Tillotson Carb Mods

After pouring over every possible website, i decided to do a little investigation to see what can be done to these POS's. naturally the only market that is still interested in these carbs are go karts. they use them mainly because of their "jet on the fly" features. IE- there are no jets just needles to adjust the flow.

i invested 120 dollars into this and recieve a tillotson mod manual, and trick pressure guages to set the carb up. almost no one knows about these mods, so they "help" give you an edge when they are used. i recommend practicing on a junk carb, just so you don't screw up that good one you just put a new gasket kit in. first off, you have to open up the bore so that more air can get in. take the two screws out of the choke shaft, pull the brass flapper out, and remove the shaft. a small ball will most likely roll out. this is normal, it just allowed the shaft to rotate, and is not needed anymore. once the choke is out, mix up a batch of jb weld or other epoxy and fill the choke shaft holes in. make sure you do a good job, and don't get any in the inside of the carb. this will restrict some air flow, this is why i said to practice on a junk carb.

once the holes are plugged you can move onto the next step. which is removing some material off the dog house found inside the bore. HR's and HD's have this doghouse, but the HL's do not. the doghouse is the little dounut like thing over the high speed jet opening. using a small file or a steady hand, and a dremel shape the top and sides (the outside, don't mess with the inside!) until you have a knife edge all the way around. if you are using a dremel, you will have to use a small file to clean up the spots you can't reach. this can take some time!

next comes cleaning the casting slag off the pump stack plates. you know those two-three plates on the bottom that make up the fuel pump. using a needle nose file (the smallest ones you can buy) gently clean the slag off. don't open the holes up anymore, just clean them up. the little black inlet on the bottom, can be taken off and drilled out using a .140" drill bit. go through both the top and inlet hole to make sure that everything is drilled out to those specs. BE VERY CAREFUL! the drill will want to grab the plastic, and shoot right through the bottom making the inlet a piece of useless plastic.

PART #2- Next will come the more advanced part. Using a dremel with a porting attachment, "port" the bore out to the largest possible size. This will take time, and a careful hand. again, preactice on a junk carb to get the technique down. now is a good time to remove any of the epoxy that you may have gotten down inside the bore. Only if the epoxy is dry.

Next pull the throttle shaft out the same way that you took the choke out. take the brass flapper, and using one of the files (not the dremel) sharpen the edge until it is like a razor blade. you only have to do the front edge, but if you want to you can do the back, but it isn't really going to affect anything greatly. after you are done filing it down, start with 600 grit, clean up any scratches the file created. then move down to 1000 grit paper, and finally to the mother's aluminum polish. also polish the whle thing until it is a mirror. put the flapper back in the shaft and eith just bolt it in, and file down the spots where the screws don't go through. also file the screws down to the shaft, so that nothing sticks out. then repeat the super polish job. i have also heard that plumbing solder works to hold the flapper on the shaft also, but i have not tried this. when the solder method is used the screws can be removed completely. then file the whole assembly down to 1.5 mm. this last mod is only for sleds being race on ice. otherwise a rougher surface could break the throttle shaft.

tee slotting is also another option that won't add power, but helps the smaller carbs run like larger carbs. basically it involves machining a T in the carb casting from the needle seat to the little holes where needles pick the fuel up from. only machine the casting as deep as the spot where relief is already cast. this is the area right in front of the needle and seat.


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		HOW TO MOD A TILLOTSON CARB



		After pouring over every possible website, i decided to do a little investigation to see what can be done to these POS's. naturally the only market that is still interested in these carbs are go karts. they use them mainly because of their "jet on the fly" features. IE- there are no jets just needles to adjust the flow. i invested 120 dollars into this and recieve a tillotson mod manual, and trick pressure guages to set the carb up. almost no one knows about these mods, so they "help" give you an edge when they are used. i recommend practicing on a junk carb, just so you don't screw up that good one you just put a new gasket kit in. first off, you have to open up the bore so that more air can get in. take the two screws out of the choke shaft, pull the brass flapper out, and remove the shaft. a small ball will most likely roll out. this is normal, it just allowed the shaft to rotate, and is not needed anymore. once the choke is out, mix up a batch of jb weld or other epoxy and fill the choke shaft holes in. make sure you do a good job, and don't get any in the inside of the carb. this will restrict some air flow, this is why i said to practice on a junk carb. once the holes are plugged you can move onto the next step. which is removing some material off the dog house found inside the bore. HR's and HD's have this doghouse, but the HL's do not. the doghouse is the little dounut like thing over the high speed jet opening. using a small file or a steady hand, and a dremel shape the top and sides (the outside, don't mess with the inside!) until you have a knife edge all the way around. if you are using a dremel, you will have to use a small file to clean up the spots you can't reach. this can take some time! next comes cleaning the casting slag off the pump stack plates. you know those two-three plates on the bottom that make up the fuel pump. using a needle nose file (the smallest ones you can buy) gently clean the slag off. don't open the holes up anymore, just clean them up. the little black inlet on the bottom, can be taken off and drilled out using a .140" drill bit. go through both the top and inlet hole to make sure that everything is drilled out to those specs. BE VERY CAREFUL! the drill will want to grab the plastic, and shoot right through the bottom making the inlet a piece of useless plastic. PART #2- Next will come the more advanced part. Using a dremel with a porting attachment, "port" the bore out to the largest possible size. This will take time, and a careful hand. again, preactice on a junk carb to get the technique down. now is a good time to remove any of the epoxy that you may have gotten down inside the bore. Only if the epoxy is dry. Next pull the throttle shaft out the same way that you took the choke out. take the brass flapper, and using one of the files (not the dremel) sharpen the edge until it is like a razor blade. you only have to do the front edge, but if you want to you can do the back, but it isn't really going to affect anything greatly. after you are done filing it down, start with 600 grit, clean up any scratches the file created. then move down to 1000 grit paper, and finally to the mother's aluminum polish. also polish the whle thing until it is a mirror. put the flapper back in the shaft and eith just bolt it in, and file down the spots where the screws don't go through. also file the screws down to the shaft, so that nothing sticks out. then repeat the super polish job. i have also heard that plumbing solder works to hold the flapper on the shaft also, but i have not tried this. when the solder method is used the screws can be removed completely. then file the whole assembly down to 1.5 mm. this last mod is only for sleds being race on ice. otherwise a rougher surface could break the throttle shaft. some extra things that can be done include polish all the pump stack plates using the super polishing method i descibed before. this is just to make the fuel flow easier. i have not seen any power improvement though. tee slotting is also another option that won't add power, but helps the smaller carbs run like larger carbs. basically it involves machining a T in the carb casting from the needle seat to the little holes where needles pick the fuel up from. only machine the casting as deep as the spot where relief is already cast. this is the area right in front of the needle and seat. happy modding! kawicat~ *WARNING:* in the event you get hurt, ruin your carburetor, or snowmobile engine, it is no fault of mine. Use the above procedures at your own risk!