Expert: Bill Silver - 10/12/2006

Question
i have a cb250 hawk which iam trying to restore it looks exactly like the cb400t hawk from 1978-1979.the problem is that the bike wont start without the choke and when it does start it does not idel. it will run for a while and die down so again start the bike with the choke and the same cycle is repeated again and again.i have to play with the throttle to keep the bike in idle,the idel is also not a constant idle, suddenly the reves goes up and it stays there for about 10-15 sec bofore the reves comes back down. the throttle responce it very sluggish and there is a miss in the left cylinder when i give it gass.

do the carbs on my bike have air cut off valve i ask u this because when i open the small plate on the side of the carb there is nothing inside...
could this be the problem...i will send u a foto of my carb and my bike so that u can tell me if there is any parts that are missing which could be the cause for my problems

hope u can help me bill.

Answer
Rohan, there is only so much I can do for you for a non-US bike. Using the PARTSFISH website, I can only access the CB400T series machines. Those carbs DO have air cut valves, so if you have drilled/open passages, then the parts are missing and that would create a huge air leak on that cylinder.
You may have to check with www.davidsilverspares.com or www.cmsnl.com for parts information on your 250cc machine.

Beyond that, you need to know that there is good compression on both cylinders, that the carbs are both clean inside and jetted for whatever intake/exhaust system is on the bike. Check valve clearances, camchain adjustment and do the balancer shaft chain adjustment, too.

There were issues with the 1978 machines, concerning the CDI pulser coils and CDI controls, but that usually just killed the spark altogether. Check the spark plug caps for matching resistance values, around 5k ohms.

Bill Silver