I thought the amount of torque and HP gain from 351 kit blew slip-on muffler swap out of the water? Don't the mufflers tend to just add a little power up at top of rev range and not do much for low-end torque?

It's a shame the DG-R is so loud or I'd be more interested in it since it's so cheap. I wonder what the quietest - but still effective - aftermarket muffler is. There's a FMF that's 94 dB but I don't know what the stock exhaust dB is.

Most of the aftermarket mufflers are $300-500 - withOUT headpipe, and that's approaching cost of 351 kit. On your mod list you mentioned "Exhaust header port matched to exhaust port"... what did this entail?

What's the airbox insert you refer to? Is that the post where someone tried to smooth out some of the sharp corners in the airbox with a hardening agent (epoxy?) of some kind?

I already have the KDX snorkel on the bike but I could pull the lid completely. The MCM looks pretty intimidating... I haven't even worked up the nerve to pull the carb yet and I really need to due to the rough idle (and need to adjust/replace fuel-air screw with extended screw).

If I went 351 kit in the future, I'd have someone else do the work :b

 

the fact is it is possible to approach the 351 hp peak with other means, but the bigger displacement has a higher torque curve over the entire power range. If nothing else is done except the big bore it will have virtually identical reliability. I've been running a big bore in my 650 for the past 14 years and 33,000 miles without any issues what so ever. The problem is exactly what is mentioned - cost. But it is hard to beat nearly 1/3 increase in displacement. It's been going on for years in both bikes and cars.

A good pipe can boost power too. Matching the port to the pipe is basically grinding the head pipe to match the port, taking out any step. Same is frequently done on the intake manifold to port. We did it with our flat trackers, also did the transfer ports since they were two stroke. Smooth flow is what it is all about.

As for the air box work, it is interesting and I'm sure the results will be written up. The small area for air boxes due to the narrowness of a dual sport bike and the shock placement makes it a pretty poor OEM design when compared to that on a sport bike where they have plenty of space under the fuel tank. It has to be made to fit.

The biggest bang for the buck is the jetting changes needed to do away with the lean carburetion. Nex woud have to be the Marcelino cam timing revision, which is a freebie and if you disable the compression release (which is unneeded on the electric start bike) rather than retime it the whole thing is pretty much no cost if you do the cam work yourself and even if you have to pay to have it done - check and reshim the valves if needed at the same time.

Full exhausts are quite expensive and I'd recommend you see if you can find a dyno chart comparison to see if it is worth the money over a slip fit before buying.

You can do a slip fit on the cheap with an extremely open flow by doing what the KLR650 riders call the John Deere slip on. They have a mid pipe bent up, weld it to an inexpensive John Deere muffler and fit it up. Mellow tone from what they say. The muffler pretty much looks like a low buck canister. Guys laugh about it, but it works pretty effectively for them. I've seen a few Cherry Bomb style mufflers too.

One other is to keep an eye out for some sport bike slip on that can be had cheap, bend up a mid pipe and stick it on. Learned a lot of tricks goofing around in a bike shop. My one buddy got a D&D for a CBR600F3, shortened it, got a pipe bent and stuck it on his XL600R. A tad loud, but picked it up a bit over the stock muffler while looking pretty trick.

Here is a link to a stripped down description of the Marcelino Cam Timing Modification. He wrote up in extreme detail. This eliminates the unneeded background information focusing on only the mechanics of the actual modification. It is actually easier than it sounds. The worst problem I had was getting the proper number of tooth movement to do. I kept going either the wrong way or was one tooth off. Took me several trys to get it right, but it was quite obvious when I made a mistake and when it was right.

Regardless of what you choose to do, be attentive to the details and triple check everything as you do it.

Here is a document another rider put together of cheap mods, I've done a few my brother did virtually all of them. The rider wrote:

I've done these modifications they work good.
You will smile.

16009-1912 Kawi Needle-Jet, N1TC
92037-1401 Kawi Clamp, Jet Needle
92143-1667 Kawi Collar
Needle clip slot 2 down from the top
92063-1069 Kawi Main Jet #125 or 92063-1074 Kawi Main Jet #128
92064-1108 pilot jet #40 Air screw at 2 turns out to start
drill the slide vent to 7/64ths

Airbox snorkel (14073-1577) high flow unit

open up the crank case vent hole in the airbox

10-4313-K250 big gun evo x exhaust system


air valve removal ( Air Injection System ): This won't do squat for performance but it will lower exhaust temp significantly and cleans up the under-tank area.
just plug: the hole in the airbox,
the vacuum port on the carb,
and the intake to the reed valve on the front left side of the head
( I took it off and made a cover to replace the reed and cover )

Here are the most common I have read about.

