KR-1S.co.uk Forum

I have a set of C2 carbs that I'm preparing for another valve I have, so far I have tapped a nipple into the corresponding blank for oil feed.







I was thinking of tapping another nipple into the blank at the rear of the carb for opening the diaphram in the fuel tap.



I have been advised that the diaphram won't open properly when the throttle is closed and was advised to use a vacuum from the reed sidenot the airbox side.



any thoughts on this little project?

cheers.

You can not use the airbox side for a depression (vacuum). The airbox is designed to be a low restiction, hence the difference between atmospheric pressure and the inlet to the carburettor is small.

Therefore no depression (vacuum) at low speeds/loads. The reed side does offer significant restriction when the slide is closed or part way open causing the tap to open. At high engine speeds or loads when the slide is fully open the airflow past the point where the tapping is acts as a diffuser and draws air out (or fuel if your tap has a failed diaphragm). This needs to be around 1 or 1.5 mm to work properly.

This brings me to the oil feed you put in. It is simply too big, the depression across the hole will not be large enough to disperse the oil and you will end up with blobs going through. Not what you need to lubricate, you need a mist. If you look at the stndard part, this should give you an idea of what you need. Blobs will not lubricate and will cause poor running until the bearings seize because they have no lubrication.

I would take out the nipple you have put in and use Devcon or JB weld to glue the KR oil feed into the hole, hanging about 10mm into the carb throat.

Connect your oil pump to that and it will work fine. You will have to experiment with the setting, but if you keep backing it off until it is barely smoking it will be fine.

cheers mate, that's interesting. There is a slight problem with using the KR oil pipes, they are NLA and they are all in one so don't fit a YPVS anyway.

So I was wondering what you think of cutting off the blank and fitting the nipple so it is about 5-6mm proud of the venturi.

Something like this:




What do you think?

That would work better, but you will have to machine the thread away.

For it to work properly, you need a round form, preferably about 3mm high and slightly bigger than the diameter of the delivery hole. Your delivery hole should be in the 0.5 to 1mm maximum range.

If the nipple you have is bigger than this it will e very difficult to set up and make it lubricate.

Might be easier to pop out to a model shop and buy a bit of the thin wall brass tubing they have for model trains and soft solder that in. The nipple and tube would be both brass so soldering with an electrical iron would be easy. You could then use your original hole, with a bit of jb weld in to get rid of the big diameter and thread in the throat, and then trim the pipe so it protrudes between 5 and 10mm into the throat. The brass tubing I am thinking of comes in various diameters, so if you have a supply of nipples, you could experiment to get the best one.

Smaller bore tubes will give higher flow of oil at a given engine condition, bigger will be lower flow. Bigger will create a heavier mist, smaller a much finer mist. Smaller will clog easier if your oil is a bit naff, or there are bits coming through the oil sysytem.

Thanks for the info.

I have compared the KR1 oil feed with the nipple I have and, with the thread filed off, they are almost identical. So it looks good to go.

Hopefully get one done over the weekend, if I post a couple of pics would you give me your opinion on them?


cheers.

Managed to get a bit more done.






I can probably get it 2mm further into the venturi with a bit more filing.

The nipple is now the same dimensions as the KR oil feed.

What do you think so far?