Dyno Tuning

[Greg Cothern]

All of this is taking place in Michigan?????  Not Texas???

[BA]

Yes, unfortunately. 

[lragan]

All of this is taking place in Michigan?????  Not Texas???

Hey, its OK.  He does all the work, and we all benefit from the results.  Doesn't get any better than that!!

[BA]

And I do live in Texas one weekend a month.  My wife's been working in Brownsville the past two years and we just bought and renovated a Townhouse there.  Met Dave Carrales at the SPI Bikefest a couple weeks ago.  My wife and I graduated from Texas Tech back in '85, we were married in San Antonio, daughter was born at Baylor University Medical Center in Dallas. 

[BA]

Houston, we have a problem.

When I put in the 110 main jets the A/F ratio went leaner by about 7/10th's (13.34 to 14.06), but the horsepower and torque were basically the same (80 hp & 46 ft-lbs).  We thought maybe I had an intake leak at one of the boots, but all cylinders exhibit similar A/F ratio's.  Now we suspect the 110 jets my instructor gave me are not Keihin, and are actually smaller than the 108's we ran last week.  Now I've got to get a set of the 110's from the dealer and put those in this weekend and we'll run it again next week.

At idle the A/F ratio was 13.0 with the 40 idle jets and 2-3/4 turns out, and was 13.2 and 2-1/4 turns out.  These are both pretty rich, so when I put in the 110 mains, I will put the idle mixture screws at 2 turns out.  This should bring the A/F ratio closer to 13.5 which is OK with a water cooled engine, and should improve my gas mileage.

We also did a carb sync tonight.  They were close, but cylinder 3 and 4 were slightly out.  Now all 4 are spot on with each other.

[Greg Cothern]

Not trying to be contrary, BUT isnt perfect A/F ratio 14.7 with ANY # lower than that being towards the richer side, any # higher than that being leaner??????!!!!

So it says your rich..

[roboto65]

I am so GOOD at Copy and Paste 


Theoretically, the ideal stoichiometric A/F mixture (the chemically ideal mixture of air and fuel that is required to provide a complete burn) for a properly tuned engine running on pure gasoline is 14.7:1; that is, 14.7 lbs. of air to 1 lb. of fuel. However, because of operating losses in the induction system due to intake runner and cylinder wall wetting, plus the fact that fuel may not fully vaporize in the combustion chamber, a 14.7:1 A/F mixture is often too lean for actual operating needs. A more realistic light-load, cruise A/F mixture for a stock carbureted engine running on reformulated unleaded gasoline is in the 14.1:1 range.

The A/F mixture always varies from cylinder to cylinder, therefore we tend to tune the average A/F mixture slightly on the rich side to avoid engine misfire in the leanest cylinder. It is possible to target an A/F mixture leaner than 14.7:1 for maximum fuel economy but this can lead to driveabilty problems if any one cylinder is leaner than the others. The power mixture we target for maximum horsepower is in the 12.2:1 - 13.5:1 A/F range, depending on the engine package and its combustion chamber design.

[BA]

From Wikipedia - For gasoline fuel, the perfect stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. Any mixture less is considered to be a rich, any more is a lean mixture - given perfect (ideal) fuel. In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (methyl tert-butyl ether) or ethanol/methanol. These compounds all alter the stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at time of combustions; for MTBE-laden fuel, a stoichiometric ratio can be as low as 14.1:1). Vehicles using an oxygen sensor(s) or other feedback-loop to control fuel to air ratios (usually by controlling fuel volume) will usually compensate automatically for this change in the fuel's stoichiometric rate by measuring the exhaust gas composition, while vehicles without such controls (such as most motorcycles until recently) may have difficulties running certain blends of fuels and may need to be rejetted (or otherwise have the fueling ratios altered) to compensate.

The advantage of tuning the carburetors on the dyno is that you can verify the effects of the jet changes on the A/F ratio and the power output from the bike.  A richer mixture can provide increases in torque and horsepower up to a point, then it deteriorates.  I'm looking for that point on my bike.  My instructor is telling me to give the bike what it's asking for, and he thinks it wants more fuel to get the higher performance.  Now this is just the main circuit (including the idle circuit) at WOT.  The majority of your riding is done at less than 20% throttle, so once we get the idle and main circuits optimized, we conduct step testing (various RPM and throttle positions) under steady state load to tune the needles.

One of the guys in my class drag races his Honda 600RR and to get the most HP and torque out of it, so to achieve that he reprogrammed the fuel injection to give him an A/F ratio at 13.1:1.  That's running way rich, but it gets him the most HP, and he's always at WOT and doesn't care about fuel economy.

[Greg Cothern]

14.7 - 1 gives the MOST thorough fuel burn, NOT the most power, etc.  HOWEVER its the best of all realms.

With that said, I personally would want to hit #'s as close to 14 flat as I could for strong power, good fuel economy, and longevity, etc.

Again in my opinion #'s in the lower 13 range is too rich, sure will give good power #'s, but your fuel economy is down typically double digit percentages, and increase in carbon deposits, etc.

[BA]

Like I said, the rich mixture is needed only during WOT.  When you tune in the mid range you are only concerned with steady torque and A/F ratio.  That's where you're tuning for drivability and fuel economy.

