Keihin MK1

Hey Steve,

that is a small change. might be obvious but could be useful to know that if you are able to acurately measure the drill or wire then you can also make whichever size reamer is required. a lathe is best to spin the wire but there is nothing wrong with an electric drill. use #400 grit paper to reduce the diameter. Reducing more than 0.1mm by this method is a bit dodgy but works.

hows that song go? an engineer told me before he died ah hum ah hum........then we come to the tragic bit..... think it means that if you can measure things accurately you can make anything you want with nothing. might not be 100% right but helps sometimes.

Cheers
Bushy

.....there was no way of stopping it, a rum ***** bum ***** bum ***** bum!

hey! i have a lil honda CRF230F here and the thing is a ******* to start and keep running, even after 10 minutes blipping it you still stall it leaving the yard. i'm told from TT that the answer is to take the MJ from 102 out to 120.

what drill size would that be lads?

regards

Taffy

steve said:

For playing with jet sizes you can get some jet drills and number drills, and get a pin vice to hold them too, I have got some from ebay fairly cheaply. You can then solder up the jets with normal lead solder used for electrical work and then drill them out to smaller sizes. A good idea is to use a micrometer to check the drill sizes too, just in case.

As an aside, I've been playing with my wifes KLX 250. I installed a 300 kit in it and a big bore Staintune header, keeping the standard muffler, for her Christmas present. I've got it running well with a 120 main, that happens to be a bored and drilled FCR start jet I had lying around from my Berg experiments that happens to fit nicely into its CV carb main jet holder. 120 is down from the 132 standard for the 250. The kit includes a needle which I believe is a standard KLX 300 needle from other markets which I'm running on the middle clip and a 138 main. So I'm down from a kit supplied 138 to a 120 and by comparison to standard its now a torque monster, she is pulling 1 to 2 gears higher up long hills now, and is finding it easier to ride, which was the objective. An automatic would actually be her ideal, but then we are getting further off topic.

A long winded way of saying that some solder and some drills can be a lot cheaper than buying lots of jets.

Steve

Click to expand...

Might work on a main jet, but not on a pilot jet as I presume a 38 pilot jet is 0,38mm hole?

I wouldn't even manage to get a bit that small in the drill without breaking or loosing it.

I'm all for cheap solutions but this a step to far even for me

Offcourse if you have a machine shop with everything you need this could be possible but if you only have a cheap drill press like me wich has at least a 1mm runout this will not work

Hi BB,

The smallest drill in my kit is 0.30 mm, which is small. Careful use of a pin vice, which is a small chuck tool used to hold these drills and with care its no problems. You turn them by hand, and drilling/reaming brass is easy, and solder even easier. I must admit though, that most of my exploits have been with mains and over 1 mm in size.

Small changes in small jets make big changes to performance too, remembering that the flow is a function of the cross sectional area and is a function of the square of the radius, so double the radius for 4 times the surface area. You also change the ratio of the wetted surface, or the perimeter by the same ratio, the perimeter being just a linear function of the radius. The wetted perimeter suffers from surface tension/friction effects, in other words its easier to suck a given amount of liquid through a bigger bore than a smaller one as their is less friction.

Here are some sample numbers, all in mm

dia perimeter % increase area % increase
0.3 0.942 0.000 0.071 0.000
0.4 1.257 0.333 0.126 0.778
0.5 1.571 0.250 0.196 0.563
0.6 1.885 0.200 0.283 0.440
0.7 2.199 0.167 0.385 0.361
0.8 2.513 0.143 0.503 0.306
0.9 2.827 0.125 0.636 0.266
1.0 3.142 0.111 0.785 0.235
1.1 3.456 0.100 0.950 0.210
1.2 3.770 0.091 1.131 0.190
1.3 4.084 0.083 1.327 0.174

Note that to go from 0.3 to 0.4 is a 77.8% increase in area, where as the same incremental increase from 1.2 to 1.3 is only 17.4%

I see that the table is not displaying nicely, but hopefully you get the idea. It looks OK when I try to edit it.

Many of these small tools and drills, and the wire mentioned by Bushie can be obtained from hobby/model shops. Check out a place that supports guys that scratch build model trains, planes and cars, they do some amazing stuff.

Have fun,
Cheers
Steve

RE pilot jets; Have made a 48 pilot into 38 pilot using a $30 hand held electric drill a staightened peice of return spring out of my sons brocken plastic train a pair of vise grips and some solder, thanks China!

Living out in the bush makes people try dodgy things ....doesn't mean it won't work in populated areas

Have a go!!

Hey Taffy,

pilot jet was split from ar$ e 2 tit and the whole bl... thing covered in solder rum tity rum tity bum....

Cheers
Bushie

i need a reason to call them tomorrow!

give me your address in a PM and if i can get you a 35 and 38 i will!

regards

Taffy

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