Author Topic: Concentric carbs  (Read 215 times)

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Mike Farmer

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Concentric carbs
« on: 26 October, 2020, 20:30:03 »
 :) :) :)

Hi gents. Two Q's on this subject.

1. :) I have looked at two or three books over the last couple of days and none of them show a washer on the inlet union that goes through inlet filter. on the float bowl. So query this.

My rebuilt A65 is running seriously rich.(Black plugs after only 2or three minutes running). So I have a washer fitted, would this washer alter the off position of the float enough to cause a continuous minor flood. By which I mean does this situation allow the float to ride higher because of the altered depth of the inlet union.

If no washer, how do I seal it

It starts easily, but runs black and very lumpy as you would expect from this condition. If I turn the fuel off and let it run out the last few seconds are sweet and very smooth.

Anything else you can think of that might be the problem. It has all new jets and needles etc direct from Amal.

Mike 8) 8) 8)

Nanonevol

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Re: Concentric carbs
« Reply #1 on: 26 October, 2020, 21:22:58 »
You have a washer between your carb fuel filter and the bowl?  So do I on 4 Concentrics.  They will have no effect on the float seat height or needle.
How's your float height by the way?  How to you set it?  What pilot jet do you have?

Mike Farmer

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Re: Concentric carbs
« Reply #2 on: 26 October, 2020, 22:23:11 »
 :) :) :)

Needle position 1, jetted 106 and 240.

My washer is not between the filter and the bowl. Its between the filter housing and the inlet "bolt" but there isn't one shown in any of the drawings that I can find. There is no apparent float adjustment on the plastic float.

So I am in an uncertain situation.

We'll see---thanks for your input.

Mike 8) 8) 8) 8)

Nanonevol

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Re: Concentric carbs
« Reply #3 on: 27 October, 2020, 00:54:25 »
Hmmm.  Still the washer on the bolt would have no effect on your fueling or float level.
I imagine you have the pilot jet that is behind the pilot air adjusting screw.  Could it be that someone cleaned it out too agressively and enlarged it?
How many turns out do you have the pilot air screw?

DAVE BRADY

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Re: Concentric carbs
« Reply #4 on: 27 October, 2020, 07:50:35 »
Good morning Mike,

If you have not already taken the carb off,  does the bike pick up and rev freely when the throttle is opened up and what was it like before fitting the new parts?  It looks like the problem is with the primary/pilot jet/settings.  It may be worth checking the carb again just incase.
I use a Colortune for checking carb settings.  As you probably know, you can see the colour of the combustion and make changes to get the colour right.  It also means that as you rev the engine you can see the combustion colour right up to full throttle.  This could help to see at what position the richness occurs.
The Colortune kits are available on ebay, Amazon and Halfords etc.

Dave.
« Last Edit: 27 October, 2020, 07:52:32 by DAVE BRADY »

craigc11g

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Re: Concentric carbs
« Reply #5 on: 27 October, 2020, 09:26:54 »
i think the bolt you talk of is also the float needle seat , so yes it will alter the fuel level .

DAVE BRADY

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Re: Concentric carbs
« Reply #6 on: 27 October, 2020, 09:40:26 »
Hi,

The float needle sits against an insert in the float bowl and the banjo bolt holds the banjo and filter in place.  The filter serves as a washer against the float bowl and a thin fibre washer can be used between the banjo bolt and the banjo.

Dave.

JulianS

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Re: Concentric carbs
« Reply #7 on: 27 October, 2020, 09:49:46 »
There is a useful article on the Amal website which deals with the Mk1 Concentric.

http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter

You will see that the float needle seat is fixed and that the fuel banjo bolt does no have any effect on fuel level.

The later stay up float has metal tabs which can be used to slightly adjust the fuel level.

http://amalcarb.co.uk/mk-i-concentric-series/900-series/floats/mk1-mk2-stayup-float-kit.html

Also if you carb is a mix of early and later parts you need to be sure that the jet holder is the later one to be compatible with your new jets and jet needle.

Paco2cv

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Re: Concentric carbs
« Reply #8 on: 27 October, 2020, 12:48:09 »
The float height on carbs with the plastic floats can be altered by moving the bush up and down in the bowl, it is mentioned in the factory manual somewhere and mentioned here https://youtu.be/TfOeDd5lnPE at 8.30 minutes in. Bit of a pain by all accounts.....

Mike Farmer

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Re: Concentric carbs
« Reply #9 on: 27 October, 2020, 20:08:25 »
 :) :) :)

Thanks to you all for your posts and advice.

Situation is at the end of nuts and bolts rebuild so has never run in its current state.

Today I did a few measures and checks and as the carb(s) are used :), I did a bit of fiddling. And concluded most of what you are advising. So I rebuilt and fitted and got rid of flooding only to have seriously weak etc etc etc---Conclusion----stuff it.

Previously I have known and recommended that ultimately rebuilding used carbs of doubtful history is normally as expensive as buying new. I have just proven this to myself again. If I had any excuse at this point I would use.

So tomo I shall talk to Mr Amal and get a new one. Not sure which way to go but will discuss it with them. May even go for a Mk2.

Take care guys---at the end of a rebuild whats another couple of hundred quid?????????????/

Mike 8) 8) 8)

DAVE BRADY

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Re: Concentric carbs
« Reply #10 on: 27 October, 2020, 20:23:59 »
Hi,

I have a Mk2 on one of my bikes and one of the problems is space for a filter. To rubber mount the carb there is a manifold bit then the rubber sleeve and then the carb so no room even for thin pancake filter.  If you use a Mikuni manifold this has the rubber integral with it so a bit shorter so a thin pancake filter should just about fit.

Dave.

Mike Farmer

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Re: Concentric carbs
« Reply #11 on: 28 October, 2020, 09:53:05 »
 :) :) :)

Thanks for that so I shan't do that then.

One other point; I am fairly certain that someone has that at some stage the carb body has been zealously cleaned and seriously re-orificed. So thanks for bringing that to my attention.

Probably before I purchase a new one I shall boil the better of my carb bodies in kitchen soda for half an hour or so. Some times it works and sometimes etc

Mike 8) 8) 8)