Topic: Vacuum Reference ports for aftermarket carbs

[Turbogrimace]

I am running a set of VM29's and want to vacuum balance them.  I bench synced them and found that they were quite off.  After the bench sync, they ran a lot better, but there is still a noticeable imbalance. 

Does anyone have any experience or suggestions with adding vacuum reference ports to the intake boots, carb body, or the head?  I have some threaded 5 mm vacuum bungs that I was planning on using.  My thought was to machine a brass insert with external threads and a nut.  the insert would go through the carb boot with sealant and then get bolted snug with the nut on the outside of the boot.  Ping the threads above the nut to prevent it from walking out.  I would tap the insert with 5 mm threads to accept the vacuum bungs and then plug with a rubber end cap.  Has anyone added a vac port to the boots before?  Any problems?

[Tintop]

Try this thread, should help - http://forums.sohc4.net/index.php?topic=75362.0

[Turbogrimace]

Thanks for the link.  If that's the case I could just thread/glue these into the boots. 

http://www.jetsrus.com/individual_parts/950_722_su.html.

Any thoughts on a good flexible glue/sealant?

[bwaller]

Because you have to run the 29's with the caps off my understanding is a good bench sync is probably best. Readings otherwise may be skewed.

Edit, I run these on my race bike and it even idles well with only a bench sync. I did install vacuum tubes (550) but never used them.

[MCRider]

Because you have to run the 29's with the caps off my understanding is a good bench sync is probably best. Readings otherwise may be skewed.

That's what it seems to me. First hand experience, I ran them for 15+ years, 50000+ miles and never balanced them. Too daunting.

Putting fittingss in the boots to take a reading might be a good thing. Then bench balance, reinstall, rinse and repeat.

[Mitchell]

you  could'nt use a gauge that fits over the mouth of each carb? like this one below and do it one carb at a time.

http://www.ebay.com/itm/Weber-Dellorto-Mikuni-SU-EMPI-Carb-Carburetor-Sync-Synchronizer-Synchrometer-NEW-/330917359139?pt=Motors_Automotive_Tools&hash=item4d0c362e23&vxp=mtr

[MCRider]

you  could'nt use a gauge that fits over the mouth of each carb? like this one below and do it one carb at a time.

http://www.ebay.com/itm/Weber-Dellorto-Mikuni-SU-EMPI-Carb-Carburetor-Sync-Synchronizer-Synchrometer-NEW-/330917359139?pt=Motors_Automotive_Tools&hash=item4d0c362e23&vxp=mtr

Those that have tried report fouling by the frame tubes. But the proper size/shape of gauge may work, trial and error.

More elegant is the nipples in the manifolds with gang of 4 gauges. Always thought that looked cool.   

[Tintop]

The Weber syncometer is a great tool (have one) as it doesn't restrict air flow.  However it is designed to work with stacks, and as mentioned the frame will interfer with getting proper postion & seal.  The 4 gauge method works best for a 4 carb setup, but if bwaller hasn't needed more than a good bench sync I'd go that route.

[Turbogrimace]

Because you have to run the 29's with the caps off my understanding is a good bench sync is probably best. Readings otherwise may be skewed.

Edit, I run these on my race bike and it even idles well with only a bench sync. I did install vacuum tubes (550) but never used them.

What do you mean by "run the 29's with the caps off"?  I synced them pretty close with the end of a small drill bit.  The No. 4 and No. 2 carb were a tad high and this could be seen in the spark plug colors.  They were not developing as many deposits when running rich, but would come out a tad damp after idling.  As for the Syncometer, My oil tank sits about 1" from the inner edges of the 2/3 carbs.  It was hard enough to fit filters and stacks, so a gauge is out of the question. 

After the bench sync, the plugs started looking similar; though I feel like there's more to be had with some vacuum balancing.  Maybe a little more crisp throttle response and less occasional hesitation when cruising with just a slight throttle turn off idle.

[trueblue]

No different than the PD carbs in regard to removing the cap. I just take note of which one is reading high or low, shut off the bike and adjust.  Restart and repeat, normally only takes a few goes to get it dialed in.  I have a set of CV mikunis off a GS650 that I have modded for my 650, you can drill a port anywhere in the intake as long as it is between the slide/butterfly (depending on carb type) and the intake valve.  I personally drilled and tapped into the body of the carb.

[Turbogrimace]

Ohh hahaha the top cap.  Yeahhhh,  derr.  I used to run the late model PD's on a few bikes.  I'll add some bungs to the boots to get them dialed in nicely.  It'd be nice to tap the carb body or the head, but both of those locations are pretty crowded.

[trueblue]

On The CV's there was a nice spot on the top, one of the carbs had a tube running off the top for the vacuum petcock and the rest had a nice little flat spot there.

[Medyo Bastos]

julio was working on making some adapters with nipples for them a while back.  hit him up!  btw, i said nipples!

[MRieck]

I ran insulators with small  brass hose menders for years ( like over 20) so I could synch CR's. I have a set that are in excellent shape if you are interested.

[Turbogrimace]

I am interested.  you have my email!  Toss me some pics and info.