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118 Posts
rogsvr said:
I still think you should drill and turn, but since you were commenting on doing the easy thing (mixture first) I just thought that I'd mention you'd picked the wrong one as easiest.

Hey Roger, ok thanks, thats definately good info. And yeah I'm basing the relative difficulty of the two things on diff carbs. So I need to go ahead and take the plunge and get familiar with the SV's carbs.
Got a Clymers! just need to DO it.

Discussion Starter · #22 ·
I used a friend's carb sync today and a small problem arose. At an idle, appox 1200rpm, I could zero it in. When I increased the throttle to approximately 4,000rpm the synchronizer took a step in the direction of one carb ( the front I believe). Is this normal?

Carb Sync: Twin Max Electronic Carburettor Balancer, Adventure Motorcycles Gear
The range of the meter went from 0 to 3 (don't know the units) in both direction.

It could be that the Sync was made in France.

It started to rain so I couldn't take it out to see if it solved the lean surge.

109 Posts
Twinmaxes work fine. No particular units. Just a display to achieve balance.
Are you using both the individual throttle screw, and the balance screw?
W/o doing that, then you'll naturally get the results you saw.

Also, the valves should be adjusted about the same.
Lastly, I've personally not been able to get these quite perfect, as the two
cylinders simply do not flow quite identically. I'm spoiled by mostly boxer
and 2V duc motors, which match really well, but these are tougher. Just
get as close as you can.

To do this correctly, you really need to get the idle balanced, not only in terms of total
balance, as shown on the meter or stix, but in terms of composition of idle.
Note that two things determine idle. Mixture screw, and throttle stop.

You can picture the idea scenario where the two mixture screws are each contributing
the same amount, and the two throttle stops see the butterflies with identical openings
and thus the flows are pretty darn balanced, and you see your sync tool showing balance.

But, picture another scenario. One carb has the mixture a bit rich or lean, which slows
idle on that cylinder. It's compensated by turning the throttle stop screw to get back to
the same speed. So, you can have the two cylinders showing balanced, but one is getting,
say, 25% of it's contribution from the mixture screw, and 75% from where the throttle screw
is holding the butterfly. The other carb/cylinder could be 75/25, or 60/40 or even 50/50.
Those are all arbitrary number possibilities, but the point is, that you now have balance at
idle, but your butterflies are in different positions. One will lag the other. That is masked by
the idle mixture at idle, but as you open the throttle and the idle mixture plays a decreasing
overall roll, you're left with two butterflies that are open different amounts throughout the rev
range, and you'll certainly see an imbalance.

These carbs, though tougher to get perfect than on the boxers I'm more used to, (where cylinder flows are much more equal) are a good deal easier to get at least very close (rigid connection between throttles so that relationship stays more constant that with independent cables)

Have you twiddled the mixture screws until you get the smoothest idle (and each screw is in the middle of the range of motion that provides smoothest idle?) That will help too. Of course, the mixture affects the idle balance,and visa-versa, so getting both sides identical (or very close) is an interative process.

Once that is done, then the screw that sets one throttle's position vs the other, will get you a pretty close balance.
The 1/2 tick on the twinmax is pretty readily achievable.

118 Posts
"Sorry for this newb question, but what's a lean surge?"

here's my take on it, and I welcome any corrections anyone else may have.
When the carbs on a given engine are jetted towards the "lean" side (using the absolute least gas poss and still have it run decently) which the EPA WANTS, btw, then in a certain rpm range the engine runs ever so slightly "not good".

It doesn't actually miss or back fire or anything, but just isn't quite making optimal power at that range and at certain times the fuel catches up to the need a bit and it surges a bit. I.e. doesn't hold a certain throttle pos. exactly even though you are not "moving" the twist grip or cable.
Whereas if it were jetted/adjusted just a bit richer (more gas in the mix) it would be more smooth at whatever rpm its doing it at.
On my bike I notice it when holding @4k rpm. Which I pretty much have learned not to do. I ride "through" that rpm range. Was the same deal on my old Honda Magna ( 4 cyl bike).
Rev on up and out of that range, or stay below it - which was more acceptable on a cruiser like the Magna. Staying below that rpm range kinda sucks with the SV.
Anyway, thats my take. Looking forward to what others might say.
Aunty Em
'02 SV650 black
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