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Technique for drilling out a carb Jet?
Ivan - 25/1/12 at 04:29 PM

I think I need to increase the jet size of my Holly accelerator pump jets from .025" to .032" (or possibly bigger) because of a massive bog and 2 X backfires before the engine accelerates like hell when you floor the accelerator when cruising at lowish speed.

Any technique I should be aware of before drilling to make sure the hole is good and round - I guess the highest speed and ultra slow feed rate with lubrication is the secret but am I right.

The reason I am drilling and not buying a bigger jet is that although standard jets are available in RSA larger ones are not so if drilling doesn't work I can always go back to standard for about 2 Pounds a jet.

tegwin - 25/1/12 at 04:40 PM

Do you have a lathe?

With a drill that small it would be the easiest option.... But yes, high RMPS slow feed and a suitable lube for the material

britishtrident - 25/1/12 at 05:13 PM

I drill out LPG nozzles from 1.2mm upwards.
A simple Jewellers Spiral "Push Drill" (sometimes called an Archimedes drill) will do the job with sufficient accuracy but it will take about 30 minutes for each jet to drill through. A Dremmel type tool will also do the job but will require and patience to produce an accurate hole.

Fred W B - 25/1/12 at 06:09 PM

To do jet drilling at the track we always just used to hold a loose chuck with the drill bit in it in the hand and turn the jet onto the drill with the other hand. We may have held the jet in a tap holder. The brass (at least with the jets we used) was soft enough.

It's not like the hole needs to be a precision fit.

Cheers

Fred W B


[Edited on 25/1/12 by Fred W B]

jacko - 25/1/12 at 07:04 PM

Put the drill bit in a vice and twist the jet by hand

MikeRJ - 25/1/12 at 07:04 PM

A pin vice and a steady hand works perfectly.

JoelP - 25/1/12 at 07:43 PM

i just used a normal drill bit, a cordless drill, and did them by hand. Took a few seconds on each.

Ivan - 26/1/12 at 03:16 AM

Thanks all for advice - seems like slow feed is the answer otherwise any speed from dead slow to fast works. Now to decide what size to drill them. I think I will go up in 10% increments - i.e. approximately 20% increases in flow.

Fred W B - 26/1/12 at 06:02 AM

If you go too big you can close them up again with solder and redrill

Cheers

Fred W B

jossey - 26/1/12 at 07:59 AM

Take carbs apart. Take to a bike shop.... Give them £20-25 and let them do it. Pick up later all done :-)

sprouts-car - 26/1/12 at 09:38 AM

quote:
Originally posted by jossey
Take carbs apart. Take to a bike shop.... Give them £20-25 and let them do it. Pick up later all done :-)


Thats not the locost way!

Peteff - 26/1/12 at 09:56 AM

quote:
Originally posted by JoelP
i just used a normal drill bit, a cordless drill, and did them by hand. Took a few seconds on each.


I did the same but with an Aldi Dremel type tool. If I run a drill that small at a slow speed it will just snap off guaranteed.