"sticking" revs question

J

jc100

Well-known member
Not sure how to completely explain this but I'll have a go...

I have a 2006 Z750S. Since the beginning of the season I've noticed something that I'm reasonably sure wasn't there before...when I twist the throttle, regardless of gear, the revs build steadily along with the engine noise until I get to about 6k, then somewhere between 6k and 7k the steady noise build up stays static (the revs don't actually "stick") until around after 7k when it's business as usual again. It's kind of like something "sticks" between these revs. I don't seem to be losing power, the bike runs fine otherwise, it's probably due for a valve adjustment and I do my own oil changes etc. There's a few rattley bits of plasti on the bike that I've been trying to dampen with sticky sided foam and I thought it could just be a vibration issue but I'm reasonably certain it's the engine noise I'm hearing and not vibration noise. It does the same thing on deceleration at the same point in the revs scale. I put in two cans of seafoam since the beginning of the season too in case anything was gumming up.

I have a power commander on the bike too and an aftermarket slip on but these were on last season too and I didn't notice the problem then (at least I don't think it was there).


It doesn't seem serious...but it's a little annoying


Any ideas?
 
Sounds like a fuel issue likely in the map. Why dont you save the map to your harddrive and mess with the range in question? Just highlight the 6-7K at whatever throttle position your at, then page up once or twice and send. If its better you know your in the right direction if not then try to go down a couple and repeat until the problem is cleared up. Dont worry about messing it up, worse case scenario just load the original map back again. Or pay a shop to slap it on the dyno and clean up the map.
 
Thanks Ken,

The map on the PCIII I have is unchanged from the original owner. It's for a Hindle slip on with aftermarket air filter (I have a Delkevic with aftermarket air filter), I figured it would be better than anything I could manage though and it "seemed" OK at the beginning but I did put it on at the end of last season. I'll try to play with it a bit although I've not done much with it at all so far. I really got it to deal with a bit of twitchyness at low revs which it seems to have done.

Edit: Although I'm not in the GTA, what's the approx cost of a dyno and map adjustment by a shop?
 
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any shop could do it for an hours dyno time. Its pretty easy to do yourself though. The maps that you download are just a starting point they are never spot on. After all when they are written it could be at sea level or 4K feet......it could be 80F and 50% humidity or 20F and 0%........it could be a brand new bike or one with 40K on it........
 
Sounds like a classic 'flat spot'.
This is caused by a too-rich mixture (very smooth but down on power).
If too lean, the motor would 'break up' and stutter.
You don't really need a dyno to tune your mixture.
But it's definitely the best way, if you wish to invest a coupla bucks...
It is, after all, a noble cause.
 
I had a look at the software for the PCIII last night and I now know what you're talking about for the adjustments. So my process would be to adjust the values slightly in the range where the flatspot is then ride...adjust...ride etc? Is there a guide as to whether to adjust upwards or downwards with these things? What am I looking for to tell me that the adjustments are working? Will the flatspot just vanish or will the revs range over which it happens decrease or increase?

Sorry about the questions...that PowerCommander box is like voodoo magic to me.

Edit: I also found a place that does dyno tuning near Ottawa (one in Kingston too but they didn't have a price list), does it really cost $300 for a custom map? This was their suggested starting point.
 
$100/hr for dyno work is normal.
Just save the map you have. Make small adjustments and try it. The flatspot should either disappear or at least improve. If it gets worse go the other way. If you get over your head and make a mess that you cant fix just reload the original map and start again. Its pretty simple really.
 
OK I'll play with it myself for a bit. I got a quote of $340+tax for a custom map from a place near Kingston so I might save up for that too.
 
'I don't seem to be losing power, the bike runs fine otherwise'

From what you have described sounds like a noise issue that does not stay with the bike between 6-7k. (not a power issue) I would look more closely at your valve train and what you were doing earlier with the rattly bits. I think you were on the right track with the vibration and resulting harmonics.Cheers
Paul
 
Now that I understand a bit more about my PowerCommander it seems like it is a flat spot though. It happens at certain points of throttle position I find now...and I can power through it by opening the throttle more. I found a guide on the web that described how to mark out the throttle positions with tape (0, 25%, 50%, WOT) and then go for a ride and note the throttle position and revs at the flatspot. Then adjust in that specific region where throttle position and revs coincide. I'm guessing increasing the numbers in the PowerCommander software increases fuel flow and decreasing them cuts it down. I'm thinking then that as the revs aren't "rising" in that area that I'll need to increase the numbers a little there. We'll see anyway.
 
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