If you lose the spark to one cylinder on your Ascot, it is usually
easy to troubleshoot. We're not talking "it doesn't seem to be
but that you know that there is no spark happening on either the front
or rear cylinder but not both. The Ascot has a pretty reliable
system. Other than the plugs themselves, think Coils, Spark
and Pulse generators (pickup).
Under the seat there are two identical connectors. Each of
goes to a sensor, spark box, and coil. You can SWAP the
and it swaps the spark boxes between front and back. If you know
one cylinder has no spark and you swap these two identical connectors,
look for the problem to move to the other cylinder. If it does,
problem is probably the spark box.
The spark boxes are hidden behind the battery. Honda only sold them by pairs last time I needed one, so look for a used unit if you can.
There's the little devils! I've had one of the boxes apart, and they're really pretty low tech. Inside that plastic box is a pretty crappy little printed circuit board. It could be worth your time to disassemble the box, slide out the card, and check all the solder connections and components before ordering a NEW PAIR. You may save yourself a couple of hundred bucks!
If the problem isn't identified by the first test, pull the tank and
coil cover. Swap the pair of SMALL wires that go into the
of the coil between the two coils. If the problem is a bad coil,
the problem will NOT switch cylinders. Unlike the above test, the
bike will NOT run on one cylinder with these wires swapped. Two
bolts hold each coil to the mount, an easy replacement. If you
anything like a crack or bulging on the coils replace them even if
working now because they'll be dead soon.
There are some specs for checking the ohms of the primary and secondary
also in the manual, so double check before you spring for a new coil!
So the third likely (and the most trouble to fix) suspect are the
pulse generators. They are mounted inside the clutch cover and
tell the spark when to go off. The outside connector is just a
little above the coils, though both the manuals may mislead you.
I spent a lot of time looking for it where the manual shows, but it's
really up here!
I managed to find the connector by following the sort of "woven"
insulation up from the front of the clutch case. The color coding
on the pulse generator wires were NOT what they say in the manual, but
it was right on the chassis wires leading to it.
The resistance between the wires of each pair (front and rear) should be 430-530 ohms (480 nominal). My problem was the front pickup - infinite (open) resistance. So I got to rip into the primary side of the engine to replace the pickup. Luckily, I had a parts bike - but that meant that I had to do all the disassembly twice. The Honda shop manual and Clymer manuals are both pretty good about disassembly order which includes the exhaust system, brake pedal, unboltable frame section, and then the primary cover. It's not easy, but not impossible. Before I removed the pickup assembly, I tapped into the wires by the pickup and ohmed out the circuit to each pin of the connector and through the pickup as well - hoping that it was just a broken wire. Nope, open pickup.
The only thing that took extra time was removing the old pickup harness and threading in the new one between the frame and upper radiator hose. I ended up removing the upper radiator mounting screw which allowed me to push the connectors through the gap.
The symptom of my pickup going out was progressed over about two
weeks. First one cylinder would randomly cut out and come back,
then it would cut out after about a mile of riding and only come back
after the engine had cooled a little. Finally it died all
together, and made it possible to troubleshoot the problem. If it
stayed as an intermittent problem, I might still be scratching my head
That was enough to make that 250cc single back into a V-twin again. I just felt lucky that I had a two cylinder motorcycle with two independent ignition systems to get me home.