Any ideas? (OK on full choke but not on anything less)

[Rex]

The plunger A7  finally reached the time for lift-off; closed the choke (yes it has got a choke fitted) tickled her up and a genuine first kick fire up. It ran for about a minute I opened the choke and it died. Closed the choke again, kicked and away it went only to spit splutter and die when I opened the choke. So, off with the brand new Amal Premier to see if the pilot jet is blocked. All clear, and carb body blown through with compressed air just in case there's swarf present (something I've had with brand new Amals before) and all clean as a whistle.
Float height/fuel level checked, all good. Carb inlet checked for air leaks, all good. Stripped and blew carb out again and checked needle position (I know it has no bearing on tick-over but I checked anyway) but still the same. Runs OK on full choke but not on anything less.
The Premier has a removable pilot jet (not blocked) but I'm wondering of there's various sizes and this carb has a too-small component fitted?
The other sizes fitted are 140 main,E106 needle and 3.5 slide. It will run at higher throttle openings ie above the pilot jet range.
Obviously given the spitting back and the need to run on full choke the mixture is too weak, but I can't think of any more causes at the moment. Any suggestions?

[ellis]

Premiers have a range of pilot jets of 15 17 19 21 thou. The 15 has one ring the 17 has two rings and so on. The ring markings are at the end nearest to the jet so you can see what the jet size is. Hope this helps.

ELLIS

[Rex]

Something to check tomorrow. Thanks Ellis.

[Rex]

The jet has two rings. Clearly that isn't sufficient for a 500 twin, so a call to the carb supplier tomorrow is in order.

[Triton Thrasher]

Another cause of such problems is an air leak into the inlet manifold.

[ellis]

Hi Rex,

That will be a number 17 jet so could be weak mixture. I fitted a new pair of Premiers to my mk3 commando. That was running weak and popping back in the silencers. On inspection one float level was 6.5mm down from the top of the float bowl the other was 9mm down. Should have been 4.5-6mm. re set the floats and the bike ran perfectly. I have heard new Amal's have had the wrong jets in from new before. Hope the correct pilot jet cures your problem.


ELLIS 

[muskrat]

G'day Rex.
I haven't seen a new Premier carb yet. They must have changed the way they number the pilot jets if their in thous". The old numbers were milliliters per minute at sea level. The usual size of our A's was #25 which had a 16 thou" hole.
Check for air leaks first then try the next size up pilot.
Cheers

[Rex]

Just a follow-up. I bought and fitted a three-ring pilot jet and it's all OK now.
Thanks to Ellis for pointing out this method of identification of the pilot jet. The leaflet Hitchcocks supplied was for the "standard" Concentric carb with no mention of this aspect.

[ellis]

Hi Rex.

Glad you now have it sorted. We are all here to help when we can. 

ELLIS