Mixture Screw Starting Point - # Turns

[CRXSi90]

I got the carbs for my 81H put back together. They seem to be the correct carbs from what I can gather...plastic floats, same jets all the way across (unlike the full manual, which I have ascertained is wrong, or at least not necessarily correct in all cases), etc...

Anyway, based on further searching, it sounds like 1.5-2 turns out is a "good starting point." I got rough mixture screw positions before I took them apart...

#1: 1/4 turn
#2: 3/4 turn
#3: 1-1/2 turn
#4: 1-1/2 turn

I'm a little concerned about buttoning it back up for the first run with the setting on #1, and to a lesser extent, #2. Is this warranted? I'd sort of like to start at 1-1/2 all the way across, and see where things go from there. I know syncing them should be my next step, not that I have a manometer, but I guess when it comes down to it, here's my question...

Does 1/4 turn out make any sense, or is that automatically an invalid setting?

Thanks!

[mack]

starting point

For the 81 carbs, I think even 1 1/2 turns maybe pretty lean. When I fired up my LH, I started at 2 turns and didn't get good colour on my plugs until I was at 3 turns out from lightly seated.

[DGXSER]

Think of it this way, those mixture screw settings were what worked best with your carbs gunked up or with bad seals, or other parts you replaced. Now your carbs are clean and have good parts throughout. So I recommend going back to a starting point of 1-1/2 to 2 turns out from lightly seated all across the board. As Mack stated, even 2-1/2 turns out is not a bad place to start. Definitely do some form of a bench synch!! On the Katana (GSX600F) I recently finished and sold, I forgot to bench synch the carbs, I had one dead cylinder on start up. No vacuum at all! Then I synched them, and that cylinder was hitting great from then on.

If you are trying to do this on the cheap, my best recommendation is to buy a Mity-Vac or similar tool, has a vacuum gage built into it. Then build the PVC chamber shown in the tech tips for synching. I never had any luck with an aquarium valve, so I just moved my tube from carb to carb, adjusting as I went and checking the readings. Not as accurate as a CarbTune or such, but it will get you pretty dang close for not a lot of money.

From experience I tell you that synching the carbs and tuning the mixture will make a measurable difference in performance.

[CRXSi90]

I love this site! The last thing I did before I went to bed was post, and great replies come in before I even go to sleep. Thanks mack & DGXSER!

I checked out the bench sync tech tip.
http://www.xs11.com/forum/showthread.php?t=88
I gave it a shot, and as best I can tell from using a wire, they're pretty close as-is, so I don't think I can really make any improvement at this stage.

I also found the carb sync tool thread in the tech tips.
http://www.xs11.com/forum/showthread.php?t=986
That looks like something I should be able to do. I found twelve (!) vacuum gauges in my box o' junk, but unfortunately they only go down to 100 in H20 / 7.3 in Hg and it looks like 10 in Hg might be more typical for engine vacuum, so they won't do the job.

A harbor freight vacuum gauge (93547) similar to the one shown in the tech tip is only $15, so that seems like a decent way to go. But you bring up a good point about the hand vacuum pump (Mity-Vac) because I have some brake bleeding to do later on!

So...............back to the mixture screws... Thank you for the info! I'll back them out and see what happens.

[motoman]

I love this site! The last thing I did before I went to bed was post, and great replies come in before I even go to sleep. Thanks mack & DGXSER!

I checked out the bench sync tech tip.
http://www.xs11.com/forum/showthread.php?t=88
I gave it a shot, and as best I can tell from using a wire, they're pretty close as-is, so I don't think I can really make any improvement at this stage.

I also found the carb sync tool thread in the tech tips.
http://www.xs11.com/forum/showthread.php?t=986
That looks like something I should be able to do. I found twelve (!) vacuum gauges in my box o' junk, but unfortunately they only go down to 100 in H20 / 7.3 in Hg and it looks like 10 in Hg might be more typical for engine vacuum, so they won't do the job.

A harbor freight vacuum gauge (93547) similar to the one shown in the tech tip is only $15, so that seems like a decent way to go. But you bring up a good point about the hand vacuum pump (Mity-Vac) because I have some brake bleeding to do later on!

So...............back to the mixture screws... Thank you for the info! I'll back them out and see what happens.

