I figured I'd put this topic out there for anyone who may wonder... and because I just feel like making the whole thing clear. It is quite a misunderstood topic.

Everyone gets all wound up about emissions equipment on this bike. That and the novices comment about the bike "overheating" or "running hot" because heat,oddly enough, radiates up from the exhaust, coursing through which there are gasses well over 1200 degrees.

For obvious reasons the heat is not unusual. Fact is any research done would provide the fact that maintaining the temperature will actually maintain higher velocity and aid in the scavenging of the cylinder.

There seems to be some myth that when one's exhaust glows a bit red it is bad. If you do any research what so ever you will find this is of no big issue. In fact it is a relatively common occurrence in many IC engine performance industries like the automotive industry. No airflow will allow an exhaust to heat up to a temperature where it will glow. There have been pictures of motocross racers sitting and waiting to race, exhaust glowing as they heat up due to no air flow over the pipe.


"Check out the glow of the header pipe on Ryan Villopoto’s No. 2 Kawasaki KX450F."

And from Dubach Racing:


"One of our riders sent us this cool picture from last round of the German supercross. Yes its normal for the pipe to glow red hot when there is a lack of air flow to cool it down."

I would say Dubach knows a bit as did Ryan Villopoto's tuners. Seems to back up what I'd experienced and learned over the years and backed up through research.

If cooler exhaust headers was a major plus, manufacturers would never have used double wall tubing, shrouding the single internal tube inside another, on street bikes. That was done to try to keep chrome from turning blue. If it was necessary to have a cool header there would be fins on the pipe and scoops directing flow to the pipe. Some sort of attempt to cool the head pipe. Heck, now Yamaha wraps it around the engine on its motocrossers and sport bikes used to run them up under the seat. So it seems the manufacturers aren't too worried about exhaust temps in general. As long as the pipes aren't melting or damaging anything around them they don't seem to care.

How to deal with the exhaust heat if you don't like it? Racers of all types are doing ceramic coatings to hold heat in for multiple reasons, including cutting the heat radiation down, especially under the hood of cars. I did my on 650's pipe for three reasons:

• Lower heat radiation from the pipe, more heat stays in the exhaust gasses and goes out the muffler. When it was bare steel it was almost intolerable to have my leg next to it, the stock pipe had a shield. After coating, far less issue.
• No corrosion - rust - on the head pipe due to coating and, in fact, the internal surface of the head pipe is coated too, actually providing a bit of insulation to the pipe although more as an anti-corrosive. It was bare steel to start.
• Ease of mainenance - aka none really needed.

I did not do it for high performance reasons. It was about not cycling between paint and rust and paint and rust - I wanted a way out. Coating was it.

Header wrap comes into question from many sources, read up on it. I personally think wrap makes sense at the rearward areas of a pipe, like the expansion chambers on some of the hi-performance bikes, but further up the tubes - definitely questionable.

Then comes the emissions plumbing myth, that there is some gain by removing the emissions equipment. There is only one gain, that is the savings of maybe a pound of equipment, about 1/2% loss of bike weight. It may cool the exhaust temps a bit, but no gain in performance. In fact it theoretically would reduce performance, but I doubt any difference would show up either with or without the stuff.

Now if you want to take off the emissions plumbing, have at it. It will open things up under the tank, but again no big deal if you don't.

I liked Marcelino's comment about it in his cam timing mod article. He basically said he left it on because he was in favor of cutting a bit of the emissions from his environment. Kind of recycling in a way. It may not do anything directly for you, but it certainly doesn't hurt anything for the bit of bother it is.

Of course I left it on because I didn't have the bits to plug up everything and figured it wasn't a big deal to plug it all back in where it is needed. But that's just my choice.

I guess until someone can factually contradict sources like NASCAR and NHRA tuners, Dubach racing, and all the other performance sources I'll hang on to my comprehension of the facts (aka not opinion).

 

I propose that by wrapping the header right out of the engine would give the best benefit. By having a higher temp all the way to the tuning chamber, it will maintain higher velocities and lower pressure.

 

It would make sense, but do the research. Seems the heat wrap can be an issue with the metalurgy. The NASCAR teams would have to replace headers every race due to deterioration.

