750 twin pilot screws

I just spent a good hour trying to search for the answer to this, and finally decided to ask and get it over with, as it is a simple thing.

On the 79 twin pilot screws, is in leaner, out richer, or the other way 'round?

I have some popping on deceleration, but it does not happen if I have the starter circuit (choke) up a bit, so I think I am lean.

Having zero experience with this carb (appears CV), will offer the following while awaiting some actually competent advice on the matter.

Vaguely recall reading somewhere that most pilot adjuster screws on engine side of carb turn in to lean and out to richen (at least on Mikuni VM styles). Opposite where screws closer to intake side of carb.

With pilot adjuster screws on KZ750 twin carbs appearing to be engine side, first guess would be out to enrichen. If wrong, won't be the first time memory and logic(?) have failed me. :lol:

Post edited by: Patton, at: 2007/05/19 07:39

Post edited by: Patton, at: 2007/05/19 07:51

EsaPro wrote:

I just spent a good hour trying to search for the answer to this, and finally decided to ask and get it over with, as it is a simple thing.

On the 79 twin pilot screws, is in leaner, out richer, or the other way 'round?

I have some popping on deceleration, but it does not happen if I have the starter circuit (choke) up a bit, so I think I am lean.

In is lean, out is richer.
Make sure your floats are adjusted correctly first!

Thanks Biquetoast, just what I needed. Patton, I do not know if these are CV or VM, or what that even means! :lol: The book says they are Mikuni BS38's - I probably should have said that initially, sorry.

Make sure your floats are adjusted correctly first!

I know I need to do that, but I am somewhat put off on how. I presume a short piece of tubing that fits in the drain hole and hold it again the carb body, right? The FSM says the fuel service level should be "4.5-6.5mm below from the bottom edge of the carburetor body to the fuel level". Then in the carb spec chart, it says fuel level (from bore center) is 31mm, give or take 1mm. I am cornfused. :blink:

Is it possible to do this dance without the lather, rinse, repeat process of checking the level, taking off the carb, adjusting the tang on the floats, putting them back on, re-check the level, taking off the carbs, adjusting the tang on the floats.... :S

Hmm... I think I hijacked my own thread. DOH! :pinch:

Thanks guys.

Regarding fuel level, I can tell you what works for me on the 79 BS38 CV (yes the carbs you have are CV type) carbs of the 750B4.

I flip the carb upside down, then set the float so there is 25mm between the gasket mating surface and the top (bottom when carb is upright) surface of the float.

This is not the "proper" way to set the float level, but so far it has worked for me

And I have "got" to get off of here and go finish assembling my 79 KZ750B4 :lol:

Post edited by: steell, at: 2007/05/19 13:32

I think I might just go and try that now. Thanks steell.

I have got to stop cleaning house (mother-in-law is coming home with wifey Monday!) and work on my B4. But all I wanna do is ride - it's sunny, breezy, and 71 degrees right now!

Here's my understanding --

Constant velocity (CV) carburetors common in street bike applications are intended to produce smooth acceleration and reduce engine bog. CV's prevent an engine from being fed more fuel than it can handle, achieved by using intake vacuum on a rubber diaphragm. Whereas the VM carb permits direct throttle slide control by hard cable connection without any diaphragm.

VM refers to a round slide carb, but am uncertain what the initials VM stand for.

OK, I did the float level as steell recommended, the set the pilots 1 1/2 turns out. Still popped a bit, so I backed them out another 1/4 turn, and that did the trick! Idles schweet too! Here is the highly specialized tool I developed for the float procedure.




Thanks guys!

EsaPro wrote:

OK, I did the float level as steell recommended, the set the pilots 1 1/2 turns out. Still popped a bit, so I backed them out another 1/4 turn...

To be honest, I've done both of my 750's floats this way too. It works perfectly for me too, but you should always validate that the level is correct once on the bike with some host and a fitting.

My pilot screws are about 2 or so turn out. I can't remember where they are exactly, but I do remember that they are different between my two 750s. Weird.

It is the "fitting" part that is the problem, Biquetoast. I did find some tubing that is the right size to actually "screw" into the hole. Is there a way to make a fitting? It looks like if I am handy with a small drill, I could fab one up using a screw / bolt of the proper size (Drill down the center, then into the side), but I seriously doubt I am that steady!!

Sometimes I wish I had a shop and a drill press (and a table saw, a lathe, router table, well, bloody everything!) :woohoo:

EsaPro wrote:

It is the "fitting" part that is the problem, Biquetoast. I did find some tubing that is the right size to actually "screw" into the hole. Is there a way to make a fitting? ...

Ok, yeah well, you caught me again. That's what I do, too.

The problem is, you must "fix" the position of the plastic tube so it does not move. The fuel level cannot be trusted if it moves.

"fix position" - is this more than simply holding the end of said tube up against the carb body? I am picturing about 4" of tube, stuck in the float drain screw hole at the bottom of the bowl, and me holding the end up (as still as humanly possible) to the carb body. This would give a U-shaped tube, and gravity does the rest. Right?