Differences between Amal 389/4 and 389/1 carb

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Bondy1066
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Differences between Amal 389/4 and 389/1 carb

Post by Bondy1066 »

Hi, I am trying to establish why my 1955 AJS 18S is running rich and sometimes stalling at junctions unless I tickle the throttle. All jets and needle settings are standard, however I have just noticed that the carb has 389/4 (and a small 6) stamped on it, whereas the spec says it should be a 389/1. I have been unable to find anything on the internet to explain the differences.
Can anyone advise me what the differences are and could it be contributing to the running problems I am getting?
Many thanks Colin.
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Janet
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Janet »

Have you asked Burlen Ltd who make new Amal carbs? I suspect the 389/1 and 389/4 have different bore sizes.
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Bondy1066
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Bondy1066 »

Hi Janet, Many thanks for your advice. I did try to contact them before I submitted my post, but their office is closed until Monday. I will contact them Monday unless I get further responses from this thread.
Kind Regards Colin
Bondy1066
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Bondy1066 »

Just to confuse things further the throttle slide has got 389/3 stamped on it. Sounds like I have a right mismatch of parts :(
SPRIDDLER
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Re: Differences between Amal 389/4 and 389/1 carb

Post by SPRIDDLER »

How long have you had the bike? Has it ever run O.K? Has it been standing unused for a few weeks? Is the carb intake 'open' or is an air filter fitted?

Why do you say it's running rich? Running rich and having to tickle the carb is a bit contradictory unless your assumption that it's running rich is because the plug is sooty. However, the plug may be sooty because you keep tickling the carb to stop it stalling on tickover, which is necessary because the pilot jet or the very fine pilot drillings in the carb body are constricted or blocked as a result of the bike being unused for a few weeks or so. This has been a common issue since the intro of ethanol which when it evaporates leaves a residue of lacquer or gum in the pipes, filters and jets.

If you don't already have it, this Amal rebuilding and tuning guide may be handy:

http://amalcarb.co.uk/downloadfiles/ama ... d_Tips.pdf
Last edited by SPRIDDLER on Sat Nov 11, 2017 3:27 pm, edited 2 times in total.
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dave16mct
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Re: Differences between Amal 389/4 and 389/1 carb

Post by dave16mct »

The original carb was 389/1 which was the first monobloc and had no 'O' ring groove. 389/1 is just a code denoting which jets etc. The slide is correct ie 389/3. The original spec is 1 5/32" bore, slide 3, main jet 260, pilot 30 and the needle in central notch. Your 389/4 will be OK, it's probabely 1 1/8" bore. If you check that the jets are correct, then it's just a matter of tuning it to run well.
Dave.
Bondy1066
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Bondy1066 »

Thanks Dave for that. Other than the/4 number I found nothing untoward when I stripped the carb down. I am going to put it back together and have another play. I want to try adjusting the petrol air mixture screw. Currently out 1.5 turns from seated.
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Rob Harknett
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Rob Harknett »

Do not confuse part numbers of the parts. With the complete carb type part number. For a throttle slide there will be different types and cut a way's. You should notice for 389/1 carb the throttle valve ( slide ) is 389/3 1/2. You should also notice your correct carb should have 1 5/32" bore. So you can also check the bore of the carb fitted. If it is 1 5/32" then all you need to really do then is fit all the correct internal parts. Which you have found are listed. There were other 389 crab types with different bore size. e.g. 1 1/8" & 1 3/16" So if the 389/4 carb you have differs in bore size you need, you may not be able to get the carb converted with parts to suit your bike, to run properly. I not seem able to find the 368/4 listed for a motor Cycle. So perhaps it was used on something else.
I was called away and note other comments have been made. eg Dave says 369/3 slide is correct, I am sure I read 389/ 3 1/2 correct for 389/1 carb. you can check all the correct internals yourself as 389/1 carb is listed. Here http://archives.jampot.dk/technical/Car ... _523-5.pdf
cbranni
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Re: Differences between Amal 389/4 and 389/1 carb

Post by cbranni »

Porklips is a handy listing

http://porklips.org/~mason/moto/amal_specs.html

Colin
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Rob Harknett
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Re: Differences between Amal 389/4 and 389/1 carb

Post by Rob Harknett »

cbranni wrote:Porklips is a handy listing

http://porklips.org/~mason/moto/amal_specs.html

Colin
It is on this list that I noticed many 389 type carbs not listed as being used on a motor cycle 389/4 being one of them.
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