homemade carb sync ?

The problem with the 180° bent tube manometer is the fluid geting sucked into one cylinder so quickly the cylinder hydraulic locks! You don't want that. Use a jet or small orifice at the top of the tube so the liquid can't get through with any speed and fill the combustion chamber. Also, the engine should already have a crude carb balance as the manometer is for fine balance.

A simple single vacuum gauge is a nice balancer. A gauge manifold is made of inexpensive aquarium parts which opens one side and closes the other. As has been mentioned, the pulsating vacuum still needs to be damped with a small jet or adjustable orifice of some sort.

Tom Graham
 
From my personal experience on Saturday....

I used 20 feet of 5/16" OD, 3/16" ID tubing...filled about 1 - 1/2' with red transmission fluid.

Prior to hooking the tubes to the barbs, I adjusted each of the 34mm Mikunis to 3 turns out. Hooked the tubes up to the barbs...fired it up. It worked tremendously...with a few turns of the synch screw, we had an even setting.

This is a great tool and cost me about 6 bucks! Thanks for all the help!
 
I know this is an older thread but I was looking for some tips on syncing. What of the following things are you looking for when syncing:

Even displacement of the fluid (this is probably a definite)
Same speed between in the movement of fluid.

I have a feeling I just answered my own question. Any tips on syncing would help. I'm sure i've gotten it pretty close a few times but I'm such a OCD perfectionist that I can't stop until it's "perfect", thanks in advance for any advice.

EDIT: I'm using a diy manometer like those have described here.
 
It's not unusual to have a fair amount of flutter at idle, (about 3-5 fingers worth sometimes) but if it does not smooth out at about 1500 rpm on up, It's usually an air leak.
Make sure and get the tubes pulled back out of your way. If you yank one off, the other can draw your fluid in, and sometimes the air leak does not warn you fast enough, and in she goes. The ATF fluid can be ingested into the intake if something goes wrong, and it will make stinky white smoke, lube your top end, and quite possibly foul the plug, but otherwise it won't hurt anything.
 
Thanks guys. I'll give it another go here tomorrow. Is it typical for the two carb idle screws to have a great difference between them? One side pulling more than the other? In my case the left hand side?

A bit off topic but related when running dellorto phf's from mikesxs (l/r matched) does anyone bridge the carbs across the barbs, read that once.
 
On my manometer in use the fluid moves up and down about 3/4 inch. Up on one side down on the other. This leaves a bit of fluid on the tube so you can see the upward end of the movement with a very light red color. Tjhe lower is solid ATF red color. I adjust so the edge of the light red lev els match as well as the solid red colors match. The amount the levels vary can be adjusted by restricting the vaccumm to the manometer. Some use very small idle jets in the lines. XSJohn liked the air controllers for fishtank air lines.
Bridging the vaccum lines at the carb holders helps as a last step in carb tuning. Bridging the vaccumm ports in the carbs, may do the same.
Leo
 
I have a set of Mercury sticks I've had forever. Yes it's toxic as hell and $100.00 a pound (0.8 fluid oz) but nothing works better. Sadly, you can't buy them anymore. If anybody knows a source let me know.
 
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You can still buy the same sticks from Motion Pro. You can buy vials of mercury on flea bay, but they are pricey!
I never bought a set specifically because of the hazards of having it in your house.
 
rebel542 said:
I have a set of Mercury sticks I've had forever. Yes it's toxic as hell and $100.00 a pound (0.8 fluid oz) but nothing works better. Sadly, you can't buy them anymore. If anybody knows a source let me know.
Click to expand...

A simple plastic u-tube, using Stabil, or ATF or similar, is 13 times more accurate than mercury. Total cost about $6 to $8 and non toxic. No one should be using mercury these days, when there are better, cheaper and safer choices.
 
I don't know about more accurate but your way is cheaper and safer. I do a lot of 4 cyl work so the stix are the only way to go for me. I'll give it up when they pry it from my cold dead Mad Hatter hands. Thanks for the info.
 
You've got a valid point Gent and I agree. I don't advocate guys looking for mercury to sync carbs. I've just had these things forever and they work great on all engines. Just old school I guess.
 
In reference to a set of carbs from '79:
gggGary said:
Then you should have the barbs that feed the vacuum petcocks on the intake spigots use those for your manometer. You can turn the petcocks to prime to get fuel flow.
Click to expand...


Where do you hook this up to on a bike that doesn't have barbs on the carb boots?

I'm running '77 38's, JBM manifolds so no barbs on the boots. Haha, kinda sounds funny.

Do the tubes for the manometer hook up to anything in this pic?
71fc1607.jpg
 
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Wait, I just figured it out.

http://www.amckayltd.com/carbguide.pdf

Post 10, part 9. Here's the picture. Look at the two unlabeled arrows. They're pointing at the same port on both carbs, one has the barbed attachment screwed into it and one still has the regular screw.
He's using a standard M6 x 1.00 with a barbed end and an o-ring.

BS38MixScrews.jpg


Viola:thumbsup:
 
Good on you and your search abilities! Some years of BS38's have those ports with plugs in them, others don't. A few have drilled and tapped holes in the intake passage on the head to get a vacuum reading when they had carbs and manifolds without ports.
Early (1970-71?) bikes have the two manifolds connected on the head so you can't read them separately.
 
Another little tip is placing cigarette filters in the tubes (ones you get for rolling them yourself) cheap solution to slow down the movement of what ever fluid you got in the tubes. Will keep you from lubing your top end!
 
so i am trying to syncing carbs with oil filed u-tube and they are not equal so do i turn down the vacuum or do i turn up the suck. or alittle of both?

when bike is idling the carbs are uneven one way and with throttle they reverse know what im saying? is that normal?

cheers!
 
hello all so as the title says i had a loss today but also a big win in firing my bike up.
i put together a manometer copy of pic below, im running brand new vm34s from 650central & think syncing is a must.
the 34s i have have the vacuum barbs on the body of the carb not on the ruber manifolds & i always thought the carbs would suck the fluid in the clear hose straight into the carb....Thats exactly what happend :doh:
i used fuel injector cleaner as it was red in colour & i thought this may happen.
so im feeling like a complete dope thinking ive missed understanding a critical step to this way of syncing.
please help! cheers guys
 

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