Jump to content

The Taming of the Mighty TM 300en

Recommended Posts

I've had my 2000 TM300en for a little over a year now and it sure has been a kick in the pants. I have gone completely through it and even had the cylinder re-plated. I don't race, but mostly ride desert with some woods. The bike is kind of a split personality engine wise. I can putt around with the kids and lug it up shale hills, or open it up and go for a rocket ride. However, I got some @#$#@ mystery illness, so now I have Post Viral Fatigue Syndrome. I'm not giving up riding, I just have to take it a little easier.

Consequently, that mid hit that used to be so much fun, now tends to wear me out sooner. I talked with a few engine builders and the general consensus was to drop the compression and retard the timing. This is supposed to make the power band more manageable, with less of a hit. However, the trade is that I would lose some low end (not good). However, after talking with a friend of my dad's (builds everything from top fuels to shifter karts), I went with a four part approach that is totally different then the other advice I got. This approach is carb, port timing, head squish and ignition timing.

Curve1.jpg

Curve2.jpg

The approach I am taking is to raise the low end everywhere. In theory, with more low end and the low end lasing longer, the mid hit should be tamed. The black line represents the stock power band. You can see the hit at the point where the line turns more vertical. The red line represents the power band I am seeking. If you notice, the transition is smoother and would occur later in the power band hopefully reducing the hit and making the bike less tiring to ride.

The best part is that all of the changes can be undone, if the power band is not the way I like it. The first change was to go to a smaller carburetor. The TM comes with a keihin 38mm airstriker carb. This carb was swapped to a 36mm keihin pwk from a KTM 300 ex. The carb swap was actually the hardest part of the whole conversion. The Airstriker is a large and long carb, so an adapter piece had to be machined in order for the carb to fit.

carbspacer.jpg

The port timing and squish were changed by using a 0.2mm base gas gasket. This change lowers the port timing, reduces the squish and raises the compression. All three of these changes "should" increase the low end.

The last change was to advance the timing by about 3 degrees. For this change, I had to make a degree wheel on AutoCAD as well as a Timing scale. Then using a timing light I measured the stock timing, then made a mark for 3 degrees of advance.

I run AV gas so hopefully I won't have a problem with detonation. I am also converting the electrical to run with a battery. Since I can't ride as hard, I am switching over to more of an exploring mode. With the battery upgrade, I will be able to hard wire my GPS and not worry about the GPS internal batteries. To accomplish this I am using a voltage regulator from a Suzuki DR350 and I am using a 4,000 mAH RC battery pack mounted in the airbox.

VR.jpg

Bat.jpg

While I was playing with the mods, I also added foot pegs from an 02 KTM, big difference.

Pegs.jpg

I also changed out the rear brake pedal from a RM250. The old brake pedal was pretty bent. Also, I couldn't adjust it low enough without cutting the master cylinder bolt. While I was at it I also added a heavy return spring at the master cylinder.

BP.jpg

This may seem to be a lot of work for an old bike, but I really love the suspension and the way it handles. A good friend of mine has a 2008 ktm300 and he says the suspension is better then his bike. Also, I enjoy upgrading and making my own mods and this bike is defiantly not your typical cookie cutter bike out on the trail.

I'm just getting it finished up. Hopefully I will take it to a friends property on Saturday and start playing with the jetting. I won't know the outcome until Christmas though, we have a week trip planned for the desert around Ridgecrest so then I can report back. :bonk:

Share this post


Link to post
Share on other sites

Very cool report thanks for taking the time to write it up. My son has the 2011 TM 250 MX and in stock trim it had a very soft bottom good mid and ripping top. We sent the head and carb to RB and now we run it on 93 pump gas and it has awesome power form the bottom to the top with a great long pull in the mid-range.

Share this post


Link to post
Share on other sites

You might find that with the smaller carb and all the other mods you might get way to much yank off idle, think sx race bike, very demanding. Your gonna be losing alot of cfm but gaining secondary compression and the velocities through the carb will be much higher so you will almost certainly have to jet fatter everywhere. Should be an interesting experiment none the less as if I remember correctly, that year cylinder had huge ports. Better hang on tight!

Edited by widebear
forgot how to spell

Share this post


Link to post
Share on other sites

Cool :bonk: Sounds like a fun project hope it turns out the way you want it.

One thing I do to mellow out the "hit" of all my bikes is install a high tooth count on the front sprocket. A few years back I installed a 12T front on my old RM250 trying to lower the gearing a bit for the technical sections of single track. Lower gearing was what I got alright, but also by going from 13 to 12 it increased the torque (more leverage I'm guessing) enough for me to quickly remove it--I could not believe how quickly I wore my self out trying to hang on at even the lowest of speed--it was a night and day difference in a really bad way. After that I went the opposite direction and added a 14 to the front (I also increased the rear tooth count to still have lower gearing) and I found it was far more manageable than even the 13. It might be tricky finding a higher tooth count for the rear of a TM, but I would definitely try out a 14 or 15 tooth front and see if that mellows it out a bit. Just a thought :smirk:

Share this post


Link to post
Share on other sites

Gearing is an issue that I have been thinking about. Stock CS is a 13T, the other option is a 12T. Right now my stratagy is to try the 12T and run a gear high everywhere. We always camp in the same spot and there is a good testing hill right by us. Last time out (before the mods), I was running the 13T CS and it was 50, 50 if I could make it in 3rd. This time I will start with the 12T and the mods.

