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Followup To
Question -
Hi Chris, I have a Honda CB250 and have cleaned the 2 carburators thoroughly with carby cleaner and air pressure.When I rev the engine a little it then starts to rev up to about 3-4000 rpm by itself. I have heard there might be an air leak but have checked the rubber mounts at the cylinder heads and they are quite tight and no holes are apparent.Do you have any other suggestions? Thanks. David
Answer -
Hi David.
Have you tried adjusting the idle speed? You didn't say if you had tried that or not and it is normally the first thing that one would do to reduce the idle when it is high.
Air leaks in the manifolds would cause the idle speed would be lower, not higher.
If you are concerned about leaks in the manifolds, then start the bike and spray some ether at the manifolds from a few different angles. If there are air leaks, then the rpms will increase when you spray the manifolds.
Start with those and let me know what you find.
Good luck and ride safe.
FALCON
Hi Chris,The idle is set about 1200rpm,there appears to be no leaks around the manifold, the engine runs at idle then revs start increasing all by itself to about 3-4000rpm? I noticed the right spark plug is black (carby running too rich?),left side is OK. I also notice when I open the throttle on each individual carby that the right one isn't as smooth in accelerating as the left one (taking into account that only one side is being tested at a time)What do you think? How do you tell in the main jet is worn? Thanks again. David
AnswerHi David.
Both carbs must pull together at the same time. They need to be synchronized. A static synchro will do to start with. Adjust them so that you have both of them moving at the same time. If one opens before the other, then the carbs are not in synch.
Once the bike is running clean, then do a proper synch of the carbs.
How about the air filter? Is it clean?
Has the mixture been changed on either carb (particularly the one with the blackened plug)?
If so, then you will need to lean out the carb. This is a long, drawn out process.
ONLY IF THE MIXTURE HAS BEEN PREVIOUSLY CHANGED, here is the process;
1) Make sure that the mixture screws have been turned in to the stop. NOT TIGHT. Just til they stop.
2) Put in new, clean spark plugs and turn both mixture screws out 4 full turns.
3) Start the bike and run it for a few minutes. Ride it around for a bit.
4) Pull the spark plugs and check them.
5) Adjust the mixture accordingly. Turn the screws 1/2 turn out to enrichen the mixture 1/2 turn in to lean it out. Clean the plugs and re-install them.
6) Repeat steps 2 thru 4.
7) Make adjustments (as needed) to the mixture in 1/4 turn increments. Both mixture screws MUST be turned the same amount in the same direction (in or out). Clean the plugs and re-install them.
8) Repeat steps 2, 3, 4 and 7 as needed til the plugs come out looking normal.
Start with that and let me know what happens.
Good luck and ride safe.
FALCON
