Ahhhh, the smell of half burnt fuel in the evening air...

[Zeston]

1979 1100xs Special
Stock everything
Bike sat for 15 years, exhaust does run clean on start up/ idle.

I've recently cleaned (yes +3 times) my carbs and now i'm trying to synch them. Being cheap and unwilling wait for a proper setup, i tried to duplicate the 4 valve vacuum setup. I think i did a fair job but i'm really struggling with the sync, but maybe its something else?
The bike fires up great, but doesnt respond to throttle well.
When i start to synch them i seem to be able to get 1/2 good, then 3/4 pretty good, and when i try to get the 2 groups together- epic fail. I seem to get lots of fuel out the exhaust etc. then one of two things happen-
1. I get frustrated and start all over by reseting the screws,
2. the engine revs start aggressively climbing and i have to kill the engine to keep it from exploding. This happens alot... Ultimatley i walk away and come back to reset the screws as well

Are the carbs so out of synch that i really just need to buy a poper syncer? Does it sound like a timing issue? Something else?
When i back all the adjusting screws on the carbs out, and go by ear, i can get it to sound nice, and have decent throttle response, but i know that close isnt good enough.

[BA80]

Proper tools are much less expensive than engines.

[James England]

1979 1100xs Special
Stock everything
Bike sat for 15 years, exhaust does run clean on start up/ idle.

I've recently cleaned (yes +3 times) my carbs and now i'm trying to synch them. Being cheap and unwilling wait for a proper setup, i tried to duplicate the 4 valve vacuum setup. I think i did a fair job but i'm really struggling with the sync, but maybe its something else?
The bike fires up great, but doesnt respond to throttle well.
When i start to synch them i seem to be able to get 1/2 good, then 3/4 pretty good, and when i try to get the 2 groups together- epic fail. I seem to get lots of fuel out the exhaust etc. then one of two things happen-
1. I get frustrated and start all over by reseting the screws,
2. the engine revs start aggressively climbing and i have to kill the engine to keep it from exploding. This happens alot... Ultimatley i walk away and come back to reset the screws as well

Are the carbs so out of synch that i really just need to buy a poper syncer? Does it sound like a timing issue? Something else?
When i back all the adjusting screws on the carbs out, and go by ear, i can get it to sound nice, and have decent throttle response, but i know that close isnt good enough.

you really need a set of four vacuum gauges. They are not expensive. I bought a set and have not regretted it. You can't really tune a bike on the cheap, as it were. You need the equipment.

[GLoweVA]

1979 1100xs Special
Stock everything
Bike sat for 15 years, exhaust does run clean on start up/ idle.

I've recently cleaned (yes +3 times) my carbs and now i'm trying to synch them. Being cheap and unwilling wait for a proper setup, i tried to duplicate the 4 valve vacuum setup. I think i did a fair job but i'm really struggling with the sync, but maybe its something else?
The bike fires up great, but doesnt respond to throttle well.
When i start to synch them i seem to be able to get 1/2 good, then 3/4 pretty good, and when i try to get the 2 groups together- epic fail. I seem to get lots of fuel out the exhaust etc. then one of two things happen-
1. I get frustrated and start all over by reseting the screws,
2. the engine revs start aggressively climbing and i have to kill the engine to keep it from exploding. This happens alot... Ultimatley i walk away and come back to reset the screws as well

Are the carbs so out of synch that i really just need to buy a poper syncer? Does it sound like a timing issue? Something else?
When i back all the adjusting screws on the carbs out, and go by ear, i can get it to sound nice, and have decent throttle response, but i know that close isnt good enough.

Alright Ed, let me take a crack at this.
Some of the things I suggest may sound a little like common sense, but I've got to cover all the bases. (disclaimer and trying not to offend you )

Best to start at a baseline aka bench sync. (this is where all 4 butterflys are just barely open/cracked, some use a bread tie wire as a gauge)

First, the single vac gauge and 4 way aquarium valve set up WILL work.
Only have one valve open at a time to see what the vacuum is on that cylinder.
No choke right?
Bike warmed up okay?
Fuel heights in the carbs at spec? (height is according to carb set(78/79) or 80/81) not year of bike)
So, you can adjust 1 & 2 to match and 3 & 4 to match, but trying to get 1/2 to match 3/4 is the issue?
Are you using the screws between the carb shafts?
(stupidest question yet and I hate asking it, are you adjusting the correct screw in between #2 and #3 carbs? the idle set screw is in between there too)

I hope you're not playing with the idle mixture screws on the top front of the carbs. These should be set about 2+ turns open and left there UNTIL you get the carbs sync'd then you can 'dial' those mixtures in and FINE tune it.

