Carb, jets & restriction question.

[Paralax]

Hello everybody. Greetings from Estonia (little baltic country near by Finland). I read every day this forum and its good one. I have little problem, maybe someone can help or direct me.

I have stock '92 GS500E with 30k km on it. When i bought it, i thought, that it is restricted (in technical passport may read 20kw). Its max speed was 90-95 mph (like restricted one). On highway it makes ~80 MPG. I was certain that it is restricted but if I taked its carburetors apart to clean them, i found nothing that may indicate, that they are restricted. Main jets are 120 and pilots 40. No airflow restriction in carb. Its wierd. Motor starts and runs good, only under 4000rpm its little bit weak and does not respond for acelerator too well like mixture is lean or so (just a tought). What can i do to make it run 115 mph like normal ones and how can i fix that not-well-responding-under-4k thing? Fuel level is ok, screws are 2 turns out. Needle is in middle position. Must i change main jets (no sport filters or mufflers are installed and will not)?  

Thanks advance.

..i know, my english is little bit  :mrgreen:  

[MarkusN]

Does the slider go all the way up, opening the venturi fully? If so, then the restriction really has been removed, because that's the other part that's done to castrate power: There's a stop in the cover of the carb restricting slider travel. Quite an effective way to throttle airflow.

There are several ways how this stop was made. Some are removable, in others it is integrated in the carb cover and you have to exchange the cover.

Sluggish response below 4000 RPM is just the character of the GS motor. Removing restriction or richening mixture will not change a whole lot about that. Top performance should be better, however.

[MarkusN]

Oh, and I know richening mixture is popular in the States. I personally have never seen the need for that. She runs fine with the 120 mains. She needs a bit of choke during the first two minutes, so what?

[Paralax]

Any removable stopper for slider travel there is'nt. Slider goes almoust all the way up. If its all up, i can see about 3 mm of slider. Is it normal or must it disappear fully?

[MarkusN]

I had the same status (3mm of slider left) on mine when I got it. Slider stops are normally something like 18 mm, thus a whole lot more than you have.

I have replaced my covers with ones that allow the slider to disappear fully. Didn't notice any difference, so I don't assume that this is a major factor.

Another way to limit slider travel is a 4 mm hole in the flank of the slider that "short-circuits" the vacuum chamber at a certain slider position. You'll have to disassemble the carb at least partially to see that. Remove the cover, take out the diaphragm and the slider and look at the latter. if it has a hole in the side it is restricted that way. This was not common on the 92, but you never know. You can simply close that hole with epoxy, just make sure that nothing gets on the outer surface of the slider.

Mine, BTW, isn't such a hot runner either. 165 km/h per speedo is about the maximum I get. A friend said that in Switzerland the GSses were restricted in a way that is more complicated to remove. The only way I can think of how that would work is via camshaft or CDI, but I don't know really.

[Paralax]

On slider flat surface is no holes. But on bottom (where the needle comes out) is 2 holes (+1 needle hole). 2mm and 4mm!!

Another way to limit slider travel is a 4 mm hole in the flank of the slider

didnt understand, where exactly this restriction hole must be  

[MarkusN]

The holes on the bottom must be there (at least one*). They conduct the vacuum in the venturi into the chamber over the diaphragm. That vacuum then lifts the slider up with increasing airflow. The hole in the side (which you don't have) lets the vacuum escape into the chamber with athmospheric pressure under the diaphragm. This way the upward movement is stopped as soon as that hole comes out of the guide in the carb body.

I'd say we have established that your carbs are not restricted.

*) The behaviour of the carburetor when the throttle is opened quickly can be slightly adapted by closing one of those holes, that's why I wrote "at least one". You normally don't have to fiddle with that, however.

[Paralax]

If i want to know, will main jets changing give me some more hp-s, can i test it that way: with puting choke on (richer mixture) i will try to get top speed? If speed will be higher than usualy, then changing jets will help me. Is that theory correct?

[MarkusN]

Re-jetting does not really give you more top-HP, but even out some bumps in the characteristic. So you probably won't se an increase in topspeed anyhow. But better let the experts on that business answer that question, because as I said before, I have never considered it necessary for myself.

[Paralax]

I think you are right. Thers no big point to chase those few hp-s with rejetting, i just hoped my ride is restricred and I can easely get +14kw from it. Littlebit disapointed now because i cant.

But thanks a lot for help and advice

[MarkusN]

But then, 95 mph for unrestricted is pretty low. you may want to have the following things checked on your bike:

- Valve clearance
- Compression

To correct problems with the first item is easy.
If it's 2; uh, oh!

[The Buddha]

I'd basically restrict a bikt by limiting the max throttle opening ... you can open past 3/4 maybe ... so see if the butterflies will open fully ... That'd be the least dangerous way I think and the most easily reversible.
Cool.
Srinath.