diy manometer vs. hands behind exhaust pipes

griennehornette

griennehornette

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Welp, it was one of those days. They happen a lot with me; but that's another story. Suffice it to say, I tend to take the long way around on most projects.

Today was no different, in that I made a number of breathtaking errors along the way, which cost me time and effort. But I should probably stick to the point.

I made one of those DIY manometers; the kind using 2 bottles. The Youtube vids say this is better than the length of hose, as no fluid will get into your carbs. Clearly they have never dealt with anyone of my bumbling calibre. But at least I was able to rip the tube out of the carb before much fluid got in. Let's just say my carbs were not even close to balanced.

Anyway, after drying everything out and dropping the carbs so I could bench sync the butterflies and get them back to somewhat close to synched, a weird thing happened. I did manage to get the manometer to balance. But I could tell just from the noise and shaking of the bike that the carbs were *not* balanced.

I pulled out the tubes, replaced the air screws, and put my hands behind the pipes. One side was way stronger than the other. So I futzed around and got them fairly equal feeling. The idle revs went down nicely (which is what got me started on this adventure this morning - high idle revs).

So then I took out the air screws, and plugged in the manometer again. One jar drained like a toilet into the other. I got them somewhat close to balanced again, and the bike sounded like shit. Popped the air screws back in, and again, hands behind the pipes could feel a large difference.

So I just balanced with the feel of the exhaust. I dunno what went wrong with the manometer. I made one with just the long hose years ago, and it worked fine.

Is balancing by the feel of the exhaust pressure at all accurate? The bike sounded happier with it; but I dunno how accurate the feel of puffs of exhaust are gonna be.
 
That sounds about right for me, bench synching and then adjusting the idle mixture screws while feeling the pulse of the exhaust.
I oft times can't understand what my wife says but I understand my bikes when they're talking.

I use 2 straight pins, one under each of the throttle plates to bench synch. I start by opening the right carb throttle plate a bit more than the left, and then adjust the left throttle plate to just grip its pin and then bring the right throttle plate down to just grip its pin, and then only adjusting the right throttle plate, getting the same drag/feel for each carb. Once the carbs are remounted and the bike is started, be ready to make adjustments on the idle screw for 12 to 1500 rpm and then work the mix, each carb.......about as sophisticated as I get.
Other opinions may vary.....lol

My homemade manometer sits on a shelf with two stroke oil still in its mason jar. If the above ever fails me I may try to work out the bugs and install one of them regulator thingys into the mix.
 
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Paleo, you crack me up! I love your philosophy.

Here's a question which betrays my ignorance. When you say "adjusting the idle air mix pulse of the exhaust" are you talking about messing with the idle speed screws? 'Cause there's also the idle mixture screws, which I kept looking at today, and thinking, "Am I supposed to mess with you boys as well?" I turned them out as per the manual (plus a bit, as I'm running pod filters), and hopefully that's all I gotta do. It's just that you used the word "mix" and that got me thinking maybe the mixtures screws do come into play, and maybe that's why what seemed like a straightforward job today turned into a lengthy ordeal.

Of course, I'm quite capable to turning ordinary and straightforward into complicated and difficult, all on my own. But if those mixture screws played a part, that would make me feel a little bit better ;-)

Thanks Paleo. I'm in good company, putting the manometer up on a shelf!
 
Paleo & Grien put me on bench sync as well ! both sets of BS38's cleaned and jetted on the kitchen stove this winter were synced with light & feel.. Both sets required idle adj of course and mixture screw adj.. Close enough as I have not had a further reason to sync more. If you are particular and try on assembly very close can be easily achieved ! -RT
 
If you do a bench sync, using a slip of paper as a feeler gauge, under the butterflys, the sync will be so close that a manometer is probably not needed. However, I use a simple U tube manometer as a second step to be a little more precise.
You do not adjust the mixture screws while doing a carb sync.
I've never done the holding hands behind the exhaust pipes method.
 
Griennehornette, the idle mixture screws for final tuning, like you said.
On the bs34's they're capped from the factory, yeah, them'ns.

I reworded the original post for clarity.
 