Sync'ing the carbs is 'balancing' how much suction they have at idle so that all 4 suck the same amount of air thru the carb. Then you can dial in the idle mixtures so that none are too lean or too rich, but this also slightly gets your 'suction' sync outta whack, so you'll have to go back and check the vacuum sync again after adjusting the mixures.

Hope this helps,

[Zeston]

No offense over here, only bad question is the one that didnt get asked. I really want to avoid pulling the carbs off again, i assume you mean stick the bread tie in the opening when the airbox is removed right? I will just back the screws out until theres justa bit of pressure on them
I'm adjusting the screws that are NOT the idle mix screws, meaning the ones i'm turning are not housed with the plastic caps and ARE nestled down between the carbs with the choke rod. This is correct right? The throttle adjustment screw is on the air intake side, and looks more like a nob then a screw yes? I did mess with it a bit, should it be turned clockwise or counter clockwise to get to a good starting point?
I really appreciate the help! Do you think the rapid engine reving is just a symptom of my messed up balance?

[GLoweVA]

No offense over here, only bad question is the one that didnt get asked. I really want to avoid pulling the carbs off again, i assume you mean stick the bread tie in the opening when the airbox is removed right? I will just back the screws out until theres justa bit of pressure on them
I'm adjusting the screws that are NOT the idle mix screws, meaning the ones i'm turning are not housed with the plastic caps and ARE nestled down between the carbs with the choke rod. This is correct right? The throttle adjustment screw is on the air intake side, and looks more like a nob then a screw yes? I did mess with it a bit, should it be turned clockwise or counter clockwise to get to a good starting point?
I really appreciate the help! Do you think the rapid engine reving is just a symptom of my messed up balance?

Okay, so you're turning the right adjusters. (Whew! )
I suppose you can use the bread tie method from the airbox side of the carbs.
Basically it's to get you at some uniform closeness so that all 4 carbs butterflys are open about the same amount. Once you do that, and you start the bike and with no choke (aka bike warmed up), you may have to adjust your idle down a little to get it to idle about 1100rpm.
Then you can start tweaking the carbs. Like you said, start with 1 and 2 then adjust 3 and 4, then if you remember what approximate vacuum you had on 1/2 and can see what's on 3/4 then you can adjust 3/4 (the one your watching) up or down to get it closer to what you saw on 1/2. Then go back and check 1/2 to see if it's closer to 3/4 now. You may have to dial you idle down again. As the carbs get closer to sync, the machine gets more efficient and thus idles better/more and you'll need to adjust the idle back down to 1100ish otherwise it'll scream away from you.

On a few different notes, you may have other issues that make the bike's idle run away from you.
Is your airbox on while you're sync'ing? (too much air without some restriction of flow)
Does it run/idle okay before you start your sync?
Are all your tube/hose connections with your sync rig tight? (ie. no vacuum leaks)
Don't open your selector valve too much, it may suck air in and allow the bike to rev more.

Just a few ideas to look at.

[Zeston]

ok, out of town on business will try this wwhen I get back...what do you mean "don't open selector valve too much?" I'm a little confused here.. Thanks!

[GLoweVA]

ok, out of town on business will try this wwhen I get back...what do you mean "don't open selector valve too much?" I'm a little confused here.. Thanks!

Are you using one of these aquarium selector valves to select which cylinder you're watching?


I've got one and when I open the valve too much, air will get sucked in thru the knob and my vacuum readings will go down. Remember to measure one cylinder at a time, that way the vacuums won't get crossed/connected between the two that you're trying to adjust.

Here's the tech thread with the homemade sync rig.
http://www.xs11.com/forum/showthread.php?t=986

[jetmechmarty]

Take the carburetors off. Do the bench synch Crazy Steve's way. You'll never get it done right with the carbs on the bike.

http://www.xs11.com/forum/showthread.php?t=36021

[DiverRay]

Also, just to make sure, you DO have a fan blowing over the engine while doing the sync? IF not, grab the box fan out of the window and use it.(that's what I use). If the engine gets too hot, you CAN end up with a LOT of problems. Remember, the oil will take a while to get hot, but the engine, with NO AIRFLOW, can overheat in about five minutes. This will throw the sync out the window and may be part of your problem. I don't know, just putting this out as I do about once a year.
And yes, the first time trying to sync is a B!TCH, we've all been there.

