Is a carb balance the same as a rejet?

[Silver_Fox]

My new steed has an aftermarket can on the back. The previous owner had the carbs balanced, and said it transformed the bike. Is that the same as having a rejet after fitting a new pipe?

[Itchy]

No.
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[MarJay]

No... Why would that be the same thing? A carb balance makes sure all four carbs are synchronised so that they give the same air and fuel for a given throttle opening. A rejet changes the size of the jets inside the carbs so that the fuelling is matched to the other changes made to the bike.
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[c_dug]

You'd probably find that if the jets were changed they'd balance the carbs as part of the same work, but you couldn't make the same assumption the other way.

In other words the bike may still potentially be running lean.
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[Silver_Fox]

Thank you. I thought it was different (but as I'm new to biking and Googling didn't give me a clear answer) I thought it best to check. Any idea on prices for such a job?

[MCN]

The new can can affect how air flows through the engine and that can affect the operation of the carburettors.
To accommodate a different can different jets may be fitted. (But adjustment of the carbs can sometimes manage this.)
If new jets were fitted then the carbs would need to be balanced.

Multi-Cylinder engines can suffer from fuel-ing problems due to the way air is routed to the cylinders. Cylinders further from the carb get less fuel. To rule this leaning out the mixture is enriched. But that means the nearer cylinders run rich. It is a compromise.
To rule out this effect and improve performance, each cylinder can be fitted with it's own carb. (Due to cost/technology constraints, some engines use one carb between two cylinder and etc.)

As each cylinder has it's own carburettor they all have to provide the same amount of fuel for each cylinder to provide a 'balance' of power. If not balanced properly the engine can run 'lumpy' (unevenly), run rich/lean on one or more cylinders among other issues.

You can buy balance gauges and tune the carbs yourself or let a shop do it. The main cost for this is labour to remove/refit the tank and air-filter-box to gain access to the carbs though. 2 hours labour at a guess. But they shop may operate a fixed price for this as it's a fairly common task.

You may have to check balance at each yearly service as it can change if there has been any dirt through the fuel system. Or general wear on linkages. So you might decide to buy the kit and become an expert. It's not rocket surgery.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Silver_Fox]

Thanks. I'd seen posts suggesting try it and many suggesting to leave it to the professionals. I'm getting 53.9mpg which strikes me as a bit much

[MCN]

[Silver_Fox]

You know what it's like. Buy a new (first) bike and want to make sure it's running as well as it can

[MCN.]

[Rogerborg]

Bike is a 1997 CBR600 F3, yes?

Cost is what the local dyno/tuning place wants to charge. I'd want to get an analysis run first before committing to stripping it down and re-jetting.

Plastics to remove, 4 carbs, 18 year old rubbers, could ramp up sharpish.
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[Silver_Fox]

Yes indeedy. Sounds like the most sensible idea is to remove a spark plug and check the colour first

[Polarbear]

If it has just had an end can it will probably be fine.

A lot of the worries/panic stems from the effect playing around with an exhaust has on the strokers, it's not usually a problem on 4 strokes until you change the whole system for something racing.
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[Silver_Fox]

It does have stainless downpipes too, but I'm unsure if they're anything more than a direct replacement as I can't see branding on them

[MCN]

[janner_10]

I think you're fretting over nothing.
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[Ariel Badger]

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