Motorcycle Repair: carburator problem?, honda cb350, meg ohms

Question
i've a honda cb350 1973 model. i cleaned the carburator then reinstalled. i took it for a test spin and everything seemed ok for a couple of minutes. then i found out that only the pistons #2 and #3 were working. i removed the carburator and cleaned all the jets, floats, bevel pins, and made sure all the holes are free from obstructions. after the reinstalling the carburator everything seemed to work fine for a couple of minutes, now only #1 and #4 are working (firing) and #2 and #3 are dead. i've already installed new spark plugs. checked for the sparks, all four of them seem to be producing sparks! currently, #2 and #3 won't fire at idle or any other speed! any ideas?

Answer
Hi Kuber,

I suspect checking the breaker points gap and ignition timing would the place to start troubleshooting. See the info that follows.

Respectfully,
Mark Shively


Electrical Testing Early Honda's

Ignition source Coil
1. With the magneto wiring disconnected, block the breaker points open with a piece of paper such as a business card.
2. Measure the resistance between the ignition source coil wire and ground with a low range ohmmeter. If resistance is about 0.5 ohm, the coil is probably good.
3. If possible, disconnect the ground wire between the ignition coil and the magneto base. Measure insulation resistance between the iron core and the coil. Insulation resistance should be at least 5 Meg ohms.

Condenser
Unless you have a special condenser tester, do this quick test:
Connect the negative lead (-) to the negative terminal of a 6-volt battery, and the positive lead (+) to the positive terminal. Allow the condenser to charge for a few seconds, then quickly disconnect the battery and touch the leads together. If you observe a spark as the leads touch, the condenser is good. Arcing between the breaker points is a common symptom of a defective condenser.

Charging Coil
Measure the resistance from each coil output lead to ground. For most coils, resistance should be in the range of 0.3 to 0.6 ohms. If possible, disconnect the ground wire from each coil, then measure insulation resistance between the coil and ground. Any indication of less than 0.5 Meg ohms means that the coil is shorted. Some magnetos have built-in diodes (rectifiers) for battery charging current. If so, resistance should be very high measured in one direction, and very low in the other (switch leads).

Rectifier
Same as last sentence, high resistance one direction, low the other.

Ignition Coils
1. Measure resistance of between the positive and negative primary terminals (small wires). Resistance should indicate about 5 ohms for most coils of this type. Some have a primary resistance of less than 1 ohm.
2. Measure resistance between either primary terminal, and the secondary high voltage terminal (spark plug wire). Should be between 5K and 11k ohms.
3. Check condition of spark plug cap. Look for cracks, dirt, and defects.