Saturday, April 11, 2015

Drilling the Slides

A couple of days ago, I finally got around to picking up the 7/64" drill needed to drill the slides on the Ural CV (constant velocity) carbs. The picture on the left shows the slide removed and the small drill bit. The actual difference between the existing hole and new is on the order of 1/64". This is a common modification on other engines that use the Kiehin carburetors such as the KLR 650. It is described as a minor. safe modification that should improve throttle response.

Last Sunday, I mentioned that I had added some shims to the needle. Here is the picture that I didn't take at that time showing the needle and the 2xM3 washers that I added to each needle before dropping them into the slide. Not in the same hole that I drilled but one right next to it (just below the drill bit in the first picture).

Also, as an experiment, I put the original 122 main jets back in replacing the 130 jets I installed last August. Just curious to see what the CHT will be with the smaller jets. It may have to wait a while as I head up to Barrow on Monday afternoon.


  1. So you opened up the hole in the slide by .016"? How thick are your washers?

    1. Supposedly it makes a noticeable difference. A very small difference but the claim is better throttle response. The washers are 1mm thick each and they made a noticeable improvement in the upper mid-range. On some minor hills around here that used to take close to full throttle to maintain 50 mph, now needs just a bit more throttle.

    2. The CV carburetor is still nothing like I've worked on in the past. Still trying to figure them out. Not looking for more HP but better "drivability".