Author Topic: Initial carb setup  (Read 321 times)

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Offline Alan.c67

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Initial carb setup
« on: March 11, 2020, 02:32:02 pm »
Hi.

Hoping someone can help, I'm sure I saw a very good guide on here in the first 40 pages or so but can't find it again!

Got my Amal 274 back after being sleeved and the carb is leaking like a sieve so I'm going to dismantle it and put new gaskets in to see if that will stop or at least slow the leaks down! So after it is rebuilt what are good settings to start with? I seem to remember air screw all the way in then back,off by 1.5 turns and throttle slide screw in just as far as it starts lifting the slide.

Could be  completely wrong but help most definitely appreciated.
1938 BSA C10
2004 SV650S
2008 ER6F
2011 VFR1200F

Online hampshirebiker

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Re: Initial carb setup
« Reply #1 on: March 11, 2020, 03:52:45 pm »
Sounds about right Alan. Once running and warmed up set the stop screw to fast idle and adjust the pilot screw until best idle is achieved. Finally reduce the idling speed to what seems reasonable.
After I renewed the gaskets (fibre washers) on a 274 I had to retighten things a few times over several days. Always assuming that the leak isn't caused by too high a fuel level.
I also got new idle and stop screws which came with springs instead of locknuts. Far easier to use.
Postal - Liphook Hants - But just into West Sussex.

Online camman3

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Re: Initial carb setup
« Reply #2 on: March 11, 2020, 04:09:27 pm »
You dont say what model or year the carb is fitted too, so i have attached link to spec sheets so you can check you have correct jets, needles, throttle slide etc
As HB says you are correct on starting point for final set up.....and also as hb says, are you sure carb is leaking through gaskets, and not flooding due to incorrect float levelor leaking needle seat?...fuel will leak from carb body at base of jet block if float cut off level is too high
Graham
https://bsac10c11c12.co.uk/smf/carburettor/carburetor-data/
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Offline Alan.c67

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Re: Initial carb setup
« Reply #3 on: March 11, 2020, 05:27:09 pm »
On a 1938 C10.

The metal float is set to the upper groove on the needle, after flooding on the tickler it doesn't leak out the vent holes on the top cap but it does come out of the joint at the base of the carb body, probably the vent holes there and it does seem to leak quite badly at the float bowl joint to the body. Before it was sent off for refurbishment it didn't leak as badly as far as I remember, I don't believe any gaskets were replaced as I asked for the sleeve to be done and everything else left original, I have issues with nice bright shiny new things being put on what we think is essentially an original bike.

On reflection probably a mistake so now got a gasket kit but concerned it might not work and I'm always concerned I over tighten things!
1938 BSA C10
2004 SV650S
2008 ER6F
2011 VFR1200F

Online Owen

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Re: Initial carb setup
« Reply #4 on: March 11, 2020, 06:59:57 pm »
Have you lapped the float needle onto it's seat?
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11

Online camman3

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Re: Initial carb setup
« Reply #5 on: March 11, 2020, 07:03:07 pm »
I had a 39 c10, and the float was on middle groove to stop leaking at jet block level.
Simple way to find out if gasket or level, is to remove float  chamber lid and tickler, then control the fuel level by hand.
Hold the float needle down and fuel flow in until it floods out of jet block level, then hold the needle up by hand, ensuring no more fuel flows into bowl.
If it does, the nedle seat is leaking, if it doesnt, and the fuel stops leaking, then it is float level too high, but if it continues to leak from that area, it must be the gasket.
I suspect you just need to lower the float or clean float needle seat.
Graham

P.S. typed at same time as Owen...yes lap the seat with a bit of brasso
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Offline Alan.c67

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Re: Initial carb setup
« Reply #6 on: March 11, 2020, 11:20:29 pm »
Only got 2 grooves on the float needle. Was told to use the upper one with a metal float and the lower one if I was replacing mine with a plastic float. Would the float actually stay in place if I was to position it between the grooves?

I'll investigate tomorrow the flow control by hand and we'll see what the outcome is, thank you for the fault finding tips Graham and Owen.
1938 BSA C10
2004 SV650S
2008 ER6F
2011 VFR1200F

Online timsdad

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Re: Initial carb setup
« Reply #7 on: March 12, 2020, 07:40:18 am »
To keep my ancient carbs fuel-tight, Alan, I coat the fibre, copper or alloy washers with Hylomar Blue to help them seal. I'm sure other gasket sealers would do the same job, apart from silicone which will only last about ten minutes.


