carb tuneing

[reed]

i in no way will try and tell anybody i know what iam talking about in this field, but here is my best attemt. i noticed that with the carbs on, ive turned the synch screw not even a 1/16
of a turn one way or the other and ended up with all kinds of lean sinarios, one side getting hotter, popping on deccel. till i was reading on the 650 site,a guy said to properly adjust timming chain, gap vavles ,dead cylinder mix screws,then manometer synch. iam thinking if a person was to do these he might have a better chance at determining what else might be causing a problem instead of masking one over the other. i put some carb foam in my pods added some washers to my strait through pipes synched, other than cleaning did not touch inside. did i just get lucky. dunno, just tryn to keep it simle. my 2, lookin for feed back. what did you do to make it work. you can tell me if you think iam crazy if ya want many have. lol

 

[reed]

does anyone know should you mamometer synck after each change?

 

[bcware]

I don't know for certain, but it is my thinking that once you are synched you shouldn't really have to synch again. The synch is simply controlling raw volume flow through the carburetor and logically I would think once a balance is achieved the idle mix is really the only thing that could have an affect on a single side independent of the other (because the other settings are so easy to perfectly match). I am also thinking that regardless of the air/fuel mixture flowing through the carburetor, the vacuum pressure will remain the same at a constant rpm. If I recall, the identity of the gas is largely irrelevant.

I am thinking of a synch as mechanical and constant, while the idle mix is more dynamic. You wouldn't change the size of one air filter over another if one side started running lean would you? No, you would adjust the air/fuel mixture on the respective side.

Again, I could be wrong but this line of thinking makes sense to me. I am also not considering that certain mixtures, lean or rich, tend to want to climb rpms. A synch should be good at a constant rpm, however.

 

[reed]

hea bc i was starting to think i had bad breath ha ha,do you know what throws a synch out over time.and no. i think your right i would not change one air filter at atime. but that being said if one flow changes would that not change the synch. thanks for launching into the discussion whith me.

 

[bcware]

This whole line of reasoning assumes your synch is perfect already, so it my still be necessary to adjust it should it not be.

What could throw the synch out over time? Well, looking at the mechanism used to adjust the synch I can see that it is controlled by a spring's pressure on a flange. Over time the spring may shorten, or opening and closing the throttle could cause a slight shift until a settling point is achieved.

If those butterfly valves are open exactly the same amount, you shouldn't have to change them again in an ideal situation. In reality there may be some variability from one carb to the other.

Before changing the synch, however, I would verify that all other settings are perfectly equal on each carb. After all other possibilities are exhausted I would then finalize with a synch.

The synch is powerful a idle and low rpms; it can mask lean or rich conditions. If the synch is used to "tune" your throttle response will suffer. This is essentially the same as wrapping your air filters with duct tape on one side

 

[reed]

ya i think iam understanding what your saying to me. this is my first bike (that i have worked on) and first 400 that ive owned i would like to drive another to get a feel of wher mines at it does pull through all gears pretty good with no flats ive only had it to 75 though and that was only a couple miles

 

[reed]

if all is the same on both carbs jets needles ect, and one side is rich and one side lean then why would you change both carbs leaner or richer ie jets needles ect

 

[Unknownz24]

if all is the same on both carbs jets needles ect, and one side is rich and one side lean then why would you change both carbs leaner or richer ie jets needles ect

Ideally if properly synced and both having the same jet settings, one shouldn't be richer/leaner than the other. But this is the real world, so in that case you actually WOULD change the jets individually for each carb while still maintaining the sync.

 

[reed]

ya know i have read somewhere that the or some carbs came stock with different jet settings to compensate for a hotter cylnder.ya know iam always wanting to learn and i think i can learn something from any one individual. but i guess nothing replaces real world experiance. if sombody can make something work iam willing to listen. you are prob right there when the bugs are flying and the asphalt is hot ya never know. i do know from the little bit that i have messed with a duell carb setup that the synch is a very touchy device seems just making sure the springs are properly greased can make a diff

 

[new kid on the brat]

it is normal for a v-twin to have different size jets because the front cylinder runs cooler than the back cylinder!!! my shadow runs a 120 and a 145 i believe , and that is a stock jetting!!

as far as synchronising after every jetting? absolutely!! i have access to a 4-set of vacuum gauges and everything effects vacuum at the carbs!!! compression,timing, fuel air ratio,

next time you have your mamometer hooked up to your carbs try pulling a plug wire!! or bottom out a mixture screw and watch the vacuum change.

always synch, adjust mixture for max vacuum and rpm, and then resynch! after every jet change

of course if you have a bad valve or low compresion or fouled plug or a CRACKED DIAPHRAGM!!!
" that's never a good thing" they will never balance!!!

funny, but i just searched everywher on the net and no one rechecks the balance after setting the idle adjustments! my vw's definately change vacuum with every adjustment

 

[xschris]

when you adjust valves or timing its good to check the carb sync. It also should be done with the engine fully warm. I have found that vacuum gauges are not that accurate. A manometer or a mercury gauge are the best. I use a mercury gauge.

 

[bcware]

Those mercury sticks are fairly expensive these days; at least I never saw any cheap ones. It's easy to build one for a few bucks, however.

 

[xschris]

These are the best things to use. I got them from a friend that had them in his basement from the 1970's Because of the mercury I don't think they make them anymore.