colortune VS airflow syncronizer

[strangethursday]

I'm about to buy something to tune my carbs (triple webers) & thought of something. When using something like a unisyn to tune, you get all the carbs flowing the same cfm which in my mind might not actually be optimal. Now with a colortune you get ur ratios perfect (well atleast very close). The reason I think this way is better for me at the moment is because I don't plan on buying any jets or anything else right now & I think the individual requirements of each cylinder will vary slightly. So I'm leaning towards buying the colortune for now. It seems to me that the unisyn type would be better suited for testing the airflow requirements of ur engine. For instance if you have to step up in carb size because ur engine is running out of breath up high.

 

Any thoughts or experience on this any wants to share?

[naviathan]

You should actually use both if you want a proper tune. Keeps everything balanced and burning clean.

[strangethursday]

Can you be more detailed? If ur afr is perfectly tuned for each cylinder than how would cfm matching on each do that? I think varibles such as spark, combustion chamber, airflow getting to the carb, etc being slightly different in relation to each other would mak the color tune method more precise. At least with something like tripples. On a car that basically has less than 1 carb per cylinder I can see there is more benefit from using both methods but I just don't see it for other than what I mentioned b4.

 

Thanks

[ktm]

They are two entirely different tools used to "measure" to different parameters in your engine. The unisyn measures airflow, the Colortune "measures" air/fuel ratios. You should use both to properly tune your car. Do you need to use a unisyn? Yes. Do you need to use a Colortune. No, however, you will have no way to 'precisely' (I say 'precisely' because you are not actually measuring your A/F ratio) measure your A/F ratio.

 

The purpose behind the unisyn is to synch the airflow between the carburetors. Once the airflow is synchronized, you can then use the Colortune to adjust your fuel, but either adjusting the mixture nuts, or changing jets/needles.

 

Others will use a narrowband O2 sensor to measure their A/F ratio.

[strangethursday]

I see what ur saying. I'm fairly new to webers. I have to buy that tuning book from pierce soon also. Is the amount of fuel goin thru the carb controlled soley by jetting or can it be adjusted a little by

other means?

 

NM I missed the part about mixture nuts at the end.

 

I really need to get a book or 2.... or 6..... lol

 

Thanks

[ktm]

I am not familiar with Webers. On SUs, you adjust the mixture using two nuts located on the bottom of the carburetors. If you put SUs on an L28, you may need to switch to a larger needle (other than the stock needle that came with the SUs on an L24) otherwise you could start to lean out at higher RPMs.

 

There has got to be a similar way to adjust Webers. Think of the needles/jets as coarse tuning and the mixture nuts as fine tuning.

[Tony D]

Think of it this way:

You flow 12cfm in one cylinder, and in the one next to it you flow 10cfm.

(Unsynchronised)

So you set your jetting so that with the colortune you get the optimum AFR in each cylinder respectively.

 

The one with 12cfm is flowing more 'pounds per hour' of air, stands to reason, right? So that means it needs more 'pounds per hour of fuel' to get that correct AFR.

 

And you know that (roughly) for every half a pound of fuel burned, you get one horsepower (This is a REALLY simplified version so he can follow it, don't crucify me for oversimpliufication!). Meaning that the cylinder flowing the ideal AFR for 12CFM will make MORE horsepower than one flowing only 10CFM.

 

It's roughly the same as having 6 single-cylinder Briggs-n-Stratton Lawnmower Engines running all onto the same crankshaft: you don't want one at 1/2 throttle, three at wide open, 2 at idle, and the last one 3/4 throttle.

 

This imbalance in flow will impart torsionals into the crankshaft. A million cycles or so, and things can break! That's extreme, but hopefully you see why you want airflow equalized between all cylinders.

 

And a piece of advice, get the WEBER synchrometer with a dial and numbers on it---a Uni-Syn will choke out a cylinder if you hold it there too long. The Weber tool is actually an airflow meter, and you can leave it there forever and not affect how the engine is running. You want to synchornise the airflow at idle, and it's hard as hell to check off-idle (say 2000rpms) for proper synch with a UNi-Syn---with the Weber tool, you open another orifice and just read the number, easy peasy!

 

Hopefully that explanation why you need both CFM and AFR to be matched.

[strangethursday]

THERE WE GO! Damnit I hate mondays. It just was NOT clickin! Alright. You mean don't use the 1 that's just a flat piece with a glass tube? The 1s that look like they were made in 1910?

[TBK]

Ok I havw the unisinc, Where do I get the weber flow meter???

[strangethursday]

This is the 1 I think he's talkin about

 

http://www.racetep.com/weberX.html#websynch

[Sven]

TonyD, I have a question that you'll probably answer, since you're the resident sidedraft expert (who now uses custom EFI setups - is there a message there?). Anyone else that has knowledge on carb measurement, feel free to chime in...

 

How do these "sync meters" work, and what is their construction? Some background; I am a HVAC Test & Balance Technician. I measure airflow on a daily basis, and have some extremely accurate and expensive devices at my disposal for measuring cfm, fpm, and pressure. I should have the capability to seriously dial in my Mikunis, right?

 

Is the Weber tool measuring the pressure drop at the carb inlet, or velocity? I'm thinking a homemade "bore adapter" (basically a plate with 6 holes the same size as the carb bores, fitted to all at once so the restriction would be uniform) would accomplish the same thing. This would have pressure taps to orifices on the inside diameter. I would then connect my digital micro-manometer, and take readings on all cyl, one at a time, then adjust & proportionally balance the airflow at idle.

