The case of the blown carb.

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C'mon, along, help me with this?
R just called and came dropped it off.
KIMG8518.JPG
A pretty build all by R. BUT... It's been kicking his ass and he wants fresh eyes to take a look.
He was riding one day, the stock TCI gave up one cylinder, choking that side got it home, but next "try to start" blew off a carb. And in spite a of a lot of work, parts, and changes, it hasn't run since.
What i know so far:
After it died he changed out the stock TCI and charging system for a Mikes XS charge and ignition. An OEM advance rod, mikes. advance. weights. ignition coil, etc.
That didn't "fix it", It only blew off a carb, again.
Changed to an Accel coil same result.
Then since he had a head gasket leak anyways, he topped the motor, hone, new rings new exhaust valves, This isn't R's' first XS650 rodeo.
lots of head scratching and trying this and that later, he called in a pinch hitter. Yup Ole GG at bat now.
After couple questions, I ohmed that Accel and yeah primary is .7 ohms, that's a 140401 number not a 140403 so that'll be changed next.
Also; Kicking it through by hand, compression doesn't seem "right" and sounds like I'm hearing air coming back out the intakes.
Bike has battery and electric start (whew)
The sluething will start today, good activity for a winter week eh?
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Allison gives r the once over
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Great workmanship, tidy, graceful and well thought out, no loose ends.

KIMG8524.JPGKIMG8523.JPGKIMG8522.JPGKIMG8521.JPGKIMG8520.JPG

While Allison was looking it over I pulled the plugs and did the compression, RH 20 psi, left 70, ooch! The plot thickens.
Next up; check cam timing and valve clearances.
 
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I suspect timing and clearances will tell the tale. If cam timing was off, you'd expect the low compression, but... you'd expect to see about the same on both sides. 20 and 70 is a pretty fair difference. So either that's not the problem or there's another.
Kinda sounds like intakes too tight.
 
the stock TCI gave up one cylinder, choking that side got it home
I think there is a clue there. How can a TCI drop 1 cylinder when it fires a dual output coil every 360 degrees of rotation? Can a dual output coil short out internally so that it only fires 1 plug? I don't know. Also if it was electrical what good would the chock do?
Sounds like he may have had a vacuum leak. Would be nice to know what the compression was before he fixed the oil leak.
Now all Gary can do is first find why compression is low and uneven. Starting with valve timing and valve clearance is where to start. Will be interesting to see what he finds there.
 
How can a TCI drop 1 cylinder when it fires a dual output coil every 360 degrees of rotation? Can a dual output coil short out internally so that it only fires 1 plug?
Been thinking about that too. I don't see how it's possible. The box provides a ground for the coil... one wire to ground and unground the coil... so that's out of the question. It'll fire the coil, or not. No way it can tell the coil to fire only one cylinder.
Same with the crank sensor/pickup. It tells the box "when" to fire the coil. Impossible for it to tell the box to fire only one side.
The coil. It's a dual output "floating" coil. In other words it's one circuit... out the secondary, across one plug gap, across the head, across the gap in the other plug and back to the other end of the secondary. Short the secondary and it "all" stops... both sides. Same if you open the secondary... it all stops.

I don't see how it's possible. These aren't the droids you're looking for. :wink2:
 
Gaining ground...
Valves were WAY tight (not closing tight) :unsure: set em, and I've got 70 R 150 Left, those are it'll run numbers for sure.
A rod in the plug hole to find TDC and where the non compression side valves settle between the ramps, sez the cam is timed right.
Changed the coil to an Accel 140403 and I have strong spark, both sides, plugs grounded on the block.
Mikes PMA rotor so no timing marks but I marked something close to TDC, I'll add a "thumbnail" retard and advance mark, time it and and see if it runs.
My guess on the TCI was a battery going low started it mis-firing, pretty hard to tell which cylinder is acting up while riding. A rich mixture is easier to light? There is a slight difference in secondary voltage between the sides. Ever had a timing light clamped on the negative side plug wire act all grumpy? I have.
More later.
Even on a pretty bike you can run into some unseen details that leave a bit to be desired. made a couple small improvments to the coil mounting set up to make it easier for the next guy. :pimp:
PS it's got the Mike's flat side carbs,
what me worry.jpg
 
So put the light on and I'll be damned timing is at BDC :umm:
all the pins in the cam/advance rod only allow 180 degree choices which is ALWAYS TDC on the crank, hmm
looking at the ignition.

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hmm take it off see the rotor could be installed with the small end either in OR out.
Run to mikesXS, read the installation instructions, aaand

10. Install the “rotor” on the advance rod shaft.
* Please note: On the Gen-II ignitions, the small inner rotor is installed with the skinny side IN. *
:thumbsup::heart::bike:
11. Install the large washer and nut with the lock washer.


Flip the rotor over,
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find a washer that fits, reinstall, set the plate at retarded, check and yeah we're on my timing marks now. WOOP WOOP
:rock:
Put the valves covers on, turn on the gas set the chokes and brrm brmm!!
We're done here.
Gotta love the easy gals eh?
So it was several things, all adding up, methodical wins the day, wait. ME, methodical? :laughing:
Would be fun to take 'R round the block :sneaky: but don't think that's gonna happen.
R will come and pick it up.
And that's it for this weeks game of stump the gggGary.
Thanks all for joining in and giving hints n clues.
 
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Well heck Gary, you didn’t drag that out nearly long enough! 😄 Lots of fun following your trouble shooting though. 👍🏻

I’m guessing it’s still got low compression on one cylinder though, or did loosening the valves solve that issue too?

One side was still low (up to 70 from 20psi) but I'd run it a few times set the valves and check again before worrying about it.
 
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Well heck Gary, you didn’t drag that out nearly long enough! 😄 Lots of fun following your trouble shooting though. 👍🏻

I’m guessing it’s still got low compression on one cylinder though, or did loosening the valves solve that issue too?
So it ran for a mebbe a minute yesterday (on the lift low on fuel)
but that darned @Mailman made me go down and pull ANOTHER compression test on the right cylinder. It's up to 90 now. I'd expect it to keep climbing.
 
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