Carb balancing

[Hoon]

I've got shitloads of work to do on my ZXR400....

Check/clean carbs
Check Valve shims
Check/replace cam chain
Balance carbs
Fit new chain and sprockets
Strip & clean front calipers/replace seals

Should keep me busy for the next few weekends - luckily its mostly labour and not much $$$ (just chain sprockets shims and brake seals). For balancing the carbs I was looking at getting one of these Carbtune II jobbies. Brand new it costs £65 but you can get used ones on ebay for cheaper.

What do you guys use to balance your carbs and it is very accurate??

[White trash]

I use a fuel injected method.

[vifferman]

I bought a 4-dial set from Motomail for $145.
It works.
Shame I've only got two carbs.
But they don't import the 2-dial ones anymore.

[erik]

I got a 4 dial set thing, same as what they've got at Motomail, except I got it from Mt Eden Motorcycles for a bit cheaper ($130 IIRC). They had to order it in, but it didn't take long.

When I used it, I connected it up in the reverse order, after balancing the carbs, to check if the gauges still showed it was balance (ie. to kinda make sure the gauges were calibrated with each other properly). It seemed to work ok, and they were pretty similar.

[Jackrat]

For a twin I just use a long piece of clear plastic tube 1/3 filled with light oil.
It needs to be about 4-5 meters long so it goes from one carb up and down to form a large M between the carbs.The two center bits are tyed to a rule so the oil finds a level on the scale.Hook it up to both carb's an start the bike,you can read the imbalance on the rule and adjust accordingly.
You can use the same system on muti's by seting two carbs and then adjusting the others to the same measurements.
accuracy,spot on.Cost, about thirty bucks for the tube.
If you over rev, the bike before you have set the balance you will suck the oil out of the tube and into the carb with the most suck going on.

[What?]

You can do the same thing using one tube for each carb, set in a U shape. Cheap as, and you can do as many cylinders as you like. Run the tubes through a board, then you only see the side showing the level. Precise measurement doesn't matter - just have all 2,3,4,6 even. Don't know about others, but Honda fours use the No. 2 carb as reference; you adjust the others to match that.

[Milky]

You might have to come along to some KB meet to explain that better to me... it makes little or no sense depending on which way i turn my head Where are you supposed to join the tubes to on the carbs?
I have heard also that those balancing gauges arent always good if there are differences in the condition of the rings/valves/pistons in each cylinder... ie you can do all the balancing you like but it wont get the bike running properly because you are fixing the wrong thing

[FROSTY:Me]

sounds like ittd be a good thing to do for a spanner evening

[Jackrat]

You might have to come along to some KB meet to explain that better to me... it makes little or no sense depending on which way i turn my head Where are you supposed to join the tubes to on the carbs?
I have heard also that those balancing gauges arent always good if there are differences in the condition of the rings/valves/pistons in each cylinder... ie you can do all the balancing you like but it wont get the bike running properly because you are fixing the wrong thing

Yeah I wondered if I could explain it all that well.Sorry.
The tube connects to the vacuum hole in each carb.
So the tube goes from the vacuum hole up,down,up and down to the vacuum hole in the other carb.The tube ends up a tight M shape with the oil siting in the center.
When you start the bike the oil will be drawn to ward the carb with the most suck going on.you then adjust either carb to bring the oil back level.
If it looks like the oil is going to get sucked into either carb you just pinch the pipe to stop it,that will only happen if the pipe is to short to begin with or your carbs are WAY out of balance.A little oil in the top end does no harm so don't panic, just wait for the smoke to clear and wind the air screw on that carb in a bit then start over.

I will see if I can post a link to a site that exsplains it better with pic's ect.

[erik]

Darn, I wish I'd heard about that when I was balancing my carbs before I bought the gauges! It sounds like a good idea and I could've saved myself $100! Oh well...

[k14]

Yeah, was thinking of having a go at balancing my carbs sometime.

What are the symptoms to looks for if your carbs are out of balance? My bike seems to surge a bit at idle, is that a symptom of unbalanced carbs??

[White trash]

Yeah I wondered if I could explain it all that well.Sorry.
The tube connects to the vacuum hole in each carb.
So the tube goes from the vacuum hole up,down,up and down to the vacuum hole in the other carb.The tube ends up a tight M shape with the oil siting in the center.
When you start the bike the oil will be drawn to ward the carb with the most suck going on.you then adjust either carb to bring the oil back level.
If it looks like the oil is going to get sucked into either carb you just pinch the pipe to stop it,that will only happen if the pipe is to short to begin with or your carbs are WAY out of balance.A little oil in the top end does no harm so don't panic, just wait for the smoke to clear and wind the air screw on that carb in a bit then start over.

I will see if I can post a link to a site that exsplains it better with pic's ect.

Well explained, Jack. I hadn't thought it would be that simple.

You learn something every day, they reckon.

[Jackrat]

Yeah, was thinking of having a go at balancing my carbs sometime.

What are the symptoms to looks for if your carbs are out of balance? My bike seems to surge a bit at idle, is that a symptom of unbalanced carbs??

This is what my book on trouble shooting says.

Poor idling,hunting or surging may be caused by incorrect timing,carburetor adjustment,or ignition system faults.Check the fuel cap vent for obtructions.

Thats sounds a bit vauge to me,but I have for myself found that timing is most likely to be the cause if it is only at idle that you notice a problem.When it's the carb's I normaly notice stumbling or hesitation at higher rev's.A blocked fuel cap vent would I imagine also show it's self at higher rev's.
When I tune my carb's (CVs) I first check that the slides are in sin'c first,then do the Vacuum balance.If you can see the slides with the air box removed like I can then it's easy to just watch them to see if they at the same level.If you can't see the slides then just slip and ice block stick in under each slide and you can then see if they are both at the same level as the slides move up an down.
Sounds a bit bush but it works.

[Hoon]

From the carbtune site:

"Carb balance will affect the response, smoothness, mileage, performance and running temperature of your engine.

Carb synchronisation consists of adjusting each throttle valve for carburettors or fuel injection throats so that they pass as much fuel-air mixture as all the others. This balances the load carried by each piston.

If one carb is opened further than the others that cylinder will run hotter than the others. The other carbs will also supply a richer mixture and mileage will suffer."

Darn, I wish I'd heard about that when I was balancing my carbs before I bought the gauges! It sounds like a good idea and I could've saved myself $100! Oh well...

Yeah I was just about to order mine when I thought "Hmmm I'll just ask the KBers first!". Glad I did...Now I'm off to score some plastic hose from Mitre10 this weekend instead!

[vifferman]

The plastic hose method is all very well, and somewhat appealatising to a cheap bastid like me, but I'm not sorry I bought the proper tools. Just remember:

No-one ever regretted buying good tools.

Besides which, it's much easier just taking the plugs out of the end of the vacuum tubes I've plumbed in on the bike, sticking them into the gauges, starting the bike, and there you go! The 'plastic tubes and erl' method sounds like a lot of shaggin about to me, especially in the cluttered garage the FahrtSturm has to share with a whole bunch of junk and two Peugeots...
Two carb tunes, and I reckon I'm ahead. One done, and one to go...