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Discussion Starter · #1 ·
While trying to dial my bike in (before oil line got a hole) it was running pretty rough when cold. Once it warmed up it ran a whole lot better (really good running it hard) but cruising was still choppy (not smooth) which points to the needles. Do I need to raise or lower them? My set up is 89 1100 38 flatslides (135mains/17.5 pilots/floats at 17mm,needle in middle position) timing advancer and sidewinder exhaust. Thanks for any tips
 

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If it's running bad when cold i'd say it needs more fuel.

From factoryPro:
If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
 

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That Side Winder give approx: 0 back pressure, I bet it sound good on the pipe. I agree with both previous post, its just lean. Maybe even back the mixture screws out in 1/8" increments to help get it started easier. The wheather in Florida is starting to cool off I bet? Also, when adding an ignition advancer, the bottom end can usually take a little more fuel the without, same for adding a Side Winder. That thing will require a main jet change from a good running set-up using a pipe with some sort of muffler. If you dyno it, you should see 2 very pronouced "dips" in the torque curve, I think in the 3,500-4,500 rpm range and the second in the 6,500 to 7,500 range. The ignition advancer may help that but be advised. Adding static timing will increase dynamic combustion chamber pressure and increase throttle response on the bottom end and midrange, however. That same pressure building will sometime cause the engine to actually loose torque up top because the piston must push up against the rising chamber pressure BEFORE top dead center. If you can, tune the bike on a dyno, two runs (it is cheaper that way). First, get the bike running the way you like it then take it to a dyno and run with the advancer and without.
 

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Discussion Starter · #5 ·
Thanks, its been a little cooler here but today its HOT. I havent had a chance to really ride it yet to see if the main needs changing, I just finished getting it back together. The previous owner had a 165 main in it (running a system with a muffler) but I was told that was way too big. I have the 135 now. Any ideas what I should go to? These jets are expensive buying them individually. My dealer used to charge 2.95 now there 4.33. Are the dips you are talking about due to the pipe?
 

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Yes, the "dips" are cause by the 4-1 exhaust design. A 4-1 will always make more peak torque then a 4-2-1 but, at the expense of midrange torque (flat spots). As for jetting, I'd rather not advise but, the 135 should be it for the top end. Raise the needles to add full to the midrange. Let me say this up front... 1127cc, 10-1 compression engine is NOT enough motor for 38mm Mikuni flat-slide pumper carburetors and certainly not enough to need a 1 5/8 header tube Side Winder. If there was anything you could do to destroy the fat torque of the 1127 motor, those are to very good starts. That motor needs some sort of back pressure to get it to carburate properly below WFO throttle. If you were spraying the hell out of it, I can see the big flowing pipe and open intake. I bet if you were running 36mm Mikuni flat slide carbureters along with a Vance and Hines Super Sport WITHOUT the Quiet Tech baffle installed, you'd think you added 35hp to the mid range. Your carburetion is full of holes because you have big carbs. and a big header and open baffle, that is Pro Stock tuning on a street bike. I have made all these mistakes before with my previous streetbike. Remember the oil cooled GSXR side draft head does not/can not use the complete and total valve area because of the cylinder head design. Most GSXR with "head work" and can really use the big carburetors either have epoxy on the port floor to raise it are run a Sling Shot 750 head which come from the factory with as cast .600" higher floor ports...
 

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Discussion Starter · #7 ·
Thanks for the advice rajay. Mybe I will look into getting a different muffler set up. I went with that set up mostly for look and ground clearance (I didnt know it would hurt performance). Maybe I will use the sidewinder header and try to run a different muffler set up. I am going to be spraying and doing headwork in the future (as money allows with a 1200/month child support payment) but I am almost 100% sure its a stock head for now. Where are you located in florida? I am in Palm Harbor. Thanks for all the advice. Are all the 750 heads better or just the slingshot?
 

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Just 1988-1989 GSXR750 AND the early 750 Katana head. They all come with the same size 28.3-28.5 (depends on who is measuring) intake valves and 25mm exhaust valves as all year 1100 heads, however. Those head from the 750's mentioned before come with raised port floors, this basicly tries to make the port to intake valve section "think" it is a downdraft head...... and thus exposes more of the intake valve to the incoming fuel/air mixture. Those heads will also raise static compression by 1.5 points as they have a smaller combustion chamber. Me personnally would only use the 750 head on a stock sompression 1100 motor with no other mod the a good camshaft. If I was spraying are building "monster" engine, I stay with the 1100 head. The draw back of the Sling Shot head was tendency to crack between the exhaust valves and the spark plug hole. This common on air/cooled high out-put four stroke engines..... Bottom line, if you are going to add a power booster, keep your current set-up. Try to get your jetting as "best" it can be keeping mind the type set up you have. If the header is a Vance and Hines Side Winder, buy one of there "tuning" kits which will come with three different size restictor which go in the collector to increase back pressure. then you could remove it when at the track and on the bottle...

If you are adding a power adder, no real point in getting head work. Your horsepower is being delivered externally.............

Go the Pro Star race this weekend in Gainesville and look at the other GSXR set-ups, talk to people there. The Shnitz table will more then likely have the Vance and Hines Exhaust tuning kit I mentioned before.. Take only a small amount of cash, it is the end of the season and EVERYTHING will be on sale...it is easy spens TOO much... ha, ha, ha.
 
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