Topic: Vacuum gauge numbers and Sync adjustements?

[LoopsAndLogic]

After adjusting my carbs on the 400F, I found using just one gauge and a splitter that turns off each hose independently, I can use
my 1 vacuum gauge to set my carbs.

So, I would turn 3 off and adjust one to 17hg cm, cause the book calls for 16-24hg cm.

Once I would get to the last carb, and recheck all 4 again, the first one that I started with would jump all the way to 30hg!!
 And the second from the first, would be somewhere around 21hg cm.

I also have to adjust the idle after adjusting just 2 carbs.
 
 Does all this sound normal?

I was only able to get my carbs to settle around 27-28hg cm evenly.

Why won't they go lower?  Should I be using 4 gauges to set the carbs??

Everything is stock besides the MAC muffler of which with testing, I decided the mid-range was suffering a little and bumped the needle jets up by just one position.
 
I didn't touch the main jets, cause I never reach 7/8 to WOT. And the muffler does seem to be restrictive at higher RPM's.

The plugs look a little black with some area's of the ceramic still slightly white, but at least she's not running lean!

She runs great!!! No hiccups, but if someone could answer my questions, this would really help me in the near future with my other SOHC-4.

Thank you

LL

[NickC]

As you adjust one, the others will change.
So if you are doing #1 carb, then move on and change the #2 carb, the #1 carb will most likely change. You need to look at all the carbs at the same time, to get the right configuration

[kslrr]

and don't worry about getting to a specific vacuum reading.  The idea is to get all 4 carbs as close as possible to the SAME vacuum value over the throttle range.  You will find that the difference between carbs will very from idle to WOT.

[eurban]

Right on; worry about equal vacuum not some specific number.  Stop being a cheapskate and get yourself a four gauge synchronizing tool   Wasting your time otherwise . . . .

[MoTo-BunnY]

Roll yer own, doOd! - I made mine for like $50 or less! (and with German gauges, Italian valves, USA brass fittings & hose - better than any China set and cheaper!)

They worked great and tuned my bike right up all purdy like 

http://forums.sohc4.net/index.php?topic=23038.0







Other people made different types too (like this one) - check out the above thread link:

[mrbreeze]

Right on; worry about equal vacuum not some specific number.  Stop being a cheapskate and get yourself a four gauge synchronizing tool   Wasting your time otherwise . . . .

AMEN!!!!!!

[BobbyR]

After adjusting my carbs on the 400F, I found using just one gauge and a splitter that turns off each hose independently, I can use
my 1 vacuum gauge to set my carbs.

So, I would turn 3 off and adjust one to 17hg cm, cause the book calls for 16-24hg cm.

Once I would get to the last carb, and recheck all 4 again, the first one that I started with would jump all the way to 30hg!!
 And the second from the first, would be somewhere around 21hg cm.

I also have to adjust the idle after adjusting just 2 carbs.
 
 Does all this sound normal?

I was only able to get my carbs to settle around 27-28hg cm evenly.

Why won't they go lower?  Should I be using 4 gauges to set the carbs??

Everything is stock besides the MAC muffler of which with testing, I decided the mid-range was suffering a little and bumped the needle jets up by just one position.
 
I didn't touch the main jets, cause I never reach 7/8 to WOT. And the muffler does seem to be restrictive at higher RPM's.

The plugs look a little black with some area's of the ceramic still slightly white, but at least she's not running lean!

She runs great!!! No hiccups, but if someone could answer my questions, this would really help me in the near future with my other SOHC-4.

Thank you

LL

I calibrate my four guages to a single cylinder so I am very close to all of the guages reading the same. Once i am sure they are reading the same I them hook each to an individual carb. Trying to do what you are doing could be done, but man it would take forever. You could spend that time picking up bottles on the side of the road and cashing them in for enough money to buy or build a four guage setup.

[MoTo-BunnY]

I calibrate my four guages to a single cylinder so I am very close to all of the guages reading the same. Once i am sure they are reading the same I them hook each to an individual carb. Trying to do what you are doing could be done, but man it would take forever. You could spend that time picking up bottles on the side of the road and cashing them in for enough money to buy or build a four guage setup.

You can also use a big ole syringe thingy for calibration:



Hook it on one of the hoses and draw it back 60cc ml - it will show about 20" Hg on the gauge (on this size, syringe, at least). Check them all, one at a time, and note any deviation. You can replicate the exact same vacuum reading on the gauge, over and over, by drawing the same cc - so its real accurate.

Oh, and in case any of you 'city folk' don't know where to find these (lol), you can pick them up at any "farm & feed" type store in the husbandry section. This one was like $3 or something.     

