The Un-Syncable Carb Contest

[manshack_one]

I'm just plain tired of hitting brick walls trying to get my bike dialed in. I've taken it from not running to running but badly. I just don't have the experience to troubleshoot this any more so I'm calling out for help.

To anyone who will show up at my house and solve my un-syncable carb problem I will pay you back with a hefty bounty of beer and BBQ.

Let's face it, I just need a tech day. I'm sure the sync isn't the only problem. Maybe my floats are off kilter. Maybe it's the slides. Who knows! I'm sure the carbs will end up coming back off for a once over before it's said and done. I've got a nice work area with plenty of bench space and when we're done dialing the bike in I've got plenty of country roads to test it out on. And, when we're done riding for the day we can relax in front of my 10 ft hi-definition home theater setup. I'll even let you sit in the lazyboy!

So, who's up for the challenge? I'm in Crockett TX and can be home every weekend. All roads leading to Crockett are great cruising roads so you're drive in should be great. If you live farther away and want to fly in to Houston or something, no problem. I'll come to pick you up and even drop you back off again!

Keep in mind that Crockett is 2 hrs from anything important so if we run in to needing a part we're S.O.L. because any part I have to order will require for UPS to hand deliver it to me.

Or, here's another idea. I could be talked in to sending the carbs to some willing individual who would enjoy the challenge of getting my carbs dialed in on their bike. Of course, I can't pay you in beer and bbq this way but I could definitely compensate you for your time.

And as a last resort there is trailering it to someone. I would definitely enjoy having a visitor more than being one but if that's what it takes then that may be what I have to do.

[trbig]

The only problem with the latter suggestion is that different compression values are going to lead to different settings on the carbs. It may get you close enough to be able to then synch yours, but the ideal situation is going to be to tune them on your bike. Hopefully someone can help you out.


Tod

[prometheus578]

"Interesting point, TRBIG."

Like the one on top of your head... but not really that important. (either of them).
As I've had too much coffee,(which is evident) let me play with this a little...
I would think that, provided that the "donor" bike's engine isn't trashed that it would matter very little.
Yes, a bike with an obvious leak somewhere would have different compression ratios due to bad rings, leaking valves, whatever.
But, when synching carbs, one is not using engine compression for anything. One is using the draw provided from the piston moving downward in the cylinder.
Now yes, I suppose technically, if one piston has bad rings it will provide less of a draw than the other three goodly ringed pistons.
But recall... on the downstroke used to provided the rush of air past the throttle plates and the vacuum caused being measured... the intake valve is wide open.
This is rather free flowing... doesn't place much stress on the rings to draw air through an open valve.
Of course... were the rings bad enough to cause such an effect that it would booger up a carb synch... The bike would have such runability problems that the owner would be too embarrassed to offer his help in the first place.
The only concern with synching carbs on one bike and then transferring them to another is... in wrestling the carbs in and out from one machine to the next... the twisting involved(yours... and to the carb bank) does tend to mess up the synch. But then again, it's to a very small degree, but still can be noticeable on a gauge.

Think this over while I go pour myself another cup... and dream of more ways to torment you.

[randy]

Prom,

Before you O.D. on caffiene, consider this. No two engines are the same. Differences in exhaust/intake combinations alone can cause a carb bank to operate well on one and poorly on another. Throw in intake manifold air leaks & exhaust leaks, and manshack may be worse off using a set tuned on another engine. So I guess I'm partly agreeing with Tod on this one.

Manshack, if you have the proper tools, and make sure you don't have air or exhaust leaks, there should be no reason why you can't synch the carbs yourself.

[81xsproject]

Send them to Prom, he's got nothing better to do The good thing about having someone else do them on a different bike, is that it often removes the carbs from the 'troubleshooting equation.' I sold a tested set of carbs to a guy on ebay that got them and tried to say they didn't work. Low and behold, his pick-up coil wires were bad . Imagine that . These carbs are very forgiving. Floats off a mm, a couple jet sizes off, a little out of synch, they will still run decently. If they run great on someone elses XS and don't work worth a damn on yours, then there is probably something else wrong with the bike itself. Manshack, if you don't get any help, let me know and we can work something out.

[red bandit]

I've synced MANY (30+) carbs on mine and they mad someone elses bike run great. I'm sure it would show on a gauge, but the gauge doesn't have to be perfect for the bike to run great. It eliminates the carbs as a problem. As long as one of the engines doesn't have other problems.

[webbcraft2150]

Geez, to think I went thru Crockett twice this weekend! (I missed the first pass thru cause I sneezed ). Was on four wheels 'stead of two. You didn't say if you were using a carb stix or some other syncing devise. Heres a couple options for ya. Send me your carbs and I will run them on my 80g and see whats up. Sometimes you work on something so damn hard you miss a simple thing and your start tearing your hair out. Since my G is a runner, it would eliminate any engine/ing. problems that might be lurking in your rig. Or, load that sucker up and bring it here, have a large Man Cave to work in and its gotta be easier to get stuff to Austin than it is Crockett. Even if it dosen't get fixed that day, you can leave it for anothe set of "eyes" to look at it and hopefully figure out whats up. Third, bring Prom out (ship him as a "live animal" and the price of freight will be lower ), but then again, I ain't sure if Crockett Texass is ready for that.

[prometheus578]

Send them to Prom, he's got nothing better to do

Uhmmm...
I just received two banks o' carbs needin' fixin' in the mail yesterday!

If I'm gonna make this a life-long career move... I'm gonna be chargin' a hell of a lot more than... "just include a box of home-made cookies".

Randy:
I agree with everything you said, other than the part concerning the caffeine. As a serious abuser of this drug, I have quite the high tolerence.

(Let me take my mid-morning nap and consider your thoughts before re-offering mine.)


