carbs... on a learning curve

[freak_leg]

Ok guys, I call upon you once again. I've got a 78xs that I've been ridding / working on since last fall (nothing like buying a bike in the last month of ridding weather) Anyhow here is my question I spent the better part of the morning "Carb Tuning" I got her idoling real nice and smooth. Adjusted idol screw. Turned all the mixture screws all the way in (Gently) and turned each one out 1.5 turns. This lead me to the best idol i think the bike has EVER seen. However when i give the throttle a twist it starts poping and back fires once and while. When ridding is sounds pretty crappy at low RPMs and studders some. When i lay on it and the RPMs come up it goes like a raped ape I know usually this is a Rich condition but if i lean it out it runs worse! I havent checked the mix screw tips yet but i have given each pipe the evaporation test all 4 pipes seem to be about the same temp. Ideas??
Thanks again,
Tony

[tarzan]

try turning the pilot screws out a 1/2 turn.It sounds like you are lean on the bottom end.

[XJOK2PLAY]

+1 w/ Tarzan...

Might consider checking your float levels, and doing a good synch too.

I had a similar problem w/ mine... did all that... still popped back through the exhaust on decel... couldn't keep a consistant idle speed...

so we re-synched again, and noticed a low reading on the vacuum... even though we could get the same readings across all 4 carbs, setting up w/ the #3 carb reading first like you're supposed to...

it wasn't until we were able to adjust that vac reading higher, and then synch the rest there that it straightened up the idle speed, stopped the popping back, and it began to run right.

Something to keep in mind... just because you can get the other 3 carbs to synch to the same readings as the #3, doesn't mean you shouldn't try to achieve the highest reading w/ #3 first.... and it does make a difference.
HTH's.

[Larrym]

Blind Man Feeling a Painting??

I know usually this is a Rich condition but if i lean it out it runs worse!

So which way does one turn the idle mixture screws to "lean it out"? IIRC then turning the idle mixture screws CCW backs the screws out and serves to richen the idle mixture. Just checkin' to make sure we're on the same page here.

If you've tweaked the idle mixture screws to a new position without documenting where they were in the beginning then you've lost your original reference point. Can't go back to the way they were set before and walk away from it if that's the situation.

IMO if you're going to disturb the integrity of the settings of the idle mixture screws then each time this is the procedure to use:

http://www.xs11.com/xs11-info/tech-t...colortune.html

JMO, but just setting the screws to a pre-determined number of turns out from lightly seated is only the beginning point of the above process. The tune-by-ear method usually results in none of the carb misbehavior you've described. (Barring any electrical or individual carb component snafu's...)

The tune-by-ear method usually requires the carb sync with gauges be done beforehand to ensure best results.



Not saying that doing the tune-by-ear won't be a fun thing to do this afternoon. It may solve your immediate problem.

But if it doesn't you know which way to go next.

[Yard Dogg]

When you rip on the throttle the pilot jets have much less to do with things. As your rpms and vacuum increases, the throttle slides move up allowing the main jets to take over. You need to tune your pilot screws by ear and sync your carbs. You should read the permanent carb sync threads written by our smarter members. Even before you sync you should check your valve shim clearance, with your year bike a little valve noise is normal, but if you have an 80' or newer the valve noise should be much quieter.

Note: You can't sync by ear, you can only set your pilot screws by ear.

[XSBell]

Alltitude will make a difference as well. Here in Denver we are above 5000 ft, mine are backed out between 3 and 4 turns.