QuestionHello
I have a 1977 Honda XL100 Dirt bike that Igot running I have been looking at the past answers and I have got my bike timed with the TDC and the cam gear in the right place. and my valve clearences at .002 for intake and .003 for exhaust.How ever I have a problem because when I try to reeve it up all the way it starts to sputter. I believe I still need to correct my points and my carberator. If you could give me some info on hoew to set them and any other idea of why it sputters I would greatly appreciate it.
PS When I set my points so it sparks after the top of the ignition cycle its seems to run better but flames come out of the exhaust. When I set it a little bit before like I think it should be it doesnt want to reeve up at all.
AnswerStephen, first be sure that the motor is capable of making good power at high rpms, by doing a compression check. This will also confirm that you installed the camshaft correctly. Stock compression with a wide-open throttle is around 150-175 psi. If you got that, then you can move onto the spark timing issues. Be sure that the mechanical spark advancer (behind the point plate) is functioning properly, before you try to set up the points/timing.
Your engine should have the 2 piece head, so hopefully, there is very little or no play in the camshaft when you try to wiggle it in the cylinder head. ANY play will translate into varying ignition timing and poor performance.
Honda specs show that the points should be gapped at .016" when they are at the widest gap, then move the point plate until the points just open at the F mark alignment. This should result in your point plate being located about in the middle of the adjustment slot on the backing plate. If you are WAY off to one end or the other of the slot, then the point gap is off or the camtiming is incorrect.
The F mark is at 12 degrees before TDC (T mark), so that is where the timing should be set. If the engine is not running well at the F mark and better AFTER the T mark, then you do have camshaft timing problems.
Once camshaft timing, compression and ignition timing are complete and correct, THEN you start with the carburetor.
If you have a STOCK bike with original air cleaner and exhaust muffler, then the settings should be 12.5mm float level (PD90A carburetor), #95 main jet, #38 idle jet, mixture screw at 1.5 turns out from closed and needle clip on the 2nd notch from the top.
If you DO NOT have stock parts, like air cleaner and muffler, then the carb settings will not be correct and you will get to adjust the needle clip position and the main jet size until it comes into the range where it wants to be fed properly. Carburetion is the LAST thing to do/adjust, so don't start fiddling with it before you get the foundation solid, which is the combination of compression and timing. A bad condenser will cause a lot of arcing across the points and the bike will barely run, in most cases. Sometimes the lead is loose in the connector, so check all the wiring connectors, plus use a FULLY charged battery to run the bike.
Bill Silver
