Slow speed stumble

[OB_Sonic Boom]

Jeff, re. Marc and the PCII that would definitely be an issue. I will go with TMH's advice for now and diddle with the TPS before shelling out some clams.

 

[OB_Dennis D.]

I search and read everything "TPS" related on this board going back almost a full year. I gained some further insight into this problem from a number of other owners.

It would appear that this is not a fluke or ocassional gripe about the Busa, rather a lot of Busas exhibit symptoms of the same problem. Unfortunately, in numerous posts about the so-called stumble, or "surge", there does not seem to be a definitive solution. It is beginning to sound like a design characteristic on at least a significant number of Busas.

The most effective "remedy" mentioned most often, in a lot of the posts, including inside this one, is readjusting the TPS. However, some are saying to deliberately misadjust or bias the "-" indicator high to seek a smoother running bike.

I'm now fairly certain that simply remapping the low end a PC-II does little or nothing to really solve the problem. I'm going to experiment with the TPS next. Already did the jumper plug test and in my particular case, LCD displays "-" on top, not center. This is supposedly a good thing to solve this problem, but contradicts Suzuki's optimum adjustment procedure.

As soon as I get a tamper proof T-20 torx tool, I will reset back in the middle and then verify it switches back to top of the LCD display at 2000 rpm. I will use my PC-II to see what, if any, affect this has on the TPS readout. Using that method now, "as is", from the dealer, TPS at idle is reading 1%, corresponding to the "-" in top position on LCD, (again in my particular case). Stumble is still very noticeable nevertheless.

Quite frankly, at this point I am shooting in the dark, but several have commented on this problem and recommend investigating the TPS. As if to be saying there just may be something mysterious about this particular sensor that affects the off idle smoothness and since simple enough to check, it is definitely worth a shot. Agreed.

[This message has been edited by dsinned (edited 08 August 2000).]

 

[OB_THE MOTORHEAD]

the stumble is easilly remedied with a yosh at 1030 or some tinkering with the pc2.some are lean some are rich so you need to take readings each time to see what works for you

 

[OB_Dennis D.]

MH, I've tried PC-II changing the low speed MP table to rich. Did not help. Then went the other way to leaner. That did not help either. I thought you were one of the most
persuasive to set the TPS "-" indicator to the top setting? That's the way mine is now and as just mentioned not producing desired result like others have reported.

 

[OB_NumbNuts]

dSINNED

I had the pleasure of letting Gasabusa ride my stumbly machine on sunday. He said there is definetly a problem.

I know its not TPS out, or throrrle bodies out or filters etc. they have all been checked (TPS has been increased in increments of 0.05V and tested. Makes no difference. Right up untill she dies from too much fuel.)

Gasabusa suggested I check the Input Air Pressure Sensor (the sensor screwed to the back of the airbox) as this is the main sensor that affects running under 4000rpm

My bike is totally stock, 12,000 miles, stumbles in EVERY gear, little worse when hot, stumbles under 4000rpm on a neutral throttle. No PCII, no pipe, no nothing. Above 4000rpm, she runs like a Patriot Missile. Under 4000rpm, like a SCUD

I would buy a new IAPS and fit, but they are like £140 each!!

Your views??
Thanks

Nuts

 

[OB_Dennis D.]

Nuts, you could be right. IAPS probably does have a dominate effect and could very well be defective. I hope not at that price.

There seem to be many other Busas exhibiting the same problem, including bikes that are still relatively new (like mine). Possible a bad lot of sensors were assembled on Busas in the factory without detection? Possible, but I think not very likely.

As a last resort, I guess I could exercise warranty, but would have to reinstall stock pipes, which tends to mask the problem by diminishing the severity. It's still there, just harder to sense, especially if you use the throttle agressively.

I think this is turning out to be a very subtle problem. Perhaps the average person would not even notice it.

I suppose one thing we could try is simply disconnecting the IAPS and see if that makes any diference. If no change in symptoms, connected vs. disconnected, that could mean the sensor is defective.

[This message has been edited by dsinned (edited 09 August 2000).]

 

[OB_Gary Evans]

Dennis D.
You may already know this but, when fuel changes are made they should be made in very small steps taken one by one until it either shows improvement or a worsening condition. If you don't take it in small steps far enough each way you can easily miss the sweet spot.

 

[OB_Sonic Boom]

Nuts, you CRACK me up! Nice analogy.

 

[OB_Hayawoody]

Dennis, check the gap on your spark plugs and make sure they're torqued down tight, try 31k gap on them and let me know if that helps.