On the road again at 40.............the bike that is

Ya WER. If I warm it up and rev it up in the shop with BP7ES plugs I see white/grey smoke. gggGary suggested running BP6ES plugs and it's running much better. Would have oil fouled 7's by now, as I used to in the past, but have put quite a few miles on with the hotter plugs without a problem. Except for burning oil that is....lol.
 
Daniel Black, Mailman and I have been discussing our carb conundrums.

As I reported a few days ago after syncing with an ATF manometer my carb mix screws were quite a bit off. Should be 2 ¼ turns out.
Right was 1 ½, and left was 3 ¼. It was running great but I know they should be a lot closer than a 1 ¾ turn difference. 5twins recently discussed this in Mailman's thread.
This was bugging me.

Daniel-san gave a gentle nudge that maybe a pilot circuit was still blocked in spite of how many times I had been in there, or maybe the right float was off spec.

Rain day the other day so I was ‘forced’ to spend the afternoon in the shop.
I was going to finally rebuild the 78/79 carbs from Black Betty, my 78E next project and see what might happen if I installed them, but then thought I might just as well tear into these again if they’re off. When they were previously rebuilt, installed new Mikuni stock sized Jets, new needle valves, new o-rings, new OEM throttle shaft seals, new choke housing gaskets and new XSDirect floats. (Didn’t know better at the time, should have, but OK so far)

TwoManyXS1Bs said:
Come to think of it, there WAS a glaring omission in this thread:

"Chronic complaints about carb pulls and installs".
Click to expand...

Came real close to griping about it this time 2M.

Everything was clear in all circuits, but that's not to say I didn't dislodge something without seeing it.
Also had noticed when coming to a stop my idle will drop 200 - 300 RPM's or so and then climb back up after about 5 secs. or so.
DB suggested raising floats to 23mm might help with the fuel sloshing/starvation issue on rapid decel.

After 170 km / 105 mile test ride mostly highway miles, she ran great, pulled hard through all the gears, but still had the idle drop coming to a stop in neutral.

DB again suggested it might be clutch related as he had experienced a similar problem when clutch drag was a contributing factor on his Stella. Spent some time messing with clutch adjustment. Seems to be a recurring theme around here lately. Shifting when running/warm was no problem but I could not get it to shift into first when bike was off/cold. Pulled the left case to make sure all was good, ball bearing was there. I had previously lubed worm gear but took it apart again, greased everything up, cleaned up some chain lube spatter.

Took quite a bit of fiddling but finally got it. Turns out I was too tight. Using that tighten until you feel the point of resistance while lightly fanning the clutch lever to stack everything I was over tightening. Additionally I may have also done too much adjusting at the lever end thus reducing the available range of motion for the worm gear arm.

Kept backing it off and finally found the spot.

After 100 km/60 mile mostly highway test ride today, she's still running great, pulling hard, but idle drop of 200-300 rpm when I come to a stop is still there. Doesn't stall but idle drops and then climbs back up to setting.

Other than that, all’s still good, or at least as good as can be for an engine that needs a top end job and is burning a lot of oil. Gonna enjoy riding out the last couple of chilly months of our season here and then let the games begin.
Oil consumption is staying pretty steady at a rate of a litre in 600 miles so my valve seals and rings haven’t magically fixed themselves.
Mileage is averaging 52.1 mpg.

I had also noticed a lot of tach needle bounce of 200-300 rpm's at 3500 and up. Mailman suggested lubing tach cable. This had been done last summer before any miles but did again now and bounce is down to almost nothing, about 0.5 rpms. Thanks Bob!

So carbs now: Factory spec 2 1/4. New settings Left 2 3/8, Right 3. Tuned by ear and dead cylinder method. For now gonna call this close enough and done.

I am curious though and do have a couple of questions:
  1. Could it be that the needle tips on the mix screws are worn differently thus causing the settings to be different or are there other internal carb differences that cause this?
  2. Carb and clutch adjustments have done nothing to eliminate the dropping idle when stopping situation. Could this be related to a weak, tired motor that needs a rebuild, or is there something else going on?
Thanks again guys for all your input and direction here and elsewhere on the forum that has answered tons of other questions.
 
