i got an 86 R with a keihin 37 mm carb. i burnt a hole in the piston a couple of weeks ago cause i didn`t rejet. stock jet size is a 140 i think, how much bigger should i go? its got aftermarket paul turn. pipe, boyesen rad valve, new filter. its a PE carb too. any input would be helpful thanx.

 

The stock main jet size for a stock carb for an 86 is a .150! If you're running a .140 all you're gonna do is burn pistons! ! !
With the pipe/filter/reeds mods, start with at least a .160 and plan to go bigger. Do plug chops and if you get a white plug, go bigger and keep going bigger until you get a brown plug.

 

hey this isn`t the stock carb. this is brand new aftermarket carb and i checked the main jet. its a 140. so try again

 

There is no jet size that anyone can tell you that will deffinately work for your quad. You MUST learn to jet. How long where you riding before it quit? If it was a fairly short amount of time (20 mins or so) then once you get it all back together you should start out big right off the bat like trapperb was saying- somewhere around the 155-160 mark. Have about 5 spark plugs, 5 different jet sizes, and any tools you may need to change the pug and jet. Put all of these in a fanny pack or something convenient and warm your quad up. Once it is good and warm, hit the river (I know where you ride). Put in a fresh plug and as soon as you start it back up, TAKE OFF! Do a full speed hauling a$$ run to 5th or 6th gear, immediately shut it down and pull the plug out. If it is white or greyish, jet up. If it is black, jet down. Keep doing this exact same run over and over again, each time with a brand new plug until you get a good cocoa brown plug. If you get this, you should nearly never foul a plug and your engine will run cool. My guess is you will be running about 155 main; but it's better to start big. The last thing you want is to burn a hole in your brand new piston!


Oh, don't forget proper break in. Do this with the larger jet as well, BEFORE you do all the jetting runs.

JP