I tested the CVK carb with the air box that I'd added the small K&N filter to this morning.. (The K&N looks huge in this close up foto, but it's fairly small)





The bike ran through my test section of road in just 5.22 sec from a 17kph roll, only 1/10 sec behind the 36mm's best effort. Boy it felt really strong too with lots of torque pulling it through each gear. I crossed the finish line a second or two after shifting into 4th. I still have to recheck the WOT jetting which was perfect on Nov 15, but may be lean now after the addition of this filter. It didn't seem inclined to want to hit the rev limiter today, so that may be a sign the jetting's off. My previous CVK jetting check was well before I reinstalled the CVK with the air box boot askew, so that mistake was not in place and the a/f reading back in mid November was accurate.

I also have to check the performance with the stock boot. (It's raining now)

So, there may now be an new performance option for people who don't want to buy a bigger carb. The little K&N is a tight fit in there with little clearance all the way round, but I think a 1" section of hose (or larger) could be run from the top of the boot to the air box after drilling into the the air box above the current boot spigot. If you can locate a pre-bent 90 deg hose made for some other application it'd make the mod easier yet. Then you just need a short flanged spigot piece at each end that can be held in by a spring washer and you're in business.

Buy a used air box boot off eBay and try it yourself. Or just take your hose off and take a test ride. Once I get the correct WOT jetting figured out, you'll know where to start with your boot mod jetting.

I submerged the top of the boot just below the water line in a container, than froze it to make drilling it with a hole saw easier. Eliminating the risk of the hole saw grabbing the rubber and screwing it up.

Before it's all over, I may experiment with a larger hole in this boot just to see there's any gain by going bigger.

 

My theory is that the stock intake tract length from carb to air box inlet is too long for the CVK's higher velocity capability, hurting max performance. Where that same intake tract length probably aids the bigger carbs' performance.

With the air box being placed where it is not for performance, but because that's the only place left to put it-it wouldn't be a surprise if the intake tract length is not optimum for the CVK.

 

WOW.. Could 1/10 second be within your margin of error ? Meaning that a little variance on the TM-36 time and the CVKs' time, in the right directions, would have them neck-n-neck..?

At any rate, this is HUGE info.. Kinda puts merit to those that have said, for quite a while, that the TM-36 really only offers enhanced throttle response via accell pump and not any discernible HP/TRQ increase..

This mod and its' testing could really change the KLX modding landscape.. Atta Boy Richard !

 

I think you would have more performance to remove the side filter, get rid of the air box & filter and put a short intake trumpet on the end of the stock air boot. Or just use a trumpet on the carb and get ride of the air boot. You would probably need to richen it up a little.

 

Maybe, but either of those arrangements are not good for off-road, and you'd be sucking in a lot of header heat.

 

Ya I think it's kind of a nice big r-evolutionary step-of a sort. 1/10 sec is a very small gap. If I was doing say 70 mph at the end, I'd have only been about 10.5 feet behind a bike running 5.12 with a 36mm carb. Right, with the variance leaning towards each other, the two set ups could be dead even.

With the stock air box boot in place, then I am pretty sure the CVK will be further behind the TM36 . So evidently carb for carb there was a gain to be had with the 36s bulk flow ability. We'll see what the real performance gap between the two carbs is when I get around to testing with just the stock boot and CVK.

Remember too that the 36 is normally still breathing through the stock intake and ports, which right away limits its potential.

 

Isn't your bike a supermoto style, you seem intensely interested in pure acceleration. You could put a metal plate between the exhaust on the right side and the carb area so the only air would come in from the top or left side.

 

It was made as a sumo, but it now has 18/21 wheels and knobbies. I use it where ever I want to go. I was just speaking in general usefulness terms regarding the shorter stack.

You never know, a much shorter filter might even slow the bike depending on whether the CVK needs some of the intake boot for max efficiency.

I pulled the boot all the way off one of my larger carbs just to test and that slowed the bike by quite a bit.

 

I didn't say to take the boot all the way off, you did. Yes the exact length needs to be determined, but the cam is not very hot, so it would be forgiving.
But if you ride in the dirt forget it.

 

This was just an experiment to follow up on the performance increase I thought I felt with the boot accidentally installed half on/half off at the carb end previously. I've taken it about as far as I can or want to go unless I can find or have something with a larger ID made up to stick into the boot. Since there's already a hole in this extra boot I guess there's no reason not to try something with a larger ID at some point. I don't know if I want to leave that filter arrangement the way it is anyway. Though there isn't a lot of room in that area of the bike for many other options.

So far though, nothing I've done with either of the 3 carbs has moved the bike's performance down into say the 4.9X range. Unless I find the CVK WOT jetting is off a lot because of the increased air flow; hopefully a couple sizes - which could yield a nice power increase once corrected, I'll still be stuck where I am with all 3 carbs timing in at or very near 5.1X sec.

I tend to think the previously perfect CVK jetting is off more than a size now, because since the boot mod it seems there was a lot of power right up to a certain rpm, and then there was no hint of the engine wanting to rev to the limiter.


I'll be checking the jetting as soon as the weather clears.


Otherwise, I'll probably have to look elsewhere for a quantum leap in performance.