1972 cb/cl 100

This is the kind of stuff barnett468 "walks the dog" on so you might pm him. Maybe he will take a break from his studies on prefabulated amulite and take time to post here.
Does the timing light itself have a built in adjustable advance feature? I know that some do. And THAT could really muck things up.

Just to be clear. Idling at 1200rpm, pull the trigger on the strobe and it shows you the "F" mark is lined up w "L" on the stator. And the bike runs worse than ever ?

I dont know what the effects can be when these are a tooth off on the cam sprocket.

Use a wrench on the rotor bolt, turn the engine CCW to line the "T & L" (tdc) up on the COMPRESSION stroke, Check both tappets clearances to valve stems are at the widest points. .002mm. If they both hit the widest point either before or after the "T" mark. Theres a cam to crank alignment issue of some kind.

If thats all good. Pull the advancer and make darn sure the little 3mm alignment pin is in place. The pin traps the advancer to the cam shaft. If the pin is not in position the advancer will spin on the camshaft.

Here is where mine sits after setting her w the strobe.


Heres a generic pic from the manual. Set virtually the same.


IM gonna send this link to PJ and pick his brains.
sorry . . i havent had time to read your thread.

does the timing change when you connect the tach?

does it run bad when you connect the tach?

does it run bad when you pull the trigger on the timing lite?

what brand is the lite, chinese?

wiggle the advance up and down to see if it has play.

rotate it to see if it rotates and returns properly.

connect a continuity tester to the points and rotate the crank until they lose continuity . . they will fire the plug when they lose continuity so rotate the timing plate so that the points open when the F mark is lined up . . the timing lite should now flash on the F mark at idle . . if it does not, disconnect the tach and try again . . if it does not your timing lite is chinese or your springs in your advance unit are bad or your idle is too high.

also see if it runs better without the tach . . some tachs will cause an engine to run bad.
I've got some more work ahead of me. Thanks for all the info. I will check into things and get back to you with answers. I can tell you it ran no different with tach on or off. Maybe the springs are bad, last time I checked tappets, point gap, advance pin, continuity off at F. They were all good. Strobe is an old one I borrowed from a friend with only trigger. No settings. Not sure where it is made. I'll check that as well. Thanks guys.
also put a mark on the advancer bolt and advancer cam with liquid white out and check it at idle . . if they are not lined up, yur springs are weak or your lite sucks.
OK bro. I have found a "thing". Because Im am taking longer rides in the evenings. I put the regular old stock headlight back in. With that light installed this thing runs like shit...cutting out, bogging down and dies. Once I am getting up to speed. Over 20-25mph.

The headlight sucks enough juice theres not enough left to feed the coil and sparkplug. put the led lamp in and it runs great again.

unplug all your lights and give it a try.
Haven't had time to read thread yet but I will. Do you have the correct carb to head manifold? I don't remember the 100 having carb at such a steep angle.
Check alternator output wires for damage. The 100 has always had running problems even with a new battery. Best conversion is to use the XL100/125 generator, CDI and coil, it always starts and runs then ;)
So I didn't do much over the winter, and have had a little time to work on this thing recently. I Checked timing again with a strobe just to make sure I'm not crazy. Still the same problems as last year. Have not checked the cam chain yet because someone before me tried and possibly opened it up, and now I can't get the stripped bolt free. Going to try a few methods before just drilling it out. I bought new points today, hope to swap those on soon, and am going to take the advancer apart again. I've been reading iatethepeach 's thread, and he is having the same problem as me with timing, though his seemed to be running much better than mine. OK, that's all for now.
Picture on page 1.
I haven't done a 100 for a long (long) time
That's the later motor same as 125 instead of the early XR/XL75/80/100 motor with tensioner on rear of cylinder (and CB50)
You can just see the busted off bolt on top of cam chain tensioner to rear of cylinder on top of crankcase
It's 6x1mm about 10mm long.
If you file whats left of the top off and get a 'left hand' drill bit it should come out pretty easy.
After you get tthe screwed up bolt out, you need a 3mm screw about 40~50mm long. (indicator lens screw is a bit too short)
You may be able to find a bicycle spoke the right thread
Screw it into the top of adjuster 'plunger '
Loosen the 14mm and pull up on 3mm screw (it can be done with engine running but is 'safer' just turning crank by hand with socket on generator nut)
You should feel the tensioner moving due to spring pressure on blade when turning engine. Chain is tightest when screw is as high as it will go.
Don't use a needle nose pliers to pull it tighter, chain will be too tight when engine warms up and tensioner will wear out (or even brake)
Re-tighten the 14mm sleeve nut (maybe 12mm on late model?) fit a short 6x1 bolt with a copper or alloy washer and it's fixed
Crazypj, do you mean the cam chain tensioner bolt? That one looks good. The screw on the cover is shot. The p.o. painted the engine with everything attached, and the screw was already just about stripped when I got it.


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OK, The tensioner looks fine.
The screw thats chewed up, get a flat end punch and re-form the screw head. If you go around in 'quarters' it's possible to get the metal to move and close the slots back up. You need a number 3 Phillips driver, preferable on a socket. Bash it in to reform the 'cross' then either use impact driver or breaker bar to keep pressure on while beating on top of socket (I find breaker bar better than impact driver as it doesn't force bit to turn, you control how much torque is being applied)
I'm sure crazypj has removed more stuck screws than I have, so you're probably better off following his advice, but if it were me, after soaking with PB I'd re-slot that screw along the existing bottom-left to top-right line with a small-diameter dremel cutoff wheel, extending the groove to fit a wide impact-driver blade bit. I've done a bunch of munged screws on my bikes this way and they all came right out. You could also try filling the hole in the screw head with a dab of JB weld before you slot it, but I doubt it's necessary.
Got the bolt off and checked the cam chain. The chain looks good, and it lined up proper. I then replaced the stripped screws with new Allen heads. I ordered a nos advancer, so I'll update again soon.


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Put the nos advancer on, my original was definitely not functioning properly. I dropped the 110 main jet back in the carb and put the clip back in the center spot on the needle. It runs much better, I still need to fully tune the carb. The only big problem is when it is timed right with a strobe, it runs well but I get pre-ignition, and it doesn't want to shut off when the key and switch are in the off position.
Picture doesn't make it too clear but it looks 'off' at least 1 tooth to me?
Does that sprocket have the 'O' or a ' l ' line?
If you can't see any timing marks on top sprocket it's probably on backwards?
Lines or dots should be vertical when the line next to the 'T' lines up with mark on case, I can't remember if advancer locating pin should be 'vertical' (in line with cylinder centre) or at 11:00 o'clock?
Could also have short lines either side that will be horizontal compared to rocker box mounting face
'F' is 'fire' where you set static timing.
The two lines ( l l )at around 4:00 o'clock should line up with timing mark at full advance, anywhere between them is also fine (using a strobe at 3,000rpm)
It has the circle. I zoomed in on the original picture, it is lined up with the indent on the head. Do you think it on a tooth off?
With the strobe, in full advance it lined up right with the two advance lines, at idle it lined up with the F. I do have the points plate way off from the manual and pics of other 100's. I had to turn the plate counter clockwise to get the timing to line up. Way advanced compared to others.
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