Admin
05-01-2001, 05:09 PM
1996 GSX-R750 Jet Kit Installation
from Digital Sportbike Magazine
OVERVIEW
For the 1996 Suzuki GSX-R 750, we went with a Dynojet model C3149 (US Model 3149) which consisted of six main jets, four needles, four springs and a drill bit. The six jets are three pairs of different sizes, allows the modification to support stock and race exhaust systems. Based on Dynojet's recommendations, we installed the large medium jets (130) on the outside cylinders (#1 & #4) and the small jets (128) on the inside cylinders (#2 & #3). If the motorcycle was equipped with an aftermarket free-flowing exhaust system, the medium jets would have been installed on the inside cylinders and the large jets would have been installed on the outside.
Some sharp readers might have notices that the larger jets are installed on the outside rather than on the inside. Dynojet discovered that the current GSX-R engine runs hotter on the outside rather than on the inside like most other engines. In case you're wondering, the size differences compensates for temperature induce intake manifold pressure differences.
For both standard and performance exhaust systems, the needles should be set with the clips on the fourth notch. It is recommended (source unknown) to advance the intake cams 10 degrees from 112 to 102. I have also heard that 106 degrees work well. It's my suggestion that cams should be fitted with slotted sprockets (easily adjustable) and run a series of test to determine the optimal settings for each engine. If the intake cam is advanced, Dynojet recommends setting the needles to the third slot. This modification is said to improve horsepower in the mid-range with no effect on the top end performance. Ultimately, if your engine undergoes serious modification (cam timing, exhaust and jetting), a fair amount of tuning will be involved. This installation used the stock Suzuki exhaust system with the both cams set at 112 degrees (stock).
RESULTS
This bike is a psycho machine, there is not other way to put it. A stock GSX-R delivers power very much like a light switch, now it performs as if the light switch had a direct connection to a nuclear power station. Think Barqs has bike? Ouch! It would be realistic to say that the output gains were less than or equal to five horsepower. That may not sound like much horsepower but don't forget that Dynojet's kit was designed to improve other characteristics of engine performance. Throttle response is fantastic, any throttle adjustment results in a sharp reaction in engine power. The faster you can get the revs up, the faster you will go. High performance riders will appreciate how easy it is to blip the throttle when downshifting and match engine speed to the bikes velocity.
I have to admit this is the first modification I've made to this bike and I haven't ridden many other sportbikes (ZX-7 and ZX-10) but I know this bike is not longer a normal 750. Previous to this installation the power delivery was very much on or off. Once driven past 9000 RPM the GSX-R was like a raging storm but the mid-range could only be considered poor. I found the ZX-7 to me much stronger in mid-range performance... and the ZX-10, well... that was a liter bike.
The engine improved mostly in the upper rev range but I've noticed more change from 7000 to 9000 RPM, possible due to the modification to the carburetor slides (drilled). Power delivery comes on strong at approximately 7000 RPM and the previous power surge at 9000 RPM is less significant because the mid-range has improved in comparison. Combined with snappy throttle response, the engine will drive the front wheel skyward under full throttle in first gear. Without any clutch action, the front wheel lifts at 7000 RPM and draws upwards as the bike continues through the rev range. On a good day, it is possible to flip the bike under full first gear acceleration. Big second gear clutch wheelies are possible by fanning the clutch slightly while under full throttle at 10 000 RPM (Warning: Very Addictive).
On the drag strip the ¼ mile times have dropped from 11.0xx to 10.892 and the gate speed has risen from 124 to 129.08 mph. I can't exactly be sure on the ¼ mile improvements because I had only run the bike in stock form eight times prior to the modifications and I hadn't dragged at all prior to that. I'm sure that with practice I could have run the stock bike in the 10.9s but during my last outing I ran two 10.8s, two 10.9s and three 11.0s. Getting into the 10.8s wasn't too hard and I'm sure I could break into a 10.7 dial-in with some effort. As for the 10.6's the magazines claim the GSX-R is capable of... yeah right. Suzuki didn't deliver me the bike, I bought it from a dealer just like everyone else.
On a side note. Your own GSX-R is probably punching out approximately 110 HP. If you want the other nine horsies that it's suppose to make all you have to do is rebuild your engine from top to bottom with zero tolerances. Suzuki ships the GSX-R with a ± 8° tolerance relative to top dead center. I don't know when their piston & piston sleeve clearances are but cylinder friction is the number one point of lost power. Consider suicide engines used by racers, no air filters and only one of three piston rings are installed. Works great for about an hour...
