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.
Hi kommandoOld pilot circuit
New pilot circuit
Was editing as you postedHi kommando
Just incase anyone gets confused by this maybe add that the blanking screw on the left side in the top photo has been added by someone
It'd be just a casting originally
Cheers
Excellant!!!Old pilot circuit modified for removable screw for easy access to pilot bush for cleaning. Normally blanked off with no hole.
New pilot circuit