 

-Would this work? If you have any other ideas or suggestions, I'm all ears. Are there any more sophisticated ways of balancing multiple carbs? What did big dollar race teams use way back when? I'm fairly decent at fabbing, and will be picking up my new/old lathe as soon as I get access to a forklift.

[cygnusx1]

More sophisticated? No, but I had much success with a piece of fuel hose to my ear listening to the flow of each carb and adjusting them so they all make the same sound. Personally, I would skip the "high-tech" synchronizer and tune with a heated wideband O2 in the collector and a box of jets and emulsion tubes. I used to set the idle mixtures by pulling off the plug wires one at a time and observing the RPM drop for each cylinder individually. I know it's crude but it works and it's the way the old timer weber guys did it. Weber tuning is more about driveability and throttle response than efficiency.

 

I just my opinion and yes, I like ol' skool.

[Sven]

The human ear is a useful tool. Cygnusx1, I don't disagree with you on the wideband point, but I don't have one yet. Also, wouldn't syncing the carbs be important also, regardless of AFR? Nothing says they will be uniformUnless you mount O2 sensors in every primary tube, you are only looking at a total afr, which could be misleading, unless grossly out of whack.

[cygnusx1]

Well undoubtably you are going to jet each carb the same. So it would not be necessary to monitor each runner with an O2 sensor. Just monitor the exhaust collector under varying load conditions. The only mixture that will be different for each carb barrel is the idle mixture adjustment. You set that with the idle mix screw and pull the plug wires off one at a time to make each one behave the same at idle. Before you do ANY tuning, synchronizing must be done. It can be done well enough with a peice of hose in the carb choke while listening to the other end.

[Tony D]

Yes, they are measuring actual flow through the barrel. The important thing in the synch is not only that all three carburettors are flowing the same (and you can use HVAC stuff, CFM is fine, FPM is fine---so long as they are ALL flowing similarly) but that each barrel in each individual carb is flowing the same! Mikuinis are notorious for sticking and then tweaking their throttle shafts. I have seen VERY serious flow differences between barrels from tweaked / twisted throttle shafts! So that is another check you are doing.

 

As for 'old school' I synched carbs for years using the back of my fingers and judging the 'flow' across and between my fingers. People with a unisynch would literally stomp their feet in defiance as to how I could do that!

 

For years motorcycle guys used multiple manometers to set the balance on thier multiple setups, and I recently bought a Gunson's setup that had a similar float setup to a Unisynch, but used a VERY BIG fixed orifice, and a small tube with floating ring in it---so it can measure very fine differences in airflow while not restricting the flow to any one cylinder. You can leave it connected while the engine idles. So that would be very similar to your setup proposed, Sven. Yours would probably be more accurate. I know with the new digital manometers I have been tempted to hook them up to the Gunsons' setup to actually Digitize the readout. But putting a $500 digital precision manometer kind of defeats the purpose of me buying a 12 Pound Sterling Gunson's Plastic Synchroniser Gadget...LOL

 

I like the Weber meter because it gives a number and does not alter the airflow through the cylinder. If you use a Uni-Synch to get a decent reading you end up choking the cylinder you put it on---so you either take a series of quick 'flash readings' and move on...or you risk the engine slowing down and giving you a false low reading. The Weber unit can sit there all day and not affect how the engine gets it's air. And to do an off-idle check---say at 2000rpms---with a UNi-Synch? FAGGADEBAUDIT! WIth the Weber, you pull a plug and it rescales as more air is bypassed around the sensing element, giving you a reading you can read cylinder to cylinder without killing or altering the speed one whit. Actual measurement of the idle, AND OFF IDLE synch of the carbs!

 

As for doing a cylinder balance test that is how I still do it. Curiously now I do it by removing injector connections! Singles out a dirty or misfiring injector QUICK!

 

I have also used the garden hose method. Still use it today for detonation checks while driving... Imagine that sight driving down the road and passing a guy lugging his turbo Z up a hill holding a green garden hose to his ear straining with a look of consternation on his face!!! LOL

[Sven]

Thanks for the input Tony. I've scoured the internet and found and saved all your carb tips I could find. Good stuff. I'm going to have to check those throttle shafts. I have this nagging suspicion my linkage isn't even opening the throttles fully. That's going to be a pain in the ass to check w/o a helper.

 

I've got an idea in my head for a pitot/airfoil "manifold" much like I mentioned in my earlier post. I need to draw it up. I'll try to dig out the manual for the micro, as I seem to recall the Shortridge being accurate down to around an inch dia duct with the itty-bitty pitot tube. The only issue is, you need a decent pipe run to achieve laminar flow that is repeatable. A nice rule of thumb is three diameters before your measuring station. I'm not sure I can fit that between my carb inlet and strut tower. I might be taking this too far, if little red balls in clear plexi-tube have been good enough for so long...

 

I also thought of buying a Uni-Syn or Weber meter to reverse engineer it, but I'm cheap in odd ways (spending $400 on brake calipers is nothing, $30 on a carb tuning tool bugs me for some reason).

 

-Say, can we get a picture of you on a detonation run... just to, uhh, show us how it's done?