b52bombardier1
Well-Known Member
Give it just a little dab of choke when it is mis-firing. If that fixes it, you are running lean. Every one of my 90 and 100 CC bikes had to have the main jet increased and I believe that is because today's fuel is different than the stuff we pumped back then. My ST90 and CT90 bikes are at about a 74 for a main jet size. A 76 also works if you can't find a 74. And I've never seen a 75.
Have you checked the operation of your spark advancer with a stroboscopic timing light? Just power it with a 12 volt car battery and it works the same as if you were using it on a car harmonic balancer except its the bike flywheel. With the strobe light aimed at the flywheel, you should see the timing change as you rev the engine if the spark advancer is working properly. Curiously, if the advancer springs are weakened by heat, the springs won't pull the counterweight arms back in as the rpm returns to idle. The same springs were used on the Honda 750 of that era and Tamiya has a set for about 30 bucks depending on the yen exchange rate. Kinda' spendy.
But my money is on your carb being too lean. Word has it that the California bikes back then got a 62 main and the 49 state bikes got a 65 and I have seen the 62 in carbs I have purchased on Ebay. I have several of these in my can that contains old carb brass - never to be used again in this case. Both are too lean for today's dead dinosaur juice, IMHO.
Rick
Have you checked the operation of your spark advancer with a stroboscopic timing light? Just power it with a 12 volt car battery and it works the same as if you were using it on a car harmonic balancer except its the bike flywheel. With the strobe light aimed at the flywheel, you should see the timing change as you rev the engine if the spark advancer is working properly. Curiously, if the advancer springs are weakened by heat, the springs won't pull the counterweight arms back in as the rpm returns to idle. The same springs were used on the Honda 750 of that era and Tamiya has a set for about 30 bucks depending on the yen exchange rate. Kinda' spendy.
But my money is on your carb being too lean. Word has it that the California bikes back then got a 62 main and the 49 state bikes got a 65 and I have seen the 62 in carbs I have purchased on Ebay. I have several of these in my can that contains old carb brass - never to be used again in this case. Both are too lean for today's dead dinosaur juice, IMHO.
Rick
