Topic: 1981 cb650c jetting questions

[racing33]

I have a question that I am sure has been asked a million times but even after reading the FAQ on carbs and reading a ton of other posts I still have a question. I have been fighting a surging or blubbering problem since I have owned this bike. I have adjusted the valves twice, checked the timing numerous times and have cleaned the carbs more times than I would care to say. Now after reading the FAQ on carbs I pulled the air cleaner out of the air box and the bike ran awesome. No blubbering or surging. Crisp throttle response all the way through the rpm range. Long story short the bike ran beautifully after the air cleaner was taken out. Before that it would run all right up to about 4500rpm and then it would act like the choke was on or it was running out of gas. I could not get above 65 mph. Today, without the air cleaner in I cracked the ton on this bike. Now if I understand the information in the FAQ correctly, if the bike runs better without the air cleaner then the main jet is to large, correct, or am I backwards on that? Or would it be better to scrap the stock air box and go with the pod set up? What are some of the drawbacks to running pods?
I just want to get the bike to run right with an air cleaner of some sort because we all know that riding without an air cleaner is not good for a motor.
Also where do you folks go to buy jet kits for this style of Honda bike?
Thanks for any help.
Cheers
Bruce

[DammitDan]

Try taking the airbox filter cover off and hold the air filter in with washers.

I had the same problem with my '82 cb650sc until I did this.  Now it runs beautifully (although it tops out at 90... not that I'm complaining... I doubt the little 650 motor could push my fat ass much faster!  )

Try getting rid of the stock airbox's cover. Leave the stock air box and filter, but replace the cover with a few washers instead.

Edit:

-POWER LOSS:
Some people have complained about a general lack of power, usually problems revving past 5500 rpm or so under load.  I limited the options down to fuel delivery, air delivery, and timing. To make a long story short, it was air delivery - even with a new filter.  The inlet cover that holds the filter in place was restricting the airflow!  I discarded the cover and used washers to hold the filter in place. See picture below. Another idea mentioned to me was the gas cap vent becomming plugged, preventing adaquate fuel flow to the carbs at the higher rpm.  Hopefully one of these ideas will work for you.

[racing33]

 Sorry I did not mention that I had already tried removing the air filter cover. It helped, but only slightly.
Bruce

[Short Round]

what size jets do you have and where do you live?

[cb650]

You could also try a K&N replacement.    Yes your jet is too large/rich.   Did someone else feel the need to change it?




                    Terry

[racing33]

 Terry,
I do not know if someone else has changed the jets before me or not. I am the third owner of this machine. As for the size of the jets I will have to pull a fuel bowl off and check that out again. I had the jet size written down, but I have misplaced it so I will have to look again. I will post the jet size here as soon as I know for sure what it is. Thanks again for all your help.
Cheers
Bruce