Amal carb adjustment problem

[Gromit]

Hi Guys

Now then .... I have a problem with my Morton 650SS.
new carbs 300 miles ago,  everything set up OK on the magneto , was sorted and timed by Les Emery at Norvil and not disturbed since that was about the same time as the carbs were fitted.

Bike was stood for a couple of years and this month I have had the carbs to bits to clean them out and found nothing really wrong just needed the old petrol cleaned out and the slides feed off ... was  OK before I dismantled them Doh ! should leave things alone.

All is well runs like an express train and idles perfectly except when you open the throttle it slows down before it picks up which is very disconcerting as it feels like it will stall ...but never quite does.
Colourtune plugs show the mixture is spot on at idle but goes rich as it comes off of idle and I am talking about squeezing the twist grip to take up the slack. Then when it picks up it is blue combustion again.

Don't seem to be able to adjust this out ... seems like as the cables start to tighten up it cures a slight air leak and the mixture richens up. Weakening the idle doesn't cure it ....

Any ideas guys ??

Wondered if it needs the float level checked and lowered a gnats perhaps ?

Gromit

[L.A.B.]

It's unlikely that the same problem would affect both carbs at the same time but did you make absolutely sure that the pilot jets (pilot bushes) were clear, as Amal pilot jets or the pilot fuel drillings can often block up if the carbs are left standing for long periods with fuel in them.

As you have recently rebuilt the carbs I suggest you remove the carb tops and check that both needle clips are correctly seated below the throttle springs and that one clip hasn't got caught up in the spring coils as it raises the needle higher than it should be.

You could check the fuel level (as it's the fuel level that's important)  http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=13 


     
 

[Gromit]

Yes been in there today on both carbs no problems in that department. Have taken all the slack out of the cables too and that didn't make any difference... the bottom of a monobloc slide is peppered with holes and slots so I don't think it is the cables suddenly shutting off an air path.

Ah now pilot drilling's ... the monoblocs have a separate jet under a little cover which I will have a look at tomorrow afternoon .... forgot those little b****ers

Cheers ...something at least to have a go at.

Regards Gromit

[L.A.B.]

Ah now pilot drilling's ... the monoblocs have a separate jet under a little cover which I will have a look at tomorrow afternoon .... forgot those little b****ers

Yes, I was really thinking more about Concentrics rather than Monoblocs.

[Gromit]

Yes have been there with concentrics a number of times .... rotters at Amal should have realised that bike tanks get crud and crap in them and not made the damn things unmoveable.

However on another web forum the suggestion has been made to drill them to the correct size using number series drills and a hand chuck. An going to give it a go on my Bonnie when it is back in loose formation again.

Regards Gromit

[phil_h]

Sounds to me like your slides are worn and you've adjusted the idle to compensate, but as the cable starts pulling, the slide moves to one side and seals its leaky gap before sliding up the carb bore and doing its job.
It'll be ok for a while still, but then it'll start idling badly.

[raptorkev]

IF YOU ASK ME THE MK1 CONCENTRIC IS THE WORST CARB EVER MADE BY AMAL THEY ARE CRAP EVEN NEW THE ONLY WAY TO GET THEM HALF DECENT IS TO GET BRASS SLIDES HARD CHROMED AND GROUND TO SIZE
EVEN WITH A BRAND NEW ONE THE SLIDE IS LIKE A PEA IN A DUSTBIN