carburetor trouble.

[mason s]

hey ya'll, looked through threads and can't seem to find an answer to my problem.
i have a 76 with bs38s, purchased with stock jetting. (122.5 mains) which i believe is the most lean they came. put some uni's on, and aftermarket exhaust. went up 1 size on the pilot and runs pretty good, no backfiring or anything, but feels somewhat weak at the top. so, as you should i tried a size up on the main. but now my bike is popping really bad on deceleration. seems a bit backwards to me. why would a bigger main effect my low end as such? and it seems odd it would feel lean in the idle/pilot circuit when it was running well beforehand. am i missing something simple? do my screws need to be turned out more? can't seem to find a happy place with tuning her. thanks in advance.
-mason

 

[TwoManyXS1Bs]

Could just be crud getting into the pilots. Try the reverse flush trick.

http://www.xs650.com/forum/showthread.php?t=42002

 

[mason s]

thank you for the reply twomany. so to humor myself, I just put the 122.5s back in, viola, no more popping. that's what is confusing me in all of this.

 

[nj1639]

I've just started playing around with a set of 38's. They may be - may be - a bit more forgiving on the Uni and aftermarket exhaust then the 34's.

 

[mason s]

yeah I could see that. figured since the main was already so lean stock it would probably like a size or two up. but man it's getting tough to dial these in. just seems odd my pilot circuit is where I'm having a drastic change.

 

[TwoManyXS1Bs]

Are you pulling the bowls to rejet, or just swapping thru the drain holes?

 

[mason s]

recently, just through the drain bolts on the bowl. gave the carbs a good cleaning early this spring. I've just left them on while playing with the jetting.

 

[mason s]

so I've been messing with a few things trying to get the tuning dialed & I'm starting to wonder if my left coil may be going tits up. it's really weak on that cylinder. which was causing some of the backfiring I believe. now correct me if I'm wrong but if I put a test light to each of the leads on my coil (mine are brown & orange) I assume they should all light up? 3 of the 4 leads do but the left side orange doesn't light up at all.

 

[TwoManyXS1Bs]

...the left side orange doesn't light up at all.

It won't if its point is closed...

 

[5twins]

Do a proper coil test. The #4 wire listed as red/white is the brown .....

 

[mason s]

ahh thank you. makes perfect sense.

 

[mason s]

thank you kindly 5twins. that's a great little reference. I'll grab my multi-meter from work today & give it a run through. I've been through the ringer with this thing, replaced the charging system to a hughs pma a month or so back. did a full tune up (valves, cam chain etc) replaced most of the wiring, got it running quite well but now seems I'm onto the next dilemma. this is my first bike so at least ill know my way around it.

 

[5twins]

That comes directly from the factory service manual. You can view and/or download it here .....

http://www.biker.net/650_service/650service main.html

This manual is for the '78 model but much will still apply to your '76.

 

[mason s]

thank you. coil tested bad so I put a new one on & still no spark. going to try new resister plugs I guess. that's the only other part that is old still.

 

[5twins]

If you have resistor spark plug caps then you don't want resistor plugs too. One instance of resistance in the path to the coil is all you need or want. In fact, if you're still running points, you don't need any resistance in the system. While I still had points, I ran these 0Ω NGK caps .....

 

[mason s]

pardon me I meant to say resistor caps. not the actual spark plugs. but that is good to know i will have to double check that I'm not running x2 resistance. didn't know that points don't need any at all.

 

[mason s]

hey guys, sorry to keep bringing things up. should've titled this post "help Mason's Xs" ha, but anyways, I got my bike running pretty good with a new coil. everything seems tuned okay sans just off idle. I've read the carb guide through a couple times & have a few jets to work with, my question is I can't really tell if my bikes too lean or too rich off idle, it boggs a bit & almost stalls until I give it enough juice to get her moving. runs strong otherwise. based off the description in the carb guide I feel like I have symptoms of lean & rich. hard to distinguish the difference. my right side carb is leaking out of the overflow, I triple checked float height, needle and seat seem to functioning properly, & float holds when soaked in cup of gas. could that be a sign of something as well? a second opinion would be greatly helpful before I start throwing different jets in. 76 Xs 650 with bs38s, unis & aftermarket exhaust.

 

[hooser]

Mason, here has been my thinking that served me will for many year.. But I run only vm 34's .. should apply to you also..
Pilot to lean if I can't blip the throttle of idle, it will what to die, or spit back.
pilot to lean
if I can hold a constant throttle positon at 2-5K rpm, mid range needs work.
The ideal setting for the needle is in the middle, on all my bikes when done.
On the main.. go wide open if it feels like is sluggish or stopped increasing, back off on the throttle a 1/4" and if it picks up you are fat.
Look at the plug, not on top, look down on the insulator , I see on this site picture of plugs showing the tip,
and if all else fails come see me for some Vm34s ,
My brother in law had me put Vm34's on his 73(my old one) and a powerdynamo ignition and it ran great , started 1st kick. He said it has never been better. he don't use the computer so I figured I would blow my own horn. My 80 has the same set up. with no problems.
As always thank you for your support, Gary

 

[mason s]

Thanks for the reply hooser. appreciate it. so I can blip the throttle & it seems fine, just when I'm in gear from stop to go. picks up once I get to 1/4 ish throttle then runs fine but it chugs & glitches a bit on the initial opening of throttle. think I'm a bit rich? plugs look pretty good but like I said it pulls great through the mid/upper.
& I'm sorry but what do you mean by "if I can hold constant throttle position from 2-5k the mid needs work" ?
vm34s seem great id love to run a set sometime, perhaps on my next build.. I've heard great things!

 

[hooser]

From what you said I would go bigger on the pilot to start. In the midrange you should be able to hold the throttle (on a flat running road) at on spot without the big poping jerking ect. figure 1/4 to 3/4 you are on the needle. it should be a nice and smooth through out.