Open pipe=Must ReJet?

[Ironbutt]

Washers from hardware stores should only be considered a temporary fix. They are not made to as tight tolerances as the washers made for the needles. Sometimes they're all pretty close on thickness, sometimes they vary widely.

Yeah, like i was saying, an interm solution while I figure out what to do..

 

[Carlo]

The need for backpressure is a myth based on people not having an understanding of how exhaust systems work.

But it will still be loud and annoying, and still require a rejet.

I keep saying that, but nobody listens.

It's not "backpressure" but positive and negative pressure pulsations bouncing back and forth within the system.

As for "rejetting", that's another myth. Main jets only cover full-throttle operation. Raising the slide needles a notch will cover 80% of all engine operating conditions. Unless you do a lot of track time, for the few times you actually run at full throttle for any length of time, your stock main jets shouldn't be a problem.

 

[Carlo]

Yeah, like i was saying, an interm solution while I figure out what to do..

The best thing you can do is install aftermarket needles with the little "E" clips that hold them up. They have 5 positions you can set the clips to. But even more important is that these needles usually have a much smoother and longer taper than stock needles, which have almost no taper until the very tip.

This keeps the fuel mixture lean until almost full throttle.

Used to be, all slide needles were like this. Carb tuning was simple and quick.

 

[fjackie]

The best thing you can do is install aftermarket needles with the little "E" clips that hold them up. They have 5 positions you can set the clips to. But even more important is that these needles usually have a much smoother and longer taper than stock needles, which have almost no taper until the very tip.

This keeps the fuel mixture lean until almost full throttle.

Used to be, all slide needles were like this. Carb tuning was simple and quick.

Now, the EPA dosent want you to fiddle with any carb adjustments.

 

[ST Guy]

I keep saying that, but nobody listens.

It's not "backpressure" but positive and negative pressure pulsations bouncing back and forth within the system.

As for "rejetting", that's another myth. Main jets only cover full-throttle operation. Raising the slide needles a notch will cover 80% of all engine operating conditions. Unless you do a lot of track time, for the few times you actually run at full throttle for any length of time, your stock main jets shouldn't be a problem.

Strictly speaking "backpressure" doesn't cover it accurately. But for the masses, it works. Yea, pressure waves and scavenging and all that are part of the picture.

 

[ST Guy]

I keep saying that, but nobody listens.

As for "rejetting", that's another myth. Main jets only cover full-throttle operation. Raising the slide needles a notch will cover 80% of all engine operating conditions. Unless you do a lot of track time, for the few times you actually run at full throttle for any length of time, your stock main jets shouldn't be a problem.

Right on. Most bikes come from the factory with the main jet pretty much right on. They can do this because the EPA doesn't test the bike at full throttle with the slide all the way up which is where the main jet has it's greatest effect. Lean conditions as a result of EPA mandated emission restrictions affect the idle, low and lower midranges most. And these are corrected with mix screws, slow speed jets, and needle changes.

 

[elskipador]

you ever put a stock, carbed bike, from say the mid to late 90's on a dyno with a EGA? if so you might think differently about whethers its lean @ WOT.

 

[ST Guy]

you ever put a stock, carbed bike, from say the mid to late 90's on a dyno with a EGA? if so you might think differently about whethers its lean @ WOT.

Response to my post?

 

[Diezel]

Strictly speaking "backpressure" doesn't cover it accurately. But for the masses, it works. Yea, pressure waves and scavenging and all that are part of the picture.

Welp either way you tend to think of this.. I know for a fact that a certain ammount of "restriction" (since you don't want to call it backpressure) on an exhaust leads to more effective overall output from an engine. Free flowing exhaust, tend to help smooth out pressure waves (dependant upon design!) and allow the exhaust to flow quickly and smoothly. Which tends to increase gain in very narrow areas of the engines operating rpm.

Either way, if you want smooth, managable power, with gains in all areas. it is 110% demanded that a well designed Exhaust system, and Fuel (injection or carbs) be dialed to benefit the system.


Also the comment of the "main jet" not meaning anything on bikes.. WHATEVER.. Most bikes are LEAN on 100% of the curve.

 

[fjackie]

Attn: Elskipador

How will my bike run with stock pipe and air filter installed? I assume a slightly richer mixture would not effect performance much on a stock bike. Thanks.

 

[elskipador]

i'm beating you'll need to drop down to 137.5 or 140's with the stock can and stock filter.