Kawi2strokes.com Forum

I just visited the KTOG site, and found a topic about the Carb-Tune mercury manometers. These items are a set of clear tubes, nested in a cavity that acts like a pool, for a liquid substance to be drawn up the tubes, by engine vacuum through inlet systems. The difference in the level of fluid indicates a carburetor unbalance, level, balanced.

These tools are primarily for multiple cylinder 4 strike engines, but, they work as well on two stroke twins and multi's. One difference is, the two stroke will not have the primary vacuum level the 4 strikers have, but, it is adequate enough to use on any two stroke engine.

As we have one carb on our bikes that has a vacuum spud for the fuel valve vacuum diaphragm, I used to add one each of same, to the other two carbs, making it possible to read all 3 carbs primary vacuum levels with the engine tuning, not having to move one test device from carb to carb.

The way to use this device is to connect it to the vacuum spuds on each carb, and run the engine off Prime on the fuel valve, with the bike sitting straight up, and front wheel facing straight forward. Two adjustment phases are needed. First, carbs balanced with their idle screws with engine idling. Second, after setting the idle speed, run the engine rpms up to 2,000/2,500 rpms by adjusting the throttle cable slack adjuster up at the throttle to hold the rpms up off idle. As needed, adjust each cable adjuster on the top of each carb to get the liquid levels even all across the manometer.

Then, reduce the cable back to the correct clearance, done, finished with adjustment. There used to be a service bulletin on changing the vacuum spuds on Zi bikes, that threaded the head, and installed a factory threaded spud, after the pressed in at the factory ones fell out. I used these, but, any threaded in hose spud the correct spec, that threads into the carb boss on the side of the bore, would work. I also used the factory Z1 rubber spud covers, straight off the stock street bikes, never had one fall of, blow off, rot off.

I have also used the drill bits in the bore, fingers on the slides, hold your hand just behind the pipe and feel the exhaust intensity, and every other method known to man method, Uni-Syn, and, when done right, the Uni-Syn works well, but, this one with the mercury manometer, IS the best so far. ALL my twin and multi cylinder two strokes have these spuds and covers on them, including my two RZ500's, ALL my race bikes, 2 and 4 stroke, and they make carb synch a lot more civilized. I build my own 12 cylinder manometer, also not hard to do, for use in dialing in 12 cylinder Ferrarri, and other multiple cylinder engines, and it works as the Carb-Tune does. It doesn't have to be mercury in the manometer, if you wanted to use root beer, go for it, just has to be a liquid, with a fair specific gravity rate. I had initially intended to build an 8 cylinder manometer, for use on stuff like Hilborn drag racing injectors, when used/converted for street use, to electronic nozzles, instead of the manual ones. I still use it for the 8 stack injectors, and 4 port Hilborn, all sorts of multiple cylinder engines that have one individual throttle plated venturi per cylinder.

We just had a car show I put on here in early June, and one of the cars that drove there was a 1925 Chevrolet board track racer car speedster. The owner is a friend of mine, and I built the engine for it, 1925 Chevy inline 4, 4 striker, Riley 3 port cross flow racing head, special pistons, Winfield cam, insert bearings, counter weighted crank, and one of my MSD trigger only distributors. It also runs a pair of Linkert carbs designed for a 1937 Harley flathead engine, special intake manifold with balance tube between the two inlet sides. I built the identical carbs as well.

When we barked the engine off for the first time, we timed it, then already had my 12 cylinder manometer on it, two lines only. We proceeded to set the idle speed and balance, then, adjusted the linkage between the two carbs, like we would do on a two stroke cor the throttle cables. Took a whole two minutes, and they are dead on balanced, no fuss, no muss, just easy to do, and, done. It took two jetting changes, and drives GREAT.

Main point is, the manometer IS the way to go on any twin, multiple engine.

So, to answer the question that was posed at KTOG, YES, IN MY HANDS-ON, WORKING EXPERIENCED OPINION, THIS ISTHE BEST WAY TO GO FOR CARB BALANCING.

Building a manometer is not expensive, nor hard to do. If anyone wants to hash it out on how to do it, contact me in a PM from thins site, and we can get to getting it done.

