Are We All Balancing our Carbs Wrong

[VTRDark]

One of the more common complaints on these bikes is carb farts and/or cutting out when coming to a stop. Could it be that we are balancing our carbs wrong.

I was browsing through the archives over on the OZ forum and came across something very interesting regarding Carb balancing and it now makes sense to me when reading the Workshop manual after reading the following.
http://ozfirestorm.proboards.com/post/133338/thread
We all know Jap manuals can be a little difficult to interpret at times with their strange formatting.

The front carb is the base carb and the rear should be 20hg more than the front. This is unusual for a carb balance and not something I have heard of before and they usually have to be balanced evenly across the board, but the majority of bikes have all their carbs set up with the same jetting and don't have the quirks that a V Twin has.

Is it that we are interpreting the workshop manual wrong where is says Carburettor Vacuum Difference. The info seems to have come from a very reliable source. Pretty much direct from Honda themselves as the guy in question (Pip) is or was the Assistant Manager Motorcycle Service at Honda MPE and also a Technical training officer

Apparently they do this if the carbies are in sync, and that they need to be out of sync to work properly. If they are in sync the rear cylinder doesn't charge correctly and causes stalling and rough running at idle.

You never know, it may even help with fuel consumption

Your thoughts please.

(:-})

[countrymick]

good point there carl.twins are always set up slightly different front to back to compensate for enevitable differences in running temp etc and something as simple as that could account for a lot of head scratching over poor running isues

[darkember]

OK if this is the case. During the balancing process how do we figure out which is the front and which is the rear in order to offset them slightly??

[Flatline]

Front one is at the front under the handlebars

The rear must be the other one I assume

Didn't realise it needed figuring out

[lloydie]

I balance the carbs so they both read the same at 2.5 rpm and I never get carb farts and you can feel both cylinders pulling the same on the throttle .

[Animal]

I have been using a Haines manual for all my bike maintenance. It states that the carbs are balanced the same. However after looking at a Honda service manual I downloaded it states that the rear cylinder should be 20mm HG more.
Next time I have some time on my hands I'll be balancing the carbs to the Honda manual spec.

[darkember]

Front one is at the front under the handlebars

The rear must be the other one I assume

Didn't realise it needed figuring out

Well tell me as you balance them using one screw adjuster which way for the front and which way for the rear..............

[simo]

Well don't know where I read it 3 or 4 years ago, the 'base' settings for the mixture screws are different so I've always gone from there.

[VTRDark]

I balance the carbs so they both read the same at 2.5 rpm and I never get carb farts and you can feel both cylinders pulling the same on the throttle .

Same here, maybe we have managed to tune around it so we don't suffer the stall. It's a strange one and has got me thinking. It's like, why is the rear carb slightly richer, it's not necessarily cooling with a liquid cooled machine. There must be a reason for Honda doing it.

There's only one way to find out and that's to put it to the test so I'm going to try it and see, though I'm not sure it will make much difference with my bike as it don't stall and I have other stuff going on at the moment so it wont be a fair test. I'll do mine anyway but AP's Yellow one will be a perfect test for it as it's totally standard apart from aftermarket cans and he is suffering from the cutting out bad and I have had to turn the idle up for him. Bizarrely enough it may have started messing around after I balanced the carbs for him. So when he gets back I shall be putting this to the test and see if it improves.

Well tell me as you balance them using one screw adjuster which way for the front and which way for the rear..............

Err... you have two separate vacuum take off's which attach too separate gauges with their own independent measuring scale (mm hg) on a manometer/carb balancer If your using a coiled hose which is not really the proper tool for the job then I guess the fluid, ball bearing or whatever, moves one way or the other. I've never used one so don't know but I doubt it's designed for getting an accurate measurement on individual carbs.

(:-})

[8541Hawk]

This came up a while back in some other places.

In the end if was the consensus that what they are trying to say is that you need to be within 20mm Hg

In any case, I my findings, they run like shite when set that way and have gone back to the "standard" way of sync'ing them.

And sorry Carl I haven't sent you that stuff on the evolution of the HP kit with the small tubes for the carbs.
But in short it is for the same issues as pulling the vent lines from the carb stays.

[sirch345]

My 2p worth

Very interesting Carl
Considering how much better they run once you've balanced the carbs (if they are out of balance in the first place of course), I personally can't see how setting them up out of sync is going to work better either. But then, how much out of sync is 20mm Hg I wonder.

Honda on the other hand ought to know what they are talking about, so it will be interesting to hear what you find out Carl

Good to hear your outcome Hawk

Chris.

[tony.mon]

If that works, surely by now someone would have ended up with their bike running like this and been faster than everyone else....

Although having said that the readouts I have fitted that show lambda readouts in each downpipe certainly don't make sense- they're all over the place.
Different readings on par throttle- needle heights i would have assumed- but adjusting needle clip settings doesn't make much difference.But then I've just found that I had a big hole in the fuel tap diaphragm, and so I've started setting the carbs up from scratch now that's all sorted.

[Watty]

Well don't know where I read it 3 or 4 years ago, the 'base' settings for the mixture screws are different so I've always gone from there.

Mixture and balance are totally separate things mate!

[agentpineapple]

we can try on my yellow bike, the main reason for my bike stalling, was a poorly refitted stick coil.....doh!!!!
but even so, it still carb farts and stalls from time to time, so no different to many other storms, it does have the full two brothers system , pairs system has been removed and a factory pro jet kit, oh and the aforementioned stick coils, but other than that its standard air filter, and no engine work has been done to it, it even has the standard velocity stacks.
but the bike still needs some fine tuning and i'm willing to tinker when it comes to carb syncing, plus I have a dyno only 200yds away, and Saturdays are only £15 a run....

[Phil_H]

I balance the carbs so they both read the same at 2.5 rpm and I never get carb farts and you can feel both cylinders pulling the same on the throttle .

I'm very interested to know why you choose to balance them specifically at 2500rpm?

Phil

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