Back them out while idleing to just when it hits highest in. vacuum. Idle should come up as should vacuum, somewhere around the 17-18in. range. Back idle off each time down just below the 1100rpm range. Go to next one,etc. Below 1100rpm range down to 800rpm if still will idle smooth for the sync. When all is perfect, it should actually idle smooth down to 450-500rpm range, even though thats NOT where you want it normally. The continued lower oil pressure at that low an idle if left is NOT a good thing.

[CRXSi90]

Back them out while idleing to just when it hits highest in. vacuum. Idle should come up as should vacuum, somewhere around the 17-18in. range. Back idle off each time down just below the 1100rpm range. Go to next one,etc. Below 1100rpm range down to 800rpm if still will idle smooth for the sync. When all is perfect, it should actually idle smooth down to 450-500rpm range, even though thats NOT where you want it normally. The continued lower oil pressure at that low an idle if left is NOT a good thing.

Thanks, I was also reading your post in a recent thread (post 11) about syncing the carbs. So it sounds like this is the best order to do it:

1. sync mixture screws to highest vacuum and idle
2. sync carbs (throttle linkages) to within 1/4" Hg of each other

In my case, it doesn't seem like it would hurt to swing back and check both the mixture and linkage sync again, just to make sure that one didn't affect the other.

[DGXSER]

Not just in your case, in all cases.

[motoman]

Not just in your case, in all cases.

.........ditto.

[donebysunday]

I got the carbs for my 81H put back together. They seem to be the correct carbs from what I can gather...plastic floats, same jets all the way across (unlike the full manual, which I have ascertained is wrong, or at least not necessarily correct in all cases), etc...

Anyway, based on further searching, it sounds like 1.5-2 turns out is a "good starting point." I got rough mixture screw positions before I took them apart...

#1: 1/4 turn
#2: 3/4 turn
#3: 1-1/2 turn
#4: 1-1/2 turn

I'm a little concerned about buttoning it back up for the first run with the setting on #1, and to a lesser extent, #2. Is this warranted? I'd sort of like to start at 1-1/2 all the way across, and see where things go from there. I know syncing them should be my next step, not that I have a manometer, but I guess when it comes down to it, here's my question...

Does 1/4 turn out make any sense, or is that automatically an invalid setting?

Thanks!

What are you running for pipes, muffs and air filters ?

[CRXSi90]

Here's what I believe to be the case. Tell me if I'm wrong about the pipes/exhaust.

• Pipes = stock
• Muffler = stock
• Filter = UNI foam in stock airbox

I believe the exhaust is leaking somewhere underneath, though.

[motoman]

Here's what I believe to be the case. Tell me if I'm wrong about the pipes/exhaust.

• Pipes = stock
• Muffler = stock
• Filter = UNI foam in stock airbox

I believe the exhaust is leaking somewhere underneath, though.

Your exhaust leak, if not obvious at the head or cross-over gasket IS gonna be under where the shield is where the two go into one. Would'nt worry bout that for now. Actually for the later carbs, start with 3 turns out on the mixture screws....if those teeny-tiny o-rings on them have been replaced. Otherwise, turning the mixture screws will likely loose there vacuum seal if there the original o-rings(or whats left of them). If all that is good, don't be surprised if they end up almost 4turns out to run good(least for some here). Mine are roughly at 2 3/8 turns out(varies a tad from cyl. to cyl.), but got my bowl fuel levels dead-nuts on at 3mm down from carb casting while idleing. Any slight varience on all other settings, floats,etc. is gonna give different results as you've seen on here. BTW, do all this tuning on the centerstand.

[motoman]

Here's what I believe to be the case. Tell me if I'm wrong about the pipes/exhaust.

• Pipes = stock
• Muffler = stock
• Filter = UNI foam in stock airbox

I believe the exhaust is leaking somewhere underneath, though.

Your exhaust leak, if not obvious at the head or cross-over gasket IS gonna be under where the shield is where the two go into one. Would'nt worry bout that for now. Actually for the later carbs, start with 3 turns out on the mixture screws....if those teeny-tiny o-rings on them have been replaced. Otherwise, turning the mixture screws will likely loose there vacuum seal if there the original o-rings(or whats left of them). If all that is good, don't be surprised if they end up almost 4turns out to run good(least for some here). Mine are roughly at 2 3/8 turns out(varies a tad from cyl. to cyl.), but got my bowl fuel levels dead-nuts on at 3mm down from carb casting while idleing. Any slight varience on all other settings, floats,etc. is gonna give different results as you've seen on here. BTW, do all this tuning on the centerstand.

