Topic: Bench Balancing

[MattFreeman]

When bench balancing carbs does one put the 1/8 inch gap on the engine side or the filter side?

Thanks in advance.

[Deltarider]

I used a small allen key engine side.

[OldSchool_IsCool]

You could do the flashlight method, rendering the question moot.

[malcolmgb]

Engine side. The size isn't important, just the fact that all slides are at an identical height.

You could do the flashlight method, rendering the question moot.

Never heard of this but I do know about the 'Rhythm Method' 

[OldSchool_IsCool]

Rhythm Method! HAHAHA!  That's what my parents used!!

[srbakker]

...and look how well that worked out.

[Bob Wessner]

Well, most accidents do happen in the home. 

[OldSchool_IsCool]

 

[TwoTired]

This is a repeat of previous posts.

The drill method can work, but in some model carbs it can yield a carb set where the slides can't close completely or worse, can't achieve a proper idle RPM, because the slides can't close enough.  I've seen this occur and also read about it here in this forum.  A slide that can only close to a 1/8 inch opening produces and unloaded idle RPM of about 4-6000.

The light method makes the high idle speed issue vanish.

It goes like this.
  Back out the idle knob so it can't effect slide opening position.  Shine a light at the far end of the carb bore and find a slide that has the light blocked.  Assign that carb as your master carb and/or make at least one slide fully close and block light, and assign that as your master carb.  Don't make any further adjustments to this carb either on the bench or while performing a vacuum balance.  The Master carb is the carb all others will be adjusted to match.  Some carbs have no adjustment on #2 making it the default master carb.
Now that you have your master carb slide closed and blocking light from the other end, you adjust each carb slide in turn so that it *just* blocks light.  You can verify your adjustment by operating the slides and ensuring that each slide blocks light at the same time when the slides move toward closure.
When satisfied, screw in the big idle knob so the slides are open about 1/16 of inch.  This is so it can breathe enough to have an idle, and when the engine is running adjust the idle knob for 1000 RPM when the engine is at operating temperature.

You should still vacuum sync the carbs after a valve adjustment, to get a finer balance on the carbs and have all cylinders pulling the same amount.  But, remember not to mess with the master carb adjustment.  This will ensure you maintain full slide travel in all carbs.

Cheers,

[lucky]

When bench balancing carbs does one put the 1/8 inch gap on the engine side or the filter side?

Thanks in advance.

Just make sure that the slides are all the same and they are all the way down,bottomed out. Make sure when the master carb slide is all the way down
and the idle screw is backed off, that the other slides are set to match the master slide.

Always do the inspection from the filter side since you can see it and get to it. NOT the engine side.

[MattFreeman]

This is a repeat of previous posts.

The drill method can work, but in some model carbs it can yield a carb set where the slides can't close completely or worse, can't achieve a proper idle RPM, because the slides can't close enough.  I've seen this occur and also read about it here in this forum.  A slide that can only close to a 1/8 inch opening produces and unloaded idle RPM of about 4-6000.

The light method makes the high idle speed issue vanish.

It goes like this.
  Back out the idle knob so it can't effect slide opening position.  Shine a light at the far end of the carb bore and find a slide that has the light blocked.  Assign that carb as your master carb and/or make at least one slide fully close and block light, and assign that as your master carb.  Don't make any further adjustments to this carb either on the bench or while performing a vacuum balance.  The Master carb is the carb all others will be adjusted to match.  Some carbs have no adjustment on #2 making it the default master carb.
Now that you have your master carb slide closed and blocking light from the other end, you adjust each carb slide in turn so that it *just* blocks light.  You can verify your adjustment by operating the slides and ensuring that each slide blocks light at the same time when the slides move toward closure.
When satisfied, screw in the big idle knob so the slides are open about 1/16 of inch.  This is so it can breathe enough to have an idle, and when the engine is running adjust the idle knob for 1000 RPM when the engine is at operating temperature.

You should still vacuum sync the carbs after a valve adjustment, to get a finer balance on the carbs and have all cylinders pulling the same amount.  But, remember not to mess with the master carb adjustment.  This will ensure you maintain full slide travel in all carbs.

Cheers,

Cool, thanks.

[lucky]

You could do the flashlight method, rendering the question moot.

How do you fit the flashlight under the slide?

Very funny!

[MattFreeman]

TwoTired: Just for grins which side of the carbs gets the gap with the drill method?

[MattFreeman]

Oh... and sorry for the redundant topic, I'm definitely a lazy internet user.

[TwoTired]

TwoTired: Just for grins which side of the carbs gets the gap with the drill method?

The slide side with the cutaway is actually arch shaped, as well as the carb bore, making placement more problematic, imo.  At least the engine side has a flat bottom on the slide.  So, if you are conscientious with equal placement of the drill bit among carbs, then the engine side would be preferred.  It's not that critical, though really.  You just need to get close.  Mechanical slide equality is only important if each cylinder has exactly the same volumetric efficiency.  They seldom do in reality, which is why a vacuum sync is required after a bench sync using any method.  The light method just ensures you can achieve an idle setting, whereas the drill bit method has no such assurance.

Cheers,

[andrewk]

^^  That's exactly how it is.  The light method is by far superior, but any method you use, you want to be working on (so, either using your drill bit, or looking at light blockage) the engine side of the carbs.  Using the engine side with the drill bit method is best because of the flat spot TwoTired mentioned- the flat spot helps ensure consistency between carbs.  With the light method, it really doesn't matter what side the light is shone from, but I find that shining it on the filter side and adjusting while looking at the engine side is the easiest.  Lastly, on any of the smaller SOHC fours and the later 750, you'll have to work around the chokes on the filter side.

[MattFreeman]

Thanks for the help guys.