Dyno Testing Results

[Mike Hart]

Nice links, Ben.

To keep this thread on topic (XS/XJ), I'll quote your post and make a new thread in Other Bike Discussion to follow up on some of your comments.

Those of you wondering where to get a dyno run - start calling or visiting every bike shop (esp. independents) in your area, ask them if they know of any free dyno run events coming up (might be way too late in the season except for those in the southern states), and where regular dyno runs can be made.

[Jeremy_Sells]

http://www.dynojet.com/lbike.shtml

Try this link to find a bike shop in your area. I'm pretty lucky, my brother is a mechanic at the major harley shop here in Portland, so my dyno runs are free afterhours. The thing you need to tell the shop when calling around is that you want a baseline fuel ratio map. It usually takes 4 or 5 pulls at WOT to get a consistent number and then they will print you out a chart and your done. It shouldn't take more than 30 minutes. Some shops might turn you down because they don't want to work on our old bikes, so just let them know you only want your bike mapped. My brother had to dyno a dirt bike the other day, pain in the ass!!

Mike, what's up?
We measured the a/f with a sniffer up the tail pipe. The richeness down low is bothersome. I thought about moving the needle down one click, but that would mess with the main circuit, so I am inclined right now to go with one size smaller pilot jet and see what happens. A/F looks to greatly affect power, so I definately should get a flatter torque curve if I could get that mix right down low. We'll see, its going to be a fun winter project so I'll keep you all posted.

Take care,

[TopCatGr58]

Attempted Image Edit of message

Hey there Jeremy,

I attempted to try to post your graphics from the link that was created when I went to your file cabinet thru the link you provided, on Geocities. I was able to see the graphics.

I put in the following image links using the image button,

http://www.geocities.com/jl_sells/dyno1.jpg
http://www.geocities.com/jl_sells/dyno2.jpg

but they wouldn't link/ just had those little red "X" boxes like the following:



So...apparently Geocities won't allow direct linking to files in your cabinet!? Sorry.

HINT: for folks, once you get to the graphics, and they pop up, first click your mouse outside the graphic, then roll it back over the graphic and then hold it still, and you'll 2 little popup icon sets if you're using IE; in the upper left, you can save the files, and in the lower right corner, little box with 4 arrows, click on it and the image will be magnified to it's original size for viewing and reading!!

[pgg]

Regarding the 'less is better' jet theory, no matter what, the same princible still applies to all bike motors - an EFFICIENT exhaust flow plus MORE air plus MORE petrol equals more stomp! On the 2nd bike you mentioned, I'd say (feel free to disagree) that if you added a non-restrictive air filter to the drilled airbox, you'd then be able to enlarge those jets for more response and a livelier motor, as that 4-1 system sounds a good design. Turning the rubber air-scoop into 'holey cheese' should lean those ratios out fine.

As for the 1st bike mentioned, the plugs should have been overly carboned at main jet operation, so naturally you'd go down a size or two on the jets. As the mixture was fine with only standard jets, that suggests the 4-1 system wasn't an efficient design.

[Jeremy_Sells]

With so many details to cover about tuning and how things were set up, I had to leave some minor details out so that the first post wouldn't turn in a small novel. In both bikes, I am running a K&N airfilter. What I mean by drilled air box is not really drilled but rather cut out. I took the lower tray that the filter sits in and removed all of the plastic that exists inside of the filter oval area, as these bikes draw air from the inside of the filter.

On both bikes, plug color has remained fairly constant in all configurations. Plug color can be a good indicator for extreme cases but factors like slightly worn rings, air temperature and density, float height, etc. can give one the run around when trying to "fine tune" a motor.
Also, on both bikes, HP increased around 10% with the new configurations and stock jet sizes. The first bike I initially set up with larger than standard jets at the recommendation of several sources, but it was the dyno test that revealed that more power was to be had by going back to the smaller, stock 110 mains. Not to mention, the bike was noticeably quicker set up that way.
I also think it is important to mention that before any dyno work was performed, all aspects of tuning and balancing were obsessivley worked out. Floats were balanced both on the bench and then on the bike while running. Although incredibly time consuming, it really is the only way to get the most accurate setting. The idle mixtures were set with a Colortune and the vacuum balance was set with a Carbtune sync. The valves were adjusted exactly within factory spec and compression on both bikes warm, with WOT was 170-180 psi.

