BS38 Tuning Issue

[gggGary]

I went back up this thread,

Before I initially tuned the carbs (only like 40 miles ago) I adjusted everything else (timing, cam chain, etc.) first like you’re supposed to. Now just so you know, this bike is running open headers and pod filters.

lets see some pics of the bike including the air filters.
You might want to do a second round;
set timing with a light (both sides), look at idle, advanced and smooth action between.
cam chain tension valve clearance,
Check for strong spark, both sides, etc. condenser issue comes to mind.
Compression test recently? results?
This is out there but it HAS happened more than once, the stock headers are double wall, a few guys have found a collapsed inner wall, severely restricting the exhaust on that side.

 

[79josh81]

I went back up this thread,

lets see some pics of the bike including the air filters.
You might want to do a second round;
set timing with a light (both sides), look at idle, advanced and smooth action between.
cam chain tension valve clearance,
Check for strong spark, both sides, etc. condenser issue comes to mind.
Compression test recently? results?
This is out there but it HAS happened more than once, the stock headers are double wall, a few guys have found a collapsed inner wall, severely restricting the exhaust on that side.

When I get everything back together I’ll probably go through some of that stuff again just to double check my work.

The bike is the one in my profile pic. This is about the best shot I have of the air filters. They’re just Uni pod filters and they’re far enough back where the inside rubber isn’t blocking any of the carb holes.

 

[79josh81]

On a completely different topic and while I got the majority of the great mind on this forum here....I’ve been messing with my 81’ wide tire project. Today I pulled the carbs to add bigger main jets just to see what would happen. I’m running open headers and uni pod filters. I was running #142.5 mains and the bike didn’t have any issues when driven. I stayed within the limits in the carb guide (mikesxs suggestion for the bs34’s) and went up to the #147.5 mains. I took it out for a spin and it seemed to accelerate fine until I would get to 4000rpm’s in any gear. Once I would get to 4000, the engine would just take off up to like 6000 but it was like I was in neutral. Once it hit 6000 it would then actually start to accelerate the bike like normal. Could this be caused by the larger jets? It wasn’t what I would describe as “break-up” or a “flat spot” as far as rich or lean but then again I’m new to tuning these carbs.

What it almost felt like was the clutch slipping at 4000 rpm and then catching at 6000 rpm in any gear but it doesn’t do it no matter how hard I hit the throttle at any other rpm. No slipping feeling or anything and the bike just takes off like it should until I hit that 4000 rpm mark. I recently replaced a broken shift drum detent spring that I found because I was having the bike find false neutrals and this is the first time I’ve had it out with a spring in there. If it is a clutch issue, if I adjust the worm gear any more to prevent slipping, I’ll never be able to find the gears because my clutch lever won’t be doing a whole lot if I run the clutch plates that tight.

Is this a feeling that too large of mains would give me?

 

[gggGary]

Yeah a clutch starting to slip when the motor gets to the power band is a typical warning it's nearing clutch life over. Somewhere around 4000 is where the slides go full open under power. Usually you have to back off the throttle to get the clutch to hook up again.

 

[79josh81]

Yeah a clutch starting to slip when the motor gets to the power band is a typical warning it's nearing clutch life over. Somewhere around 4000 is where the slides go full open under power. Usually you have to back off the throttle to get the clutch to hook up again.

Jeeze...it never ends. lol So what I described sounds like the clutch huh? Would it be safe for me to just go and order new clutch discs? Or is there something else I should check before I go spending money? If it felt like a clutch issue to me, and you understand the symptoms of a bad clutch on these bikes as what I'm describing, I'm guessing it's a clutch issue. It would actually explain why whenever I set the clutch on this bike where I feel it should be the right position, it slips like crazy right out of the gate. It would also explain that when I get the clutch set to where it doesn't slip, it's then harder than hell to shift.

