DYNO RUN w/904cc

[ggRAT]

Finally got around to having a dyno run at a local shop.
Yikes! A/F Ratio is indicating a really lean situation.

Perhaps the Uni Pods are "breathing" better than the K&N Cones I replaced a few months ago, but not this much!

140 Main, 45 Pilots, no airbox, air injection removed, Predator exhaust.
(Check my signature for more details.)

GREG

 

[sweatmachine]

something is wrong with that A/F plot or sniffer. The bike wouldn't run worth a damn, or at all, if the A/F ratio was that lean.

 

[ggRAT]

Thanks a lot, Sweat for your reply. And you're right the bike has been running great, gas mileage is about 42-45 mpg, spark plugs are dry and tan. I'll give the dyno shop a call tomorrow.

Wednesday followup: The shop called and said they had the dyno incorrectly set to an altitude of 4500 ft. instead of 300 ft.. We'll get another run on Saturday.

 

[ggRAT]

Second Dyno Run (bigger jets)

Changed the main jets from 140 to 150.
Changed the pilot jets from 45 to 42.

Before: 73 HP / 56 Torque and A/F off the chart (suspect)
After: 71 HP / 53 Torque and A/F around 15

Still lean. Should I try 155 Main Jets?

BIKE: 904cc with manifold, no airbox, no air injection
stock carbs, Thruxton needles, no shims, -1.5 turns
UNI Pod 4" air filters, Predator exhaust, Pieman igniter

 

[sweatmachine]

I would go to a 152.5 and maybe add (or at least try) a shim on each needle.

 

[ggRAT]

Thanks, Sweat. I appreciate your expertise.

 

[mikenva]

I dont know your first run made more hp.I think I would try another dyno

 

[ggRAT]

Mike,

Trying another dyno occured to me, too. Although the air temp/pressure were quite different, I wasn't expecting a DROP in both HP and torque. It's hard to believe the A/F ratio results. How would a bike run at 15? I only ask, because she's really running strong, always has. I do suspect that the UNI Pods you recommended "breathe" better than the K&Ns, too.

Carb tuning is VOODOO!

 

[Bottle_Fed]

Actually, I think I would just shim it and be done. Nice tq curve, but I think a shim will pump it up a little. I suspect you lost hp because you upped your main.

 

[PieMan]

+1 Sweat.

 

[nigel]

Glad to hear I'm not the only one with problems,
Hope they both get sorted quick

Nige

 

[mikenva]

Actually, I think I would just shim it and be done. Nice tq curve, but I think a shim will pump it up a little. I suspect you lost hp because you upped your main.

Yep thats kinda what I was thinking his 2nd dyno run was done in better air it had a c/f of .99 .His first run was 1.00 .I think the guys a/f meter is off.From what little I know about dyno jet dynos I think what that guy told him about altitude setting is bs.As far as I know air pressure temp and humity are the only things that afect the dynojet program .The altitude setting is just to show altitude on the sheet.
ggrat you might even find you make more hp on a nother dyno I think that one is fucked up.
The one thing alot of people dont understand is that the right a/f mix for max hp on a given bike is not a one size fits all thing.It allso changes from day to day with weather changes.You got to give the bike what it wants, a good dyno with the right guy running it is the only way to know.A/F gauges tell you what the mix is but not what the bike needs.

 

[mikenva]

One more thing next dyno run tell the guy you want rpm not mph.You have to play with the main jet by looking at the top end hp,with cv carbs the lower rpms will fool you when getting the main right.You allso need to see what kind of weather you are doing the dyno run in.This is kinda how that goes lets say the run was done in bad air (hot southern summer day say 89deg f 29.5 air pressure80%humity You test and find a 138 main makes the most power and that gives you 13.5 a/f ratio .Then we do another run in cold weather with same jet 60f 30.5 air pressure and 20%humity guess what the a/f mix is now 14 to 1 or higher hp might be down .So you rejet end up with a 145 hp goes up even higher.Now what did we learn? what is the right jet? We need a 140 because it will run good (maybe not the best ) in both good and bad air.Thats the best you can do for the highway.After you get the main right then work on the slide to make the bike take off good with the right main jet.Shims ,niddles and so on.
I allso get the guy to turn off c/f factors on my dyno runs it makes it easyer to see what hp the bike is making the day of the run .C/F factors are bull shit anyway they just dont work in the real world.

 

[ggRAT]

Good stuff, guys. Thanks a lot. Next week I'll get a run on another shop's dyno.
Please...stay tuned.

 

[ivar]

I allso get the guy to turn off c/f factors on my dyno runs it makes it easyer to see what hp the bike is making the day of the run .C/F factors are bull shit anyway they just dont work in the real world.

I guess the c/f's were intended to better compare results between different dynos and operators - but as you say, that don't work in the real world.

 

[sweatmachine]

I guess the c/f's were intended to better compare results between different dynos and operators - but as you say, that don't work in the real world.

more like to compare dyno runs done on the same dyno but on different days in different weather conditions.

 

[mikenva]

more like to compare dyno runs done on the same dyno but on different days in different weather conditions.

They dont even work for that.they correct way more then they should in real world.I saw that last year on my bike,had it tuned for middle weather cond .ran it on a bad day ran it on a good day raw hp numbers where with in 1/2 hp of each other but on the bad day it made way more hp with the c/f.
Years ago I built a dyno useing a daveport kit for gokarts (its a real brake hp dyno)computer weather station and all.I talked to dave davenport about the c/f is told me if I was raceing to turn them off because they are bull shit.
I did alot of testing and found what he said to be true.The c/f factors are just should be hp not real world hp.carb motors dont change any where near as much as the c/f shows.When you use raw numbers you know what that motor made the day of the run,if you are raceing you need to find what it will take to make the most hp on race day that takes dyno time to learn.But thats one of the things that wins races.

 

[cafenoir900]

Dyno, shmyno. I've had mine dynoed for curiosity's sake, but it only confirmed what the Gunson's Colortune told me, for a lot less cash.

For a street bike you have to look for a compromise, to average performance in different weather conditions. Race day, fine tune for the daily conditions... this can be done with the Colortune, too.

Above comments are on the money, too. Start working with the main at high RPM and work your way down through the pilot/needle, air screws and float height.

Gotta' love that old school British tech... (lol)