Sorry, Webbcraft... you posted while I was still typing.
(Don't put any airholes in the box... shipping is even cheaper for dead animals.)

[81xsproject]

You get COOKIES? Now why didn't I think of that? If I lose my privlages to the ultrasonic machine at the college, I am definately going to have to go the cookie route.

[manshack_one]

lol, like a bunch of grumpy old men. "it matters" "no it doesn't" "yes it does"

I'm trying to work it out but a trip to Austin might be in the near future for me with the bike in tow.

Oh, and I"m using my homemade plastic tube/ATF carb stick.

Thanks for all the responses so far. I imagine I would have gotten even more of a response if I'd titled it "Free beer and bbq".

[Ken Talbot]

And, if you're looking for a nice holiday, manshack, please feel free to put the bike on a trailer and bring it up here to me in Western Canada.

I've got a spare room you can crash in and I'll introduce you to our local microbrew products. I'll teach you how to set the floats, do a full vacuum sync, and perform a colortune. Guaranteed your bike will be in excellent running condition when we're done. Over the years, more than a few folks have had "the full meal deal" in my carport, but most of them have ridden in, with the farthest one coming from Ontario!

[manshack_one]

Trailer it to BC?

Let's see. Google maps shows 2371 miles from my town to yours. At 3.05 a gallon for gas and considering I'm lucky to get 20 mpg pulling the trailer with my caravan's wimpy v6 I'd spend $361 bucks in fuel alone. Not to mention motels and food (I like to eat a lot).

But it's not that I don't appreciate the offer! I'm just going to hold out for someone I can get to in under 3 hrs rather than 36.

[Ken Talbot]

Yeah, I guess if you put it that way. You could take that amount of money and simply go out and buy one that runs good already!

[prometheus578]

"Fresh pot o' coffee brewin'..."

Manshack,
If I'm not mocking someone, or pointing out trivial differences... then my time on this planet is wasted.

Ok, on to Randy...

Differences in exhaust/intake combinations alone can cause a carb bank to operate well on one and poorly on another. Throw in intake manifold air leaks & exhaust leaks, and manshack may be worse off using a set tuned on another engine.

Yes, but that's not the point concerning a carb synch.
The idea isn't to tune your carbs to the various burps and farts of a malfunctioning or poorly running engine.
What you are trying to do is ensure that the throttle plates of four carbs are all opening in unison, supplying equal amounts of fuel mixture to a good running engine.
Yes, due to the variables you described there may be differences in carb synch settings from bike to bike... but there shouldn't be. And if there are, they should be minor.

Now then... due to how carbs are supposed to operate, changing the position of the throttle plates(as during a carb synch) also changes the amount of fuel delivered.
An intake leak at #1 cylinder's manifold means that a percentage of the air drawn into the cylinder is not coming through the carb.
And by doing so, it is also not drawing the required fuel, so that cylinder now runs lean.
This we all understand.
Now, if one were to adjust #1's throttle plate opening to compensate for the decreased vacuum though the carb body(as registered on the synch gauge) this would also affect the fuel/air mixture for that cylinder.
Opening the throttle plate would bring the carb more into balance regards to the other three's vacuum readings... but could also be supplying #1 cylinder with more fuel. This may, or may not be sufficient to correct the lean condition.
Let's walk through a practical demonstration(as that's the only way I can make myself believe my own theories!)
#1 cylinder draws a certain amount of air. Let's call it 100%. We have a bad intake leak that sucks off 25%. That leaves only 75% flowing through the carb. (I know these percentages are extremely radical, but this is a generalization) This shows up as a vacuum deficiency on the synch tool. This also means that an insufficient supply of fuel is also being taken up by the decreased amount of air passing past the pilot port opening. (Lean condition)
One would then(mistakenly)adjust that throttle plate to open more to try to synch the vacuum to the other three carb's readings. Doing so would bring the measured vacuum reading up, but it can never be perfect as we still have that damned manifold leak sucking up 25% no matter what we do. (actually, that 25% would go down as the throttle plate opens wider and allows a freer flowing airflow, but it will never disappear completely.)
What we end up doing... We have now increased the airflow through the carb and picked up a different amount of fuel corresponding to match the now increased flow, but as this new fuel/air mixture passes past the vacuum leak at the manifold, it still gets leaned out. A synch will not change this.
To now compensate, one could adjust the fuel mixture by dickin' with the pilot screw, yes? Tuning it by ear...
This is all fine and dandy for an idle speed.
"Off-idle" and the other circuits also rely on the position to some degree of the throttle plates, too, to regulate air flow, and fuel uptake.
Unfortunetly, there is no screw to re-regulate their new fuel requirements due to the changed throttle plate position.(Larger jet? Increase float level?)
Starts to get complicated.

Maybe someone should have fixed the manifold leak in the first place... and I wouldn't have had to spend two hours sitting here drinking coffee and talking to myself!

81xsproject's post sums up this arguement more succintly then my ramblings.

(Comments and opposing views are always welcome.)

[Do Lee]

Not much info [79 Special Engine/80 Special Body]
I call her "Half&Half".
OK a few questions, 79 carbs or 80 carbs? Airbox or pods? Does engine idol or does engine rpm ramp up high like the chock is on when you first start bike? When you rap on the throttle does the rpm stay high? While running the bike does it bough down, sputter, what?
If your using 79 carbs with an 80's airbox are there holes where the upper hoses are connected to the airbox.
If you want to send me your carbs I can go through them, set them up off my bike send them back and set up a time to meet and complete the dial in on your bike.
I have an extra set of carbs from a 1980, 81 XS1100 Special that I can clean up sinc on my bike and send you to use while I go through your carbs.
Just let me know.
oh yea I'm about 250 miles southwest of you