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83 GS750ES IS STARVING?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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OK. having been through a lot of electrical trauma, i finally have new gauges and can ask a question about performance.

i have no experience with motorcycle carbs and am really kind of weary about taking them off apart, etc. there are other threads about this, but i am not sure with the odd behavior if the advise in those threads is related to my problem or not....

the bikes has vance and hines 4 into 1 exhaust. i have no idea if the carbs were re-jetted or not, but i am assuming yes since it runs normally under most circumstance. i will most likely be replacing it with a new same brand / type of exhaust soon.

freeway speeds (4 or 5th gear between 4000-5000 rpms) the bike seems like it is starving. it has the stock air box with k&n filter. is there an easy way to tell if it needs fuel or needs air?

filter is new. i planned on putting in new plugs and checking them against the official 'chart'. throttle is responsive under 4000 and if you accelerate hard, it goes right through the range with no problem. it also has no problem going at 6-7000 rpms without any issues for long stretches.
the only problem is trying to cruise at 55 or 60 mph.

any help is appreciated.

thanks,
jay
 
I have the same problem on my bike, although my flatspot is between 5000 and 6000rpm. Luckily for me this is above "cruising speed", but it is an issue when overtaking in 5th gear. Like you I have found that accelerating hard as opposed to gently gets through the range.

I suspect that the carbs are slightly out of adjustment, but I can live with it for now.

My bike has a 4-1 Harris Performance Exhaust, bigger main jets, stock airbox and stock airfilter.
 
vacuum vacuum vacuum

vacuum vacuum vacuum

The problem is due to poor vacuum prohibiting throttlelift. It doesnt matter how big main jets you put in since the throttle wont lift the needle enough to give the benefits of a bigger jet. On my previous 750-83 I put in a Dyno-Jet st.1 kit that solved the problem. On this bike you drill the vacuum-holes bigger in the throttles to get a quicker and reliable lift even with KN:s and 4-1.
However, an old/ bad exhaust could also give these symptoms if the muffler is in need of re-packing or as in my case, a piece of pipe that had vibrated loose inside the collector making the flow partially rotate 180 degrees giving a lot of turbulence in the system. That resulted in very blurry almost richfeeling performance just at 5000rpm.

But I would go, in this case, for the carbs.

GOOD LUCK :D
 
Well I'm not sure of how the inside of the exhaust looks, but I know that I am missing four springs that are supposed to be mounted where the four pipes combine into one beneath the engine. On cold mornings I have noticed that it's been leaking a bit of exhaust there.

If I get it tightened, could this help with the 5~6krpm flatspot ?
 
D|sElMiNk said:
I have the same problem on my bike, although my flatspot is between 5000 and 6000rpm.
Click to expand...
I am not sure if this is what you are experiencing, but the engine in original condition (OE air filter, carb jets, exhaust, etc) showed a slight decrease in torque in the 4500 - 5500 rpm range, accompanied by a corresponding decrease in the rate of hp increase with rpms. By 6000 rpms, the torque starts to increase again, with a steep rise in hp up towards red line.
 
For starters....Try operating the choke (enrichens fuel) at the speeds you mentioned and note any changes for better or worse. If the bike performs better then you're lean, if worse then you're too rich. Suzuki's were jetted on the lean side so with the addition of a pipe and high flow K&N would only lean it out more. You may be able to verify that your bike has a jet kit installed by pulling one of the slides and checking if your needles are adjustable.
 
Simon Waters said:
I am not sure if this is what you are experiencing, but the engine in original condition (OE air filter, carb jets, exhaust, etc) showed a slight decrease in torque in the 4500 - 5500 rpm range, accompanied by a corresponding decrease in the rate of hp increase with rpms. By 6000 rpms, the torque starts to increase again, with a steep rise in hp up towards red line.
Click to expand...

Well, unless my tachometer is inaccurate the range is presicely 5000-6000rpm. Above 7000 is where it really takes off, I have to really hold on not to slide back off the seat 8O

I will try the choke trick tomorrow though, if weather allows. Got the valves adjusted today plus some other small fixes, I'm really itching to get riding again.
 
It seems, after reading the replies here that the bikes in the U.S are restricted in many ways such as pilot screws and needles. Here in Scandinavia we dont have that on our bikes. Good for us? Propably.
It must be a b***h to adjust an engine that runs poor or similar over where you guys live. Anyway, that is because of regulations in different countries.

As for D|sElMiNk: Put in a DynoJet st.1 and your middle will increase and flatten out the power-curve. It did a lot to my 750.

I just got the 1100 to gain more torque than the 750 could give me. But the 750 was a much more funny bike on twisty roads than the 1100.
 
Thanks for the great info on this subject from everyone, but my bike has mysteriously cleared up all by itself. (after a new tank of gas and about 100 miles)

:P
 
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