Last edited:
Y'know that feeling that a parent gets when they turn loose of the bicycle, watch their child nervously wiggle the handlebars while petaling, and begin to master the challenge of balance?

There you go.

You've got a pretty good grasp on the engine and carb principles. What's left is the excruciating experiments, oddball tips & tricks, fellow member war stories.

All I can think of at the moment, is doing silly little things that may add to the clue list. As suggested by others in the past.

While it's doing it's high-idle thing:

Nudge the carbs up/down, etc., stressing the spigot sealing.

Nudge the throttle shafts up/down/fore/aft/in/out, testing their sealing and butterfly closures.

Nudge the choke plunger(s) up/down, testing their sealing.

Cover a pilot air vent, note the change, compare to other side.

What kind of results should you get?
What kind of results do you actually get?
 
OK, thanks 2M.

LOL. Sounds like you think it's still likely a carb issue that's causing my idle drop when coming to a stop. And here I was hoping it's due to engine condition.

I'll play around with those things you have suggested. I know plugging a pilot air vent will cause it to stumble and stall, and do think I tested choke plungers awhile back but will give it a go again. Also think I played around with throttle shaft tests after changing the seals but easy to test again.

It really is running great otherwise but I know this idle drop when coming to a stop shouldn't be. It doesn't stall but I would think idle should return to where it's set and not below and then climb back up.

The experiments you have suggested are easy to do and will rule out those carb issues at least. Will give them a go and see what we see.

Thanks again!
 
Last edited:
robinc said:
... Sounds like you think it's still likely a carb issue ...
Click to expand...

Yeah, it does, doesn't it? Actually, I think in terms of stimulus/reaction, trying to build up a clue table. As a kid, I used to play a code breaking game. Similar to Sudoku, you try to build a list of clues. Google "Mastermind game".

Mastermind.jpg

The problem solving skills developed from these games seems to help with diagnosing this stuff.

Sometimes the problem is obvious.
Customer: "My bike handles funny."
Mechanic: "You have a flat tire."

Sometimes it's much more complicated. There's the usual stuff you encounter on new and low-time bikes. Then there's the wierdness that pops up with 45-year-old machines, that we never expected to last more than 5 years. It gets worse when you add in Previous Owner creativity. So, this code-breaking game skill is just something I use to help figure this stuff out.

Another test you could try would be on a steep hill. Roll down a steep hill, engine idling and in neutral. Do a quick stop, observe the reaction. Do the same thing uphill. Start with some speed, pull in the clutch, let the engine idle, coast up the hill, quick stop, observe.

Get creative, try things that may add to your clue list. While doing 10-20 mph, pull in the clutch, let the engine idle, and ride over a really bumpy road. That kinda stuff.


None of these tests are necessarily definitive, just part of the big picture...
 
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Ya, we've kinda been here before haven't we 2M?

As it's running so good other than this idle drop at decel, it seemed to me to be float, needle valve - fuel starvation related. Needle valves are new genuine Mikuni. I also noticed putting the bike on the centerstand while running, the idle would do this same drop, (similar effect to your slow speed bumpy road test)
Thought Daniels idea of raising the floats to 23mm to add more fuel to the bowls might solve it but no luck.

Also going to try swapping in some other genuine Mikuni floats from another set and see if it has something to do with the Mikes/XSDirect floats. Can't see how but can't hurt.

Will keep testing.

Thanks for hanging in!
 
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I'm going to bet on the oil consumption being the root cause. Worn intake valve seals will pass a lot of oil on decel when you have a strong vacuum in the intake. The 6's struggle mightily and manage to burn off the 2 stroke mix o_O you are running. Good news is it should help with the mosquito population.
 
Thanks gggGary. LOL. Ya does seem to be less mosquitos around here lately.

