- Dec 16, 2019
Is it possable to convert a standerd mk1 carb idle jet to a premier? screw in type?
There's several web sites that do describe the process of drilling the blanking plug out to clean the fixed jet, but no-one seems to have written about using the Premier bit.Is it possable to convert a standerd mk1 carb idle jet to a premier? screw in type?
Yes, but not recommended. The first concentrics all came that way, but very shortly it was found the 4 strokes did not perform well at idle and the pilot bush was adopted for all 4 stokes as the solution and the float chamber position was then only use for 2 strokes.Wouldn't it be possible to knock out the pilot bush as described above, and fit a pilot jet in the threaded hole in the top of the float chamber ?
No from a pre premier and 9mm would work, I do not have a premier, just the jets and took the measurement off the jet. The endmill will give a flat instead of a chamfer at the bottom of the 1/4" section but the jet will bottom out on the hole where the pilot bush was so it just reduces the length of the threaded section which I like to maximise, it does not affect the final position of the premier jet.I guess the 8,85 mm depth measurement was taken from a Premier carb?
As I have converted a non premier to a premier I can confirm the new pilot circuit does lean the pilot mixture off a bit, it must be the extra turns the fuel must make or the 2 cross drilled holes in the jet are too small. A 25 pilot bush has a 17 thou holes as does the #17 premier pilot, the 25 pilot was standard on virtually all 4 strokes but on premiers its hit or miss as to whether the #17 or #19 works best on 4 strokes, 850 Commando's are now fitted with #19 premiers as standard.I believe they could do with #19 pilot jets.
I ground the end of a small screwdriver to point and used that to punch the bush out, it was not easy. Cliffs post covers what the thread is needed for. Amal have a cutaway photo on their site showing the new pilot premier jet in position. Out for a couple of days so cannot answer until late this week.Manny thanks for your replies esp. Kommando. I am still a little lost,when knocking out the brass pilot bush ,what do l use and what do l replace it with and how do l fit it ( is this what the 4mm 2ba thread is for)? If it is not too much to ask could l please have cross section sketch . Thanks Ian
This what you replace it with...
View attachment 82198
And if you have a look here you can get a better idea of what you're doing ( although that carb has already been modified with an access screw on the left instead of the blank).
Thank you Cliffa l understand now, everytime l looked at the jet pics my mind went to the air screw as they look the same MY DUMBI ground the end of a small screwdriver to point and used that to punch the bush out, it was not easy. Cliffs post covers what the thread is needed for. Amal have a cutaway photo on their site showing the new pilot premier jet in position. Out for a couple of days so cannot answer until late this week.