Was told I was lean...but the dyno says rich

JP50515

XS650 Junkie
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Hey guys....very interesting day here.

We had a mobile dyno at my work and I threw the XS up for everyone to laugh at...and that's what happened.

I knew the carbs were way off on it, but it runs and will break 100mph if I push it to without complaining.

which contradicts the numbers...on the dyno today it made 26hp lol, which is 10-15hp below what it should be making at the wheels (right?) and half of the crank hp stock. The "huh" moment was when it printed me rich. I was told by a mechanic a while back I was lean...which made sense with the open exhaust, pod filters, and ever so casual popping on deceleration when ever I gunned it. Also doesn't fit with the red hot headers earlier this season, unless my understanding of rich and lean is a$$ backwards...which i'm PRETTY sure isn't.

So now I turn to the magic of this forum for some possible explanations...I bumped my mains and pilots when I built the bike but not dramatically (at least not enough to create a rich environment I thought)

Either way i'm at a loss for power here and wondering if anyone might have some ideas as to why the bike acts lean, but prints rich?
 
If you have incomplete combustion, unburned fuel will show up in the sniffer and read as 'rich', AND give you the decel popping. Afterburn in the exhaust can make the pipes hot. Can be caused by incomplete vaporization, when airbleed/jetting balance is off...
 
Jet up until it breaks up, then down a size or two. This is nothing new. This is how you re-jet any bike with mods. As much as we love our 650s, they're nothing special. They adhere to the same jetting principles and practices that are used on any or all bikes. I tried to detail it more in regards to the 650 in the Carb Guide but nobody seems to read that. So, you're pretty much on your own here. Buy every size main and pilot within 3 above and below your stock sizes. Start experimenting ..... I did ..... I contributed to writing a guide about it ...... nobody listened apparently.
 
Yeah, 5twins, it's so much fun rewriting the Guide one piece at a time that I've stopped doing it. Nobody listens when it comes to exhaust systems, either.

JP, a dyno is only as good as its calibration. You can't get the 100-plus mph that you are getting out of an XS650 with a motor so out of tune that it's putting out only 25 peak hp net. Somebody might be pulling your leg.
 
..... and don't get me started on the Sawzall thing, lol ..... how could anyone think this makes a bike better ???? No matter, you can't make them run right, might as well cut them up, lol. Then they've got the "look".
 
Appreciate the help folks. 5twins I'm busting out your guide tomorrow. Have had it printed off for a couple years now, just gotta dig up that file of stuff. I understand your frustration, honestly tho if this forum weren't so great at responding to posts a lot more people would read it. I do appreciate the help, sarcastic as it may have been.

Lol to each their own on the sawzall thing eh?

I think its time for new carbs on this bike anyway. I've been trying to make some bs38's with a few issues work for the last year, may be worth it to invest in a new setup.
 
Carbs can be rich and/or lean in different areas of their operating range. You could be rich in the RPM range that the dyno was reading, lean elsewhere. Your carbs are a complete "system". They need to be tuned right throughout that system. Many don't understand this. They mod and up the mains 10 sizes, done. Well, not quite. They're carb tuning idiots. I read some other forums for other bikes a bit. They don't understand their carbs either. Even their carb "gurus" don't. The RD350 is a case in point. That needs massive main jet increases when you mod it and add chambers. Naturally, that buggers the midrange all up. Those guys accept that and live with it. Duh, ever hear of a needle jet? They come in different sizes and are available for RD350 carbs yet nobody ever has had that "light bulb" go on in their heads to try them.
 
Yeah, 5twins, don't you love that look? I mean the glassy-eyed look of guys who sit in front of the tube, tool in hand, watching Jesse James and OCC, moaning "Oh, me too, me too...."
 
I think I know which tool they're holding, lol, and I imagine there's some stroking of it involved, which results ultimately in some nut tightening, and then ....
 
Dyno's are BS any way. A mere tuning tool. But if you know your carbs are not right, then do some jetting work as said.. At least you know it runs and in the ball park...
 
Popping on closed throttle is pilot jetting or the pipe seal is leaking at the head.

Retarded timing will act rich and is the main cause of overheated pipes. Weak ignition shows false rich also.

Short open pipes can have more back pressure at some rpm except where they show up as tuned. A large volume muffler that flows freely is the best for street power.

What exhaust sensor did the dyno use? An O2 sensor reads lean when the mixture is very rich or the ignition is off because it reads oxygen not excess fuel.



Tom
 
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