Carburetor Jet Drills

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PATRIOT

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Does anyone have experience drilling carburetor jets or have a source for jet drill bits?
I need to fabricate a main jet drilled out in the range of .0402" to .0406"
The OEM is obsolete.
 
I have never drilled the jets on a carburetor. For a DIY job you could use a #60 bit which is .040 inches in diameter which is a little smaller than you are wanting. A #59 bit is .041 inches which is a little larger than you are wanting by .004 inches. If you are determined to do it yourself you could take a #59 bit and grind the flutes down to the diameter you wish. You would have to take .002 off of both sides to get it down to .0406 inches. After grinding make sure you still have enough heel in the drill bit to keep from tearing up the hole in the jet. Myself, I would go with the #60 bit to start off with because the wobble factor may take the hole to .0402 or larger. BTW, .002 is less than the width of a human hair. Take a gauging rod and grind it down to no more than .406 inches in diameter or which diameter you choose between .402 and .406 inches. After drilling the hole see if the rod slips in. If it does not you are still under your desired size. Another thing about jets are the hole needs to be pretty well rounded and even to spray the fuel in a nice uniform pattern. If you scratch and score up the hole the jet will not work well. You kind of want the hole to be polished inside for a smooth flow.

You could take it to an auto machine shop and have it done.
 
I would go with the smaller bit and try it. With a bit you are going to get a larger hole because most times they aren't perfectly straight in the first place. If you were using a ream they would be more precise but you wouldn't find one that small.

You could also look into metric bits and mic. them.
 
Pappy said:
What engine is this for? If it is for an OMC product I probably have what you need.
1987 Nissan NS15B
351A-1
Serial No. 62305

I'm still having a hard time believing the stock jet (1.08mm) which does not run properly at 8200' above sea level and a 1.02mm jet is claimed to correct the problem. That's only .002" difference in diameter, which is only 5% smaller than stock. Can't believe a 30 year old motor would notice that difference.
 
PATRIOT said:
Pappy said:
What engine is this for? If it is for an OMC product I probably have what you need.
1987 Nissan NS15B
351A-1
Serial No. 62305

I'm still having a hard time believing the stock jet (1.08mm) which does not run properly at 8200' above sea level and a 1.02mm jet is claimed to correct the problem. That's only .002" difference in diameter, which is only 5% smaller than stock. Can't believe a 30 year old motor would notice that difference.

...something about pie arr squared..its all about the area and not the diameter. If that 5% refers to area, my bad..
 
Sinkingfast said:
PATRIOT said:
Pappy said:
What engine is this for? If it is for an OMC product I probably have what you need.
1987 Nissan NS15B
351A-1
Serial No. 62305

I'm still having a hard time believing the stock jet (1.08mm) which does not run properly at 8200' above sea level and a 1.02mm jet is claimed to correct the problem. That's only .002" difference in diameter, which is only 5% smaller than stock. Can't believe a 30 year old motor would notice that difference.

...something about pie arr squared..its all about the area and not the diameter. If that 5% refers to area, my bad..
Good call . . . yep it'd be 11% smaller area (and therefore 11% smaller volume on a column of fuel) . . . but still, you wouldn't think going from 1700' to 7500' would be that sensitive to the air/fuel mixture.
 
Higher altitude means it needs timing advanced. I lived at 6800' and still have property at 8500. Also make sure what little air you have can get thru the tiny cowl vents. I cannot believe those jets are special. What number is stamped on the jet? Not the Nissan part number. Take the jet to your local dirt bike or motorcycle shops and match it up. Advance timing first and try it first. Drilling jets is a last ditch effort to get a POS project moving again not on a keeper. If your in deep then mill the head. Your compression is down due to thin air. At 7000' you are down 20% power. Run the 85 octane gas that's sold at elevation.
 
Not sure it would help any for thsee carb jets I know for the auto world holley and edelbrock have a list of corresponding drill sizes and jet sizes.
 
Cliffshighperformance.com or quadrajetparts.com are great sources for the bits and other tools.

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