2006 Busa With Mods, Stumble and stall under 3K RPM


The Facts:

2006 Busa
Around 5,000 miles
BMC Replacement Air Filter
Hindle Full Race Exhaust
AIR Tube block-offs

Busa ran fine, and even after all mods, ran fine for a whole season.
Put fuel stabilizer in it at end of last season with 1/4 tank.
Bike is stored in a medium sized, wooden, outdoor garden shed.
Battery was dead in spring a couple months ago, so I cherged it with trickle charger.
Filled tank the rest of way with brand new 94 octane fuel.

Now for the problem,

Started bike, fine.
Seemed to sound a little more choppy or lumpy than usual,
warmed up to normal temp,
go to take off and when trying to start out in 1st, anything under 2500 to 3000 RPM makes it stumble, and sounds as though it is running on 3 cylinders, it kind of sounds like one of those old air cooled VW motors, a little backfiring, and even stalls sometimes.
Once you make it to 3K and above it takes off and runs almost exactly normal except it seems to use more fuel than usual, or I should say I am going through a tank quicker.

Just to be sure, I pulled plugs which had a reddish brown color on them, but all look the same.

Looked at air box, vacuum hoses, wires, and did an overall visual, but nothing obvious or major, and then I found the coil connector wires were either chewed a tiny bit, or scraped/rubbed, but not broken or cut through all the way. I taped them, and used my tool to check for spark at the coils while running and thats all ok.

I then tried to remove wire connectors off of one injector at a time while it was running to see if the was a noticable difference, and I had a hell of a time hearing if there was a difference. There was some, but not a drastic change.

I even reloaded the PC-III usb map, but nothing.

Then I removed the PC all together to eliminate the possibility of that being bad, and even though it changed the way it ran, it wasn't much different.

The last thing I did waas remove the TRE just in case that had anything to do with it, but nothing.

Finally here's the last thing I noticed. Last night when it had sat all day and was cooled off completely, I started the bike, and raised the idle with the choke lever. and listen the whole time it was warming up. It wasn't doing it right away, and I tried to rev it quick to check it a few times and it sounded fine, and then after about 2 to 3 minutes of warm up after the temp started coming up, there it was again. The running on 3 cylinders thing!!!!!

I checked and adusted the TPS, and there also aren't any codes coming up.

Any ideas??????

The only thing I am thinking is maybe a dead spot in TPS that isn't throwing a code, but causing a glitch at low revs, or a vacuum related issue because i know that the air box flapper is actuated up to the approximate rpm my problem seems to go away.

Just curious, but where does the air enter the air box while the flapper is closed?



If there was a dead spot or something in the throttle position switch you could easily see by hooking up to your PC3 and watching the throttle position that it indicates and see if it makes a leap in percentage or something. I would check the vacuum lines and the intake pressure switch maybe it is not seeing the vacuum or something but if it is fine till it warms up then I would kind of rule that one out.

did you check the flaps and filter inside the airbox, I know you said you looked at the airbox, but you looked inside? also maybe pull the plugs and see what they look like and maybe clean them. your fule injecters might have got clogged a little, did you run the bike for a bit when you put the stabilizer in it, you need to to get the stabalizer throuhg the whole system and not just through the tank. If you still have trouble I will continue to try and think of some stuff to check.


Actually I didn't know there was a TPS switch on the bike. Where is it and what exactly does it do, I just set the TPS didn't know about the TPS switch.

I did check in the airbox and the BMC race filter is fine, and I verified that the vacuum diaphram is actuating the flapper in the air box.

As for the plugs, like I said I had taken them out and they looked like a redish-brown color, almost like rust.

the stabilizer was run a little bit through the system, but I was thinking of figuring out how to check flow. As far as cleaning them, I have an excellent cleaner for the tank, and I have something that is intended to feed into the throttle bodies while running to clean that part of the intake system. It isn't carb cleaner it is actually designed for fuel injection systems.

Lastly, I did hook my laptop up to the PC-III and at one point the Throttle percentage went from 0 to 25% when I just barely cracked the throttle.

I was also listening to the busa running with the tank lifted, and it sounds like a knock or tapping just for the split second that the engine stumbles.


The TPS switch is inside of the TPS itself. It's a closed throttle hard contact switch most Jap products have. Basically once you crack the throttle it opens telling the computer that the throttle has moved. I can't find my manual right now (Dang it! No telling where I set it.) but I'll post up the closed throttle switch adjustment if someone doesn't beat me to it.

Oh, and your TPS percentage should go up smoother than that, my bike is acting very similar off idle in most any gear that involves barely opening the gas. I'll get off my lazy tail and check it one of these days. Just a shot without actually testing it but I'd be very suspect of your TPS.

Mr Bogus

Trouble Makers Inc.
Donating Member
fresh 89 octane fuel and a few miles before getting too excited..

TPS is not going to go out of adjustment from sitting
Vacuum lines could have dried and started leaking, so worth a check
Fresh round of plugs never hurts

if a couple tanks of fresh fuel does not bring it around.. might want to check fuel pressure and filters.. Bike is probably a bit lean on the low end..


Other than the in-tank filter what other filters or where are they? Is there a fuel pressure port on the factory rail to check pressure? What would the factory pressure spec. be? Forgive me all my questions but I don't know what I did with my manual? I had one in .pdf format on a disc and I lost it. Anyone else here have the .pdf they wouldn't mind sharing?????

I am on my 3rd tank of high octane fuel, however I will see how it is after doing an injector/tb cleaning.

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