Poor low RPM performance (first post)


Hi Guys
First post here and a problem for you to solve.
My 99 'busa that I aquired recently has a very annoying trait. When the bike is in gear at low RPM the engine is very hesitant to rev, then all of a sudden the revs will build. It almost feels like a non fi bike when you replace the stock exaust and filter, and drill the airbox but don't re-jet. I know what big jap 4s feel like at low revs (had a GSXR1100WR before) and it is not supposed to feel this way surely?

If I try to blip the throttle while on the clutch all I get is a brief burp then the revs seem to die. This doesn't happen when the bike is in neutral by the way.

This is becoming very annoying and possibly dangerous as when pulling away at less than 2500RPM I get absolutely no power then all of a sudden it all kicks in. Also happens if I let the revs drop below 2500RPM while not pulling the clutch (very low speed corners). I roll on the throttle and the bike hesitates before the power comes in. The natural reaction to the power drop is to wind on more throttle which makes the eventual power spike even worse. The only solution I have discovered so far is to never let the revs drop below 2500RPM but as you can imagine with a bike a powerful and as tall geared as the busa is somewhat difficult round town.

My bike is bog stock with 6000 miles on the clock. It was serviced the day I bought it by a main Suzuki dealer.

Any ideas? Is this the fault of the ignition retard that I hear so much about and so would fitting a TRE (or doing the resistor mod) cure it? Is it something else wrong?

AFAIK no mods were done to the bike and susequently removed before I bought it.
That is the effects of the timing retard, most likely. The effects are usually worse with aftermarket exhaust that has not been fine-tuned, but even stock will have noticeable lag.

Just get a 15K-Ohm resistor and splice it into the gear position sensor connection on the ECM side. I made detailed instructions somewhere, check the 'Modifications' section or do a search. I will look later if you can not find it (should be there, though, maybe even pinned).
Sounds like the timing chain recall was done and the cams are a tooth off... Only one tooth will make the bike run like a dog one the bottom end and kill off a bunch of top end power to... That is what it sounds like to me.
Sounds like the timing chain recall was done and the cams are a tooth off... Only one tooth will make the bike run like a dog one the bottom end and kill off a bunch of top end power to... That is what it sounds like to me.
That happened to mine. Here is the dyno run before and after the cam chain was fixed.
I agree 2 hours of labor and a manual cam chain tensioner. All together this should cost you less than $200 even at highly inflated dealer prices.
I don't think it's the cam chain being a tooth off. I had a GSXR1100 before that made 130bhp at the rear wheel and the Busa feels a LOT more powerful than that. By looking at your power curves it would appear that you were only making around 110bhp. My Busa feels like it's making a lot more than that.

I'll do the TRE resistor mod (found the instructions) and see where that gets me.
Every bike is different. It depends weather it is the intake or exhaust cam gear. Power loss would be very different.
First welcome to the board. As far as the problem I have a 2k not exactly the same but close. I know the 99s had some problems with the fuel screens getting clogged. I have not installed a TRE in mine but the problem is not as strong as you are noticing. Although I do get an occasional burp I guess I would call it when going from Decel to Accel kind of like a small chain lash where the motor kind of hesitates just for a second. This I do not like when I am cornering hard. It only happens at low RPM like you describe so maybe a similar prob no fix yet. I am going to try the ATRE which is adjustable for each gear and doesnt give you the pull in the clutch rev you get from a regular TRE more expensive but I think I like the idea better. Good luck and let us know if you find it and what it was....
I am guessing your recall has already been done (should be an oil line feeding into the tensioner). You can double-check the timing yourself with about 2-4 hours of work, if doing it for the first time. If you need a service manual, just check the pinned topic in this forum or email me for a link to my site.
The recall was done. I have the paperwork to prove it. If the timing chain has been put back wrong the previous owner would have been riding it like that for ages. If this is the problem. You would have thought that he would have noticed the different between taking it to have the recall work done and getting it back.
It is possible but a dyno run will tell you for sure. If you are mechanicaly inclined check the easy stuff first. You can pull the screens from the fuel line etc and check them for brass filings. A resistor at the local radio shack is only about a couple of bucks and easy to install Then maybe a trip to the dyno if it doesnt work. Is the air filter clean anything in the airbox up here in Maine we put our bikes up all winter sometimes you can have trouble with critters. IS your FI light on. I had an 1100 before the Busa and it has alot of power down low
Hmmm stop and think a sec... its not fuel it would not run stronger in the top end because it would not have gas flow. If the filter was clogged and it ran bad on the bottom it would not get better when the rpm came up.. Its timing.... very simple... You put on a TRE it will get a little better because it will let the timing advance come all the way on in first gear. You will feel a little more power.. All I can say is fix it right and get the full power out of the bike.. And yep the owner could have had the cam chain work done and never had any idea it was not set up right because he may have been the type of rider that was into the look and never used the power of the Busa. Or had no idea what was now wrong with the bike and unloaded it because of the loss of power.... Im not slaming on you, don't take it that way... I hope you can drop me a note and tell me in the future I was wrong and it was an easy fix and you can teach me something more. By the way when you feel its fixed run it on a dyno if you can or ride another Busa then jump on yours to see how its running. Once its fixed you will not believe the power... I have a TRE on my 2000 it helps a little in the bottom end when racing.. Good luck
200hp Every bike is different. It depends weather it is the intake or exhaust cam gear. Power loss would be very different.[/QUOTE]
He has a very good point!!!
being that it's a 99 this is not likely but if it was still on the showroom floor when the recall came out it could have been done before the guy ever rode it. That is what happened to my 2000. I had to wait until the recall was done on my bike before the dealer could release it. I never know it was wrong until it hit a dyno and the fact that I jumped up to the Busa from a 600 I never would have known it was wrong otherwise.
OK, I will take the plunge and destroy any warranty the dealer gave me with the bike by ripping the head to bits this weekend and checking the cam positions. Having looked at the factory workshop manual it shouldn't take more than 2 hours to rip apart and put back.

Thx for the advice and I'll keep you posted as to what I find.
I decided that before I go ripping the bike to pieces it would be a good idea to go and get it dynoed. I popped along to my local dyno centre and they were able to run it there and then.

Here is the chart. 161.6bhp at the rear wheel can't be bad.

External Links Missing

I did this run with the Akrapovic tails on the bike as the low RPM problem is a little worse with them on and I thought it would show up more on the chart. The dyno guys suggested that the bike may have has it's FI remapped by a monkey in the past and that I should give it back to them to have it remapped and fit a TRE.

I'll do the TRE myself and see what if feels like after. THe dyno guys agree that the response at 2000RPM and below is really poor and that something is up. They say it can't be the valve timing as there is no way it would make 161bhp at the rear wheel is that was messed up
Cool thanks for keeping us in the loop. If we ever see this problem we can go back to what you found and try it. I cant really say much about the low end power of my Busa except it pulls exceptionally large gears if I do a roll on in 4th or 5th with my buddies 1100 he will beat me even though we start at about the same RPM he is into his power range about 4k quicker than I am because my gearing is taller. My 1100 Tach didnt start till 3k (it was an 89) so You would hardly ever dip down that low in the RPMs Where is this sluggish spot are you talking about 2k and under or above 2k maybe that will help determine. Also remapping is a good idea alot of people download the map thats close and call it good. Custom maps should improve performance all through the power range maybe not peak HP numbers but smoother graph will beat peak HP every time