TOPIC:

With the adjusters hiding under the carb tops, how do you run the bike with the adjusters exposed, in order to sync the carbs, without creating an air leak past the slides?

glenncarpenter wrote:

With the adjusters hiding under the carb tops, how do you run the bike with the adjusters exposed, in order to sync the carbs, without creating an air leak past the slides?

Until WG or other worshipful guru chimes in with true gospel (as opposed to Ned-In-The-Primer -- that being me) the only carbs which should be bench synched only are the smooth bores (that being the only carbs where air leaks screw up any synching endeavor with the carb top covers removed). So without being able to relay the technical reasons, it is perfectly okay to synch your stock carbs with the top covers removed as they are apparently just there for the purpose of keeping crud on the outside. From my lowly novice viewpoint, you could just motor happily onward without most stock carb tops (except for the incoming crud of course). Happy Synching.

Post edited by: Patton, at: 2006/10/20 00:54

Just pull the tops off and synch 'em up. Not enough air will get past the slides to make any difference. You may need to hook up an extended line to your fuel tank to keep the engine running long enough to do the synch. I set my tank on the seat sideways, then used some extra fuel line to hook it up. You might want to use a couple bungee cords to hold the tank in place. If you're really good, you can synch it with the fuel that's in the floatbowls. You will need a gauge set to do it right.

there are plenty of examples floating around out there of a DIY vacuum gauge though..so don't think you *need* to spend the $100+ on a manometer.....

Unless you need extreme performance, a basic one will work well.

I use an old set from a factory i used to work for.
how do u make a simple set?
say, the most accurate simple set.

I think with using vacuum gaugers its getting the carbs balanced, so if the gases that may pass around the the slides is equil then no drama with the caps off, ajust the carbs to have the same vacuum, then job done, as long as the compression is faily equil, jetting is resonable and the engine is in good running condition

jimmy

The VM family of carburetors including the smoothbores already mention have mechanical slides. That is, the throttle cable pulls up on the throttle bellcrank which is bolted to the slide rod as are all four carb slide mechanisms. The tops being on or off make absolutely NO difference to the function of the slides... You can run the bike without the tops on any VM carb assembly including smoothbores.

Does that answer your question?

wiredgeorge wrote:

The VM family of carburetors including the smoothbores already mention have mechanical slides. That is, the throttle cable pulls up on the throttle bellcrank which is bolted to the slide rod as are all four carb slide mechanisms. The tops being on or off make absolutely NO difference to the function of the slides... You can run the bike without the tops on any VM carb assembly including smoothbores.

Does that answer your question?

Thanks to WG for a real world report okaying vacuum gauge and carb stick synch on Mikuni smoothbores. Am glad to learn this after having been faked out by the recommendation on page 13 of Sudco's Mikuni Tuning Manual (4th edition) that smoothbores only be synched mechanically because top cover removal causes a large vacuum leak and various other reasons. I've been relying only on the mechanical bench-top method, but now feel free to fine tune my Mikuni VM29 smoothbores while running with carb tops removed using a vac guage or carb stick. Book learning loses another round to real world experience. Happy Trails from Ned-In-The-Primer.

Looks like unanimous consensus that if any air leaks past the slides it just doesn't matter enough to make a difference. Thanks to all.

I've managed to get through twenty years of wrenching on bikes without a set of carb sticks. Just ordered up a set an hour ago.

I decided to make up my own gage set. Picked up 4-2 1/2" 30# vac gauges for $14. on ebay tinyurl.com/u25fc . Just need to round up some restrictors and I should be ready. I'm sure it's not going to be the most accurate but maybe it will be good enough for shade tree work;)

Mikes82KZ1100 wrote:

I decided to make up my own gage set. Picked up 4-2 1/2" 30# vac gauges for $14. on ebay tinyurl.com/u25fc . Just need to round up some restrictors and I should be ready. I'm sure it's not going to be the most accurate but maybe it will be good enough for shade tree work;)

i made my own and theyre plenty accurate. hook each one up to the same vac source to see if they all read exactly the same. if one isnt you can open it up and tweak the bourdon tube inside to get it right. i used pnuematic flow control valves for restrictors...good price on those youve got there...steve

Thanks for the tip Steve.

gratuitous shot of the homeade unit...steve