Z1A Jetting

[1GOM]

Greetings all. I've just started to restore my Z1A. It's an American import - in excellent condition APART from the previous owner decided he liked Z1 colours so all paintwork and engine are wrong. Long story told long I've stripped it and have had the engine and carbs vapoured - superb finish. Anyway I started to reassemble the carbs today and discovered it has 17.5 pilot jets whereas I believe it should have 20.0. It ran beautifully before so they are'nt a problem but my question is if I put 20s in what difference will it make and should I stick with the 17.5. It might be an obvious answer but I would like advice please.

Many thanks in advance

1 GOM

[000zeds]

Z1s had 20 pilot jet , Z1As + Z1Bs have 17.5

[Pigford]

If it ran good before, leave alone...

Going from 17.5's to 20's will make the low end richer...... 0 - 1/8 throttle openning

[RALPHARAMA]

I'm no expert on carburration; do the pilot jets do their bit during a certain rev range (ie air velocity through the venturii) as I always thought or is it related to the level of throttle opening?

[Pigford]

Ralphy,
Yes and Yes...
The pilot jet is only really noticeable at part throttle opening and the carbs rely on pressure differential in the venturi (slide opening) to draw the fuel thru, due to the negative pressure in the venturi
As the slide lifts, the needle then allows the main jet to come into play and provide more fuel as the venturi size increases:
More air needs More fuel
Carb tuning is best done working from full throttle and getting the main jets about right, before messing with needle position (mid throttle position) and finally pilot jets

[1GOM]

Thanks all for your help. I'll leave well alone and stick with what's in it. It ran beautifully before I started the rebuild so I think I'll take the advice and go back to that

Cheers

1GOM

[Bruce Sexton]

What part of Essex are you from 1GOM????????

Bruce

[1GOM]

Hi Bruce

I'm about 4 miles from Maldon

Dave