I have a feeling this whole trip will be an experiment. I haven't even gotten to fire it up yet. Found out I had some issues with the RV, so been working on it. Oh well, take a couple of sprockest, a handfull of jets, timing light and a partidge in a pair tree. :bonk:

Share this post


Link to post
Share on other sites

Wow, I can't believe that it has been almost 5 years since I started this thread.  Just got back from a week at Searles Station, with some exploring the Pinnacles, X15 crash site and Burrell Schmidt tunnel.  So I guess a ride up date is in order.  All of the engine mods that I have made to tame the mid hit have work great.  You hear write ups about the KTM 300 that keeps pulling no matter what.  Well, MY TM will do that as well.  However, there is a big difference, its not that it just won't die, but instead there is an abundance of torque down low.  I hate to say this, but it is almost 4T like (without the flame out).  This sucker has really pulled me out of some tight situations without touching the clutch, just rolling the throttle on.  There is still a hit, but it is up higher in the RPMs, plus it gives you some warning before it hits.  Have I lost top end power, nope.  On the way back from the Pinnacles, my buddy (KTM 530) and I were drag racing down Searles Station road.  We were side by side until I ran out of gearing.  This bike will still hang with just about anything "IF" I can find traction.  Of course there are a couple of down sides.  1st it takes a pretty healthy kick to fire, but never more then three, even after I have dropped it (it does start in gear though)  2nd I can't run straight gas, just for simplicity I run half AV gas in the mixture (40:1 Bel-Ray).  I also have an issue with pipe spooge.  However that is not the bikes fault, it is a little rich, and I tend to run a gear high.  For myself, this is the perfect engine.  It will climb any hill that I wish to throw at it, yet I can idle along with a CR50 on the family rides. If it had the magic button, it would be icing on the cake.   I'm just sorry it took me so long to update my results.  

 

Almost forgot, I got tired of pulling the bike up onto the center stand, so I also added a kickstand from a WR 250

Edited by toomanytoys2
  • Like 1

Share this post


Link to post
Share on other sites

your approach is all wrong in that you want to change the bike to accommodate your health problem instead of correcting it.

Yeah I know the doctors are dumber than dirt and 50 years behind the times. That's why you have to be your own expert at whatever ails you.

I had what you have for 16 years and I had to find the alternative cure for it 'cause the doctors sure were no help at all.

Look at my icon picture. That's me on the victory podium having earned 2nd place in a motocross race when I was 46. I would of never got back into racing if that f'ing virus was still in my body wrecking everything. Becoming a medical rebel was one of the best things I ever did in my life!

Share this post


Link to post
Share on other sites

Jaguar,

 

I think that you have missed my point.  I did not neuter my bike, I just tamed it down a little.  If you have read any reviews of the TM 300 in Dirt Bike, or know anyone who has ridden one, you would know that they are one fast bike, that hits hard and puts you away wet.  Also, if I listened to my doctors, I wouldn't be on a dirt bike, but five years after I started this post, I'm still at it.   I think I'm still doing pretty good, since on my last ride I did multiple 50+ milers leading up to a 70+ miler.  Not too bad for someone who cusses every morning from all the aches and pains when they roll out of bed.  Of course, I just might need a new mattress. :D  

Share this post


Link to post
Share on other sites

That Bel Ray mixed at 50 or 55-1 will reduce if not eliminate the spooge. I started with Bel Ray in the early days and have corresponded with them several times. No worries. A close friend worked till retirement at Lubrizol who produces the additives used in Bel Ray, he still tests the oil in a super modded PWC regularly. Don't worry about the oil. More great protection comes by using Bel Ray air filter oil, by far the best. Good luck with your health, great story. :thumbsup:

Share this post


Link to post
Share on other sites

i have the TM 300 MX and had the 300 SMX {supermoto} the TM 300 MX is a lot of fun to ride and the way t makes its power makes it easier to ride . i also the TM 300 SMX it was a lot of fun but not enough power and signed off way to early on the top end , but i fixed that 

 

by fitting a CR500 engine into the chassis 

IMG_3098_zpsysgicomv.jpg

  • Like 2

Share this post


Link to post
Share on other sites

i have the TM 300 MX and had the 300 SMX {supermoto} the TM 300 MX is a lot of fun to ride and the way t makes its power makes it easier to ride . i also the TM 300 SMX it was a lot of fun but not enough power and signed off way to early on the top end , but i fixed that 

 

by fitting a CR500 engine into the chassis 

IMG_3098_zpsysgicomv.jpg

Honda parts make any bike better! :thumbsup:

Share this post


Link to post
Share on other sites

Shames

What year TMs do you have? My 2000 has plenty of beans, even after I toned it down. It still hits pretty hard, and will lift the front end in fourth when it gets on the pipe. I wonder if they toned them down in the recent years.

Share this post


Link to post
Share on other sites

Shames

What year TMs do you have? My 2000 has plenty of beans, even after I toned it down. It still hits pretty hard, and will lift the front end in fourth when it gets on the pipe. I wonder if they toned them down in the recent years.

 

i have the 2014 models , rode the 16 the other week it feels smoother than the 14 but hp numbers are higher 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×