Exactly.


- It's almost zero money to buy an extra intake off eBay and try and hog it out a bit then round off the port's edges

Every mod mentioned on this forum takes some time afterall

Remember, I am talking about a 36mm carb (or larger) squeezed into an intake meant for a 34mm, bolted up to a port that who-knows may be restricting hp gains with the mcm mod on larger than 250cc bores.

Better engine builders than myself think port matching and/or matching the carb to the intake/port is worth their time..

I'm going to try it

 

I think it's worth the time on a big block or small block. But at the same time there are those who argue that running a square head with an oval intake runner causes a swirling effect and port matching would decrease hp. Lots of talk little show dyno results

My concern would be the rubber being too thin and collapsing under vacuum (heavy throttle)

 

Looking at the intake from the engine side, there appears to be an inner metal section to it that could still remain intact after opening up the intake a bit to the measurements I mentioned. But maybe the rubber I'd remove is holding it all together and if you grind much away it could all just kind of fall apart. Which is why I bought an extra used one off eBay to experiment with

If it does fall apart etc, the next step would be a custom made short spigot manifold with a section of rubber hose connecting the new intake and the carb together.

You wouldn't put an 850cfm carb on a manifold made for a 750cfm just because the bolt pattern was the same-right? Not without at least some work on the intake entrance.

I just wish there was a way measure mod gains or losses here. No dynos or drag strips available. I've taken many a dirt bike in the US to the strip and changed things while there to check mod results. Including a near stock '87 CR500 that went 12.35@107mph with the tallest gearing available for it..

 

I loved my 86 CR500 . The most explosive thrill machine money could buy.
Or was it my 84... Which year was deemed too powerful to ride at the time..?

 

My jets order arrived finally, and I went one size larger to 137.5 mj (must be 90deg F here btw). It felt strong as I rode around and rolled deep into the throttle here and there while finding an empty stretch of road to test on.

Hitting the 1-2 shift at WOT the bike pulled a gigantic wheelie-I had to back out. First time that's happened, usually it's just a couple inches. So maybe the drilled air box and richer jetting are working well together? nyuk nyuk

While the carb was out I also took off the intake manifold and reconnected it to the carb; then took a look at it from the engine side of the intake...surprise - the 36mm fits in the Kaw intake like it was made for it. No matching one to the other necessary other than a very small hump in the bottom center of the intake which I Dremel'd out of the way. (maybe it was there to slightly split the flow to the two valves ?)

I'll ride it around a bit before I install a 140mj. I thought the 135 was doing well but the 137.5 perked it right up

 

Wow I giant leap in TM36 main jet changes (for me at least) - pull off the RH side cover and exhaust and the carb's right there in front of you with nothing in the way. I upped to a 140mj today since the 137.5 worked so well and because changing the mj is such a breeze now.

I used a wide flat screw driver bit in vise grips.

No test ride till tomorrow...it'll get too rich sooner or later

Normally I'd ride it more with the main jet change from a few days ago before unbolting half the bike just to get at the main jet again, but this technique makes mj changes go so much faster that I won't fear having to reinstall the 137.5 if this one's too rich

 

Test ride today with the 140 main jet revealed no obvious signs of richness and it's still pulling the front end up nicely on the WOT 1-2 shift; though I'm leaning forward a bit nowadays after it popped way up last time. Both recent main jets seemed to perk the bike up nicely as I roll deep into throttle as well.

I may leave the 140 in it or go back to 137.5..we'll see after it cools down enough to remove the exhaust and gain access to the main jet.

Now that you guys are into warmer weather, someone with a non-CV carb try a test similar to my drilling holes in my air box by leaving your seat off or disconnecting the air box boot and see if your bike runs any better.

All the other mods you have done or will do will be working at less than 100% potential if indeed the narrow pathways air would take to the upper air box area are too congested with the seat on and it's blocking max flow. Nothing to lose; everything to gain

 

Put the 137.5 back in to ride it with that mj some more before going bigger and to time the carb/main jet access via taking off the exhaust.. The jet change was completed with the carb all sealed up in 12 minutes total. Another couple minutes fiddling withe exhaust flange nuts, but I'm getting that down to a science.

I can see 15 min to change a main jet start to finish