The easiest thing to do is either use heat shields, wrap only at the back portions like the chamber on the FMF style pipes for burn protection leaving the rest of the pipe as is. The other is to do the ceramic coating inside and out. Holds in the heat, still insulates the metal, and a second insulation on the outside to reduce heat radiaton.

For protection the heat shield is the trick. For performance it really doesn't make much difference for the average rider. Point being it really doesn't matter if the pipe glows a bit when at rest and the removal of the emissions equipment is only a personal choice without necessity. Unlike jetting and such. Knowing this will at least allow for a knowledgeable choice, not "following the herd".

Key for the glowing head pipe is to simply ride. No air flow versus even 5 mph is the difference. Key for knowledge - it doesn't matter either way. Cherry red glow happens. There are exhaust gasses flowing at around 1200 degF and that glow will happen if sitting still.

 

Once jetted and "piped", the KLX can be afflicted with annoying decel popping. What was learned years ago, in here, is that removing the air injection system and backing out the fuel screw is the cure. Search keywords - decel, backfire..

 

Back in the good-ol'-days when the Kawasaki air injection first came out on the KZ900/1000 series, the OEM header pipes were double walled. As soon as customers installed 4-into-one, single-wall, performance headers without disabling the air injection, the header pipes turned a dark blue even with proper jetting. And not that you can't blue a single-wall, chrome header pipe with proper jetting with the air injection disabled, but there was quite a bit of consternation among some customers who experienced this. My Kerker and Jardine headers back in the day blued to some degree at the headpipe even with the air injection disabled, and it didn't really bother me. Maybe it had something to do with the way I rode those bikes back then.

 

Still didn't matter either. Most all chromed pipes blued, especially when you run it a bit hard. I'm sure the air injection ran a bit hotter, but when the gasses range normally from 1200 plus degrees. Even the well oiled two strokes roasted the 1200 degree VHT off the head pipes near instantly upon reinstallation after painting... wish they'd had coating back then. Nice black cones, rusted head pipes... bummer.

Decel popping is pretty much normal regardless. Read about it about once a year in either the bike media or even the automotive media.

 

No one has to endure decel popping with the KLX250 if they don't want to - we know the cure - remove the air injection system and richen the pilot circuit.

 

Yes sir, pardon my pointing out the fact that it is nothing of any importance.

Anything else you want to berate me with, please continue.

By the way how does it work on a correctly jetted SR500 and KLX650, neither of which has any form of air injection? And why do so many performance vehicles have the same issue and knowledgeable mechanical experts say it is pretty much normal and no big deal?

Experts like like Mikuni:

4: Backfires in Exhaust

Note:

It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.
5) Completely stock Harleys do not do this until open-end mufflers, such as the popular Screamin' Eagle slip-ons, are installed. The exhaust must be both free-flowing and have an open exit for the popping to occur.


Other possible causes:

Air Leaks:

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust backfiring. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system backfiring.

A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction.

Lean Carburetion:

While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit.

Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual.

Ignition:

If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.


There have been similar summaries in some forums, but it is hard to argue with the actual really for real carb people.

"Burn Baby Burn

The last thing I want to address today is the subject of deceleration backfire, or “popping”. This topic generates a lot of concern from inexperienced riders, or even from experienced guys who just hate the noise, so lets take a look at what causes it. But first things first, lets define the issue:

Deceleration Backfire is caused by fuel burning in the exhaust manifold or header.

No ifs ands or buts, that’s what causes it. But the bigger question is how does gas get there in the first place, and that’s a bit more complicated. Generally, there are a variety of ways it gets there, and a variety of things that can make the backfiring worse. But there’s a kicker, and something you should understand before we go any farther:

A motor in perfect tune will exhibit deceleration backfiring.

Therefore, just because your motor is banging it up, doesn’t mean there’s anything wrong. And consequently:

Getting rid of the noise means de-tuning your motor.

Yup. If you’ve just got to eliminate that popping, you’ll have to accept the fact that your motor is going to be forced to run rich to do it, and that isn’t necessarily a good thing. So lets talk about what causes the problem.