 

[gggGary]

Well before spending money read the clutch threads. especially about setting cable freeplay. A lot of your hard clutch issue could just be a rusty, lacking lube or poorly routed cable.
Start here? http://www.xs650.com/threads/soft-kickstart.54506/#post-589960

 

[79josh81]

Yeah it’s not the cable. The pull is great. It has a new lever, new freshly oiled cable, and the cable is routed fine. I've been through the procedure of setting the clutch the correct way enough times now where I know it's not a "left side" issue. In fact, I wish I could get my 79’ to have a clutch pull as smooth as the 81’ is.

If I were to replace the clutch, what would you suggest I upgrade? Friction plates? Steel plates? Springs?...etc.

 

[79josh81]

Even now that I think more about it, I think adding the larger mains is actually what might have made the clutch show it's true colors so-to-speak. Before, when I was running the smaller mains, the bike didn't pull as hard in the higher rpm's as the larger mains. I'm thinking that the larger mains may actually have gotten the engine to pull hard enough to get the clutch to slip. It would make sense.

 

[gggGary]

check that all your steels are flat, read on notched clutch basket fingers. You can try stiffer springs but that has not worked for me. On a HyPo engine I was extremely happy with an ippytattoo 8 plate conversion going strong after 4 or 5K miles. Unfortunately he quit doing them. there's a thread or 2 about them.

 

[79josh81]

Yeah I was reading about the 8 plate conversion before. If I was just going to do a straight up swap for new plates and everything, is the Mikesxs kit any good? https://www.mikesxs.net/yamaha-xs650-clutch-repair-kit.html I've never done a clutch on the 650 before but I’ve watched the videos and it seems pretty straight forward.

 

[gggGary]

Don' know about mikes clutch parts but look up Gary Hoos (Hoos racing) on facebook he has some comments on some aftermarket plates. Yeah it's pretty easy, check the starter bendix while you're in their if you have an e-start.

 

[79josh81]

Yeah I'll do that. Is it usual to just replace springs and everything when you do the clutch on these or just the plates?

 

[79josh81]

Hey I popped the right cover off again just to have a peek at the clutch. Is an 81’ supposed to have 6 friction plates? Mine has 6 but my supplemental section for the
XS650 H&SH says it should have 7?

 

[TwoManyXS1Bs]

Should be 6 for the '80-up clutches.

See attached clutch parts list.

 

[79josh81]

Thanks twomany. That’s what I thought but I was confused when I read 7 in the service manual.

As far as the clutch friction plates go, they seem to be right under 3mm. I don’t have a micrometer (which I will be picking up tomorrow), just a steel rule. I mean how can you tell if the clutch plates are worn besides measuring? Does the fiber material degrade at all to the point where it doesn’t grab as well after 40 years? The clutch is definitely slipping at 4000 rpm unless I let off the throttle. It’s like the engine is putting out too much power after 4000 rpm to the point where discs aren’t grabbing.

 

[650Skull]

Might get some opinions on these

 

[650Skull]

If it is slipping the plates get burn't..........depending on how long and how bad and it will usually be a couple of plates that are the culprit and more if it has been used a lot while slipping...........Easy to tell once it is opened up.

 

[79josh81]

Yeah I'm kind of stalled out on the carbs. I can't really do much else until I get these new float bowl gaskets and pilot mix screw o-rings.

 

[gggGary]

If it comes to it, I have three sets of rebuilt BS34's on the bench, nothing like (known good) parts substitution to track down an issue.

Might get some opinions on these

View attachment 139222 View attachment 139221
View attachment 139222 View attachment 139221

Skull, ??

 

[650Skull]

While your carbs are off do a visual confirmation that the butterflies are exactly equal. If you slowly close the idle speed screw, the last tiny sliver of light looking through the intakes is a VERY accurate gauge, IMHO better than any stick, drill bit, etc. method. The thing is if you need to adjust far from this with a manometer (say more than 1/4 turn of the synch screw) that's prolly an engine, not carb issue..........

My pics with the idle screw set for riding