[CRXSi90]

Your exhaust leak, if not obvious at the head or cross-over gasket IS gonna be under where the shield is where the two go into one. Would'nt worry bout that for now.

I don't recall at the moment exactly where it is leaking. It could be the cross-over, but the bike spent a lot of time outside while under the ownership of others, so I wouldn't be surprised if it rusted through down there.

Actually for the later carbs, start with 3 turns out on the mixture screws....if those teeny-tiny o-rings on them have been replaced. Otherwise, turning the mixture screws will likely loose there vacuum seal if there the original o-rings(or whats left of them). If all that is good, don't be surprised if they end up almost 4turns out to run good(least for some here).

O-rings...o-rings......I had to think there for a minute. One of my float bowl drain screw o-rings is definitely nasty and all chewed up, but that's not what we're talking about today. The mixture screw o-rings are now more like o-washers as they've been crushed between the two metal washers on either side. But I wouldn't be surprised if they leak a little under vacuum.

I backed them out to 3 turns out now.

Mine are roughly at 2 3/8 turns out(varies a tad from cyl. to cyl.), but got my bowl fuel levels dead-nuts on at 3mm down from carb casting while idleing. Any slight varience on all other settings, floats,etc. is gonna give different results as you've seen on here. BTW, do all this tuning on the centerstand.

I bench synced the float heights with my digital caliper, but didn't end up making any changes. I didn't record the measurements, but I believe they were all at 22.5-23 mm all across. I know that the fuel level is best set using the tube at idle to 3mm like you mentioned, so I'll save any further tweaking on the float heights until I get the carbs back on.

I did just read the procedure in the manual supplement for the '81's. LOL that they advise using a golf tee as a plug in the tube. They have a clever way to ensure that the bike is level by keeping the tube connected to the same carb and moving the loose end from one side of the carb rack to the other and ensuring that the level is the same. I'm a bit surprised that the bike being level is that critical, but it's easy enough to do!

[3Phase]

... I'm a bit surprised that the bike being level is that critical, but it's easy enough to do!

It's the reference point for the fuel level in the float bowls from whence all fuel will or will not flow into the engine.

The carburetors have to provide fuel hot or cold; standing still idling; zero to fifty-nine degrees of lean at top speed, low speed, acceleration and deceleration; sailing negative gravity over whoop-dee-doos or pulling hard out of corners and dips in the road; wobbling around the parking lot or flat out passing traffic and stoplight hopping.

If the carburetors mis-feed the fuel and the engine skips a beat at the wrong time the bike'll do anything from just generally being embarrassing when you try to out-pull another bike and it sputters instead of roaring, to falling over on the low side or suddenly giving it all up at once in a thrilling full-on highside where you get to take flying, landing, and sudden-stopping lessons all rolled into one.

.

[motoman]

It's the reference point for the fuel level in the float bowls from whence all fuel will or will not flow into the engine.

The carburetors have to provide fuel hot or cold; standing still idling; zero to fifty-nine degrees of lean at top speed, low speed, acceleration and deceleration; sailing negative gravity over whoop-dee-doos or pulling hard out of corners and dips in the road; wobbling around the parking lot or flat out passing traffic and stoplight hopping.

If the carburetors mis-feed the fuel and the engine skips a beat at the wrong time the bike'll do anything from just generally being embarrassing when you try to out-pull another bike and it sputters instead of roaring, to falling over on the low side or suddenly giving it all up at once in a thrilling full-on highside where you get to take flying, landing, and sudden-stopping lessons all rolled into one.

.

Must say, that's gotta be the most comical way I've heard to emphisize the importance of being level. Reference to that, I had to even put a small piece of rubber belting under the right side of centerstand leg to get mine level. Even put a short 2"x4" under front wheel with rear wheel touching concrete like it would set if on both wheels. Didn't do this till I saw where the fuel levels were a bit higher on right outside carb than they were on left outside carb. Same for for and aft. Not much volume of actual fuel in those bowls with the floats added in there, so curiosity experimenting sure enough proved the ole' original Yammy manual is correct with the 81-82(XJ) procedure, and being level for fuel reference purposes.