Carb sync question

[texas-ss-tornado]

What would happen if you tried to sync carbs on a bike that was running on 3 cylinders as opposed to all 4? Like if you had a bad spark plug wire or something and one cylinder wasn't firing? Would the sync still be valid? Having a discussion about this on the V4 forum and I was told it wouldn't make any difference, I'm not so sure.

 

[[email protected]]

Not sure how that cylinder would be making a vacuum if it wasn't firing. If you were synching a bike with a common manifold with a tool like the weber I could see it working but on a bike like the max that has seperate manifolds pending vboost is closed I don't see that working.

 

[mr.maxx]

shure it would make a difference.....i wouldnt do a carb sync with a fouled plug or bad plug wire....yu"d never get it set right.

i could be wrong....but seems like a fruitless attempt. why sync the carbs with a bad plug:confused2: dont make sense lol:biglaugh:

 

[texas-ss-tornado]

This is the last comment that was made, I was just trying to figure out if there is any validity to this post:

The cylinder doesn't need to be firing in order for you to be able to synch it. The synch is only about balancing the air flow across the cylinders. Since each piston sweeps the same volume as all the others, synching is really about balancing the restrictions to air flow - the valve and the butterfly openings. That's why the valves really should be adjusted before doing the synch and adjusting the butterflies.

 

[davesax36]

I think you could get the other three to sync. I just worked on mine and I got three pretty close with #1 still making no vacuum. When I got that butterfly closed down enough to make vac (#1) it skewed #2 so I ended up having to redo the others some. Not too terribly much, though.

 

[[email protected]]

This is the last comment that was made, I was just trying to figure out if there is any validity to this post:

The cylinder doesn't need to be firing in order for you to be able to synch it. The synch is only about balancing the air flow across the cylinders. Since each piston sweeps the same volume as all the others, synching is really about balancing the restrictions to air flow - the valve and the butterfly openings. That's why the valves really should be adjusted before doing the synch and adjusting the butterflies.

Guess I shoulda thought about it a bit longer. That does make some sense. Its got me wondering now too:confused2:

 

[dannymax]

With a cylinder not firing there will be a variation between cylinder temps affecting ring sealing capability....resulting in the unfiring cylinder moving less air thereby throwing the sync off.

 

[Rusty McNeil]

I'd think you could synch the three that were firing.
But;
The synch tool ( I'm thinking old school mercury motion pro) balances between two cylinders so the cylinder that's not firing couldn't be used as one of the two.

I say that because even tho swept volume enters into it a cylinder that's firing has exhaust and intake reversion greater than one thats not.

Just my guess tho???

 

[NHVmaxpower]

To me it would be like doing a tune up n only replacing 3 plugs leaving a bad one in there. Just don't make senseto me to even try to synch the carbs. Jmho

 

[ZackDaniels]

Syncing carbs should be done when pretty much everything else is all good to go. It's a tuning thing, and not a fixing thing.

Tell whoever to prove their theory. Pull a plug boot, sync the carbs. Show pics or take video of the sync.

Wire the plug back up and see if the readings change at all. It's relatively simple to test a theory like this that in all likelihood is total crap, but hey I've been surprised before.

 

[RaWarrior]

I'd think the cylinder not actually firing would have an effect on the pulse when the intake valve opens which could affect the gauge's reading.

Seems like kind of a question that has a very unimportant answer. If you have a dead cylinder syncing the carbs shouldn't really be the top of your concerns.