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Tuning motorcycle carburettors
6

Tuning motorcycle carburettors

Tuning motorcycle carburettors

(OP)
Want ways of tuning and getiing air fuel mixtures on inline constant velocity carburettors to there peak performance, without the aid of dyno.

RE: Tuning motorcycle carburettors

2
A wide band oxygen sensor for each carburetor and a data logger.

I will take a wild guess that it is one carburettor per cylinder with IR manifolds.

Slightly cheaper option is one or two oxygen sensors and an exhaust gas temperature sensor on each pipe with a data logger. Move the oxygen sensor around for comparison tests to get a base line for the EGTs.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Tuning motorcycle carburettors

Of course I have been jetting carbs "by ear" for performance for some 50 odd years now and I can tell you that, even with all that experience, I would still recommend the dyno to set up the carbs on a bike...Trust me, it will be cheaper and faster to get it right the first time and avoid the risk of internal engine damage.  Dyno time for bikes may take a little looking but,  Time to jet a bike is minimal and dyno time is usually negotiable, depending on your bike and personality. I have seen "jetting check" adds for $35/hr. in some mags (I just had a portable dyno set up at my shop and did a break in and jet/power check on a new engine for my Mini at a cost of $125/hr.).

If you still insist on doing it like I did it in the 50's, try the local magazine/book store.  There is enough on this subject to keep you busy for months! Reading plugs correctly is an easy thing to learn but requires LOTS of experience to be 'spot on'.

Rod

RE: Tuning motorcycle carburettors

(OP)
Thanks thats what I thought, I'll try and find someone with a dyno near me.
Does anybody no where the closest motorbike mechanic with a dyno to Gembrook, Victoria/Australia.

RE: Tuning motorcycle carburettors

http://www.dynojet.com

They have a dealer resource link on their page which should direct you to the nearest shop carrying their equipment.  

That or find a local racetrack.  Here in the states, you can often schedule dyno time on race weekends as at least one local shop will have one there.

RE: Tuning motorcycle carburettors

I am sure there are plenty in the Melbourne Yellow pages.

Major motor cycle dealers should be able to advise.

Local race bike clubs should be able to advise.

The administrators at Phillip Island should be able to help.

Until I looked it up, I thought you must be out in the boondocks to even ask the question, not just out of Melbourne.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Tuning motorcycle carburettors

(OP)
Thanks I found a couple on the internet yesterday just waiting on prices.

RE: Tuning motorcycle carburettors

just curious, Why do you feel a dyno is better then wide band  O2 and exh gas temp readings?

I have a small 8 chan data logging set up that I use to setup fuel injection bikes when custom tuning.

and have used it on the "older" stuff too


RE: Tuning motorcycle carburettors

Likely cost.  If you're just looking to tune a carbuerated bike on occasion, I'm guessing the sensors and channel are going to set you back more than $60 (approximate cost of a dyno run up here...over $100 if you're tuning with one of the shop guys and making multiple runs to get your curve the way you want it).  

The racers I know running FI bikes are using mapping software with their Power Commanders, then verifying the bands through their practice sessions.  Frequent dyno runs are a bit pricey for club racers w/o serious sponsorship, at least in this neck of the woods.

As an FYI for me, how much did your data logging combo set you back?

RE: Tuning motorcycle carburettors

I have about 1200.00 into the data logger if you include the 8 Exh gas temp sensors and a few othe misc sensors I have, not including the lap top that can be connected to it for real time monitering on my car tuning projects.

I guess my point is a dyno will tell you when your making peak HP, but Peak HP, comes in the "lean" area of A/F ratio
so you still need some sort of A/F metter with a Dyno to be safe. ( I tune Supercharged Mustangs, some with up to 40 psi of boost, small miscalculations can = many broken parts) with my setup I can look at EGT, Calculated A/F ratio thru the wide band 02, while changing the fuel injector pulse curve in real time (on a car anyway) the data logger works ok on a bike or for monitering on-going performance of a race car.

RE: Tuning motorcycle carburettors

The dyno should have at least a wideband O2 sensor to sniff exhaust gas during the run.  The carbs should be synced prior to showing up at the dyno.  It should also have a good and properly operating ignition system. If you can be fairly certain your cylinders are all breathing and firing in a similar fashion dyno time will be reduced.  If you are showing up at a dyno tuner to fix your bike rather than tune it you will need more than a single O2 and spend a lot more cash in the process.

