robert0762 Posted June 10, 2013 Report Share Posted June 10, 2013 I have been chasing down a way to do this for a couple of months now . A lot of people say you can not do it . The reason they say you can not do it is because Keihin does not make the float valve seat replaceable . I have found two sources for these seats . I came across a set of Polaris xc 700 carbs for really cheap . 39 pwk . At the time I did not know that the seats were so hard to find . Also you will need to pop the air restrictors out of the vent holes . Very easy to do with a small pick . my carbs had oil feeds on the intake side .So I drilled them out and tapped those holes to m5x.8 . I put a socket head screw in and made it even iside the carb bore to avoid turbulence . Last thing to do is pull the old seat out . To get the seat out you tap the needle seat in the small hole then run the matching size bolt in . When the bolt bottoms out it will push the seat right out . Then you just press in the new seats and your done . You will also need the needle valve itself. I will post pics tomorrow of the install Here are the seats I purchased from Benn Herr @ Kart designs . He can cut the seats to any size you want . I went with a 3.8 which is the largest size for the pwk . HPD inc also makes them but his are 3.5 mm. keihin makes them in 3.4 and 3.8 my 35 pwk had a 3.4 and the 38 pwk had a 3.8 in it Quote Link to comment Share on other sites More sharing options...
Coupelx Posted June 11, 2013 Report Share Posted June 11, 2013 Neato. Theres loads of these out there for cheap. What did the seats cost? Quote Link to comment Share on other sites More sharing options...
KozyHeat Posted June 11, 2013 Report Share Posted June 11, 2013 I am running sled VM34's with pumper seats on them ( 1.5mm seat) 300 miles on the build so far and it doesn't show signs of problems. Your saying its necessary to change seats? Also the carb fuel inlet is 6mm inner versus the 8mm petcock. Can't find the copper/brass barbs to shrink it down correctly but it works as is. Quote Link to comment Share on other sites More sharing options...
dave5.0 Posted June 11, 2013 Report Share Posted June 11, 2013 Are the carb castings the same? I thought the fuel Inlet was actually cast smaller on a pumper? So is it just the brass elbow that's a smaller ID? Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 Neato. Theres loads of these out there for cheap. What did the seats cost? 25 a peice Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 I am running sled VM34's with pumper seats on them ( 1.5mm seat) 300 miles on the build so far and it doesn't show signs of problems. Your saying its necessary to change seats? Also the carb fuel inlet is 6mm inner versus the 8mm petcock. Can't find the copper/brass barbs to shrink it down correctly but it works as is. I have heard of people running the pumper carbs on a gravity setup without any changes.I am not gonna try it on this motor I am building right now nor would I recommend it for any motor. I have not done research on the Mikuni carbs ,but I think there seats are readily available from them and a replaceable item But they are set up differently for a reason. Also if you have a big motor or even just a 350 drag port and do a long full throttle run those small seats will NOT flow enough fuel. We hear of people sucking bowls dry all the time on a properly setup gravity feed . That's why guys run oversize bowls. Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 (edited) Are the carb castings the same? I thought the fuel Inlet was actually cast smaller on a pumper? So is it just the brass elbow that's a smaller ID? Castings are the same except for some extra material on the pumpers to allow for drilling and tapping. The sno mo pumpers usually come with pulse pickups for a pump, oil feed, some have power jets and so on. I did a side by side comparison of a PWK 38 manufactured as a gravity feed next to a PWK 39 manufactured as a pumper . The inlets were the same size. The brass fitting was different but I just replaced the 90 deg. fitting on the pumper with a straight fitting from a gravity feed. I will post some pics up of them later today Edited June 11, 2013 by robert0762 Quote Link to comment Share on other sites More sharing options...
dave5.0 Posted June 11, 2013 Report Share Posted June 11, 2013 Cool. How'd you replace those brass fittings? They threaded? Press in? Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted June 11, 2013 Report Share Posted June 11, 2013 Why not just run a pump and use the carbs how they are set up? 1 Quote Link to comment Share on other sites More sharing options...
Coupelx Posted June 11, 2013 Report Share Posted June 11, 2013 there are many applications where the pump is simply not needed I think. Im not a fan of excess shit Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 there are many applications where the pump is simply not needed I think. Im not a fan of excess shit X2. More stuff to go wrong Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 Cool. How'd you replace those brass fittings? They threaded? Press in? Press in . I just grabbed them with vuse grips n twist out then tap em back in Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted June 11, 2013 Report Share Posted June 11, 2013 X2. More stuff to go wrong Only if you're ghetto-rigging shit together... Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted June 11, 2013 Report Share Posted June 11, 2013 You could have saved yourself a lot of work and just drilled the hole through the needle valve housing a little bigger, then counter-sink it to give the needle valve a surface to seal on. Also, don't forget to remove the angled supply hose barb and install a straight one. The factory hose barb that comes on pumper carbs will screw you over if you are trying to gravity feed them. Quote Link to comment Share on other sites More sharing options...
robert0762 Posted June 11, 2013 Author Report Share Posted June 11, 2013 So here are some pics First is the air vent restrictor on 39 PWK manufactured as pumpers . I drilled it out a little bit then popped it out with a pick. There are two but I only took a picture of one restrictor still in the carb. This is just another angle of the same thing Here it is with the restrictor out. Fuel inlet on exterior. Fuel inlet interior 35 PWK manufactured as gravity feed. Fuel inlet exterior Fuel inlet interior The next two pics are showing the exterior casting of a PWK 35 gravity feed PWK 39 Pumper exterior Top left is pumper inlet. Top right gravity inlet. Bottom left Gravity seat. Bottom right pumper seat Left is gravity needle. Right is pumper needle Quote Link to comment Share on other sites More sharing options...
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