Slow speed stumble

Gary Evans
Okay, I would agree totally, but even after the purging of running for say 20 seconds, the roughness is still there.

It is always there!! just seems worse when hot, and better when tank gets just into red zone (before light comes on) I don't know, perhaps its just me HOPING that it has gone.

Could it be something to do with crud getting into the regulator?? THis was my latest thought. along with IATS or IAPS malfunction, or blocking. what do you think to that?

If all this fails, I'll have to look at buying a PCII........

EDIT
I forgot to mention. today I was under gas tank, and put my hand on the IATS. It was bloody hot!!, I had to take my hand off it it was that hot. Is this normal??
END OF EDIT !!

Appreciate your help

Nuts ;)

[This message has been edited by NumbNuts (edited 30 July 2000).]
 
Just visited the Dynojet website and read about their PC-II, then downloaded the s/w and all the available maps to study the program's functionality.

Anybody know what "AAP", "TP" and "MP" Table maps do?

For the so-called "stock" map, there are many slow speed changes (up to 3500 rpm and 5% Throttle openings) in the map for "MP", but not the others. This table must be for recalibrating the ECM to produce smoother slow speed engine operation.

I'm surprised the numbers in the same table do not change in an alternate map for a slip on exh & stock air filter, but supposedly the changes improve slow speed driveability.

It occurs to me that a PC-II device does not actually "remap" the ECM, not directly, but rather it fakes it out by biasing sensor inputs, which bring me back to wondering what these three variables correspond to by way of sensors.

Are these defined in the PC-II instruction manual? If so, what do they mean? Just curious.
 
The infamous stumble I believe is due to ignition retard in the first two gears under 4k rpms, I spoke to a guy in New York that had made some type of resistor and put it inline on the wires from the gear position sensor, tricking the ECM into thinking it is always in sixth gear. He says"its about as close to a carbed bike as you are going to get it" talking about smoothness. You may be able to correct some of it by playing with the ignition advance on a PCII but I think you can only tune that from 4k rpms and up. The infamous stumble is between 2500 to 3200 rpms, especially when shifting into second gear at cruising speeds. He is going to start making a plug in harness for the GPS to help relieve the jerkiness, I'll keep you posted.
 
The stumble appeared on mine when going from a trailed to nailed throttle in 1st and 2nd (on stock '99). Right royal pain in the rear as I spend alot of time trundling around London, where it's all stop-go low speed stuff.

Having done some mods (Full Yoshi-RS3 stainless 4-2-1, modified air-box, Yoshi Stage 1 Cams) problem was still there but better. The cure for me was fixing a kinked fuel return hose under the tank, and a little perseverance playing with a PCII and a laptop.
 
Dennis D.
There are also tutorial videos that you can download that provide more details. For Busa's table #1 is fuel between 10-100% throttle, table #3 covers 0-5% and table #4 is ignition timing. PCII does not alter the ECU map but, overlays percentage changes to map cells.
 
Gary Evans

No malfunction codes illustrated in the LCD.

I had a fettle with the pink wire yesterday, adding in a switch. not sure how this affects it, seems funny. More vibration (??) probably just me.

will put more miles on tonight to evaluate.

I might try moving the IATS to a cooler position.

Thanks

Nuts ;)
 
Thanks for all the replies so far. I learn a lot from reading "technical" posts from others. Unfortunately, there is a wide range of opinions and it is hard to know which apply to the situation actually under discussion. Nevertheless, I thank all who replied.

BTW, "dsinned" is my name spelled backwards, i.e. Dennis D., so sometimes I log on under this alias.

To clear something up, the stumble in "my" '00 bike is present in all six gears at slow "engine" speeds up to 3500, sometimes even higher. It only flares up at
very small throttle settings, under light load, right at the threshold of supplying fuel. Opening the throttle slightly more and the problem generally can be made to go away,
but then you will be "accelerating" to a higher speed (mph). This is not my definition of "cruising", i.e. trying to hold a constant speed.

I am still in the dark on the ecm variables under PC-II software control. I could not find a comprehensive tutorial on Dynojet's "powercommander.com" website. I did pick up on one thing, i.e. the PC-II for Suzuki's cannot alter ignition timing below 4000 rpm.

I also have heard about the GPS "fix", and how if affects spark retard in the lower gears. But, in this case, it does not seem to be a viable solution based on the fact that my bike still has the stumble in the higher gears as well.

I still am interested in getting more detailed info on the PC-II's inner workings from those of you in the know to supplement that which I have already read on this board.

I just put the PC-II on order, so hopefully my bike's stumble problem will be solved.
 
DENNIS, GO SEE ROB @ROBS CYCLE OVER ON LEWIS AVE, THATS ACROSS FROM ROAD RIDER.HE'S GOT A DYNO AND A YOSH BOX, HES A PRETTY GOOD TUNER, LET HIM HAVE A SHOT AT IT, SEE IF HE CAN IMPROVE FOR YOU.HE'S A FRIEND SO TELL HIM I SENT YOU WOODY!
 
Try a negative map,got gas milage and performance 165rwhp at between 38 and 45 mpg with 6000 mi. on stock chain x-ring chain may help to bring that up to 170rwhp oh ya full system w/ air box mod and bmc,pc2 good luck!!!!
 
Dennis D

Yours is exactly the ame problem as mine.
All gears, neutral throtle.

