the smooth airflow and could be part of the reason a bike will not run smoothly. Alot of aftermarket pods copy their design from the K and Ns' but they have the aforementioned internal lip check to see if this is the case

[BigDick]

Hey Ivan, did you ever see this webpage? it has different drill bit sizes matched to the jet sizes.

[Ivan]

I have seen the web page, I am not so sure it is entirely accurate, I had to go to a 41 drill to size up some from a 185 jet, which should be about a 48 drill.

The lip isnt a problem. I circumvented this, search "el cheapo" for the solution I created.

I tried the 41 and it is getting closer....