How many turns is too much

[hard_y_rd]

I think i have my timing dialed in. I turned my mix screws out 1 1/4 turns each. Seems like they are starting to richen out in color. The left more than the right. How many turns out from stock can you go? Stock is 3/4 of a turn on mine.

 

[5twins]

The max turns out is based more on carb design than any initial setting spec. The carb makers like to see no more than maybe 3 to 3.5 turns out because the screw is spring-loaded. Get too far out and you lose that spring tension. The adjustment could move on you or the screw might even fall right out. You're still well within the limit at 1 1/4 turns.

The 3/4 turn initial setting for your carb set is actually rather small. Usual spec for many, if not most carbs is around 1.5 turns. If you eventually end up out around 3 turns, you might want to try a size larger pilot.

Your pilot jet flows its fuel/air mix into the main bore through 4 tiny holes. Three run directly from the jet and the only way to change their mix strength is to change the pilot jet size. The flow to the fourth hole goes through the mix screw first and can be adjusted. This means you have control or adjustment over roughly 25% of the flow. That's why the mix screw will only do fine tuning. A jet size change is required if the limited screw adjustment range won't fix the issue.

 

[richardthemotorcycle1]

I have mine 3 turns out and its running great

 

[hard_y_rd]

I should point out that with the uni's and straight pipes, I have re-jetted to 1 up on the pilots and 2 on the mains. I'm at 45 and 135 with the needle on no.3 clip position.

 

[hard_y_rd]

I turned my mix screws out 2 turns. Gonna try that when the weather turns nice. I know you're supposed to use new plugs for the color test but i don't have 6 sets of plugs right now. Lol
The left side exhaust seems to have more force than the right. Right side has a bit of a stutter. I guess that's just a tuning thing. I don't think that you can get them perfect. Think i read that on here at one time.

 

[CDNTX650]

Lots of that will be in sync, your dealing with trying to make 2 seperate carbs and pistons connected to one crank run at the same speed. To many variables, like even compression carb differences etc. Mine, every so often has a little exhaust flubber from one side. I can make it switch sides if i mess around with sync. But, for 98% of the time she is even steven out of both pipes. Id say using cheapo vaccum guages will make that worse. I can sync better by ear than my guages.

Posted via Mobile

 

[hard_y_rd]

I haven't used guages to sync as i have no intake barbs. Just new to it but i can hear an exhaust diff in each side. I don't really care if one exhaust has a flubber. Just want the plugs to be the same color as i don't want to hole a piston. I guess the "sync by ear" will come with time.

 

[5twins]

With the bike off, back both idle speed screws out until they're not touching their cable arm. Now turn them back in until they just touch and then give each one more full turn in. Start the bike and set your idle speed. Make sure you adjust each idle speed screw equally. You're attempting to keep the same butterfly plate opening on each carb, which would be "sync". OK, that's part one, sync at idle.

Now you have to sync the cables so each plate starts to open at the same time. You do that by matching the freeplay in the cables to one another. I set the left cable to the freeplay I want (about 3/16" to 1/4") and loosen the right one way up. Then I lift the left cable sheath out of its seat on the carb top just enough to take up the play. Then roll the throttle open slightly to pull the cable sheath back down - but not enough to start opening the butterfly. While holding that position on the throttle, I adjust all the freeplay out of the right cable.

 

[hard_y_rd]

I don't know what you mean by cable arm, 5twins.
I've read about the cable adjustments. I'll have to give your method a try. Sounds like you have 3 hands, lol.

 

[5twins]

The cable arm, what the throttle cable hooks to and lifts on the carb.

 

[hard_y_rd]

O.k sorry. Had a brain fart there. Thought you were talking about the mixture screws.

 

[5twins]

The mix screws really don't have much to do with syncing, other than you want them set correctly so that you are getting the fastest, smoothest idle speed out of each carb. And one more thing, you want your throttle cables to look like this, dead straight without a big bend or kink in the exposed portion of the cable. I see fucked up cables all the time around here. Guys don't know how to properly remove and install them and they bend the fuck out of them. You won't get a good sync on a dual cable carb set if your cables are messed up like that.

 

[hard_y_rd]

Got ya on the straight cables. These 2 cable throttles are definately a pain, i seen once the cable got all twisted and cockeyed some how in the throttle housing itself. I bought some new ones from xs650direct. Not as good as the originals though. Guess they'll do.

 

[5twins]

That's a Mikes cable in the pic. It's given me no trouble in 8 years - but I keep it oiled and occasionally wad some grease in where it hooks to the arm, around the lead ball.

 

[hard_y_rd]

Well i tried a run on 2 turns. Still can't get the left to change color. Going try 3 on my next run. What's my other option to get that cylinder to richen up if 3 doesn't work? Bigger pilots?

 

[5twins]

..... or richer needle setting. Running down the road will show mostly what your midrange is doing because that's the RPM range you most likely will be cruising in. I set my mix screws at idle in the driveway. I go for fastest, smoothest idle speed. I usually set them at the richest point in the "sweet spot", just before the rich roll off point in the "sweet spot" range. This helps with popping during decel. Then a road test to check on that decel popping. If I can't tune it out with the mix screw and still keep it in the "sweet spot" range, I up the pilot jet size. Yes, you will find a "sweet spot" range even with the wrong pilot in there.

 

[hard_y_rd]

So you are supposed to "hear" an idle speed change when you turn the screws out? Then will it start to bog when turned too much? I haven't been able to hear much difference but i haven't turned them out much yet either.

 

[5twins]

Post #103, only difference for you will be the initial setting (3/4 turns out for your carb set) .....

http://www.xs650.com/forum/showthread.php?t=283&page=6

Your "pick a setting, take a ride" method for tuning the mix screws is just taking shots in the dark. You need to find the "sweet spot" range first. On a stock bike, it is usually bracketed around the initial setting given in the specs. When you do mods and re-jet, that can change. Where you find it located will tell you some things about your pilot jet selection. If you find the "sweet spot" with the mix screws nearly closed, you could need a smaller pilot jet. If it's way out at 3+ turns, you probably need a larger pilot. Now, we're talking the BS38s here. The E.P.A. stifled BS34s like 3 to 3.5 turns out and it's accepted practice to run them that way.

 

[hard_y_rd]

I admit 5twins, i was going about it the wrong way. I tried your method and can't get the engine to idle fast or stumble from 3/4 all the way to 3.5 at 1/4 turn at a time. It seems to have more exhaust pressure from the left (leaner cylinder) If you cover the exhaust with your hand, the left side will blow it off while the left side will barely move it.
I'm looking for a bigger set of pilots, I have 45's in there now. Don't really know what else to try.
If i richen the needle setting again, do i have to rejet again?

 

[5twins]

The mix screws respond best and it's easier to detect changes if you're running really, really slow, even below the 1200 RPM idle speed sometimes. Too fast and you won't notice much change. It sounds like your idle sync is off, the strong side running way faster than the weak side. I would try to equal the pressures coming out the exhausts by playing with the idle speed screws, then try the mix screw adjustment again. If you can get the exhausts equal then you may want to back each speed screw off the same amount and lower the idle speed to 8 or 900, then try the mix screw adjusting.

Also, incorrect float settings and fuel levels in the bowls can make the mix screws unresponsive.