Can't set the idle mix

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Notsospeedy
Posts: 135
Joined: Sun May 17, 2009 8:04 pm
Location: Cheshire

Can't set the idle mix

Unread post by Notsospeedy » Sat Aug 06, 2016 9:33 pm

My Triumph 5T with an Amal 276 is up and running but I cannot get the idle mix right.

Theory says start off with the pilot jet about 1to 2 turns from fully in, start the (warm) bike, screw the pilot jet in until it starts to falter then turn it out until it starts to falter. The mid point is then nicely between it being too rich and too weak. Then adjust tickover.

Great, so I started off by having the idle air screw turned out from the stop by 1-2 turns, started the (warm) bike and screwed the pilot jet in - only I got all the way in where it seemed to run better!!!!

Carb has been cleaned in an ultrasonic bath - boy did some muck come off and the various drillings all seem nicely clear.

So what's happening?

Malcolm

Simon Ratcliff
Posts: 4
Joined: Mon Jan 25, 2016 10:46 am

Re: Can't set the idle mix

Unread post by Simon Ratcliff » Sun Aug 07, 2016 12:16 pm

It's possible that there is excessive wear between the slide and carb body and drawing air through the gap instead of breathing through the pilot circuit. If this is the case then fit a new carb or have your existing one bored and a brass sleeve fitted to the slide.

Notsospeedy
Posts: 135
Joined: Sun May 17, 2009 8:04 pm
Location: Cheshire

Re: Can't set the idle mix

Unread post by Notsospeedy » Sun Aug 07, 2016 2:44 pm

Suspected there was an air leak somewhere but couldn't fathom out where!
The carb to manifold is nicely flat as is the manifold to head.
Hadn't thought of it coming past the slide.
I have a feeling I could be throwing good money after bad by having it sleeved (who does that?) as the jet block looks like it's been taken out with a hammer at some stage.
Having got a new (correct) float chamber plus main and needle jets at least I'll have a few spares! ;)

At least it runs, albeit a bit lumpy and just done 50 miles on it today.


Malcolm

Triton Thrasher
Posts: 773
Joined: Wed Feb 18, 2009 12:51 pm

Re: Can't set the idle mix

Unread post by Triton Thrasher » Wed Aug 10, 2016 1:34 pm

Is the idle jet blocked?

Notsospeedy
Posts: 135
Joined: Sun May 17, 2009 8:04 pm
Location: Cheshire

Re: Can't set the idle mix

Unread post by Notsospeedy » Wed Aug 10, 2016 11:47 pm

No, not only did I clean the body in an ultrasonic bath but I also (carefully) poked through all the small drillings.
The idle adjuster itself is new from AMAL.

Consensus is that it's leaking air round the slide - plug chop doesn't help, it is virtually clean, or is that very weak?
Sent off for a bit of TLC from Autocycle Engineering. Re-bore body, fit oversize slide, look at jet block
Enquired of Martin Bratby but he's not taking on anything at the moment due to a backlog of work and no date for accepting anything new.

Whilst it would be easy to buy a new one, I don't want to chuck £300 at it if it can be fixed much cheaper.

I need all my pennies to replace the stuff that's vibrated off! ;)

Malcolm

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