Motorcycle Repair: cold starting a Honda, cylinder machines, valve clearances

Question
Hi,
I have a Honda 250rs 1980 and am finding it very difficult to start in the colder weather. I have renewed the spark plug, checked the choke is operating but still it dosent want to start even with a push. I get very warm myself though through kicking it over!

It will eventually start after lots of kicking and sometimes leaving a few minutes in-between. It fires and stops and gradually with more kinking over will continue to run. When started and warm it runs very well and restarts normally with one kick - I would be very grateful for any ideas.
Thank you
David

Answer
David, I actually brought one of these bikes into the US, back in 1980 and enjoyed it immensely.

A couple of things that could be hampering your starting efforts....
Check the decompression cable adjustment (I think it has one) AFTER you check the valve adjustment. When the valve clearances get tight, they get harder to start and when the clearances open up during engine warmup, then it becomes easier to start. Valve clearances are .002" intake and .004" COLD. Book I have for the XL250 of that year shows 1/16" to 1/8" free play on the decompression lever on the cylinder head.

The carburetor has two diaphragms... one for the air cut (anti-backfire valve) and one for the accelerator pump function. If the carb hasn't been gone through for a long time, I would have it checked for problems in these two areas. Also check the condition of the intake manifold and try to richen up the idle mixture screw a bit.
Generally, single cylinder machines do not like any throttle fed in when you are cranking it over. If the pump is working, twist the throttle a couple of times, then leave it closed while you kickstart it.

Check the resistance of the spark plug cap... should be around 5K ohms. If too high, replace it. There is a mechanical spark advancer down in the clutch cover, but it runs in oil, so hopefully, it is not sticking or damaged or worn excessively. Spark timing can be a crucial factor in getting these things alive on a cold morning.

Check the choke cable adjustment. Sometimes the outer sleeve slips out of the holder and what feels like a full choke isn't really happening.

Full choke a quick squirt of gas and no throttle should get it alive even in cold weather. Keep the idle speed low, too....

Bill Silver