PROBLEMS
Kit and all, there were still problems. Expecting a trouble free installation when adjusting the carburetors is asking for a bit too much, but it's still frustrating when you get hit with tuning problems. Below 4000 RPM with the coolant at 70 degrees, the engine stumbled and lacked power. This problem is most notable when cruising in a tall gear when the bike would actually buck none stop. Outside of the 3500 to 4500 range and the engine was absolutely perfect. It turns out that a mixture setting of 3½ was slightly rich for bike equipped with a stock exhaust system. Considering Newfoundland's typically cool summer climate (between 15 and 25° Celsius) and low altitude, bikes in hot climates can definitely expect this problem. Your choices are simple; go with a leaner mixture such as 3 turns, install a free-flowing exhaust or buy lots of spark plugs because you're going to foul a lot of 'em
A FEW SUGGESTIONS
Don't rush the job! Precision and patients is required to ensure that your jet kit is properly installed. The Dynojet kits are supplied with a diagnostic check list. I highly recommend covering each of these points even if your engine appears to run perfectly. In my case, when the engine was cold there was absolutely no problems and the engine was never given a chance to warm up during the mechanics test drive.
Ride with spare spark plugs. My rich carbs could have easily left me stranded. As luck would have it, I broke down in a friends driveway. You may not be so fortunate. Please note that the measurement scales used by Mikuni, Keihn, Dynojet, Factory and others are not compatible. Comparing jet sizes between companies is like comparing apples and oranges.
DYNO RESULTS
Tested at 68° Fahrenheit with 79% humidity at 400' elevation, the engine performed as listed below. Engine configuration was 130 outside main jets, 128 inside main jets, 3½ mixture turns with a factory exhaust system.
112.75hp @ 11 400RPM
56Lbs/Ft @ 9700RPM
¼ Mile Trap Speed: 129.08
¼ Mile Elapsed Time: 10.892
Exhaust systems equipped with replacement headers and a track only, low resistance baffle can be set with 130 and 132 main jets. Along with the gains of a track only exhaust, the larger main jets will increase the high RPM power output. This combination should product numbers around 116 to 118 HP.
CONCLUSION
The final word on the jet kit installation... get one! Keep in mind that jet kits require professional installation services and definite fine tuning: the service involved may much more expensive than the actual jet kit.
Good luck with your own projects!
Robert J. Miller
------------------
from Digital Sportbike Magazine
OVERVIEW
For the 1996 Suzuki GSX-R 750, we went with a Dynojet model C3149 (US Model 3149) which consisted of six main jets, four needles, four springs and a drill bit. The six jets are three pairs of different sizes, allows the modification to support stock and race exhaust systems. Based on Dynojet's recommendations, we installed the large medium jets (130) on the outside cylinders (#1 & #4) and the small jets (128) on the inside cylinders (#2 & #3). If the motorcycle was equipped with an aftermarket free-flowing exhaust system, the medium jets would have been installed on the inside cylinders and the large jets would have been installed on the outside.
Some sharp readers might have notices that the larger jets are installed on the outside rather than on the inside. Dynojet discovered that the current GSX-R engine runs hotter on the outside rather than on the inside like most other engines. In case you're wondering, the size differences compensates for temperature induce intake manifold pressure differences.
For both standard and performance exhaust systems, the needles should be set with the clips on the fourth notch. It is recommended (source unknown) to advance the intake cams 10 degrees from 112 to 102. I have also heard that 106 degrees work well. It's my suggestion that cams should be fitted with slotted sprockets (easily adjustable) and run a series of test to determine the optimal settings for each engine. If the intake cam is advanced, Dynojet recommends setting the needles to the third slot. This modification is said to improve horsepower in the mid-range with no effect on the top end performance. Ultimately, if your engine undergoes serious modification (cam timing, exhaust and jetting), a fair amount of tuning will be involved. This installation used the stock Suzuki exhaust system with the both cams set at 112 degrees (stock).
RESULTS
This bike is a psycho machine, there is not other way to put it. A stock GSX-R delivers power very much like a light switch, now it performs as if the light switch had a direct connection to a nuclear power station. Think Barqs has bike? Ouch! It would be realistic to say that the output gains were less than or equal to five horsepower. That may not sound like much horsepower but don't forget that Dynojet's kit was designed to improve other characteristics of engine performance. Throttle response is fantastic, any throttle adjustment results in a sharp reaction in engine power. The faster you can get the revs up, the faster you will go. High performance riders will appreciate how easy it is to blip the throttle when downshifting and match engine speed to the bikes velocity.
