Thursday, June 4, 2015

CR250M-More Problems Solved

In my last note I indicated hope that my carburation/ignition problems had been solved. I was simply hoping that by changing my spark plug cap all would be magically transformed...silly boy!

In fact, the problem was with the carburettor. It took a bit of sleuthing but I finally figured it out. I went for a very short ride right after I installed my new plug cap. The problem re-appeared within one mile. It was clear from that ride that as long as I used at least 3/4th throttle the bike would run pretty well...not perfect...but useable. Once I slowed down and tried to idle the bike it immediately began running very rich and would only run if I held the throttle wide open. With that setting it gave a very rich idle...four stroking or rather eight or sixteen stroking...but it did keep running so I could get home without pushing. Clearly massive amounts of gas were flowing into the engine.

After significantly straining my brain, I devised a test. I was beginning to mistrust the float level. Once home, I shut off the fuel tap and kept on running the engine. Slowly but surely the rich running cleared up and the clearly nasty and argumentative tone of the engine returned. By running with the fuel tap closed I was simply lowering the level in the fuel bowl.

The next step was easy. Open up the carburettor for the fifth...or sixth...time and take a long look at the float. Had I installed it upside down. it turns out installing it upside down was impossible. Was the float at the wrong level? again...not really, at least according to my Clymer's Manual. It specified 19 mm from the bottom flange of the carburettor to the bottom of the float at just the point where the float was starting to close the needle valve. That is what I had. Something was wrong...probably Clymer!

Maybe this settling would work on the Bonneville Salt Flats, but it didn't work for me. I am rarely at full throttle and never for more than five or six seconds at a time. The rest of the time I am at no more than half throttle. So, I lowered the float by a significant amount...about 5 mm. Put it all back together again and went for a ride. This time I went about four miles with a lot of idling and part throttle and minimal full throttle. Each blast of full throttle produced an improvement in the engine's responsiveness. I may lower the float a bit more and I am going to be experimenting with plugs.

So...for now all is well and I'm looking forward to a longer ride later today. So, I'm off to mix up some fresh gas and gather up some tools. See ya!

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