Muzzy full exhaust or you can drill a hole in the stock exhaust; there are several posts on how to do that.
#125 main jet (Size depends on several factors, see posting on jetting)
pre-'96 KLX300 needle (N1TC)
pilot air screw backed out to 2.5 turns
Slide vent drilled to 7/64th
Airbox crankcase vent restriction removed
KDX200 snorkel (hi-flow)
13t counter shaft sprocket (14t is stock)

The links below show the part#'s, how to remove the carb, how to install the carb parts, and Kawasaki web site for diagrams of carb, ect.

http://www.hmfengineering.com/forums...ead.php?t=1617
https://www.kawasakiforums.com/m_17800/tm.htm
https://www.kawasakiforums.com/m_34306/tm.htm
Welcome to Kawasaki.com


I started the so called "free" mods last night in earnest. Here's what's happening in the ol' garage over the next 72 hours (I have to wait for parts on some of this):

1) Removed the Air Injection System (Air Valve) that directs clean-side air into the exhaust system right at the front of the cylinder head (some call this the smog stuff). This very simple arrangement consists of a vacuum operated valve and a couple of hoses. The air is "injected" into the exhaust via a reed valve. I just removed all the plumbing and the valve and then capped the air box hole, carb vacuum port, and the hole at the top of the reed valve chamber. This won't do squat for performance but it will lower exhaust temp significantly which helps keep pipes shiny if nothing else and cleans up the under-tank area.

2) Drilled the crankcase vent hole at the lower front right hand corner of the airbox out to 3/8". Like the KLX300, this system is plugged up and enlarging the hole helps move air out of the crankcase. It also means oil has a clear shot at your airbox if you lay the bike over.

3) Put my 13t counter sprocket on to stay (I'd been going back and forth over the last 3 days as to which I liked better, 13 or 14. No doubt about it - the 13t rocks).

4) Removed the carb to replace the needle (pre-'06 N1TC needle), drill the slide vent with a #32 drill, and replace the main jet with a #122 (for now. Also have a #125 if needed).

5) Removed the air box snorkel pending replacement with the high flow unit Tony discovered.

I should have it all back together by the weekend and will report results then.
WOOOOO HOOOO! It's back together and it ROCKS. Now we're cookin' with gas!

Here's what I did this week again:

1) 13t C/S sprocket.
2) Air valve plumbing removed and all holes plugged.
3) Pilot air screw out 2.5 turns.
4) Slide vent hole drilled out to 7/64ths.
5) Swapped in a pre-'06 KLX300 49 state needle (N1TC) with clip in slot 2 down from the top.
6) #122 Main Jet.
7) Air box snorkel replaced with 14073-1577 high flow unit
8) 1/2" hole drilled in the first baffle plate in the muffler.

Now THIS is the way this bike is supposed to run! Night and day difference! YEAAAA HAAAA!
Tony's right about the needle being fatter. Even on clip position 2 (out of 5) it sits about 1/8" higher to begin with. I need to do a plug check to be sure but it doesn't seem to be running rich at all. No bog or smoke on hard accel.
OK, I'll try to summarize to make a bit more sense of what I've done. My goals where twofold:

1) Increase RPMs to better fit the power band - This was accomplished primarily by changing the gearing, thus the 13t counter shaft sprocket.

2) Increase HP - As Marty pointed out, you do this by increasing the amount of air and fuel moving through the engine. Our little KLXs are strangled by the factory to meet EPA requirements. The key areas we examine today are:

Air box (snorkel and air cleaner) - More air in

Carb needle jet size and position - 1/4 - 3/4 throttle
Carb slide spring and vent hole - Throttle response
Carb main jet - 1/4 - full throttle
Carb pilot jet - 0 - 1/4 throttle
There are other factors but these are the key areas to consider first

Exhaust - More air out

So, let's begin:

AIRBOX - Per Tony's suggestion on this forum, I removed the OEM snorkel from the airbox lid and replaced it with a Kawasaki KDX200 snorkel part number 14073-1577. This allows mucho more air into the airbox. A less restrictive filter would be a good thing too but just changing the snorkel is a big win.

CARB - The KLX250S comes with a fixed needle jet. I elected to replace it with an adjustable needle jet from a pre-'06 KLX300R. This allows fine tuning of the midrange. I forgot to take a picture of it but you can find one easily on the web. Replacement is straight forward. Just pull the top off the carb and CAREFULLY slide the diaphragm and carb slide up and out. Don't let the spring fly away! I put the needle adjustment clip in position 2 down from the top (5 total on this needle) based on reading others experiences. This proved to be spot on for me. Be very careful not to pinch the diaphragm when replacing it. Even a tiny hole ruins it.

CARB - I increased the main jet from the stock #118 to a #122, again based on reading and guessing based on how much I intended to open the airbox and exhaust.

Here's the carb taken apart on my bench. Note that all this work could be done with the carb on the bike but its SOOOO much easier to work on if you remove it.