Good info but one step left out.... airscrew setting. That should be first.

_________________
Answers are here: http://kawatriple.com/

Great information, Thanks Dave!

_________________
1969 H1, 1971 G3SSA, 1974 G5, 1973 H2A, 1975 S3A, 1975 H1F, 1973 Z1, 1988 HD FLTC, Captain America chopper, 2000 Excelsior Henderson, 1965 Bridgestone BS90

NOPE, I NEVER forget. Air screw setting is determined at the Mikuni factory for the air corrector orifice in the carb, isn't changeable. If the idle air screw needs to be changed, fix the improper pilot jet/needle jet/needle position problem/issue.

Sorry if the top tuners here disagree, but, this is known fact about PILOT AIR SCREWS, has been for decades about both Mikuni and Keihin carbs. Now, there are PILOT FUEL SCREWS, and, they are sensitive to adjustment. There were even "transition" Mikuni's for Kawasaki 4 stroke engines, that were service bulletined for FUEL SCREW adjustment procedures that had BOTH AIR AND FUEL SCREWS. The air scre4ws on the transition carbs had a set air screw setting, variable fuel screw adjustment.

Also, on a LOT of Kawasaki used Mikuni's that had air screws, the boss around the air screw on the outside of the carb, will have a line embossed/stamped into it. That line is to set the air screw for correct air correction of the pilot circuit, and is set by going to an arbitrary setting on the screw specification, like 1 - 1/4 turns out, PLUS aligning the line with the slot, as they are set by flow testing of the individual carb.

And, NO, air screw r4eset ISN'T a function of other parts being used, not pipes, porting, bigger carbs, it is a function of flow of the pilot air orifice as to vacuum pull signal depression past the pilot jet (signal pull strength).

Air screws are set to a spec turn out, fuel screws are the infinitely adjustable ones.

I am sure this will bring giant amounts of stuff copied and pasted off the net, and "Dave is a stupid idiot", but, that is the way air screws work on Mikuni carbs that are designated to have air screws, always has been, always will be. Even today, there are dirt bike carbs that have NO air screw, NO fuel screw, and their pilot circuits are regulated only by the size of the pilot jet.

OK, copy and paste away.

Just get a UNI Sync and be done with it.

_________________
Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Well, I haven't set PILOT AIR SCREWS for over 3 years now, simply because the carbs on my H1 doesn't have them.
Can't say that I miss it

PK

thanks for some great info , always good to read your stuff, urs Al in Aus

In regards to "air screws".
I've posted this before; my dead stock H1D did not change idle quality very much at all with turning air screws.
Same thing after I rejected for pods.
My H2 with Denco's reacts the same way although I think the pilot is slightly fat.

Has anybody had significant difference in idle quality say between 3/4 turn to 2 turns out?
I get a slight variance but nothing drastic.

Have been thinking it was just me.

_________________
There are only two types of motor sport racing:
Nitro and everything else
(Sometimes referred to as fast and slow)

A lot depends on the motor mods and pipes. Sometimes there will not be a lot of variance (which "usually" means the pilot is out of tuning range, not always) and some where a 1/4 turn, you can see a change.

_________________
Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Although it is a fine tuning tool, the Uni-Syn is a lot harder to work with than a manometer is, that IS fact.

Funny thing about stock vs "modified" engines and our carbs, air screws stay the same for the most part, only the pilot jet orifii area, and, air corrector fixed orifii area change. As I said,m if the air screw must be set differently than the factory specified, fix the pilot jetting, it ain't right.

Interesting about those carbs that don't have air correction screws, one would think, from some that say, that the carbs wouldn't work without them, but, there they are, no air screws.

I also worked for 4 - 1/2 years at Holley carburetors, making split duals out of 1150 cfm Dominators. These were done for wide Pro-Stock manifolds, for MOPAR Hemi, Chevy big block "Porcupine", and Ford "Shotgun" race V8's. I also was a carb tech, went to all the races, did jetting, development, all sorts of stuff on carbs. NOT much difference in theory and application tech between a Holley vs Carter vs Mikumi vs Keihin, etc.

Carbs are interesting things.