Drilling out jets

[Mad Mackie]

A fair amount of brass jets have a countersink leading in.
With the drill bit in a pin vice, I start in a counterclockwise rotation and sometime go all the way thru in the same direction.
Holding the pin vice steady, I work the drill bit in and out smoothing up the new hole as best can be done.
I usually dip the drill bit in cutting oil before hand.
I don't recommend pushing thru a jet with a torch tip cleaning tool.
I have never got into motorcycle carbs, but I have a friend that does and he uses the same procedure that I do, in fact, I'm the one that showed him how back in the 70s. He is a retired machinist/aircraft specialty welder and now does rework of off road motorcycles used in competition. He has a watchmakers lathe and has made jets on it.
Most of my jetting work was done on two stroke outboard motors along with some high performance inboard/outboard boats, some of which turned up to 7,000 RPM and governed.
Number drills bits are manufactured to closer tolerances than jobber drill bits and can vary in size slightly between manufacturers. I use this to my advantage when resizing jets.
Sometimes all that is needed is .0005" more in hole size and this can sometimes be difficult to do.

 

[viperv10]

Thanks guys for all the input. I haven't started yet. This will probably be an early Spring project. I have been working on cleaning an rebuilding a Tecumseh
carburetor for my snow blower that surges real bad. I can not believe how many lawn mowers that I heard surging real bad last summer. Probably one out of every four or five. My neighbor got a brand new portable generator and it surged up and down terrible right out of the box.
There are not many Lawn Boys in my area. I rarely see one. My friend's wife's grandpa had a Lawn boy repair shop years ago and he still has a few.
We have to keep the old boys running.
Merry Christmas.

 

[LB8210]

Back to the reason for drilling jets. Surging because of a lean condition on the duraforce Lawn Boy. First are there any gaskets leaking in air causing a lean mixture? Have you replaced the top and bottom crank seals that are old and hardened /worn and allow air to be sucked into the crankcase and again leaning out the mixture? These all need to be corrected first. These will take care of 99% of surging motors. Drilling jets is putting a band-aid on the problem instead of fixing the source. I have tried all of the internet solutions. On a motor and nothing worked other than drinking more fuel. I went and put every mod back to factory stock condition and the motor had new crank seal and gaskets and block resealed and checked for leaks. The cause was the way the factory mounted the throttle plate in the throttle shaft. They only relied on a press fit to hold the plate centered in the bore of the carb. As the motor aged clearances changed and the plastic shaft's slot no longer holds the plate in position in the bore and the plate then is free to move and cause the shaft to bind. Motor running vibration then will vibrate the plate and let it free up and then restick, starting the surging cycle. I placed the shaft and plate and the surge was gone. This may be a common source of the surging than any other. It is a very poor way to build the carb. instead of a brass shaft and plate with a screwed in place plate.

 

[viperv10]

Thanks for the reply LB8210. I haven't layed eyes on this machine yet. I just told a friend of mine that I would help him with his mower. I have ordered new crank oil seals and have watched a couple videos and read how to change them. I also got a Briggs and Stratton carb jet part no. 801308 to switch out the one in the side of the carburetor under the sticker. Several guys on the lawn mower forums say that helps. I have also read about the throttle plate that you were talking about being a problem. Some one said that there are 2 different throttle plates with different size little holes in them and to make sure that the duraforce engine has the one with the bigger hole and that the snow blowers take the ones with the smaller hole. I will make sure we put new carburetor mounting gaskets on too when we put it back together. We will do all of these things first before even thinking about drilling out anything.
You guys are a big help to us Lawn Boy owners that aren't mechanics.
Thanks again.