Hey Guys,
I've acumulated enough spares while restoring my CL-72 that I've decided to build an AHRMA 250 GP road racer. I have a several cl-72 motors as well as CB77 parts including a frame, wheels, suspension,etc. My question for you guys has to do with the "hop-up" part of the motor build. I know that the 250 isn't the best bike to run in a class dominated by Bultaco's and Ducati's, but heck, I love Honda's. Any tips out there that can be done primarily in the garage? Here are a couple questions to get you guys started:
-How much can I shave a head and not hit valves?
-Are there any mods you can do to the stock pistons to lighten them or make them better (remove a ring?)?
-Carb's, what should I use?
-Megaphone sources?
-Bigger valves (are 305 valves bigger? Do they fit?)?
Thanks.
-Gabe
250 Road Race MotorMy experience goes back at least 40 years, but we found in those days was that increasing compression ratio by shaving the head, porting and polishing the head, using heavy duty valve springs and a Barnett clutch really perked that engine up. Let a racing machinist decide how much to take off the head. The stock carbs were found to be best, after switching to megaphones and going to larger main jet sizes. Occasionally a set of CYB megaphones comes up on ebay. The long carb funnels that were offered as CYB parts by Honda were said to be very effective.
--Randall Randall,
Thanks for the reply!! I've been checking this post daily. Stock carbs?...Well, that would save some money. I appreciate any advice, if you think of anything else, please let me know. So you have experience racing 250/305's? Any cool stories? Just curious. Thanks. -Gabe If anyone knows about how much I can shave off the head with out hitting valves, I would really appreciate it....I would hate to learn that one the hard way.
Shave the head? Just be sure you have the HIGH DOME pistons and you are Good to Go!. .......lm
You may want to go the the stock 305 26mm carbs at least. .....lm
Gabe,
I think Megacycle Cams (www.megacyclecams.com) still offers a race cam you can use. Also check with Bore Tech (www.bore-tech.com) re the head milling versus high dome pistons. I tried larger carbs on mine, but it ran worse. I was using an 11500 rpm redline, but occasionally exceeded 12K. The valves would float, but never any damage. They are very reliable engines if you treat them right. --Randall Thanks guys.
I checked the MegaCycle Cams website, they have an extensive line up, but pricey! Four stroke racing is expensive apparently-my old 250 Bultaco project is looking more tempting by the day. I just added up a few things and figured out that I could have over a grand in the head alone....hmmmm....maybe stock cams will be okay for now. Keep the tips coming, and again, thank you very much! -Gabe
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