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Message started by Routy on 08/19/12 at 00:19:39

Title: Drilling Main Jets
Post by Routy on 08/19/12 at 00:19:39

Does the # on the main jet represent any kind of measurement whereby a person could use it for reference to drill it out a little w/ a # drill ?

Thanks

Title: Re: Drilling Main Jets
Post by javajunkie on 08/19/12 at 00:34:41

That number represents the flow rate for that particular jet... Example: 150 means that jet's flow rate is 150 cc/m (cubic centimeters per minute)...for mikuni carbs anyway... Somebody correct me if I'm wrong...

Title: Re: Drilling Main Jets
Post by wambr on 08/19/12 at 03:02:44

like all true. but drill a hole larger than stock hole not that easy. the diameter of the holes in the main jet of carburetor has a value of the form transitions channels in there.

the best solution is to install the jet-kit
sorry for my english....

Title: Re: Drilling Main Jets
Post by Dave on 08/19/12 at 03:58:00

Drilling jets can make them flow more - but it is not real accurate. It is better to use Jet Reamers and Jet Gauges. If you do a lot of carb work on multi-cylinder engines it can be worthwhile to buy a set - but with a single cylinder engine you can buy a lot of jets for the cost of the reamers and gauges. The cost is more than $ 100 from these people.....maybe you can find a cheaper set somewhere or get some used ones from eBay.

http://www.cbperformance.com/catalog.asp?ProductID=1871
http://www.cbperformance.com/catalog.asp?ProductID=1872

Title: Re: Drilling Main Jets
Post by bill67 on 08/19/12 at 04:33:17

Years ago I never bought jets.My wife work were they had a tool and die maker ,and I told him to drill the next size better hole,In the low and high speed jet,It always work good for me. A jeweler might have bits.

Title: Re: Drilling Main Jets
Post by bill67 on 08/19/12 at 04:42:29

Type agk how to drill jets.

Title: Re: Drilling Main Jets
Post by Dave on 08/19/12 at 04:57:52

A few minutes ago I remembered reading somewhere that each jet is flowed and the flow rate confirmed when they are made. It didn't really sink in at the time why they did that.....but after thinking about it a little this morning it made sense. We are tuning an engine with very tiny jets to control fuel flow. On our single cylinder engine we can install a bigger jet if we need more fuel or a smaller one if we need less. If you have a small jet and need more flow you could drill it out.......if it gets too big.....you can get a smaller one and fix it.

Unlike our single.....when jetting a 2, 4 or 6 cylinder engine you need to have jets that flow exactly the same rate so you can treat each cylinder the same. Drilling the jets evidently does not always provide exactly the same flow rate - as drills don't always leave a smooth finish. (This may especially be true with jet sized drills that will probably be turned by hand).

Title: Re: Drilling Main Jets
Post by Paraquat on 08/19/12 at 07:01:47

I bought jets for 5 or 6 bucks, shipped, off ebay.
Just go a day without coffee.
Unless you're trying to achieve a size that isn't listed. I do recall reading somewhere here that a 52.5 and 55 is offered but someone really desired a 53.5. Could try a set of pin gages to check the sizes and ream one to suit?

--Steve

Title: Re: Drilling Main Jets
Post by ralfyguy on 08/19/12 at 18:30:25

4475667565617560140 wrote:

I did that one. The 52.5 was too lean and the 55 was blowing black smoke. Bad thing was that I am a machinist without any decent tools for that. But being a machinist makes you improvise and I found a safety pin with was just the right size, didn't go in the 52.5 and fell into the 55.
Opened the pin up and ground the tip like a screwdriver having sharp edges on the sides. Now the brass tends to grab suddenly when drilled, so the pin had the outer edges cutting like a reamer in an 90 degree angle, which prevents the bras from biting. It's more like shaving than cutting, and will leave smooth walls when going through. The thing that helped also was the fact that the jet was only drilled that small on the tip end. The bore was bigger on the screwdriver end and tapered down to the actual jet hole. That's what helped getting the first bite on it and keeping it centered. I put the pin in the vise and just twisted the jet back and forth until all the way through. Bike runs like a charm with that now. I'm estimating it to be a 53.5 now.

Title: Re: Drilling Main Jets
Post by justin_o_guy2 on 08/19/12 at 23:20:47

which prevents the bras from biting.

Im sure thats an important feature,,

Title: Re: Drilling Main Jets
Post by Routy on 08/20/12 at 05:48:57

Thanks for all the info.
I used to drill jets years ago using a mini hi sp drill press it worked fine.
I'd like to open up my #145 to about a #147,....just to try.
But my # drill set is not complete,....need to hit a HF one day.
I would now drill jets on my mini lathe,...would be quite accurate I believe.

Title: Re: Drilling Main Jets
Post by ralfyguy on 08/20/12 at 06:34:24

616E746F737566646C6275070 wrote:

Man I wish I had a lathe in my house. The lathe is what I loved most about being a machinist.

Title: Re: Drilling Main Jets
Post by Paraquat on 08/20/12 at 06:48:30

I hate lathes.
Give me a Bridgeport any day.

--Steve

Title: Re: Drilling Main Jets
Post by greenmonster on 08/20/12 at 12:32:29

Don't want to derail the thread but I didn't want to start an new one for something that I think is a yes or no questions.

I'm finally getting around to rejetting, do I need to take the carb off to do this or can I do it just by dropping the float bowl?

Title: Re: Drilling Main Jets
Post by verslagen1 on 08/20/12 at 12:37:06

maybe

Title: Re: Drilling Main Jets
Post by bill67 on 08/20/12 at 12:51:20

41544343484B494855524354260 wrote:

Dropping the float bowl.

Title: Re: Drilling Main Jets
Post by greenmonster on 08/20/12 at 12:51:51

;DThanks Vers, you're oh so helpful. ::)