Non premier to premier

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Is it possable to convert a standerd mk1 carb idle jet to a premier? screw in type?
 
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Yes, you have remove and extract the pilot bush, then drill and tap a 2ba threaded hole from the other side for the new premier pilot jet. I do it on a vertical mill but a good drill press with accurate depth reading would work.
 
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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.
If you have a scrap carb to try this, it could be your moment of Internet fame :)
I do notice several people who have tried modifying the carbs who report great problems in getting it to work though. The jet hole (& thus fuel flow) is very small, it will not take much to disturb the operation of the transition from pilot system to needle / slide. As always with carbs, the devil is in the detail.

Personally, I would simply bite the bullet and buy the Premiers. I've a set of 30mm Premiers that I bought off a bloke here in Denmark, thinking that they were 32mm. I'll probably try fitting them this winter, just to see how they work.
 
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Previously posted

1. I drilled a 4mm hole in on the blanked side making sure I did not go into the passageway and drill the other side, the other side is where the taper on the other end of the new pilot jet seats and you need a seal, accidentally drill it out to 4mm and it may not seal.

2. From the pilot screw side I knocked out the pilot bush so it exited through the new 4mm hole.

3. Then went back over to the 4mm hole side and using a end mill opened out the first 8.85mm to 1/4", this is the area the new pilot jet O ring seals onto.

4. Tapped the remainder of the 4mm hole to 2BA thread.

5. A good clean out.

6. Screwed in new pilot jet, it goes in so it is just slightly proud.

Note if using Drill press or Drill stand without DRO

If doing this on a Drill Press and not a Vertical Mill then do steps 1 followed by 3 before doing 2 so you can do the two diameters concentric. I have DRO on the mill and can return easily to previous positions so can mix up the sequences easier.
 
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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 ?
 
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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 ?
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.
 

Tornado

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And of course, you need to also swap over to anodized slides, viton alu needles and stay up floats to be full premier setup. If your original bodies have worn slide bores, you can get them sleeved for about $80 CDN each.
 
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Questions for kommando, I guess the 8,85 mm depth measurement was taken from a Premier carb? I can't see how I can obtain this sort of accuracy on a drill press? Is it really this accurate, or would say 9,0 mm work? I would try a sleeve on the mill bit, but still difficult to achieve without a proper mill and a DRO.
Also, is an end mill bit essential or could one use a 1/4" drill bit? After all it's the O-ring that seals, and any slight variation in depth could be compensated for by screwing the jet in or out? I know you shudder from such a frivolous approach to engineering, but would it possibly work?
I have access to a proper machinist and can have it done properly, so I'm asking for others who don't.

SR
 
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I guess the 8,85 mm depth measurement was taken from a Premier carb?
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.
 
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Thanks kommando. My friendly machinist was here just now (on his trusty B40) and he says no problem, so we're going to give it a shot. If successful I want to convert my Trident carbs next, I believe they could do with #19 pilot jets.

SR
 
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I believe they could do with #19 pilot jets.
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.
 
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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
 

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This what you replace it with...


1633974858698.png


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).

 
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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
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.
 
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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).

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.
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 DUMB
 
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Old pilot circuit modified for removable screw for easy access to pilot bush for cleaning. Normally blanked off with no hole.

Amal-cutaway.jpg


New pilot circuit

Premier-cutaway-carb-1.jpg
 
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Hi 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
Was editing as you posted ;)
 
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Thanks to all who replied ,as l have stayup floats and anodized slides in new bodies all l need now is #19 jets and a good machinest.
 
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