Looks like a lot of work to get the carb out but it really isn't

CARB - When replacing the needle jet, it's also a good idea to drill out the slide vent hole to increase the rate in which the slide moves up and down in reaction to changes in engine speed. This improves throttle response. Be careful however, too big is not good either. 7/64ths seems to be just right.

CARB - I also drilled out the little plug over the pilot air mixture screw. The EPA doesn't want you to change that screw's position but it needs to be backed out. Mine was set at 1.5 turns out from the factory. It's at 2.5 turns out now. This reduces lean popping (popping on sudden decel).

EXHAUST - I drilled out the OEM exhaust using a 1/2" bit to place a hole in the first plate you see when you look in the exhaust hole.

MISC - In addition to the above, there are two additional mods being discussed, one helps HP, the other is cosmetic.

I removed the so called Smog stuff (Called an Air Valve by Kawasaki or an Air Injection System by others). THIS IS PURELY COSMETIC for all intents and purposes. It cleans up the under-tank area and reduces the chance of a vacuum leak down the road. It also reduces the temperature of the exhaust which reduces pipe bluing (not an issue on a dirt bike).

Here's a picture of the Air Valve and plumbing.

Here's the plug I made to cap the Air Valve opening at the front of the engine head. This covers the reed valve into which air is drawn by vacuum. I elected to include a small section of hose to keep the plastic plug from getting too hot:

Here's where you plug the airbox once the plumbing is removed and a pointer to the crank case mod. The latter helps the engine by reducing pressue in the crankcase. NOTE, you also need to plug the vacuum port on the front of the carb (the place the small hose was attached too.
I found an easier way to drill out the crankcase breather hole. All I did was heat up my drill bit with a torch and she pushed right thru. You will have to reheat and clean the bit with a rag a few times to remove the left over plastic form the bits threads. Reheat the bit and push it through till you feel it’s opened up enough. No more little plastic pieces left from hand drilling. If you have an old nut driver you can cut off some of the handle to get to the nuts in the air box.

 

You win...Longest post ever!

 

Richard Avatar has created an insert - check out his posts - and I hope it is free HP once rejetted for... The stock airbox looks to be very detrimental to smooth airflow into the carb boot. I am convinced a revamped airbox throat will free up some power, and, I hope it will allow more precise jetting.

An uncorked MCM bike like mine - near sea level - cannot be jetted for max power with the DJ kit, the #132 is still too lean. I- or someone-will need to test a DJ #134 main jet.

Zeno, click on my logon, go to statistics and bring up my threads and my posts.. Here are some of the things you'll find -

A dyno shootout between the stock header + DG-R vs Full FMF - megabomb + PC4 . The charts speak for themselves . Analyze them carefully.

Pictures of the stock header before porting - I would not perform this mod. I am sure I lost throttle response and trq below 6k rpm but gained a little HP up top. Overall I was very disappointed.

The fact that the DJ #132 jet Dyno tested 1 more HP over the #128 and the bike was still lean... You can surely make a #128 work if you choke the bike with lids and KDX snorkels etc...

 

The DG-R and the FMF Power Core 4 are loud - but the DG-R maintains (very close to ) header pipe diameter up to the can, the PC4 has a larger dia. "midpipe" running from the header connection to the can and requires removal of the stock gasket from the header in order to slide into the header. I have not Dyno tested the stock header + PC4. The increased cost of the PC4 over the DG-R is so great (double) that it would have to add serious HP and TRQ to be cost effective - I am sure it will not and is not. My complete FMF (Megabomb+PC4) system produced questionable results and cost over $500.

 

This is Bill Blues dyno run of the 351 on stock exhaust and stock carb. This is straight off his web site. My last Dyno test produced 20.71/14.74 SAE Corrected HP/Trq with the FMF system and with the DG-R I'm getting 19.75 / 15.18 SAE HP/Trq.

 

I don't have the dyno sheet to prove it, but my stock carb dg exhaust 351 kit pulled 27 horsies at the free dyno event at my local powersports dealer (at the wheel).

 

Were the results questionable, or just questionable from a value standpoint?

 

Not claiming any credit for the knowledge, just putting it out there. I didn't have any link to any page that the cheap hop ups came from. All of the italicized text was what I received in the word document my brother had. Common stuff done, but all of it in one place.

Edit: I tried to find the source, but it's a compilation of stuff from a variety of sources including post 4 from this link at post 4. Wish it had the pictures with it.

 

Did you look at his torque curve... or should I say plateau! That is incredible. He has what appears to be over 90% torque from 3500 rpm on up - tractor!

That is why I've become a big fan of the big bores if one can afford to do them. Broad fat power bands.

I'd love to have that kind of torque that early. Perfect roll on power for about any situation, especially woods riding. I could run stock or even taller gearing with that kind of power.