I have to admit this is the first modification I've made to this bike and I haven't ridden many other sportbikes (ZX-7 and ZX-10) but I know this bike is not longer a normal 750. Previous to this installation the power delivery was very much on or off. Once driven past 9000 RPM the GSX-R was like a raging storm but the mid-range could only be considered poor. I found the ZX-7 to me much stronger in mid-range performance... and the ZX-10, well... that was a liter bike.
The engine improved mostly in the upper rev range but I've noticed more change from 7000 to 9000 RPM, possible due to the modification to the carburetor slides (drilled). Power delivery comes on strong at approximately 7000 RPM and the previous power surge at 9000 RPM is less significant because the mid-range has improved in comparison. Combined with snappy throttle response, the engine will drive the front wheel skyward under full throttle in first gear. Without any clutch action, the front wheel lifts at 7000 RPM and draws upwards as the bike continues through the rev range. On a good day, it is possible to flip the bike under full first gear acceleration. Big second gear clutch wheelies are possible by fanning the clutch slightly while under full throttle at 10 000 RPM (Warning: Very Addictive).
On the drag strip the ¼ mile times have dropped from 11.0xx to 10.892 and the gate speed has risen from 124 to 129.08 mph. I can't exactly be sure on the ¼ mile improvements because I had only run the bike in stock form eight times prior to the modifications and I hadn't dragged at all prior to that. I'm sure that with practice I could have run the stock bike in the 10.9s but during my last outing I ran two 10.8s, two 10.9s and three 11.0s. Getting into the 10.8s wasn't too hard and I'm sure I could break into a 10.7 dial-in with some effort. As for the 10.6's the magazines claim the GSX-R is capable of... yeah right. Suzuki didn't deliver me the bike, I bought it from a dealer just like everyone else.
On a side note. Your own GSX-R is probably punching out approximately 110 HP. If you want the other nine horsies that it's suppose to make all you have to do is rebuild your engine from top to bottom with zero tolerances. Suzuki ships the GSX-R with a ± 8° tolerance relative to top dead center. I don't know when their piston & piston sleeve clearances are but cylinder friction is the number one point of lost power. Consider suicide engines used by racers, no air filters and only one of three piston rings are installed. Works great for about an hour...
PROBLEMS
Kit and all, there were still problems. Expecting a trouble free installation when adjusting the carburetors is asking for a bit too much, but it's still frustrating when you get hit with tuning problems. Below 4000 RPM with the coolant at 70 degrees, the engine stumbled and lacked power. This problem is most notable when cruising in a tall gear when the bike would actually buck none stop. Outside of the 3500 to 4500 range and the engine was absolutely perfect. It turns out that a mixture setting of 3½ was slightly rich for bike equipped with a stock exhaust system. Considering Newfoundland's typically cool summer climate (between 15 and 25° Celsius) and low altitude, bikes in hot climates can definitely expect this problem. Your choices are simple; go with a leaner mixture such as 3 turns, install a free-flowing exhaust or buy lots of spark plugs because you're going to foul a lot of 'em
A FEW SUGGESTIONS
Don't rush the job! Precision and patients is required to ensure that your jet kit is properly installed. The Dynojet kits are supplied with a diagnostic check list. I highly recommend covering each of these points even if your engine appears to run perfectly. In my case, when the engine was cold there was absolutely no problems and the engine was never given a chance to warm up during the mechanics test drive.
Ride with spare spark plugs. My rich carbs could have easily left me stranded. As luck would have it, I broke down in a friends driveway. You may not be so fortunate. Please note that the measurement scales used by Mikuni, Keihn, Dynojet, Factory and others are not compatible. Comparing jet sizes between companies is like comparing apples and oranges.
DYNO RESULTS
Tested at 68° Fahrenheit with 79% humidity at 400' elevation, the engine performed as listed below. Engine configuration was 130 outside main jets, 128 inside main jets, 3½ mixture turns with a factory exhaust system.
112.75hp @ 11 400RPM
56Lbs/Ft @ 9700RPM
¼ Mile Trap Speed: 129.08
¼ Mile Elapsed Time: 10.892
Exhaust systems equipped with replacement headers and a track only, low resistance baffle can be set with 130 and 132 main jets. Along with the gains of a track only exhaust, the larger main jets will increase the high RPM power output. This combination should product numbers around 116 to 118 HP.
CONCLUSION
The final word on the jet kit installation... get one! Keep in mind that jet kits require professional installation services and definite fine tuning: the service involved may much more expensive than the actual jet kit.
Good luck with your own projects!
Robert J. Miller
------------------