Ray
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Offline Alan.c67

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Re: Initial carb setup
« Reply #8 on: March 12, 2020, 05:46:16 pm »
Thanks Ray, I was wondering if a smear of something would help.
1938 BSA C10
2004 SV650S
2008 ER6F
2011 VFR1200F

Online timsdad

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Re: Initial carb setup
« Reply #9 on: March 12, 2020, 07:03:34 pm »
I've got a variety of old bikes with ancient carbs Alan, and you just have to do what you've got to do. It's rare that there'll be no leaks if I've had them apart for any reason and it might take three or four goes of sealing the various joints before they stay dry.

You can usually tell what the culprit is by where the leak is if you know what should be happening inside, and where the levels are. Copper washers, jdeally, need heat-softening every time they come apart and all metal washers benefit from rubbing on an oil stone or wet & dry on a bit of glass. I usually get genuine fibre washers, seals and gaskets from Amal because they only cost pence so I can afford to keep the common ones hanging on a nail.

As an addition to hb's advice, you need to keep dropping the engine speed down with the slide stop screw as the revs pick up when the mixture screw is adjusted, otherwise there'll be a false mixture if too much air is being drawn in through the slide cut-out. The engine needs to be running as slow as possible without stalling as the mixture screw is adjusted by very small movements from its one and a 1/2 turns out from fully in. It should finish up no more than about 1/4 turn from where you started.


Ray
« Last Edit: March 12, 2020, 07:12:02 pm by timsdad »
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Offline Alan.c67

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Re: Initial carb setup
« Reply #10 on: March 12, 2020, 10:07:25 pm »
Thanks Ray. I'm learning this very quickly! All the old fibre washers are as hard as nails, almost brittle so no doubt that had a bearing on my leaky carb. If the float is a bit high on the 'correct' setting is it acceptable/possible to increase the spacing by increasing the gap in the mounting brass strips? Looks like I might squeeze a couple of thou extra height out of the float that way. I'm not convinced it would stay on the needle if it was off a groove. Looks like the seat is ok, tried moving the float by hand and it stopped filling without too much pressure.
1938 BSA C10
2004 SV650S
2008 ER6F
2011 VFR1200F

Online timsdad

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Re: Initial carb setup
« Reply #11 on: March 13, 2020, 07:50:40 am »
I wouldn't have thought a few thou' of float height would make any difference to flooding if everything else is fine, Alan, because there's more of a margin in it than that. If the fuel level is too high then it would be leaking out of the orifices like you were still tickling it and it takes more than a couple of thou' of depression of the button to flood it up. Is that where it's leaking from?

If the fibre washers are hard and brittle, they're bound to leak after being disturbed because they'll have gone back in a different place. A bit of rubbing on 400 grit may get round it if that's the case.


Ray
Just a motorcyclist.

Online camman3

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Re: Initial carb setup
« Reply #12 on: March 13, 2020, 09:16:37 am »
Is the float needle straight?
The one in my c10 was  slightly bent and would occasionally "hang up" and cause flooding.
I replaced the needle, and thought it had three grooves (can't check now as Griff has it)....but if it was two, I definitely fitted on lower groove and not top.
It wont do any harm to fit on lower groove, and you will soon know if too low with fuel starvation, but don't fit between grooves as it will certainly move after a few tickles....no harm in producing another groove though, if you have a dremmel and a lathe.
Graham
1957 C12
In sunny (sometimes) Christchurch, Dorset, UK

Offline steve70

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Re: Initial carb setup
« Reply #13 on: May 23, 2020, 11:22:21 pm »
The 274 Carb I have only has one groove on the needle, the 275 which is in use, is the same,one groove. that carb works well but will leak out jet block if over flooded which I thought would be unavoidable, Is that correct. stops when float returns to correct level,   no leaks when it its running.   

Online Owen

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Re: Initial carb setup
« Reply #14 on: May 24, 2020, 08:08:33 am »
Usually there are 3 grooves in the needles.
By holding the tickler down and thus the float needle off the seat, the carb will flood. The trick is to hold it down long enough to flood a little.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11