Acceleration problem [Archive] - GSXR.com

: Acceleration problem


msrace7
04-15-2006, 02:42 PM
I recently bought a 96 GSXR750 to use as a trackbike and have been unable to fix an acceleration problem with it so any advice would be greatly appreciated.

The bike starts to accelerate fine but at different speeds (85-104mph) it stops accelerating even though it is only doing around 7000rpm.

First time out it would not go over 100mph, so I checked the speed sensor, air filter, fuel filter, gearing, replaced the fuel and checked the wiring with no problems found. Took it out again and now it will still start accelerating fine, but stop accelerating at different points, one time at 97 mph, another at 104mph, and another at 85mph. I did notice that the sounds from the white brothers pipe are smooth and even until around 75 mph, then it sounds a little uneven. Also when it stops accelerating, it is only doing around 7000 rpm so the engine isn't struggling to move my fat a$$. Also I have been doing the testing on a flat deserted road so the road isn't the problem.

There are no good shops in my area so I want to avoid them but the bike is to slow right now for a trackbike. My first guess is a jetting problem but I have only worked on streetbikes for 5 months now so I don't know much.

mat3833
04-15-2006, 03:03 PM
is this only in higher gears? if so my advice is wrong. im thinking its a lean jetting/ ecu maping. id take the bike to a dealer

Matt

msrace7
04-15-2006, 03:18 PM
I've only tried it in 6th gear. I haven't tried doing over 90 in 4th or 5th gear and it runs fine at lower speeds.

The shops around here charge an arm and 2 legs in labor and the 2 closest ones suck so I want to avoid them if possible.

mat3833
04-15-2006, 03:20 PM
lol id try to tach it up in the other gears

Matt

msrace7
04-15-2006, 03:57 PM
Luckily my "drag strip" is close. Went back out, tested the bike again, and it still stopped accelerating within the same speed range (85-104mph in 4 runs this time), and in 5th gear it was at around 9000rpm and in 4th gear it was only around 12000 rpm. I'm only guessing but does 100mph in 4th gear at only 12000rpm say anything cause I guessed it would redline????

mat3833
04-15-2006, 03:58 PM
im stumped.... take it to the dealer, give them a BJ and get it over with lol

Matt

MotoGQ
04-15-2006, 05:08 PM
Has the gearing been messed with at all?

msrace7
04-15-2006, 06:25 PM
Don't know if the gearing has been changed. This might sound stupid but shouldn't I still be able to redline it if the gearing has been changed and it might just have a lower top speed??
Found something that is probably not the problem but just in case, the rear sprocket needs to be replaced because the teeth are worn down and about 1/16 of an inch gone and 2 are roughly half gone so could that cause the problem, maybe chain slippage at higher speed??

Got2josh
04-15-2006, 07:08 PM
if it was chain slipage you'd hear it. My old sprocket went during a 2nd gear highway wheelie and I new it, worst sound ever. Get that fixed asap.
Maybe it's jetted wrong for higher rpms?????

msrace7
04-15-2006, 08:35 PM
I didn't think that was the cause. Had some sprocket teeth break on a dirtbike and, yea sounded terrible.
The more I read and ask the more it sounds like a jetting issue. Unfortunately I know next to nothing about jetting a bike.
Anybody know anything about a "timing light". Someone suggested hooking one up to check if it loses spark when it cuts out, but they didn't say where or how to get one.

SradKiller B
04-15-2006, 08:46 PM
my 2000 GSXR 600 Srad was just doing something very similar. After cleaning the carb 12 times and doing a jet kit (120's) and running it on the dyno a dozen times they finally got it to sorta work.

There were two plugs on the back side of my carb that are the enrichener silinoids. By unplugging those the bike ran a little leaner and did not "drowned" itself.

Now it sounds strange but the shop pretty much gave up. The power is all there and she flies so the gurgling sound on decel will just be there forever.

Jetting was $305 installed and dyno tested.

msrace7
04-15-2006, 09:40 PM
Nice to know this problem isn't to unique. I could have a similiar problem since I don't what was done with the bike before I got it. It could need a serious carb cleaning and rejetting as well.

ravennh
04-16-2006, 01:02 AM
you need to describe what the bike has. full aftermarket exhaust, airbox/filterpods etc.

Carbs could have been jetted for aftermarket exhaust and filterpods, and sold it to you with stock stuff so he could save them for other bike etc.

Either case your main jets are probably too small.

Does bike overheat quickly if let idle? If it does its running lean and you'll need to increase jet size.
You'll have to remove and open carbs. clean, rejet.

If your patient you can get pretty close to optimal settings doing it yourself.
just need to get new jetkit or fix whats wrong with yours, could be busted needle, jet loose/fell out. Vacuum leak ( rubber stopper things on covers), loose clamps on carb to engine, and orr carb to airfilter.
And carbs could be out of sync..

SradKiller B
04-16-2006, 06:23 AM
The other option which I am exploring now is that the ECU is acting stupid. I am going to try and find someone with a good running SRAD and swap ECUs so i don't have to go buy one.

You may want to try the same but again this is a shot in the dark as well.

audi1031
04-16-2006, 09:11 AM
Jeeting could be problem as you say and since the bike was possibly a track bike depending on how tight the track was he did not need the higher rpm and jetted according to the track condition (shit in the dark). You need to get it re-jetted as it sounds to me is the problem and usually the problem you have is in the needles setting ( mid rpms 5k-7k ) or the main jets (7k on up) or both. Time to take in to get a service and that should help you out as well as get ya valves checked etc etc.... 400 or so is alot cheaper than assuming and since you just got this bike you need to know where its at or stands if you know what I mean :arsenal

SradKiller B
04-27-2006, 07:23 PM
msrace7 what did you find out. My bike is still acting up. Now it is doing something exactly like you said.