I see that folks are having problems adjusting the idle circuit on the GP 42 carburetor.On the GP 42 the carb has a bleed port that is activated when the barrel is shut. To adjust the idle circuit to make the motor richer you screw the idle mixture screw clockwise which turns it in. This closes down the bleed port allowingless air in and makes the mixture more rich. So to lean it out turn the sidle mixture screw out which allows more air into the mixture making it more lean.

My next post will cover what can be done to a stock motor and still be called stock.

Sorry about posting the same thread twice.

Now the subject of what is a stock motor and what is a modified motor is a very controversial subject but, as near as I can tell you can do the following and your motor is still stock.

The GP42 is really a Hi Performance motor for a bushing main bearing motor. The three that I have been into show some fine craftsmanship over earlier motors. And, right out of the box run well. But, I never run a new motor right out of the box. Even with today's standards of quality and cleanliness there will be some debris inside the motor that can score the cylinder wall/piston of the crankshaft/bushing surfaces that can slow your motor down.

So, the first thing I do when I get a new motor is read the instructions, examine the exploded parts view, and then disassemble the motor and clean all the parts with a good solvent. If you put the solvent in a clear glass jar and wash the parts you will be able to see the debris in the solvent. After cleaning my GP 42 I inspect all parts for any metal chips or flashing that could cause over heating due to increased friction. Decreasing friction is major component of getting a motor to run well. If the crankshaft bearing surface does not show any problems I polish it with 2000/3000 grit wet/dry paper with some WD 40 to wash away the powder and keep the paper clean. This does not remove any appreciable metal it just polishes the bearing surface. This is all you can do to the crankshaft and still have it stock. Removing any metal, changing the timing, filling the front of the crankshaft with JB weld/epoxy makes the motor modified. The case is next with the crankshaft bushing. use the 2000/3000 paper and polish the bearing surface. after completion make sure you clean the fine dust off the bushing paying close attention to the lubrication groove in the bearing. I use Marvel Mystery Air Tool Oil assembling my motors soo I put a few drops on the crankshaft and the case bushing and assemble the crankshaft in the case. I then turn it over slowly and feel for any interference or drag. I it feel free then I will hold the assembly nose down and spin the crankshaft. If if spins free with no drag except for your lubrication you are finished with this part of the motor.

Next, after removing the crankshaft, I reinstall the cylinder and make sure it slides into the case without to much interference. Inspect the bottom of the cylinder to insure it has no burrs on it before reinstalling and check the porting the porting also. If the cylinder has a lot of interference I will take 1000/3000 paper and polish the outside of the cylinder until it can be installed in the case with some slight interference. You don’t want the cylinder to just drop in without any resistance. Again clean all parts thoroughly before continuing.

Do not polish the inside of the cylinder unless you are very knowledgeable on engine building. It is a prepared surface that will hone itself in with the piston and make the appropriate seal between the cylinder and piston. After you have reassembled the motor you are now ready to break it in. I always use a test stand and use a much smaller propeller that the factory uses for break in. I also have a tachometer, infrared thermometer, and pen and paper to record my data.

Well, enough of this for this post and I will continue on how I break in my motors and what else you can do to your stock motor and still be stock.