Author Topic: Running!  (Read 1007 times)

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Offline hymodyne

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« on: May 19, 2005, 10:02:17 am »
After months of work, my CB500 is up and running.

Excited as I am about that, I still am nagged by some little problems. When I start the bike, after it warms up, I can open the choke completely, and it settles into an idle around 1150 rpm. last night, I took the bike out and got it up to about 40 mph in my neighborhood before the lack of plates gave me pause. Starting the bike today, I added four velocity stacks with small oiled foam elements. as soon as I did this, the bike bogged down and eventually stopped running. when I took the stacks off, the bike resumed its better running form, but still was backfiring every now and then, and the one and two pistons are putting out a little white smoke. I checked and the oil is not overfull, and the air/fuel screws are set per manual specs.

why would it run beter without air cleaners than with?

"All things are ready if our minds be so."


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Re: Running!
« Reply #1 on: May 19, 2005, 10:10:10 am »
sounds to me like it is running rich.  when you add the filter it reduces the airflow and makes the bike run rich.  without the filter it gets more air and has the proper air/fuel ratio.  too rich of a mixture= backfiring, smoking, etc.  Try putting the filters back on a playing with the adjustment screws.

Offline TwoTired

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Re: Running!
« Reply #2 on: May 19, 2005, 11:58:32 am »
Congratulations on your acheivement!
As mufflers cool down, the humidity in the air condenses inside the mufflers as water. The next time the bike runs, the exhaust heat vaporizes the water and it looks like white smoke.  If it has a blueish tinge to it, then there is likely oil being burned.  And, black exhaust smoke would be unburned hydrocarbons resulting from a mixture that is too rich.

The foam element filters use oil to capture dirt particles as they attempt to pass through.  However, if these types are over-oiled they greatly restrict the air flow into the carb and then act as a partial choke.  The foam should be just this side of dry with oil.  You may also have to clean and re-oil these monthly if they have a small surface area, because as they capture dust they plug up and progressively restrict incoming airflow.  Your mixture will get progressively richer.

Greg is right, the idle air bleed screws are adjusted with the bike in riding configuration to compensate for whatever breathing charateristics are provided by the intake and exhaust components.   The air/fuel settings in the manual are correct for a bike with the stock intake and exhaust components.  When these components are changed to pieces with unknown flow charateristics, the manual guidlines may only be applicable as starting points for further refinement.  The carb FAQ on this site will help you through the process of tuning your carbs to your current configuration.

The last thing to address is that of fuel contamination.  Are you sure the fuel in the carb bowls is still clean?  The poping sounds could be carb jets fouling or perhaps the spark plugs are fouling from the soot in the chambers.  Or, perhaps your carb sync isn't close enough.

One tip that might help you is to flash touch the head pipes to feel for even exhaust temps.  Your fingers have a heat memory that remembers very brief encounters with hot things.  The head pipe temps will tell you which cylinders are firing with the same zeal as the others.  And, you can focus you efforts on the problem at hand.  (The pun wasn't intended. But, I like it.:-)

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.