After buying a new pilot jet size 30 to replace the 25 that appears too small , I find the 30 is far smaller than the 25 ! .looks like I will be making my own . What exactly does the 30 represent . perhaps 3 thou ?.
25 and 30 refer to the flow rate in ml. So the 25 flows 25ml of fuel per min.
In fact the flowrate for pilot jets can be equated to a size, 25 jet is 17 thou, 30 jet is 19 thou. Once you get to main jets then exact sizes cannot be set to a size as the shape of the hole and markings from the drill cutting have an affect so flow rate is the sole measure.
Thanks John, I suspect that I will have to drill out to 18 thou to get somewhere close.
Hi Robert. Also make sure that the jets are genuine Amal. I’ve had some non-genuine ones that are a mile out of spec. The genuine ones have rectangular cut-outs across the hex sides of the jet.
All of this is worth knowing, thanks for posting the question and the responses
After a close examination of my new 30 pilot , I think its a pattern part and I have had to pass an 18 thou bit through it to clear away swarf. . I will let you know how it runs and if it helps the by pass supply deal better with the progression from pilot to slide cutaway.
Well that worked. The uneven and unreliable idle has gone and the spit back with it. whether its due to the bigger pilot or perhaps a minor restriction in the 25 its hard to say. A session with the colourtune and a warmed up motor is next. Its only taken a whole riding season to sort this, what chance anything complicated?.