I am curious what the I.D. of a #17 and #19 pilot jet is...what's the difference in decimals. The #19 is always the way to go though Amal and Wassel still refuse to supply them as stock. They also have a #15 pilot. Who, in all of creation, has ever used a #15? I have about 8 #17 pilots brand new and free to a good home.
Amal pilot jet
- Thread starter seattle##gs
- Start date
the metering hole in the pilot jet. # 17 should be smaller than the #19
The number refers to thousandths of an inch.
cliffa
VIP MEMBER
I think you are mixing up drill sizes with pilot jet diameters. a 19 pilot jet is 0.019" and not 0.166"
So there is only .002 difference between a #17 and a #19 pilot jet? .002 is that the difference between easy starting and 10 kicks every time?
baz
VIP MEMBER
Don't know about starting but .002 would certainly make a difference to the low speed running
cliffa
VIP MEMBER
Believe it or not the area difference is around 25% larger.
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A premier 17 pilot jet is a 17 thou hole etc, 17 is the same as the old 25 pilot jet and the 25 was the number of cc's of petrol that flowed per minute. 19 is equal to old 30 etc.
I drill out the premier 17's to 19 or close to it so I have no spare 17's. Unlike the old pilot jets the new ones are hard to drill, I use 0.5mm drills which end up with an undersize hole close to 19 thou.
I drill out the premier 17's to 19 or close to it so I have no spare 17's. Unlike the old pilot jets the new ones are hard to drill, I use 0.5mm drills which end up with an undersize hole close to 19 thou.
cliffa
VIP MEMBER
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Fast Eddie
VIP MEMBER
My understanding is that they are the same size (as you suggest) but in situ they do not flow the same amount due to the design differences. Hence the need for a bigger jet being required to get the same effect.
Thinking about it… I believe I learnt this from you ?
You did, Amal changed the route for the fuel to take when they added the accessable pilot jet but seem to have neglected to test what effect it would have on the flow rate in an installed jet as opposed to the laboratory flow in fixed repeatable conditions. So in the lab test both the 17 premier and the 25 pilot bush flow the same but installed in the carburettor the real flow rates diverge with the extra turns the fuel has to take to get to the premier reducing the flow, hence the need to fit the 19.
Because such a tiny difference in the pilot diameter creates such a big effect I don't drill them out. I doubt that I would get identical orfices.
marshg246
VIP MEMBER
No, IMHO when you put the #19 in it will still be hard to start because that's not why it's hard to start. With either a #17 or #19 you can get the correct air/fuel ratio, but you get more of it with the #19 and most bikes like that especially when idling and when quickly opening the throttle from idle. It's more likely that you have the air screw out too far, are opening the throttle while kicking, or that you have an air leak.
They don't need to be identical, unlike main jets you can adjust the air using the pilot adjustment needle. As long as you get a good idle between 1.25 and 1.75 turns out your jet is sized correctly, the 17 takes you outside that range below 1.25 turns.
I had #17 and fitted #19 on my Mk3, excellent starting, no banging on deceleration, much smoother bike down low.
No stalling at stops...PERFECT!
I had a Victor, fresh top end, new Premier with a #17. It was very reluctant to start. Replaced it with a #19 pilot and it started easily. Same with a 1956 Triumph twin. And others. Proof enough for me. Again, I have several brand new #17 pilots free to anyone that wants them. Any takers?
So true...