Only way left for me is
1 PC2
2 Yosh
3 New chain (might be a tight link.......needs replacing anyhow, done 12000 miles)

Nuts ;)
 
Frank Adams
Did your modification of the inlet and
exhaust overlap cured your stumble at
2000-3000 rpm ?
What happended ...
/Ove
 
dsinned

I was told yesterday that a stock Busa (i.e. mine) should not have a stumble. If it does there is a problem (really??!!) So I told him what I had done, he suggested the IAPS is out of sync??

could this be right?? anyone??

Everyone I have spoken too says the PCII is not needed for stock (mods coming in future you see!!!) and the stumble indicates there IS a problem. Its not timing........

Any tuner's care to comment??

Nuts ;)
 
NumbNuts, you should read ZXALAN's post reply under the topic "zxalan...need help".

This is the very same notion why I started this thread. But, as you know, this rather annoying "stumble" is present in ANY gear, so I am still thinking it is a too lean mixture condition, not timing related. I will have a PC-II by Friday and hopefully some additional insight as to the solution by Monday.
 
low speed stumble:

took my Busa into the dealers regards the "stumble" and he checked the PC-2 mapp and said it's low end had not been installed.

My map was installed by Dtno Jet in Vegas, as the map for Akrapovic with stock filter, all stock motor.

He made some adjustments and the stumble, which, by the way, was minimal, is gone!

I post this as there may be some adjustments needed for "drivability" that the normal mapping ignores.

I will get the specifics from the dealer for those interested in the change!
 
I installed PC-II preprogrammed with -001 map for stock bike. No affect on stumble.

Then I tried manually setting Low range to +5 LEDs. Still no improvement, but not any worse either. Next, I reset the same range manually to -5 LEDs. Engine ran terrible (starving for gas), so this proves the PC2 leaned out the mixture. Then tried -002 map (supposely optimized for "race" slip ons).

My Busa has V&H "race" slip ons currently installed, but with PC-II -002 default map there is still little to no improvement in slow speed operation. That is, the stumble is still evident and most troublesome from around 1500 to 2500 rpm.

Oddly, the -001 map from D-J, supposedly for "stock bike", contains no diff in "MP" fuel table (0 to 5% throttle), compared to 002 map for slip ons. WTF?

Became frustrated with provided maps, so tried experimenting with incremental changes to MP table in range from 1000 to 4k rpm. This affects fuel calibration of 0, 2 & 5% throttle only. Put most of my efforts fine tuning just 2% throttle, 1500 to 3000 cells only (ie where the stumble is most evident).

After many trail and error changes, still had stumble. Eventually found a combination that "seemed" to make bike run smoother at low speed. Better, but not great.

Stumble still not eliminated, but now little bit less noticeable even with slip on pipes. Trial and error method sucks, but as someone else said, with a lot perseverance the PC-II can help tune a Busa to run somewhat better.

Too bad there's not a product available that implements ECM scanner functions for fuel injected bikes, so sensors can be verified for proper operation. Nevertheless, based on condition of plugs (light brown porcelin tips, gapped to 0.030"), hoses (no kinks), throttle bodies (butterflies in sync), not sure what else to check.

I did pull off an plug the rubber hose going to the diaphram actuator under stock air box as the flapper valve inside does not seem to be of any value. Comments?

Could be that California emissions are just messing up the bike? Might go back to stock exhaust mufflers since seems less suceptible to stumble. First, would like to check TPS adjustment, but don't know how. Appreciate it if someone could post the procedure.
 
Dennis, I wouldn't put the stock cans back on because you'll still have the same problem. My 'busa is bone stock and it surges like a mudda anywhere between ~2 to 4K RPM, and it gets worse when it gets hot, or when the chain is slightly loose. I'm so sick of it that I am taking mine in to Factory Pro (Marc Salvisberg) to have them tune it out. Good luck.
 
Good luck with Factory. Marc is a very good guy but will not use a PC2 attached to your bike.

He will use the yosh box. it's just not fine enough (range of low - med- high) to do what you need.
 
Dennis,
The torx screws are slotted so you can turn it and re-lock. I adjusted mine last week. Its a T-20 size with a little pin in it so you can't use a regular torx (I just drilled a cheap one out cause the auto parts store didn't have one with the recess)

When I got my bike from the dealer the indicator in the dealer mode read highest of the 3 positions, and had absolutely no problems with surgeing (I couldn't understand what everyone was complaning about) but after I adjusted it to the center position I recognised the fact that the engine is hunting around low RPM's by switching fuel on and off it seems.

I prefer it adjusted to recommendations but by my experience turning the TPS will probably cure it. Like I said My bike was high on the indicator however someone with more experience will know which way is better for the bike to turn it high or low, I dont know which way relates Clockwise or CCW to high or low I just centered the indicator. I also had to play with the Idle adjust because it stalled out as I was adjusting and the service manual recommends it be set at 1150 RPM.

Hope this helps
Sorry its long
L8r
 
MH, please explain how to adjust TPS. It appears to be screw mounted outboard of left hand side throttle body. I did not find any set screw or way to adjust the pot. Does it have slotted holes for mounting screws so that it can be rotated slightly? Is this how to adjust it? If so, which direction do I turn it? Please be more specific if you find that biasing the TPS solves the off idle stumble problem?

BTW, is there any truth to the GPS spark retard theory in lower gears? Do you know of a guy in NY named "Ivan" who claims to have a fix?

TIA for your help.
 
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