Scooterotica

Standard carb (sh1/sh2) atomizers,higher number richer or weaker?
5899-1 weakest ?
5899-5 richest ?
Got a bit of a mid range running problem on a mildly tuned 175 running a SH22/2,and want to try the carburation before entering the world of failing pick ups/coils

I thought it was the other way around. The problem I can see is that 22mm carbs were never designed for 175's and there isn't really a slide for them. It may be that a 200 slide will do the trick. I don't know. But 22mm carbs seem to have been bypassed in preference for larger Dell'orto's.

They do not run simply according to rich - weak, rather they control a wide range of throttle positions and one may be richer or weaker than another for only part of the throttle range. They differ according to diameter of central drilling, number of side drillings, height of side drillings and diameter of side drillings... so they really can differ across the throttle positions, rather than simply being rich - weak.

I've had some 175s using the standard 2 atomier, others using 1 and yet others using the 5, with a massive difference in main jets to suit which atomiser was used. You cannot consider atomiser in isolation to other elements, e.g. slide and/or main, as you need to balance one off against another.

Sorry, no easy answer... however, both the 1 and 5 will clean up the progression jetting when used with a larger main, whereas the standard 2 atomiser (175 and 200) will provide too much too soon when used with a bigger than standard main.

Adam

Thanks for the info,im just having trouble after the pilot jet has done its thing,it ticks over nicely,then as the throttle is opened further its spluttering big time,i have a selection of jets and atomizers to hand,so it looks as though its trial and error time!!

I would try the 1 first, with something like a 118 main jet. If this doesn't give decent results then I'd look to try a 5, with anything up to a 125 main (!). So much will depend on spec of barrel, compression, timing and exhaust choice that it is almost impossible to advise you without knowing the engine in question.

Good luck and remember to start rich and work weaker. Having your twist grip marked against the housing to identify 1/4, 1/2, 3/4 and full throttle (note 'throttle' = slide position... NOT simply where the grip stops turning. All of these throttle positions should be marked by looking in the carb mouth to see how high it is. This way you can glance to see what throttle position you are at and judge how the motor feels. Choke tests will allow you to do instant testing at each throttle position to see how the motor responds, whereas plug colour will only ever give you an average reading if you are working up and down through various throttle positions. Doo a search on here for 'choke tests' if you want to read more.

Adam