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XS twins are so simple to tune by ear . Isn't that so much of their appeal ? Yes, the good old mercury sync tool is long lost and was very fun to use and necessary on 4cyl yamahas in my past. Now, my XS's get tuned by my experience more than relying on the tools . Measure twice cut once works well on carbs, points & timing. And hey, sometimes its even better to be lucky than good ? That too ! -RT
 
hay Greeniehornet fella ! can you post a pic of your carb sync thing you made please . Thanks....
.....
I made a hose type manometer with 2 small resivours on top to catch the oil shoild it try and be sucked in by the engine
havn't tried it yet because I ran out'a hose ! LOL
sounds to me that something about the manoimeter you made is goofie adjusting with a manometer is way more accurate than doing it by feel..... sure it can be done but with the meter you don't have to 2nd guess yourself.... and spend hours doing it.
and cuts down on the vibration on the handle bars.
f.w.i.w.
Bob...........
 
Tried a mercury manometer a long time ago, I still shudder when I think of how THAT went!
I bench set looking through the bores at a bright light then use a set gauges on bikes with vacuum taps and hand over pipes on those without. They both do the job just fine. Your on engine setting may be offsetting differences between engine cylinders, they are never PERFECTLY the same, so it may not be "quite" the balance you get on the bench. If you are moving the balance screw very far from the bench setting it may be an indicator of a cylinder problem, valve sealing, air leak, rings, whatever. If you haven't replaced throttle shaft seals, or have a worn throttle shaft bushing YRMV.
 
nj1639 said:
Griennehornette, the idle mixture screws for final tuning, like you said.
On the bs34's they're capped from the factory, yeah, them'ns. - - -
Click to expand...

Hi Paleo,
if anyone's carbs still have "them'ns" in their BS34 carbs, rip the bastards outta there!
Those little plugs don't only stop you from re-setting the EPA-mandated extra-lean idle settings
they stop you taking the needles out to clean behind them.
 
gggGary said:
Tried a mercury manometer a long time ago, I still shudder when I think of how THAT went! - - -
Click to expand...

Hi Gary,
apart from the fact that Mercury is far worse for your health than your choice of colored oil the main difference between Mercury-filled and oil-filled manometers is that oil-filled manometers are 14 times as accurate.
Thus anyone who's used to reading a Mercury-filled or rising rod manometer will still be looking for those instruments' 1/16" acceptable height difference
instead of the oil-filled manometer's 7/8" equivalent.
 
fredintoon, my mercury (Accupro?) was very accurate hung on my tetherball pole. My 4's had rollon ! -- Now, as I am just filling my new Yuasa battery I believe this compartmentalized acid container could be reused as a nifty oil carb sync tool ? Any input ? Thx, RT
20170424_103012.jpg
 
yah Fred ! do it man !!!!! thats a perfect container !...... you can even make it for a 6 cylinder bike !!!!!!
Bob......
 
makes me wish I bought a battery with one of those type of acid containers instead of a bag !!!!! Phooie ! LOL
.....I seriously doubt you would need more volume than just one of those it's already way more than the oil in the tube for a U tube type...and I assume that is the type you'll make
like the design 2M made..... in my mind it's the best one out there....super accurate !
Bob.......
 
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TimeMachine said:
fredintoon, my mercury (Accupro?) was very accurate hung on my tetherball pole. My 4's had rollon ! -- Now, as I am just filling my new Yuasa battery I believe this compartmentalized acid container could be reused as a nifty oil carb sync tool ? Any input ? Thx, RT View attachment 98651
Click to expand...

Hi TM,
perhaps I used the wrong word? Any U-tube manometer is as accurate as any other.
It's that the greater the working fluid's density the smaller it's fluid height difference will be for the same difference in pressure.
For instance, a 1psi difference on a Mercury-filled manometer gives a column height difference of ~2"
while a 1psi difference on an oil-filled manometer gives a column height difference of ~ 28"
So that while each is as accurate as the other a Mercury-filled manometer is a lot more difficult to read.
And yes! That 6-pack acid container could be used for a manometer overflow catch-pot for not only a twin but for any bike with no more than 6 carburettors.
 

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