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Can someone straighten me out???

  • Thread starter Thread starter 88mm
  • Start date Start date
8

88mm

Guest
Very new here. I have my first bike. GS250t. It is small, super cheap and perfect for me to learn with. My first in many queastions to come is about carbs and their interaction with exhaust and air filters.

Now after searching and reading I have realized that after you do mods such as aftermarket or homemade exhausts and pods your engine runs lean. (Makes sense) Now can you just increase your fuel mixture to counter the effect of more air flow? And is a rejetting of carbs only to maximise the horsepower of the mods that you do? Or is it that you have to rejet just to have the engine run properly after such air flow type mods?


Whoa! Sorry for such a long one. Any help or advice or whatever you have would be great.

Thanks,
JP
 
I'm no carb expert, but you usually can't just turn a screw or two and solve your mixture difficulty with pods and performance exhausts. Off idle, mid-range, and full throttle all use different carb "circuits" and have different adjustments. The mixture and air screws are only a part of the picture when it comes to fuel mixture. Also depends on the bike. Rejetting isn't just for increased performance but also for smooth throttle response.

In general, unless you really enjoy messing around for a while to get it right, its best to keep it stock.
 
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I see.

I wouldn't really mess with it but unfortunatly the mufflers are falling apart. (I can only use so much patch tape) I purchased a used carb for this bike so I thought I could get to know it a bit without taking apart my bike. Are there any generic universal fit mufflers that would work and possibly look different than the originals?

Thanks for the response!
 
88mm said:
I see.

I wouldn't really mess with it but unfortunatly the mufflers are falling apart. (I can only use so much patch tape) I purchased a used carb for this bike so I thought I could get to know it a bit without taking apart my bike. Are there any generic universal fit mufflers that would work and possibly look different than the originals?

Thanks for the response!
Click to expand...

The problem with aftermarket exhausts is that they flow too much air for the carbs to adjust to. OE mufflers flow less, and are much quieter. You will do well to try to adapt on some OE type mufflers to keep the carbs in their sweet spot without messing around with jetting and such. Same goes for the air filter, keep to stock.
 
Hmmmmm....

I ahve checked out some of the OE Harley Mufflers and they don't look too bad and some that are on Evil Bay are pretty affordable. That looks to be the easiest way to go right now. Just have to find a set with the proper diameter. Do you guys acually weld these on or clamp them somehow?

Thanks for the great info and help:)
 
If you make significant intake and/or exhaust changes, and these mods lean the mixture, then you have to richen the mixture to a suitable fuel/air ratio.
On a 250, I'd suggest leaving it stock. However, because you've decided on a different pipe (at least), just test the bike and take some plug reads.
There's no way of knowing for sure how the different exhaust will effect the mixture, without testing/plug reads.
The reads at full throttle, 1/3 throttle and minimal throttle positions will tell you what to do for each jetting circuit. You may get off with only a main jet change and some mixture screw adjustments, or, you may have to change all three circuits. Main, jet needle, pilot.
You may not have to make any changes.
But whatever you do, don't run the bike too lean.
 
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88mm said:
Hmmmmm....

I ahve checked out some of the OE Harley Mufflers and they don't look too bad and some that are on Evil Bay are pretty affordable. That looks to be the easiest way to go right now. Just have to find a set with the proper diameter. Do you guys acually weld these on or clamp them somehow?

Thanks for the great info and help:)
Click to expand...
Supposedly if yu go into a Harley dealer they will either give you a set no charge or dirt cheap. Most have piles of them from people switching to aftermarket exhaust. If they don't let the dealer put them on their warranty is void. You can't even change bulbs for yourself without voiding the warranty.
 
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