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For you with bike carb knowledge

General engine tech -- Drag Racing to Circle Track

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Re: For you with bike carb knowledge

Post by MadBill » Sat Jun 15, 2019 5:57 pm

Truckedup wrote:
Sat Jun 15, 2019 4:02 pm
Yup, my bike...the bike was never run with megaphones, just 32 inch straight pipes...The phone photo distorts the steering rake but it is stock,about 27 degrees..It's a modified production class so the basic frame and suspension must be similar to production...1970 engine, 1974 frame...You can see the small guards I made on the carbs to keep the riders pants from blocking airflow..bare bones, no gauges except for the oil pressure that can't be seen while riding..A finger out of place can cut speed so you make your body as small as possible,hold the throttle to the stop and hope nothing blows up. :D
A friend of mine rode a Clubman's Gold Star BSA 500 cc single back in the day and for a time was bedevilled by a misfire whenever it rained. One day he happened to glance down and noticed the belt of his raincoat being sucked into the open maw of the 1 -1/2" Amal GP carb...
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: For you with bike carb knowledge

Post by CIHUNT » Sun Jun 16, 2019 10:13 am

It has to do with the rate of acceleration. Lower acceleration rate like in higher gears gives the carb more time to supply fuel which results in a richer mixture...and visa versa. Fuel flow always lags behind air flow. 11.5 to 12 at the end of revs in top gear is not out of the ball park on that bike imho. If you set it up to be closer to 12.5-1 you may find you lose good dynamic response when shifting quickly from gear to gear. You have to find the happy medium. Most vintage bikes like a richer mixture than their modern counterparts. One of the advantages of fuel injection over carburetors.

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