I guess we'll see after rebuild.
In the meantime, it's sure running good to enjoy riding out the next couple of months..
This idle drop is more a nuisance condition that I know shouldn't be there.
 
TwoManyXS1Bs said:
Yeah, it does, doesn't it? Actually, I think in terms of stimulus/reaction, trying to build up a clue table. As a kid, I used to play a code breaking game. Similar to Sudoku, you try to build a list of clues. Google "Mastermind game".

View attachment 105262

The problem solving skills developed from these games seems to help with diagnosing this stuff.

Sometimes the problem is obvious.
Customer: "My bike handles funny."
Mechanic: "You have a flat tire."

Sometimes it's much more complicated. There's the usual stuff you encounter on new and low-time bikes. Then there's the wierdness that pops up with 45-year-old machines, that we never expected to last more than 5 years. It gets worse when you add in Previous Owner creativity. So, this code-breaking game skill is just something I use to help figure this stuff out.

Another test you could try would be on a steep hill. Roll down a steep hill, engine idling and in neutral. Do a quick stop, observe the reaction. Do the same thing uphill. Start with some speed, pull in the clutch, let the engine idle, coast up the hill, quick stop, observe.

Get creative, try things that may add to your clue list. While doing 10-20 mph, pull in the clutch, let the engine idle, and ride over a really bumpy road. That kinda stuff.


None of these tests are necessarily definitive, just part of the big picture...
Click to expand...
Sounds to me like I'm not the only one who read, "Zen and the Art of Motorcycle Maintenance" :)
 
Robin,
When you find the time to launch into the top end rebuild, I will be one of those watching closely, as I just know that I will be doing the same at some point in time, if for no other reason than to have the experience.
I built VW engines back years ago, then the little piston ported Yamaha KT100's, but these are different, and interesting lumps.
 
Robin,
I really admire your tenacity and determination to understand the intricacies of these old bikes. It's not enough for you to just make your bike run better, you want to understand how and why things work.
This forum really is like going to school, if you have the interest, there are good people here willing to teach you.
You are transitioning from student to master.
Keep up the good work.
Bob
 
Your RPM drop when coming to a stop is a sign of improper fuel levels. Did you check the levels using a clear tube? When you checked/set the floats, did you measure both sides of each float? Many times the float is twisted and one side sits higher or lower than the other. You won't catch that unless you check both sides.
 
Thanks 5twins. I did wonder if it was float/fuel level related. It seemed like that would be the problem.

Yes, was very careful about checking both sides of floats. Took about a 1mm twist out of one, and about a 1.5mm twist out of the other.
Did not verify with clear tubes this time in my rush to road test...lol.
But that's easy so will check that today, and post results.

Thanks again for the input.
 
It could be fuel level related but then again, I suppose it is possibly engine wear related. As far as a possible worn mix screw goes, you might try swapping them carb to carb and see if the required setting follows the screw.
 
5twins said:
As far as a possible worn mix screw goes, you might try swapping them carb to carb and see if the required setting follows the screw.
Click to expand...

Brilliant idea 5twins. Will give that a try as well.
 
Coupla more thoughts:

The bottom taper of pilot jets need to fully seal against the matching seat in the bowl.

On BS38 carbs, check that the bowls fit fully flat to the carb body, especially in the center region. Gaps here cause fuel metering problems. When the needle jets aren't fully seated, previous owners tend to warp the bowls and/or the carb body (at the corners) trying to tighten the screws.

This album pic, plus the previous 7 pics:

http://www.xs650.com/media/warpedba...its-to-the-carb-bowl-can-be-seen.23060/#media

Could also try swapping float bowls...
 
TwoManyXS1Bs said:
Never read it. A friend had a copy, showed it to me. Flipped thru it, didn't see any tuning secrets. All I know of it is the synopsys on Wiki...
Click to expand...
His maintenance secret, shared with the world, is something you seem to possess, that is, a careful, caring, methodological approach, and a deep appreciation for the machine and its composition.
 

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