colourtune colours ?

[dwhitehouse]

Seems to be a few Carb questions on here ATM. Must be the time of year to get the bike runnning right ready for some sun.

I have a question too. I've rebuilt my carbs with new keyster kits. Cleaned and blown out all the crap with the airline. Set the slide hieghts. Balanced them on the vacume gauge and put a colur tune in to try and get the idle mixture right.

I'm still not 100% happy. Idles nice and smooth at around 900-1000. Throttle response from anything past about a 1/4 throttle to full throttle is great. Goes like stink

However from idle with closed to 1/4 throttle I'm not getting a good response. Almost stalls if you open the trottle from shut too fast at idle.

My question is, what should the colour tune be showing when you open the trottle at idle?
I've set it as best as I can to just turn blue from yellow at idle. When you open the throttle it then goes yellow and eventually blue when revs come up.

Is it too rich ? Any help appreciated because I have more burns on my hands now than I can count

[750steve]

I may be wrong here as i'm deffo no expert but i've been reading up recently. Sounds like a pilot jet issue to me, or maybe the mixture/air screw?

[Dodgy Z1B]

Not sure what your problem maybe but the colour tune will go yellow when you open the throttle as your adding air to mixture thus weaking mixture but should settle at a constant throttle, yellow means weak mixture blue rich.

[nealblath]

well if it's anything like motocross carbs it will be an air screw/piot jet problem!

the air screw and pilot circuits cover the throttle control you are performing and the pilot jet covers throttle response from zero to 1/4 throttle positions. The needle jet covers throttle positions from 1/4 to 3/4 open but this is also overlapped with main jet from half to full throttle.

Air screw should be set at around 1 1/2 turns open (from fully closed). If throttle response cleans up below this setting then the carb is craving more fuel and a richer piot jet is needed. If throttle response cleans up with air screw more open then a leaner pilot jet is required.

HOWEVER, if the rubber boots connected to cylinder heads are pulling air then this will cock up all settings so just make sure no air is getting in. We do this with MX bikes by using talcum powder as you can see where powder is being sucked in, but this is a bit messy. Another method we have used is to squirt neat propane from a gas torch around the joints and if there is a gap you can hear the engine note change.

You may find it solves the problem just by adjusting the air screws.

As stated, the above is for MX bikes but the principles will stay the same.