TOPIC:

ok, guys and girls. i am back onto the street fighter project, i may finish this before i turn 40 (i doubt it).

anyways,carb synching. what are you really trying to get here? is it max vacuum with out bogging? i am a chevy guy here and adjusting carbs (edelbrock holley etc.)is easy for me. i just try and compare to car or truck carbs.

let me know, thanks

i also work on semi's so we do things a little different at times.

to find out if an injector is not running properly we use the exhaust temp right off the head. so about 1 " from head on manifold. this can really only be done when it is cold (the engine that is) you see how fast each one is warming up compared to the others. temp differences, works good!!!!!!!!!!

just wanted to add that,

but i really just need to know the answer to my first post,

thanksB)

Hi sbjones,
I bought a set of 4 vacuum gauges last summer to set up my carbs. Here's what I learned. My bike has four carbs, one for each cylinder. Each carb has a slide to control the volume of fuel and air entering each cylinder. Each slide is connected to its own lever that in turn is connected to a common bar. This bar is connected to the single throttle lever that is operated by the throttle cable(s) which is in turn are operated by the throttle on the right handle bar. You probably fingered out all of this stuff already but I'm just trying to be complete here.

Who cares? The motor does. Well it was found that the relatively small difference in how open each slide is makes a significant difference in the volume of fuel and air that will get into each cylinder and therefore how much each cylinder will pull or contribute to the load... the rear wheel in this case. While I haven't read this anywhere, it seems reasonable to me that any cylinder that is pulling more or even less than the others will slightly unbalance the crank and probably set up destructive vibrations that can be transmitted to the crank, the bearings, the transmission and ultimately to the rider. Seem reasonable so far?

The vacuum gauges were great for my bike. It ran soooo much better after I adjusted them this way! Mind you, I had done used the drill-bit-under-the-slide method before and I thought I did a fair job because the bike ran much better. But it was nothing compared to how it ran after using the gauges... or maybe I wasn't so great with the drill bit method.

That's the way it played out on my bike anyways.

By the way, thanks for the tutorial on big block injector troubleshooting... cool stuff! I learn so much on this site.

Best of success and have a great riding season.

Post edited by: bill_wilcox100, at: 2007/04/23 03:59

Post edited by: bill_wilcox100, at: 2007/04/23 04:00

Just to elaborate a little, one carb is fixed, non adjustable, that one is the base carb, the others are adjusted to try and match the vacuum on the base carb.

The point is to make them all equal, not to go for some maximum figure.

I see where that point didn't come across so clearly, so thanks!

It also makes sense by the way, because I seem to remember that all 4 carbs actually had individual adjustments... but I did end up only having to adjust 3 out of the 4. I remember that I ended up having to adjust the idle screw a bit because that was out of adjustment as a result of the carb sync'ing. Then I had to do a little adjusting of the throttle cables to make sure they weren’t too tight or too loose. So sure, it all makes sense.

Good stuff... thanks!

Darn... double post!

Post edited by: bill_wilcox100, at: 2007/04/23 10:21

o.k just call me an idiot. but i still do not understand.

let me explain. maybe i am over thinking this.

where do you start from? all of the carbs can be adjusted under the top caps (26mm). so where is the starting point? is this where the drill bit deal comes into play. is that my base line? and then just match all of the carbs up to this setting by vacuum reading at idle.?

i guess what i am asking is where do you get your base line reading?

again, sorry for being an idiot. but like i mentioned before i am a truck guy, so like a holley, you get max vacuum at idle, with out dropping idle rpm. and then work your way to the other venturies. so you can start with any side of the carb.(basically)

The drill bit is for your rough mechanical sync. That is where you start from.
After that you do the vacuum sync. My understanding is the actual readings don't matter at all. All you are trying to do is get them all the same. So you don't worry about what the meter actually reads, you just try to get all 4 carbs to read the same thing.
Ron

Sorry, I'm out of the country right now so I can't reach my manual to get the step-by-step on this. If you don't have a manual this would be a good time to get one. There's a lot of good stuff in there.

To make a long story short: You take your size (someone help me out here with the size) drill bit and slip it under your slide, if it will fit. You adjust the corresponding slide height screw so it just allows the bit to slide in then lock the adjustment down without letting the adjustment change. Check that the bit still fits in the same way. You repeat for the remaining 3 carbs. Then you can do the idle screw adjustment and the throttle cables adjustments. That's what I remember doing on mine.

Best of success!

On a four cylinder with constant velocity carbs; either CV34 or BS34 or most any other cv type carb, there will be three sync pots. There is NO reference carb on any constant velocity type that I know of (four cylinder that is). The reason for three sync pots is that you FIRST sync 1 to 2. Then you sync 3 to 4. Then you sync 1&2 to 3&4.

On four cylinder mechanical slide carbs, such as the VM series, MOST have independent slide height adjusters except for the early Z1/Z1A VM28SC. For the independent adjusters, you adjust each to gain the same vacuum level on a set of manometers. On the early Z1 type, the #4 carb is "reference" as it can't be adjusted (well it can be but not according to the book). It has a hex fitting hiding the adjuster... you bench sync those carefully making sure that the #4 carb is within range of operation of the idle adjust knob and then sync the other three to it.

Post edited by: wiredgeorge, at: 2007/04/24 12:59