Ok, so you’re riding along at some given rpm, and suddenly you decide to decelerate, and you reduce the amount of throttle. This causes an “overrun” – that is, the motors rpm is turning faster than the fuel provided can support, so the motor begins to spool down. This causes a couple of things to happen.

First, when you close the throttle, you are also closing the throttle plates. This reduces the air and fuel flowing into the motor, and increases the vacuum (lowers the pressure). This results in less air and fuel in the cylinder during the power stroke, which in turn results in a lower pressure in the combustion chamber. Remember I said earlier, that the A/F mix burns faster in proportion to the pressure applied? Well, when we reduce pressure this way, the mix burns slower. This results in two things happening.

1. The lower burning fuel generates less heat, and the cooling effect of the non-burning fuel tends to “quench” the flame front, or slow it down even further. Because the mix is burning much slower, the exhaust valve can open before all the fuel is consumed, and the unburnt fuel is ejected into the exhaust.
2. The engine designers, in order to promote smoother idling and better combustion, retard the spark when the throttle is shut, and this results in the mix being lit later.

So, now we end up with unburnt fuel in the exhaust, and burning fuel being ejected into the exhaust, and bang! Backfire. In addition, Manufacturers have added a device called a “programmed air injection valve” (Pair Valve) that actually injects some fresh air into the exhaust to help this process along – since fully burning the fuel results in cleaner exhaust. So the backfiring is not only a normal part of the engines operation, it’s also intentionally amplified by the manufacturer! Of course, normally, that massive bazooka pipe hanging on your bike hides most of the noise, but it’s there, even when you can’t hear it.

So the bottom line, is: That backfiring is perfectly normal and expected. If you’ve just got get rid of it, that’s up to you. You’re entitled to set your motor up the way you want, and your goals are your goals. But don’t refer to it as “fixing” the popping. Rather, the correct way to think of it is “de-tuning a bit to get rid of the popping”.

There are a few ways you can do this.

First, use the stock pipe. It will hide the sound, by absorbing it into mass, and masking it with the larger baffle space. Second, you can add more fuel during deceleration. This has the effect of raising the chamber pressure slightly, which burns a little more before the exhaust valve opens. Lastly, you can remove the Pair valve, which reduces the amount of available oxygen in the pipe to burn the unburnt fuel."


"This is exactly correct! If you think about the mechanics of what is going on upon decel, it makes perfect sense:
You start out with an engine that is turning high RPM with a carb that is open, flowing freely. Next, you close that slide. This has the effect of creating a tremendous vaccuum in the intake manifold (CHOKE!). This vaccuum does curious things:
1. It pulls air and fuel from wherever it can--including the idle and low speed jetting in the carb.
2. To counteract the vaccuum, air will take the path of least resistance--including sucking exhaust gases back into the combustion chamber during valve overlap (the brief period of time that the exhaust and intake valves are open at the same time.

So what does this mean? Well, now you have a disproportionate rich mixture heading for the cylinder AND what little oxygen is drawn in is further diluted by gases that are coming back into the chamber from the exhaust valve. The result is poor, incomplete combustion! Depending on the temperature of the exhaust pipe and gases, reignition is possible once this mixture is introduced into a more oxygen rich environment. This produces the "pop."

Why does a lean running engine have a tendency to excessively pop? The exhaust gas temperature of a lean engine is substantially higher than one that is running on the rich side ( an EGT probe will show this). Therefore, the high EGT serves to heat the pipe more and the gases themselves become a much better source of re-ignition. By richening things up, you are cooling down the exhaust temp and therefore reducing potential re-ignition sources.

Any 4 stroke engine--even those that are flawlessly tuned will pop on decel. It is harmless, but can be annoying--granted. However, I would never alter the jetting of an otherwise performing motorcycle to get rid of it. Go by the seat of your pants and the color of your spark plug rather than the popping as an indication of the jetting of your scoot!"

So it is your and other riders' choices if they want to pull emissions equipment and dump a bit more unburned hydrocarbons into the air or if they want to fatten up the idle mix to get rid of a normal circumstance and save a pound.

You don't "cure" normal.

 

Re: Nascar, are they running DOHC now?

 

Your right, and I've always wanted to be normal. I'm putting mine back on.