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367 Posts
Discussion Starter · #1 ·
Carburetor de-restricting 2005 KTM SMC 625

Parts needed KTM 57331032000 or modify your restrictor

Tools needed

8mm socket
10mm socket
13mm socket

Common pliers

3mm Allen wrench
4mm Allen wrench

A hacksaw or Dremel with cut off wheel if you do not have 57331032000

Common sense

Super easy job, ½ an hour max you do not need to take off the carb or mess with the cables or throttle linkage.

I did this outside my garage it is just not bright enough for carb work on the bike inside.

All reference to direction is as if you were sitting on the bike

1. Turn your petcock off

2. Pull your vent hose off your gas cap

3. Remove your seat (little lever under the edge of left side panel/seat junction)

4. Remove the eight 8mm bolts that attach the radiator shrouds (be careful, the lower bolt on each side is a different length than the other six. These two lower bolts also have a small aluminum spacer)

5. Remove the 13mm nut at the base (rear of the gas tank) when removing note the order of the rubber and metal washer that accompany this nut

6. Use the pliers to gently squeeze the clamp on the fuel line. While squeezed or expanded slide it up the fuel line about a half inch, past the bulge on the carb fuel line fitting (the fuel line is on the left hand side of the carb. It is a black fabric covered hose

7. Slide the fuel line off the carb fitting, you did turn off the petcock didn’t you? ( a very small amount of fuel will spill)

8. Before you pull you tank find a nice spot to set it

9. Gently pull straight up to remove your tank

10. Hooray! That’s your carb

11. The shiny aluminum casting that has CR molded into it is the top of the carb

12. Carefully remove the two 3mm Allen screws on this cover (one in front, one in rear)

13. It looks like you may have to remove a Phillips cadmium plated screw on the right top of the cover but it is not in the way, leave it alone.

14. Gently pull the top off

15. See that tall bolt looking thing? That is your restrictor

16. You can pull it up to see how the slide works, the slide will not come out

17. See those cool rollers on the slide? In the old days flat slides didn’t have rollers and could get hung up because of the intake suction!

18. Use a 10mm socket and remove the restrictor. That thing is heavy! Now you bike is even a little lighter

19. The restrictor is hollow on the bottom when you pulled it out did you also get a little spring and a cup washer on the spring?

20. If you didn’t it is still in your slide on top of the needle, get it out

21. While the restrictor is out look into the slide, that is your needle

22. If you are modifying your restrictor put it in a vise and cut as much as possible off the top the bolt looking part, not the threads. Remember you still must get a socket on this so don’t cut it too thin. Or cut it off flat and use a hacksaw or Dremel to cut a slot in it to use with a screwdriver If you are not modifying your restrictor you can buy the correct unrestricted replacement “set screw” from KTM 57331032000 (obviously this is a off-road only component) If you want to use a socket cut about 15mm off the restrictor. If you are going to slot it cut all 20mm off.

23. Gently sandwich the spring between the cup washer and the modified restrictor or new set screw whichever you have.

24. The cup washer should be facing up to cradle the spring (cup side up flat side down)

25. Carefully place this assembly back in the slide. Tighten a modified restrictor with a 10mm socket or the new set screw with a 4mm Allen wrench

26. This is a little scary and you do not want to drop anything here, but I have fingers like bratwurst and if I can do it anyone can.

27. Once in place you may pull the slide up with your fingers to help you get started screwing this back in. The angle of the top of the slide and angel the screw goes back in are not 90 degrees, it looks like it could be easy to get cross threaded, take you time here. Tighten

28. Look at the underside of you carb top make sure the rubber gasket is in place. See the shiny spot in the middle? That is where the restrictor kept banging into the carb top when you were kicking your mule to go faster.

29. Put the top back on using the 3mm Allen screws

30. Put the tank back on, reconnect the fuel line, turn the petcock on, check for leaks

31. When replacing the shrouds start the bottom bolts first they are the trickiest. Loosely start all four per side before you tighten them.

32. Put your seat back on.

33. Viola More HP


· Registered
421 Posts
:wtf: do they do it for in the first place? :headscrat

I wonder if anyone actually leaves it there. Like the WR throttle restrictor.

Nice instructions. I need to buy a SMC to go with them... :D

· Registered
1,014 Posts
Yeah instead of buying a new stop for mine I just took it out, cut the head flush where it screws into the carb and put a notch in the head with a dremel so i could screw it back in. Took about 15 minutes start to finish. Very nice instructions for people that are learning about these bikes though :thumbup:

· Registered
107 Posts
Thanks for the info scott, my dealer told me he derestricted it prior to me picking mine up, now i can check. From reading other posts some poeple were removing the slide stop, or the part # 10 on the carb site. Is this the same thing? BYW did you need to rejet after doing this?

· Registered
367 Posts
Discussion Starter · #14 ·
No, I did not rejet. really this (restrictor) is just a block in the carb that does not allow you to twist the throttle (and therefore open the slide) all the way. It does not change change jetting.

That said, this bike, like all modern street bikes, it too lean from the factory, I'm sure gains can be made, even to bikes that are going to stay 100% stock, with a little jetting.

Speaking for myself, I like to do one thing at a time.

Next I will add the airbox cover and then I will ride the bike for a few miles to see how it reacts to the change. It should be way too lean then. After that I will play with the jetting.

I am not a big fan of changing a bunch of stuff at once, if something goes wrong it can be a pain in the butt tracking it down.

I do not think I will get an exhaust, I just do not need the attention. Maybe you have slightly more power with a pipe, but you can not use it because the cops will come running like a Krispy Kreme sale. You can ride faster without a pipe, you just don't sound as fast.

I have already had about 5 cops follow me until I turned on a blinker (apparently they think I'm riding a dirt bike) Maybe I will swap out the caps, but I do not want it to be too loud (yes I am old!)

Where I live white guys ride cruisers and black guys ride sport bikes. If you ride something else it confuses the shit out of people.

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