I had my first success today. The up side is it's a monster! This thing just pulls like a freight train. The front came up so fast I was caught off guard (rode it out
). As an added plus it's big enough to feed even a 440 (my biggest peeve with the 36mm pumper). The down side is that it takes some modification and you're going to need a couple parts.
Before reading any further assume your own liability if you choose to do this mod to any machine.
What we're talking about here is the
Mikuni BST40SS. It's a 40mm modern CV style carb that will pop the front wheel even if you're luggin' in the wrong gear. I was very impressed! The carb can be found on any........... just ignore the brand.......... Suzuki DR650 made after 95. It can also be found on just about any KTM LC4 from 1999 to 2005.
The dirty deeds:
First thing we need to do is move this big 90 degree elbow (red arrow) that feeds a breather for the slide. It currently hits the right frame rail. The good thing is the place it needed to go was already casted in the housing (blue arrow) and just needs to be drilled out. The KTMs use the hole we need but I have a DR650 carb here.
First thing you do is remove the top, spring, slide and needle/ Then stick something big and solid in the 90 and twist it out. The 90 has little barbs on is and you're basically ripping the aluminum up getting it out. Comes out easy once you get it moving and it won't hurt anything for our next step.
Tape off anything you don't want shavings in unless you're doing a full teardown and cleaning later. To plug this hole you need a 1/4" pipe thread tap and a 1/4" allen head plug. You will NOT need to re-drill the hole you just opened up for the tapping. Run the tap in far enough that the plug will mount flush when installed. You can see how far I had to run it in.
Now that we have a nice tapped hole you can use either pipe thread sealer or a generous amount of
loctite. I Used a big glob of red loctite because I never plan on taking it out again. Tighten up the plug and move on to drilling out the new hole.
You will need to be accurate with your drilling here. The 90 is a press in fitting. The correct drill bit needed is a 15/32". Easily found in most hardware stores or possibly where you bought the 1/4" plug for the previous step. Line up your drill bit the best you can and keep a clean hole. I did it with a hand drill.
Now you can re-use the 90 you pulled out of the other hole. line it up so it points near the center line of the carb. This will help with routing your breather assembly later. Start it in by hand and tap it the rest of the way with a hammer. You don't need to sink in all the way, just make sure it's secure. IDK why but I put some red loctite on this too. It can't hurt.
I was able to get the breather tube and filter from the previous owner. It's kind of a must have unless you want to make an aftermarket set-up. The
OEM unit can be purchased separately, works very nice, sits right on top of the air box and only needs a simple mod.
First pic shows the original configuration. The red pic indicates the breather filter and it simply needs to be moved to the other end of the tube where the green arrow is. In pic 2 the bell created from the breather should be trimmed off with a knife and then when the carb is mounted on the bike you connect that end to your 90. Some sort of clamp should be used.
We're half way there. This next step is almost an option. The bowl vent on the right side of the carb runs right into the right frame rail too. The hose is a little kinked and although would work it doesn't look good. The good thing is Mikuni casted in what we need once again.
In pic 1 find a drill bit close to the vent hole diameter but not bigger, a little smaller isn't a bad thing. Take the bowl off the carb and if you have a long enough bit you can do what I did and drill from one side to the other for perfect alignment(red arrow). The middle has already been drilled out my Mikuni. You're just drilling out the blank on the left side of the carb (blue arrow). In pic 2 you can see up in where you are drilling through. Be sure to blow out all shavings (green arrow and pic 2). It's a real easy clean up and accessible.
Cap the right side vent (blue arrow) with a vacuum cap. Do the same for the emission port next to the mixture screw (red arrow). It won't be needed.
Okay, so far it's just been some fun with regular tools. I have talked to
Motion pro and for $70 they'll make you a set of cables to connect this carb to your stock twist throttle. I went another route and used a twist kit for a 400EX. I had the cheap-o Motion-Pro kit and it was scary close. Just had to mod the cable mount plate on the carb (red arrow). I cut the top off and welded a fat nut on the plate to accept my cable end. This was about $35. If I didn't have this kit in the shop I would have ordered a nicer kit (around $50). I know the carb is set-up for push pull but the spring is plenty strong to operate as a single cable system. The blue arrow is the new vent you just drilled.
Here it is mounted. The choke (blue arrow) is a cable operated system that sucks and needs Suzuki handle bar equipment to work. I currently have the cable removed and the choke piston blocked in the off position. The solution is to convert it to a knob style choke. I have one on order, it cost me about $20. I have 2 more coming that were closer to $10 that I think might do the same thing but those are pure guesses. After paying $20 for the one I know works I figured there had to be something better out there and I was paying someone's mark up for having already figured it out. I'll keep you posted.
64
!
Follow us: