I did some work on an 86 XR100 for a customer, cleaned the carb and got it running. It was burning a pretty good amount of oil and had low compression, around 80 psi. I took the top end apart and the top compression ring had broken into many pieces, but the bore still looked decent, and didn't have any grooves that caught on a fingernail.

I honed the bore, replaced the rings with stock size as the bore was within spec, ring end gap was around 0.020", and put it back together. The timing is set properly, the T mark on the flywheel aligning with the vertical mark on the case, the 0 on the cam gear is at the 12 o'clock position, and the cam lobes are pointing down. Valves have free play and clearance is set to 0.002". It has a new spark plug gapped to 0.028" and very strong spark as well, and compression measures 120 psi now.

It will not start at all, even with starting fluid sprayed through the cylinder or directly into the spark plug hole, it is also getting gas and the plug is wet. I have checked the timing several times, the motor turns over smoothly by hand, cam chain is tensioned, I even pulled the flywheel to verify that it did not spin on the crankshaft.

The only thing I can think of is that somehow it is sparking at the wrong time, when a valve is open, and therefore it is not getting compression and spark at the same time.

I have rebuilt many top ends but am clueless on this one since it has very strong spark, 120 psi compression, is timed properly, and has fuel and air.

Thanks for the help

Check that the points open just as the 'F' mark reaches the timing mark on the block. There should be a felt on the back side of the points that runs on the cam inside the flywheel. If it's missing it will throw your ignition timing off.

is the T mark for valve or ignition timing??!!!!?!?!?

T Mark is for Valve timing, F mark is for ignition.

Points open at the F mark, 120 psi should be plently of compression right? Still have no idea whats up with this.

theraymondguy, on 24 January 2012 - 05:07 PM, said:

How exactly would a missing felt affect ign timing.................?

Old School Al

Hey Al, welcome to yet another one of many as of late, pre-1992 ignition issue.

socalxr, on 31 January 2012 - 09:31 PM, said:

Not like you to welcome me, you been feeling ok....? But thanks....! Any idea on the felt / timing deal ................? I'm kind of thinking the answer to that may give a slight hint as to the possible reason for so many as you call them.........."issues".

Old School Al

It's been so long since I've seen or touched points, I don't even remember much about them.

If it has points, it has a condenser. Check the resistance on it. Simple inexpensive fix. Also make sure the wire going from the condenser to the points is not grounded. It should connect to the points block and be insulated from ground by the fibre washers.
Ken

Old School Al, on 31 January 2012 - 07:02 PM, said:

Well Al, the points would open late; and they'd close too soon - if they open at all... so... That is EXACTLY how it would effect ignition timing. I will try to be more inclusive in my posts, and make them simple to read for your benefit.

Condensers are capacitors, not resistors. You'll need a rather expensive meter to measure the capacitance, as it is a small amount (0.30uF). Best to replace it along with the points as an annual maintenance item for those who wish to retain points ignition.

The felt is clipped in place and rubs against the lobe. Keeps the lobe clean and retain's a little lube for the rubbing block on the points.

The felt has nothing to do with the timing nor would the timing be affected if it were missing.

A quick Google seach came up with a few methods to field test a condenser.
My fav was to charge it up and toss it to someone. If they jumped when they caught it, install it.
Below is the more humane way...

How to test a condenser / capacitor with an inexpensive old fashion VOM.

• 
  
  • 1
    
    
    Remove the condenser from the engine. Place the condenser on an insulated wooden surface such as a workbench. A metal surface may cause the test to fail. You will note that there is a small metal connector located at the top of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the ground point.
    
  • 2
    
    
    Switch the volt ohmmeter to the ohms position. Place the red lead into the "ohm" connector on the meter. Insert the black lead into the "com" or common connector on the meter.
    
  • 3
    
    
    Touch the red lead to the hot connector on the condenser. Place the black lead to the metal case or ground point on the condenser. The meter's deflection needle should have jumped slightly to the right. The needle may also slowly rise in the right hand direction. Hold the leads in place for 15 seconds to 20 seconds. This action places charge to the condenser.
    
  • 4
    
    
    Remove the leads and reverse the placement to the condenser. In other words, move the red lead from the hot connector to the metal case, and move the black lead from the metal case to the hot connector. At the moment where both leads are touching the correct points, the meter should jump towards the right. This action discharges the condenser.
    
  • 5
    
    
    Movement from the meter's needle indicates the condenser is good. If no movement was indicated on the meter in either circumstance in Step 3 or Step 4, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.

Read more: How to Test a Condenser in a Small Engine | eHow.com http://www.ehow.com/...l#ixzz1lqA0yuDZ

Here is the best way to fix a pre-92 XR100 points ignition:

1. Go to ebay.
2. Type in XR or CRF100
3. Click Electrical Components
4. Buy a complete CDI system
5. Open package with the glee of a little kid at Christmas
6. Install it.
7. Start you bike with one kick and never have an igintion problem again.
8.

theraymondguy, on 08 February 2012 - 03:55 PM, said:

Are you sure you are talking about the felt.............not the point rubbing block??? Might be a good idea to think this through............

Old School Al