OS max 20 carb

[Brian Dorricott 1]

I have been given an old OS Max 20 to try and rekindle interest in IC engines . I have it running but not well , the carb barrel has a lot of end float - is this normal ? I think its a OS 2A carb but cannot find an exploded view of it on the net. Is there a spring in the carb or something missing making it loose ? Tried OS engine site but cannot find that carb in exploded view so if anyone knows a link to exploded view that would be appreciated.

Brian

[J D 8]

Hi Brian,I have an OS Max 20 manual and the exploded diagram shows no spring inside [ It is the same with a 15 I still have,I looked .]

Is the screw and spring on top of the carb that retains the barrel in place present ? John.

[Caveman]

Brian, here's the info you're looking for

I've got 2 1A carbs and a 1G - they all have a fair amount of end float, somewhere around 1.5 to 2mm, so perhaps it's normal.

Do you have the instructions for adjusting the needle valve and air-bleed screw? If not I'll scan those and post them.

Cheers GDB

[Brian Dorricott 1]

Thanks guys so everything is complete , would appreciate setting instructions tho it is very well run in but I am a complete novice with glow motors so any help useful.

Brian

[David Davis]

I would take your engine to a more experienced modeller if I were you.

Your nearest club will have members who would be delighted to show you how to set up your engine.

[Caveman]

Hi Brian, David's comments above are probably the best way to go, but, if you want the challange of doing it yourself, the adjustment instructions are:

Have fun!

GDB

[Engine Doctor]

Hello Brian this carb is very easy to set up and will run your engine well provided that the engine is sound. By sound  I mean reasonable compression when warm but more importantly good crankcase compression . Crankcase compression will be low if the main bearing is worn or if there is a poor seal on the backplate. Start by turning the idle stop screw until you can see the throttle barrel bore just beginning to open. Now turn the idle mixture screw out until the air bleed hole on the front of the carb is open then screw it back in until you can see the screw half way across the hole. Now close main needle and open it 2 1\2 turns . Start and tune to max rpm then open one click . Now close the throttle. Allow engine to idle a few seconds and open throttle . If engine coughs and splutters then mix is too rich so open the screw a little. If it stops immediately when opened  it's too wreak so screw the mix screwing a little. You should also use a good quality glow plug OS 3 (hot)should be ok for this engine but check as I believe OS has recently changed their numbering of glow plugs ? Hope it helps and you get it running ok.

[Denis Watkins]

Many thanks ED

Have printed this out for all the lads at my club

[Jon H]

I use the 1/2 open method ED describes when setting my air bleed os carbs. I have a 15fp working well in a small model and i found a 20fp the other day when clearing up the garage. I might try to revive it!

I normally use No8 plugs but A3 work well too.