[BobbyR]

I calibrate my four guages to a single cylinder so I am very close to all of the guages reading the same. Once i am sure they are reading the same I them hook each to an individual carb. Trying to do what you are doing could be done, but man it would take forever. You could spend that time picking up bottles on the side of the road and cashing them in for enough money to buy or build a four guage setup.

You can also use a big ole syringe thingy for calibration:



Hook it on one of the hoses and draw it back 60cc - it will show about 20" Hg on the gauge (on this size, syringe, at least). Check them all, one at a time, and note any deviation. You can replicate the exact same vacuum reading on the gauge, over and over, by drawing the same cc - so its real accurate.

That is brilliant and simple. Thanks

[LoopsAndLogic]

Hi all,
  I've been away for a long time. After reading your posts and asking around here's the scoop!

Someone told me that I need to have the carbs between 16-24hg because if all of them are higher and still equal, the motor will be sucking in more fuel and less air or vise versa. I don't exactly remember the order in which he said it.

But the take off from idle would be choppy is what he ended with..... Is this right??

When the throttles are closed you get a higher vacuum reading and if the throttle valves are open, the vacuum decreases.....right?

I sync'd my VF using all 4 or my gauges and it did seem to go a lot faster. And yes, I was using the 4 gauge system before.
  I had another idea by using 1, but I guess I was wrong

And I used my vacuum pump for brakes on all 4 gauges to make sure they were all within sync.

Why would Honda put those numbers in there???

Thank you kindly

LL

[BobbyR]

What you are doing is taking 3 carbs and making the vacum reading the same as the 4th. On the 750, one carb which happens to be #2 is adjustable and that is the reference carb. The other carbs must be adjusted to pull the same vacum as #2 no matter what reads. That is what syncronization is, all carbs are pulling the same. For this exercise the numbers are meaningless.

[bradweingartner]

Hi all,
  I've been away for a long time. After reading your posts and asking around here's the scoop!

Someone told me that I need to have the carbs between 16-24hg because if all of them are higher and still equal, the motor will be sucking in more fuel and less air or vise versa. I don't exactly remember the order in which he said it.

But the take off from idle would be choppy is what he ended with..... Is this right??

When the throttles are closed you get a higher vacuum reading and if the throttle valves are open, the vacuum decreases.....right?

I sync'd my VF using all 4 or my gauges and it did seem to go a lot faster. And yes, I was using the 4 gauge system before.
  I had another idea by using 1, but I guess I was wrong

And I used my vacuum pump for brakes on all 4 gauges to make sure they were all within sync.

Why would Honda put those numbers in there???

Thank you kindly

LL

Whoever that someone is, they were wrong. Carb sync has absolutely nothing to do with fuel. All you are doing is making sure that your carbs are open the same amount at idle essentially. What your vacuum actually reads is very inconsequential. What you're looking for is BALANCE between them which will ensure a smooth idle.

Now the curious thing is that the vacuum pulled at a pot is dependent on RPM and slide position in the carb (engine condition pumping efficiency, cam overlap, etc, notwithstanding). So if you set carb 1 to XX in/mg, and susequently adjust the other three carbs to attain a higher idle RPM, your XX in/mg at carb 1 will increase.

Thus, having four EQUAL gauges connected at the same time ensures accuracy. Also, as you adjust one carb, you can observe the change made to the other in real time and compensate. At the end of the day though, as long as you have 4 equal readings, and enough adjustment in your idle screw to keep the idle in check at warm/cold extremes you are golden.

Don't be that guy who syncs his carbs to idle with the idle screw all the way in or all the way out... 

[mrbreeze]

What you are doing is taking 3 carbs and making the vacum reading the same as the 4th. On the 750, one carb which happens to be #2 is adjustable and that is the reference carb. The other carbs must be adjusted to pull the same vacum as #2 no matter what reads. That is what syncronization is, all carbs are pulling the same. For this exercise the numbers are meaningless.

Bobby...I believe that #2 reference carb is the 77-78 bikes.Mine doesn't work that way.

[BobbyR]

What you are doing is taking 3 carbs and making the vacum reading the same as the 4th. On the 750, one carb which happens to be #2 is adjustable and that is the reference carb. The other carbs must be adjusted to pull the same vacum as #2 no matter what reads. That is what syncronization is, all carbs are pulling the same. For this exercise the numbers are meaningless.

Bobby...I believe that #2 reference carb is the 77-78 bikes.Mine doesn't work that way.

I badly worded it. If yu look at the second sentence you will see carb 2 is reference. I was trying to say that only 3 carbs are adjustable which would have been clearer.

[LoopsAndLogic]

Will do. "Don't listen to other guy".......Check!!!!

Now, off to the "Babe Thread"........

  I need to relax a bit....busy week.

Bless you BobbyR and all other members for that thread!!!

[BobbyR]

My pleasure.