Many think of dyno time as expensive yet they spend $500 on a pipe, $150 on a jet kit or $300 on a power commander and throw Shite loads of cash into polishing aluminum and painting body work.  Then they say, $250 dollars to correctly set up a power commander or jet kit is too expensive.

Dyno time is cheap compared to what one spends on hot roddding and personal time testing on the street.

Additional note...your peak power will be found at 12.5 to 13.8 to 1.  Not lean at all.  Lean is mean is an old term and will lead to disaster.  If you tune for peak power you will not be lean at all.


RE: Tuning motorcycle carburettors

"Additional note...your peak power will be found at 12.5 to 13.8 to 1.  Not lean at all.  Lean is mean is an old term and will lead to disaster.  If you tune for peak power you will not be lean at all."

in a nut shell..your wrong and right, Peak HP will be achived at 14.7 to 1 A/F ratio the problem is we can not get a homogenous charge(fuel quality is another issue), but I do agree that the range you posted is the typical A/F ratio that most people find there
safe peak HP. on our race motor we have it dialed in to calculated A/F ratio of 14.1/1

street car: 89 Mustang 10.3 @ 132
Race Car: Mustang Pro Comp  6.45 @ 219

RE: Tuning motorcycle carburettors

Am I the only one who uses a Vacuum gauge to balance the carbs and peak the power.

http://www.prnewsnow.com

RE: Tuning motorcycle carburettors

A vacuum guage is handy on occasion.  Balancing multiple carbs is best done, if you have the skill, by sticking a length of small dia. hose/tubeing in your ear and the open end in the 'bell' of the carb.  Old fashioned? You bet.  Does it work?  It has, for me, for 50 years!  I have owned and used several carb balancing devices fron Uni-Syn to an electronic device that reads on a Sun Inst. CRT...I always end up with a piece of plastic hose stuck in my ear and a screwdriver! Just because something is not "new era" does not mean it doesn't work well. The 'old way' has one more advantage, it's a LOT faster. It is a skill (gift if you will) much like accurately setting valve lash...some can, most cannot!


Rod

RE: Tuning motorcycle carburettors

(OP)
Hi,
Thanksagain for every body replying,
I have a dial carb balancer and all the carbs are balanced.
It is the air fuel ratio tha t is the problem because I have put pod filters on the carbies.
I have yet to find a dynotune place that is even remotely interested in answering my emails on pricing & when I could book it in!!!!

RE: Tuning motorcycle carburettors

14.7:1 is stoichiometric (meaning scientifically correct) but peak power never occurs there, as combustion chambers in almost every engine require more fuel for peak power.  Tune an engine for 13.5:1 and measure the torque then lean out fuelling to 14:7:1 and check the power.  You will see a drop in torque.  As you lean out torque drops very quickly.  As you go richer, that max power you will find torque drops off very slowly.

If you have a dyno with O2, you can test this for yourself.  You’ll need an eddy current brake and real time torque reading or a least a programmable dyno to perform step and hold testing w/data logging.  In my case, my dyno is programmable for step and hold, sweep and manual loading on the fly.

Otherwise reference:

The Internal Combustion Engine in Theory and Practice: Vol. 1: Thermodynamics, Fluid Flow, Performance
ISBN: 0262700263 Format: Paperback, 574pp Pub. Date: March 1985 Publisher: MIT Press Edition Description: Revised Edition Number: 2

Internal Combustion Engine in Theory and Practice: Vol. 2: Combustion, Fuels, Materials, Design
ISBN: 0262700271 Format: Paperback, 800pp Pub. Date: March 1985 Publisher: MIT Press Edition Description: 2nd ed., rev Edition Number: 2

These explain the curves of Air Fuel ratios and their effect on power production using very easy to read graphs including those showing combustion pressure and knock.

Sounds like you are in a tough place to get a good tuner.  Keep hunting around to find a dyno with wideband O2 or 4-gas analyzer.  That will get you tuned up right.

RE: Tuning motorcycle carburettors

14.7 is typically the chemically balanced air to fuel ratio for commercially available petrol.

This means that if combustion is complete, all the fuel and all the free oxygen in the air is consumed.

In point of fact, the quality of the mix of air and fuel is never good enough for all fuel and all free oxygen to react or combine in the time the fuel mixture is in the combustion chamber and the piston is in a position to gain from the expansion caused by the heat of the combustion.

To get maximum power, you need to use all the air early in the power stroke so the pressure gets maximum exposure to the piston as it moves down. This requires extra fuel so there is a better chance of some fuel molecule being close to all the oxygen molecules, but not so many that it displaces to much air, or so that the combustion is so incomplete that soot deposits become a problem.

