adjusting idle mixture?

[mjpxs11sh]

hey all! my 81 specials running pretty good after pulling and cleaning the carbs. bench sync'd, 2.5 turns out on mixtures (was where they were from factory), then tried to adjust mixture by ear, but thats not workin! tried to find an external tach on the web, (used to have a perfect one for auto dwell) but i cant find one im happy with yet. then i thought, how do u connect the 2 terms to the bike. anyone with experience setting it up and adjusting mixture? it seems 1 carb pops a little on choke cold and every once in awhile at idle after riding awhile. i sealed the carb boots with silicone and spray rubber. thanks!

[BA80]

Have you got a 4 guage sync tool?

Irregardless, if you don't have the carbs properly synced the mixture adjustment is a moot point.

[Axel]

Iirc

If carbs are synched , there is a tool tip on lowering the RPM to hear the difference somewhere . Colortune is specifically for adjusting idle mixture . Recently I have read about a method using the Carbtune or other manometer setup to adjust for max vacuum . I have mine close now so I read the plug to check the mixture . Lean situation causes popping IIRC and you may need to turn the mix screw out (counterclockwise) a bit to eliminate that . Finding the lean cylinder may be shown by the plug being rather clean looking as opposed to brown or rust or grey .

[DAVINCI]

Connect your tach/dwell meter black to either the orange or gray at the TCI, and red to the positive terminal of the battery. The tach/dwell meter should be switched to read as high as possible so even minor mixture adjustments will affect the needle movement.

[mjpxs11sh]

thanks. unfortunately i dont have a carbtune or colortune. i bought a vacuum guage from Harbor Frieght to adjust mixture for the highest reading, thats how i found leaking boots cause the needle was just fluctuating. pulled all boots and sealed them, but the needle still fluctuated. carb spray tested the boots while running and they were good. so i was unable to get the mixture right. i know at least ones lean, but i'd like to get em all right. oh well, guess ive got to buy some tools and im broke!

[BA80]

Your vacuum guage will need a dampening valve in it, like for a fish tank air pump, to stop the fluctuation.

It's much better if you have a 4 guage setup like this



and sync the carbs then adjust the mixture screws to the highest vacuum then repeat that over and over until it evens out and adjusting the sync doesn't change the mixture adjustment and vise-versa.

[cywelchjr]

Yup, what he said. You need significant restriction in the line to the gauges to minimize the fluctuations to get a decent reading, it's the same issue as with the octy, the vacuum petcocks and the vacuum advance. If they run off direct vacuum, they bounce all over the place, restriction smooths things out, makes things work better, rather like a shock absorber does for suspension.

[mjpxs11sh]

so Greg, dont the 4 analog sync guages need valves and/or anybody, how does that effect the new model Carbtune. does it fluctuate? whats easiest and most accurate, analog or Carbtune?

[DAVINCI]

Whatever, Carbtune, Mercury or mechanical gauges all need restrictors in the lines.

[DGXSER]

The carbtune comes with the restrictors to install in the lines, so yes, it also needs the restrictor to dampen the fluctuations.

[BA80]

whats easiest and most accurate, analog or Carbtune?

They are both about the same as far as ease of use. I personally find the analog guages seem to be more accurate. I synced mine at a rally with the carbtune a couple of years ago and it didn't run well until I got home and resynced with my analog set.

[mjpxs11sh]

thats good 411! thanx Greg.

[cywelchjr]

I think it's really what your comfortable with. Some seem to find it easier to get an accurate sync with the carbtune, some with the analogue gauges. It's what works for you. If you shop around and make sure to calibrate them before using them, the gauges can be more than accurate enough and cheaper to boot. The carbtune on the other hand, while more expensive is easier and smaller to carry and more durable. It's all what works for you.

[mjpxs11sh]

i guess id have to try em both. thanks Cy