I have owned several old british cars as well as some old volvos that run SU carbs much like the CV's on our bikes, and with the SU's, main jet size is fixed and nonadjustable and the needle is changed often offering adjustmest in the .001 of an inch range. One thing I have learned from my "struggles" with CV carbs is that to some extent they self-adjust fuel flow based on air flow temp and density. What my theory about the XS is saying is that by evenly increasing volumetric efficiency in both the intake and exhaust systems, the vacuum diaphram is adjusting by rising faster and staying higher throughout the rpm range thereby giving me the the more fuel for the "stomp" without having to change jets. Whew!!! And the bike just screams now !!!

Anyways, I just started reading a book I got out at the library yesterday called "Scientific Design of Intake & Exhaust Systems" which actually has a section on motorcycles which might shed some light on what I've got going on.

Until then, take care

[pgg]

Jeremy, the fact that bike 1 put out more 'stomp' with smaller jets confirms my suspicion of a below-par 4-1 system. Regardless of varying vacuum pulses, when the CV slides are slammed to the ceiling at full throttle, when the 110 mikuni jets reach their maximum flow rate of 110 mls of petrol per minute, the corresponding air flow through the standard 140 air jets (air flow calculated from fuel/air ratio) will also remain constant at that required rate. As long as the exhaust system can accept a larger air flow, a larger jet will continue feeding extra volumes of petrol, and the air flow will also keep increasing.

In the xs11 carbs, the 140 air jets are still capable of extra air flow (easily provided by the improved airbox intake) Back to that formula again - more fuel, more air, more stomp. The cylinder head's demands are dictated by what the carbs feed it. The xs1100 motor may be 'legendary' but it doesn't have a brain!

Cheers.

[ratbyk]

5000 RPM Richness

Hi Jeremy. This is getting to be an interesting thread that you have started. Who knows, it might get us through the entire winter. Tee Hee
Anyway; the air/fuel ratio going rich around 5000 RPM is likely caused by the fact that you are at WOT at the throttle butterfly's (lots & lots of engine suck) but the slides are only part way up at that point. The restriction caused by the slides only being part way up is creating a great deal of vacuum (more than normal for an instant) in the venturi area. The needles are up enough to expose more of the main (allowing lots of fuel flow). Soooo during this very short extra high venturi vacuum period it is running extra rich. This will be over a very narrow RPM range until the slides rise far enough to again achieve a proper vacuum in the venturi area.
Possible solution might be to install slightly stiffer springs above the slides to slow down their rise therefore limiting the exposer of the main jet.
Or, needles that are slightly thicker at that mid range point.
Or, simply enjoy the strong running great bike that you have and now that it is running right don't try and fix what not broken.
Thanks for the dyno charts, enjoyed looking over them.
Ken/Sooke
78E Ratbyl
82 FT500 "lilRat"

[Jeremy_Sells]

Thanks for the reply, Ken. I'm glad that the charts finally made it to you!! Your scenario sounds more likely than my pilot/main overlap theory. I did order some #40 pilots the other day and I plan to have those in next week and head back to the dyno to get the results. If that doesn't do the trick, then I might move the needle down one click and then maybe go with a larger main. We'll see!! Lots of options and all winter to get it right.

Take care,

[Dan Hodges]

Dyno Test

Jeremy,you are the man.Your results on the dyno are very informative. My 81 has ported heads, one mm over Yamaha pistons, 78 model cams, Super Trapp header with 14 plates (a little loud) and 120 main jets,180 pilot air jet, 42.5 pilots, stock air box with K&N and the timing is 40 degrees @5000 rpm. I don't know how much bacon it's makin but it's stout. I have a stock V-Max which is faster, but so what.Some one was talking about a V-65 making 105 H.P. and the introductory models were but starting in 85, they were down in the mid 90's. I had a new, in 85 V-65 Sabre and it wasn't even close to my V-Max.I bought my eleven new and the way I have it now, I think it would give the Sabre all it could handle in a straight line.I got the print out's of the dyno test,they are faint but readable.

[Shuriken]

Agreed. Take us through the winter with this thread.....

Nothing like tuning/dyno stuff for the XS.

Ben