[Chad in Michigan]

I don't agree with tuning to an a/f ratio. I tune to what feels best while riding, where it matters

[lragan]

Well, I just finished putting 105 jets and one extra shim in all four carbs on the "new" .96, per Greg's instructions on the web site. 

Thanks, Allen for forwarding the kit.

I must say, from "seat of the pants" riding I did today (although not nearly enough ) it made a world of difference.  The bike came with aftermarket exhaust (I posted a pic in another thread.) and a stock filter.  Put in a K&N, and backed the "D" screws out to 3-1/4 turns.  Have yet to sync the carbs, but hope to get to it soon when I put the bike up to change the rubber (that's right, I did find some substantial cracks in the sidewalls near the rim when I lowered the pressure and rolled the tires a ways, as Charles suggested.)

So, if you are going to tune to A/F ratio, I presume that is determined from exhaust gas measurements?  If you are really a tweak freak, why not tune each carb individually?  You have access to individual exhausts...

I will be interested in reading about it, but I don't intend to spend that much effort for an extra HP or two...

One interesting side note -- when I tried to start the bike when finished, it would not start.  I was accustomed to pulling the "choke" (bypass) all the way out on cool days, which I did.  I finally figured out that I had flooded it, as the new jets, shims, and adjustments put a lot more fuel in the cylinders.  After putzing with it a while, it fired on one or two cylinders, and I knew that life was in there somewhere (I kept wondering just what I had screwed up!!) so I ran it down the hill with no bypass and opening the throttle up to about half.  After pulling through at least 30 cylinders, it fired up.  By the time I got the front gate, it was warm, and idling sweetly.  No more hesitation in low/mid ranges, no more "Fourth of July" on deceleration, and she now runs like a spotted...er, a scalded...no.. a bat out of...oops.. well, like a Magna -- lovely!! (Edited to protect myself from animal rights folks who may be reading the mail...)

[BA]

Last Thursday I pretty much completed my dyno tuning work and will be posting the data collected in a few days (just need to print it all off).  What I ended up with was the stock 40 idle jets, 108 main jets, 3 total shims on each needle, and the A/F mixture screw at 2-1/4 turns out.  The peak horsepower number really didn't get over 80, but I was able to gain a significant amount of horsepower (~10%) between 4k and 6k rpm.  And smoothed the curve out as well. 

Took her out last Saturday and put on about 120 miles (90 highway and 30 side streets).  Felt like it was pulling harder on the low end, and felt no lugging when riding slow in higher gear.  My riding style was the same as usual (80-85 on the highway), and for the one tank of gas I went through, my mileage didn't change (still at 42). 

I did ride it to class tonight, but that will probably be the last ride of the season for me here in Michigan.  I'm heading down to Brownsville this weekend and will be there about 10 days.  By the time I get back to Michigan I'm guessing it will be to cold to ride anymore.  At least I've got another bike down there that I will be able to ride.

[TLRam1]

Didn't want to skew anyone's thing so I didn't post earlier but that is almost my exact setup BA, except mine feels rich. My pilots are 2 1/2 turns is the only difference.

Running K&N (thanks Hoot)
Stock pipes with end-caps replaced with new caps, 2 large holes drilled in each (size posted somewhere on the forum, I think).

Mains - 108
Shims - 3 Total
Pilots - 2 1/2

Is the power smooth I don't have the hard pull in the area of 5-6K RPM so it's in my mind?

Would better breathing V&H's pipes correct this if it is too rich?

Go back to a stock filter, maybe I am not too rich and need to be richer?

Take out 1 shim and all will be well?

Mary Ellen who is my 2-up passenger thought I was not getting on it as hard, when she found out I was....stated it noticeably does not pull as hard.

If I ride this in the cold temps and notice a difference, that would tell me something.

I have many options to try, except one of my diaphragms is not in good shape, opening it up I am taking my chances, put silicone on it this last time.

[BA]

OK, here's my dyno comparison.  The baseline test results is the blue line and is configured as follows:

K&N Filter
Two 7/16 diameter holes drilled in the end plate of each muffler
40 idle jets with the idle mixture screws turned out 2-3/4 turns
105 main jets
3 shims on each needle
A/F ratio at idle = 13.5
A/F ratio at WOP (9k rpm) = 13.7

The final test results is shown in red and is configured as follows:

K&N Filter
Two 7/16 diameter holes drilled in the end plate of each muffler
40 idle jets with the idle mixture screws turned out 2-1/4 turns
108 main jets
3 shims on each needle
A/F ratio at idle (1k rpm) = 13.2
A/F ratio at WOP (9k rpm) = 13.4

Step testing (3rd gear @ 13% load, 5th gear @ 21% load, and 1st gear @ 5% load) was done and the A/F ratio was recorded at 500 rpm increments from 2k to 9k rpm.  Loading changes the manifold pressure, changes the position of the needle, and draws additional fuel through the jets as compared with the attached graph that is WOP with no load.  The A/F ratio during the step testing mostly ranged from around 13.5 down to 13.0, but it did show a little lean (14.0 to 14.7) during the 3rd gear 13% test up to 5k rpm.  The only correction for this would be to get needles with a sharper taper on them.  Since this is a water cooled bike and these operating conditions are very narrow, it is completely acceptable to run with this configuration.

Terry - my testing showed a 1/2 turn on the idle mixture screws had a 0.2 affect on the A/F ratio.


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