Expert: Bill Silver - 7/11/2009

Question
QUESTION: On my bike the starter motor and starting chain and sprockets spin the crank just a little bit but then it makes this grinding noise do you know what would cause this? Also i am going to get a new carb do you think a mikuni VM32mm would work good on it? (it has the same engine as the rebel it that helps)

ANSWER: Erik, basically you need three #7 springs shown on, if the rollers and caps are not damaged.

http://www.cmsnl.com/honda-cm250c-custom-1982-us_model1045/partslist/E++09.html

You will need a special tool rotor puller to get the rotor off the end of the crankshaft. Check the crankshaft seal while you are in there, as they have been known to get pushed out in high-mileage applications.

I would check with SUDCO and see if they have some recommendations for enlarging the carb size that you have now. Honda engineers these things with a lot of care and consideration, so you can't just throw on a bigger carb without consequences. With only a single port, you can flow just so much fuel through the head and valves. I think that a 32mm carb is probably way to big for a bike with the porting, cam timing, valve sizes, restricted intake/exhaust system and compression that it is designed with now.

Bill Silver


---------- FOLLOW-UP ----------

QUESTION:      Thank you for the information and i was wondering since you think a 32 would be to big do you think a I'm would do good if not please give me your opinion because it needs a new carb because the old one is junk.

    Also do you know of any ways to get that rotor off without buying the tool because im not gonna buy a tool, use it once, then put it up on the shelf. I really appreciate your time.

Answer
Erik, the tool is about 10-15 bucks.... the cost of the rotor is about 150 bucks.... What do you want to gamble on?

Unless you make some other changes to the bike, a 30mm carb might make a little difference, but you will have to fiddle with it to get it dialed in.

Bill Silver