Duraforce Re-jetting Instructions Part 2
Thanks to Tom_P_PA for the first 100 post thread, this to be a continuation of which I repost the instructions in this first post. Only 100 posts are allowed per Subject
Also, the mikuni on the suzuki 2 stroke part number is 81-1030 which is matches the Duraforce "37.5" jet and is a #40.
1) Get a NEW main jet and pilot jet. Part numbers are 98-1357 and 98-7041. Also, get the paper gaskets (1 for the carb body and 2 for the heat shield), get a fuel line and in line fuel filter.
2) Note that the main jet 98-1357 is called a "77.5" jet. The "77.5" jet is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #68 wire gauge drill bit whose diameter is 0.031 inch (and it fits into the orifice, and #67 does not).
3) Note that the pilot jet 98-7041 is called a "37.5" jet. Again, the "37.5" is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #79 wire gauge drill bit whose diameter is 0.0145 inch (and it fits into the orifice, and #78 does not).
4) Get a wire gauge drill set (from #80 to #60), or better still, get drill sizes #66 (0.033 inch) and/or #67 (0.032 inch) for the main jet and #78 (0.0160 inch) for the pilot jet. You will need a hand chuck to mount these tiny drills. Do not use power tools. This results in an approximately 10% increase in the orifices for both jets. 10% is all that is needed.
5) Carefully hand drill the jets, apply gentle pressure. Note that the pilot jet center hole is to be drilled ONLY. Do not drill through the body of the jet, drill out only the 37.5 orifice. Use the #78 drill to oversize the pilot jet orifice (it is the first oversize). To oversize the main jet, you can use a #67 drill (0.032 inch), go back and forth and ream out unit the #66 drill (0.033 inch) just fits, or you can use a #66 (0.033 inch) drill - but be careful to not oversize the orifice.
6) Carefully drain all of the gas, remove and disassemble your carb adn replace the existing jets with the new modified (oversize) jets. Not the pilot jet is on the side of the carb and is covered up with a sticker. Take the sticker off to get access to the pilot jet.
7) Be real gentle when putting the new jets in, do not apply excessive turning force...a new carb will set you back $100.
8) Reassemble the carb and adjust the speed control vane one click slower. The engine speed may run fast after these mods.
9) Reinstall the carb with a new gas line and in-line fuel filter. Note, its a real good idea to install an in-line fuel filter. The carb jets are small and can plug up easily.
- Gas and go.
Your mower will consume a bit more gas but will not surge any more because your mower's mixture will be a little richer. However, the engine will be better lubed and cooled as a result. This cures surging and makes the mower runs like mowers of 10 years ago.