[LoHo]

The over revving is probably a vacuum leak; I had such a problem and the problem was one of my aquarium valves was cracked and leaking. I finally noticed when I turned it all the way off and the gauge went to zero; it should have been locked at whatever vacuum that cylinder was pulling when I closed the valve. Going to zero meant a vacuum leak.

[fredintoon]

Starting at the beginning

I gave up on my synch job because I got confused.
There's 3 synch adjuster screws
Leftside balances #1 against #2
Rightside balances #3 against #4
Center balances #1 & #2 against #3 & #4
So far I'm good.
But then I lose it.
Does the leftside screw thread IN or OUT to open #1 more than #2?
When #1 is open more than #2 does #1 suck more or does it suck less than #2?
Ditto #3 vs #4?
Ditto #1 & #2 vs #3 & #4?

[DGXSER]

First off, lets think about the fuel smell he is getting. Are you certain your not getting a float valve sticking open and excess fuel getting dumped into the carb? Does fuel come out the air box when you shut it off and leave the petcocks on PRIME?

Also, are you letting the bike fully warm up before you start synching? My road is about 1.5 miles to the far end from my house. I start the bike, let it warm up to where it will run well with 1/2 choke, then I take the bike up my street, it will usually be idling high on half choke by then, so close the choke and bring it back down my street before I start trying to synch or tune.

As to how the synch works, I'll take this back to the simplest aspects best I can. The butterfly valve position in each carb helps determine the level of vacuum at the inlet to the engine at the carb boot. Think of it like adjusting the pressure regulator on your air compressor, only in this case the engine is like a vacuum cleaner, sucking air in instead of blowing it out. Turning the valve changes the downstream pressure from the source. The idle screw sets the opening of the number 3 carb butterfly valve. Tightening or clockwise rotation raises the idle, or opens the number 3 butterfly. Counter clockwise lowers the idle, or closes the number 3 butterfly. The synch screw between 3 and 4 adjust/moves the number 4 butterfly valve in relation to the position of number 3's. This is key to remember, the synch screws adjust one butterfly valves position or offset form its neighboring valve. It does not take alot of screw movement to see a big change in the vacuum. 1/4 turn is about the most movement you should need to synch the carbs. The synch screw between 1 and 2 adjust the position of the number 1 butterfly valve as it relates to the position of no 2's. And the synch screw between 2 and 3 adjust the position of no 2's butterfly as it relates to number 3's. When you adjust number 2's position with the center synch screw, number 1 comes along for the ride, as its position is in relation to that of number 2's. So now you have them all set in relation to number 3's position, and moving the idle screw moves number 3, and the rest go along for the ride.

Fred I am not certain if in or out opens or closes the valves right off, I believe threading in is closing the valve, and should raise the vacuum. As I said, it should not take much screw movement to see the change occurring. And you want to be careful as even pushing down hard on the screw will actually move the valves and change the reading, so only enough pressure to get the screw driver to move the screw.

The reason you see changes in both cylinders or even all four as you change the synch screw positions is that how one cylinder operates has an effect on all of the cylinders. Which is why it is important to synchronize with the bike running.

[Zeston]

*brain explodes*

Good to know others have survived this nightmare.

Ok- Yes, Carb 4 fills immediately with fuel and dumps out all over everything, which is awesome. (that's thick sarcasm) not just on PRIME but ON/RES as well. Feel free to speak to me like an infant- what does that mean??

I pulled the bottom of the airbox off to get a better look at whats going on- it is definitly #4 that is spewing gas out of the airbox. When you say Float valve do you mean the valve seat assembly?

The excessive reving continues, I tightened up the manifolds, I'm not sure what else could be allowing excess air in that causes the over-reving. The reving is happening without being hooked up to the vacuum synchronizer... so it's something 'bike' related.

I'll pull the carbs off and bench synch as everyone has suggested, but any suggestions on what else I need to do while they are aoof the bike? A reminder- all have been cleaned thoroughly, but outside of that I'll try anything.

Thanks!!

[BA80]

It's not a nightmare if you use the PROPER TOOL.