How to balance your carbs

[bazzashadow]

Yep that's exactly what I do, just pull the end caps off to reveal the the brass adapters. I use a Carbtune gauge with mine so attach the Carbtune lines which have a restrictor in them to smooth the flow to the gauge (some gauges require this for an accurate reading) and then attach them to the brass adapters under my seat.

(:-})

[bigtwinthing]

Now i don't want to be at all critical But!!! whilst we are balancing them with this procedure but are we balancing them too Rich! or too Lean! how do we know? Running rich will get 10mpg etc but wont harm anything, Running lean, normally they go better but can hole pistons if its too lean. These bikes tend to spit back occasionally through the carbs and on the overrun anyway and these can be indications of a weak mixture isn't it? (over to Tony no doubt to kick my butt with a skilful reply!! ) i have got mine checked as i fitted the different cans but may need to balance them after 10,000 miles.Regards Paul.

[AMCQ46]

BTT.........balancing has no change on the mixture, it just makes sure the buterflys are matched

[bigtwinthing]

BTT.........balancing has no change on the mixture, it just makes sure the buterflys are matched

thanks for that, thats makes sense then, i wondered why they go on about the jets as a starting point being so many turns out etc.

Ive used my Manometer to make sure there pulling the same through the carbs at different rpm and tick over etc, but wouldn't touch any mixture screws.

[VTRDark]

i wondered why they go on about the jets as a starting point being so many turns out etc

I think your in the wrong thread

As Al says balancing is adjusting the throttle plates not the air fuel ratio as such. Now the throttle plates will always leave a small gap and never close fully. The throttle plate basically allows a small mix of fuel and air into the cylinder as to allow the bike to run with no throttle. A carb balance is syncing the two carbs together so the same amount of fuel and air is getting through the throttle plates so things are consistent between the two cylinders which in turn keeps things smooth with no out of sync vibrations from idle speed with no throttle to full speed wide open throttle.

Your right about the carbs spitting back (fart) being an indication of too weak a mixture and depending at what revs and throttle opening one is at when the bike farts determines which carb circuit is the problem. 9 times out of 10 it will be the pilot circuit, especially if cutting out when coming to a full stop, or right on that crossover point onto the needles at around 3500 - 4000rpm. It's more critical to have a good balance at lower revs/speeds as this is where things are most sensitive to changes, especially with these huge twin cylinder carbs/pistons.

A carb balance is last in the chain of command and as long as valve clearances are all good and the carbs are jetted with the correct mixture and there are no intake or exhaust leaks, then a common solution to a carb fart and the simplest to adjust is to balance/sync the carbs so is always the first port of call as this often solves/alleviates it.

As for being to lean blowing holes in pistons. With standard compression ratio, one would have to be running super lean for a very long period of time, and to be honest with the quality of modern day fuels with all their additives this is not so much of a problem as it used to be so there is very little chance of damaging things to that point from running lean alone.

(:-})

[bigtwinthing]

Thanks Carl, your right too about fuel. Mind you in 1978 my Kwaka 750 triple 2 stroke threw a piston due to running lean and the bloody engine almost blew up, the centre piston had a hole the size of a 50p in it. Funny now but not then!!

[bazzashadow]

fitted the vacuum pipes yesterday, thought i could get my hand in and fit the brass outlet, how i was wrong
tank off, filter off and carbs off
pipes fitted with the carbtune brass fittings and blanks coming out behind the battery and being held down by the cable connectors bendy clip, looks very neat.
done my carb balance today
about 5mm out on my gauges, turned the screw and they went further out, back the over way (not much) and bike cut out and would not run.
turned it back and got the two gauges spot on
bike does feel crisper, more responsive
but my miss fire, back chuff what ever it is is still there
so back to the drawing board

[jztam]

Just pondering installing the extra plumbing, and I noticed that the factory vacuum connector on the front carb is not there. All I see is a threaded hole. Thinking the previous owner already installed both extra lines and forgot to thread the front one back in, but NO, the rear plumbing is untouched.

Q: What _should_ the factory fitting look like on the front carb?

Q: What ill effects would show up if there is nothing in the threaded hole in the carb?

[lloydie]

Factory it that's a 4mm Allen cap head bolt in it .
It would run nicely at all if it was missing .

[AMCQ46]

What you describe is how they left the factory.

You need to fit a vac take off to the front but make sure it is blocked when finished

[sirch345]

Brass adaptors here in link below, as AMcQ mentions in his first post:-
http://www.carbtune.co.uk/carbaccs.html

Chris.

[VTRDark]

Seems as good a place as any to post this pic as it's not already in the thread.

I noticed that the factory vacuum connector on the front carb is not there.

It's not on the carbs where the vacuum comes from. It's just below the carb boots coming out of the cylinder head. When you say threaded hole I think you may be referring to the same but this should clarify things.

The rear (right hand side in pic) is where the vacuum feed is taken from for the petcock diaphragm. Add a T piece to this and run a rear vacuum take off from that and cap it off. The rear where the threaded hole is should have a brass adapter fitted and a vacuum hose for the front is taken directly from there and capped off. It should be as standard capped off with an allen head bolt in the cylinder. With no bolt and a vacuum leak the bike will run a little rough, wont idle smoothly and maybe cough, splutter with a little more popping and banging coming out the exhaust than usual.

You might as well use the spare adapters to cap off the ends tidily. I also purchased nitrile end caps to slide nicely over the adapters which caps them off when not in use.
http://www.vtr1000.org/phpBB3/viewtopic ... 30#p259491

(:-})

[Bikermort]

Hi all,

Ive gone through a lot of threads looking for the exact size of the brass fitting with no luck. I dont want to have to remove the fiddly blanking plug to go to different stores only for them to not have one etc.

Does anyone know the type and size of thread at all?

Ive only just bought my 03 VTR. I feel a bit of a vibration in it. Mainly under slight load around the 2.5 to 3k rpm. Its still there i think at higher rpms but less noticeable. Thought balancing the carbs would be a great place to start [and hoping that is all it is (praying emoticon)]

Ps Im in Brisbane Australia

Yamaha It175
CB900F 82
Yamaha YZ250 03
Yamaha XT600e 03
Honda VTR 1000 03

[NZSpokes]

Hi all,

Ive gone through a lot of threads looking for the exact size of the brass fitting with no luck. I dont want to have to remove the fiddly blanking plug to go to different stores only for them to not have one etc.

Does anyone know the type and size of thread at all?

Ive only just bought my 03 VTR. I feel a bit of a vibration in it. Mainly under slight load around the 2.5 to 3k rpm. Its still there i think at higher rpms but less noticeable. Thought balancing the carbs would be a great place to start [and hoping that is all it is (praying emoticon)]

Ps Im in Brisbane Australia

Yamaha It175
CB900F 82
Yamaha YZ250 03
Yamaha XT600e 03
Honda VTR 1000 03

Try a fish tank supply shop. M4 from memory.

As your in Aussie, this may be of interest. https://www.facebook.com/groups/364384210361341/

[Bikermort]

Thanks NZspokes.

I finally found a brass fitting....a mechanic from a bike shop gave me his out of his toolbox after telling him about how many shops ive been too. Did a carb balance doing a minor adjustment. Seems to have made a slight difference but can still feel a vibration. I can feel it when im say at 2600rm in 5th or 6th and go to accelerate slightly. Also when i really give it the fat it just seem harsh....not smooth. Maybe this is just normal for these beasts? Im going for a ride in a couple of days with a mate who has a later model one with only 13k on it so will take his for a ride and see how it compares.