To get maximum economy you need an excess of air so that all the fuel is consumed, but there needs to be enough to sustain a stable flame front and to prevent free oxygen reacting with internal engine parts.

Only tests will determine the best ratio for either situation. Lots of interrelated variable exist that have an influence, including size and distribution of fuel particles, temperature of intake air, temperature of manifold and cylinder and cylinder head walls, air speed, shear in the airflow and turbulence, turbulence in the combustion chamber, combustion chamber size and shape, quality of ignition system, compression ratio etc.   

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Tuning motorcycle carburettors

I'd say where on the same page, I have those books and there pretty worn out from years of use.

We have dimpled our intake runners to create small eddy's
to help in A/F mixing and actually slightly reduce air flow
(Yates SB ford Heads -nascar take offs) that where opened up a bit much for supercharged use - the increased turbulance allowed us to tighten our A/F a bit.
some where I have the dyno data in excel there is no mistake in our gains in HP and torque

that said, I consider myself a good "Hobbie" tuner, better then most of the so called Pro's in the new england area anyway- there are not that many people out there with 1200 hp small blocks.

RE: Tuning motorcycle carburettors

Hi, Brett43!
    You asked "How is the best way to tune multiple carbs on my bike?" There followed a long laundry list of suggestions...ranging from mild to wild!
    Dyno time is expensive...and subject to the whims of the operator! I found only ONE post by a gentleman who knew what was real!
    Put a piece of plastis tubing in your ear...and synchronize bt the sound of the hiss! This will balance the airflows...and the mixtures to the cylinders. Then, play with the 'plug colors! Either use a "Colortune" sparkplug...or, there are lots of color pics on the 'Net / in books (remember books? LOL). Find your right colors, your right "hiss"...balance, and ride on! -whitevette

RE: Tuning motorcycle carburettors

It has been a very long time since I played around with either bikes or carbies.

But by far the fastest and easiest way to synchronise four throttles is by  eyeballing four mercury columns side by side. Very easy to make a multiple manometer. Once you have tried this, you will never do it any other way.

RE: Tuning motorcycle carburettors

Well, I guess proper instrumentation will be necessary for the vast majority of builders/tuners...can't fault that.

I've been at it a while and, yes, I have two water and one mecury manometers.  The home made one is easiest to use and the mercury one is for fuel injections, it's not sensitive enough for carbs.  Sorry to say, I still stick a piece of tubing in my ear and listen to the 'hiss'.  Faster, just as accurate and pretty cheap.  It's a learned skill...if you can do it, it's accurate.  This method is just one of those tuning aids I learned before we all had to have computers and such.  Some of this new hi tech stuff (not a manometer, I built my first one in 1957) that's necessary to keep modern cars on the road are great, don't get me wrong on that.  I'm just getting to old to learn all these new methods.  Guess I'm still stuck in the '80's.

Rod

RE: Tuning motorcycle carburettors

Im with evelrod, the tube in the ear trick!

Then you to a hard run at wide open throttle, cut the engine while there, and read the plugs.  if you let the engine idle or drive slowly the plugs wont give the correct reading.

Ken

RE: Tuning motorcycle carburettors

On a side note, I glued some plastic dowel rod to the underside of my 1150 Suzuki's CV carb tops to fill up most of the cavity above and in the slides. I theorized that engine vacuum has to empty out the slide cavity each time you wick the throttle..

 The dowel rod was small enough to fit inside the return spring(s).

 Just as on my non-CV carb applications, low speed throttle response was increased dramatically, and the increased vacuum/flow signal over the needle jet required going one size leaner on the pilot jet.

 It's worked on every bike I tried it on. The hole/slot in the bottom of the slide on non-CV bike carbs reduces signal strength over the needle jet.  

 On non-CV carbs I just put a rubber flap cut from an inner tube over the needle plate and let the return spring hold it in place.

RE: Tuning motorcycle carburettors

Kevin Cameron in his Sport Bike tuning book describes that one of the adjustments available on CV carbs is the size of the port/vent connecting the carb throat to the vac chamber. I think the sequence was if the slide rose slowly an enrichening effect similar to an eccelerator pump was obtained.  Whilst riding It's mighty hard for me to know the height of my 3 CV slides at any throttle position/rpm, and thus to know what section of the needle needs attention.  With my old Mikuni VMs a series of marks on the twist grip make it clear where the slide is.  I think the dyno would allow peeking in the carb throats to see how far it is open at a particular rpm and load.

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