new exhaust question

[zpromax777]

Hello, I've have my '93 KT RT for about a year and decided to do some modifications to it. Mostly visual stuff, but after installing a new exhaust I noticed that there is a lot of popping during deceleration and that on hills or under slightly heavier throttle, the engine just flattens out and the exhaust just sounds like its farting until you 'reset' the throttle and give it gas again.

I'm wondering what this could be. I've done no other mechanical modifications other than the new exhaust. I also chose one that had the same diameter outlet pipe as K75's exhaust.

Any idea what is causing this?

Thanks!

[The Mighty Gryphon]

Motorcycles are designed in a very competitive market environment where performance is of prime importance while government regulators enforce emission and fuel economy requirements.  OEM engineers spend a lot of time and money optimizing exhaust system performance to meet government and market mandates. 

Tests on aftermarket exhaust systems pretty much shows that they are mostly cosmetic and impede optimum performance.  Exhaust back pressure across the engine's rpm range is important to optimum engine performance.  The exhaust system will impact other engine parameters like valve timing, fuel delivery, and ignition to name a few.  Slapping on an aftermarket exhaust is only part of a new engine tune. 

[Laitch]

If if there is no verifiable service record for that Brick that shows a relatively recent tuneup then make time for valve clearance inspection, fuel tank interior inspection, replacement of the fuel filter and inspection of the fuel lines inside the tank and outside. Check the condition of the air filter, too. The OEM filter is a good one; just shake the dust, or gravel, out of it. 

One thing about Bricks, is that if the throttle is not closed completely when they're decelerating, they're likely to pop—especially with aftermarket exhausts or overdue tuning. You can try adjusting the throttle switch to eliminate some of that but throttle technique, the current state of the engine's tuning and your aftermarket muffler will also play a role.

[frankenduck]

K75s will pop (backfire) even with a stock exhaust if you engine brake too hard. Solution: Use your brakes not the engine to slow down.

[Chaos]

a KT RT?  That's a new one to me.  I have a MAC slip on pipe and it seems to backfire more than the stock, or maybe it's just more noticeable.  Performance is probably a wash but it's lighter, looks better and the tone is Sooooooo much better than the original. 

[frankenduck]

Tests on aftermarket exhaust systems pretty much shows that they are mostly cosmetic and impede optimum performance.  Exhaust back pressure across the engine's rpm range is important to optimum engine performance.

Example: Don Eilenberger did dyno runs of a stock K75 exhaust vs. a Staintune and the Staintune performs differently than a stock exhaust.



You probably know this but the term "backpressure" is a bit of a misnomer. Exhaust engineering and design is very complex and has to do with how pressure flows through the exhausts as opposed to merely backpressure.

[Martin]

You can virtually eliminate backfiring on a K75. 1/ Set the TPS. 2/ Eliminate exhaust leaks. 3/ Eliminate intake leaks. 4/ Set valve clearance.        5/ Set the CO2 mixture. 6/ Make sure the injector pattern is correct. 7/ Keep the throttle shut on overrun, or put it down to part of the 75,s character and live with it.
Regards Martin.

[frankenduck]

You can virtually eliminate backfiring on a K75. 1/ Set the TPS. 2/ Eliminate exhaust leaks. 3/ Eliminate intake leaks. 4/ Set valve clearance.        5/ Set the CO2 mixture. 6/ Make sure the injector pattern is correct. 7/ Keep the throttle shut on overrun, or put it down to part of the 75,s character and live with it.
Regards Martin.

Riding K75s for so long, the bikes have subconsciously "taught" me not to engine brake too much. My K75s hardly ever backfire. Can't remember the last time that it happened but it does pop once in a blue moon.