Author Topic: Carburetter studs?  (Read 617 times)

Online bsa-bill

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Re: Carburetter studs?
« Reply #30 on: 15.04. 2019 12:38 »
I've had a bit of this over the last year, (on a monoblock) last thing I did was to take a bit of stuff of the boss in the float chamber for the cover screw at 7 o clock, the float seemed to just touch it when rising, so far it seems to have done the trick, lots of other avenues were explored before I got to this one
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline AdrianJ

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Re: Carburetter studs?
« Reply #31 on: 15.04. 2019 14:38 »
Swarfy,
It's bottom entry with a separate float bowl. I don't think its anything to do with the tickler to be honest.
I have a lot of fuel dripping off the bottom of the carb when the petrol tap is open. I'm not entirely clear where it's coming from. It looks like the thread on the bottom of the body. There is a  breather hole on this thread which may be the source. The hole looks like it is below the normal fuel level, so why wouldn't fuel come out of it al the time? The valve cuts off the flow into the float chamber, but fuel already in there can surely just flow into the carb body.
I've checked that the float and valve are working and they seem to be. I'm obviously missing something about the operation of these carbs, because the normal fuel level looks high enough to flood the carb.
Tomorrow I'll get chance to get it on the bench and sort out exactly what's happening.
I'll change the internal seal and try adjusting the float level.
Thanks again for all your help.
Adrian.
'53 Plunger Flash, Steib S500.


Offline AdrianJ

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Re: Carburetter studs?
« Reply #32 on: 15.04. 2019 17:50 »
Joy unconfined!
Found a spare couple of hours. Dismantled carb again. Replaced seal below main jet and fibre washers.
Doesn't leak any more. Still a bit of a pain to get the bottom on as it is difficult to find the correct thread.
The engine has just started after a complete rebuild for the first time in 3 years.
Now all I have to do is find a toolbox (wrong one fitted, hoping to find one at Stafford) sort the electrics and make some sidecar fittings for my Steib S500.
When it's complete I'll post photos.
Many, many thanks for the invaluable assistance on here.
Regards,
 Adrian
'53 Plunger Flash, Steib S500.


Offline Swarfcut

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Re: Carburetter studs?
« Reply #33 on: 15.04. 2019 18:38 »
Adrian
   To answer your question, when set correctly, the float needle stabilises the fuel level  to a point just below the top edge of the throttle needle jet, Item "0" on the usual AMAL Cutaway Diagrams.
 With the level set too high, fuel can top over the needle housing, and come out of the carb at any convenient orifice.
 You can see now how the thickness of that washer between the jet block and the big nut is critical as it governs the vertical relationship between the float chamber fuel level  and the level of fuel in the carb body. Too thin a washer will raise the level too high, above the needle jet, hence the flooding.

  When the engine is running, the venturi effect of airflow into the inlet tract  lowers the pressure above the fuel, which draws the fuel into the carb mixing chamber and away you go.

 Well done for sticking with it. Looking at your previous posts I can see a fair investment of time and money. So, always check the oil return to the tank on start up, run it in without labouring, forget the chair for a while, and just enjoy it.

 Be aware that not everyone who admires  you bike has your best interests at heart, the world is sadly a different place from when it first took to the road.

  Congratulations on a runner.

   Swarfy.

Offline AdrianJ

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Re: Carburetter studs?
« Reply #34 on: 15.04. 2019 19:15 »
Thanks again Swarfy.
Still have to sort the electrics.
I have oil return - new SRM pump.
The carb operation is a lot clearer to me now. It must have been the thickness of the seal.
With regard to your other point, I've stopped working with the garage door open, I  don't want the wrong sort of attention.
Adrian.
'53 Plunger Flash, Steib S500.


Online Angus

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Re: Carburetter studs?
« Reply #35 on: 15.04. 2019 22:28 »
Adrian

Where are you, please can you come and fix my old leaky (276) on my Norton Model 7. I have changed everything and so did a Norton expert. He had a similar carb which he could get to stop leaking on my bike but he could not stop mine. It is better now but IF you over tickle the bike it just pores out and does not seam to stop even when you turn the petrol off. Start her and it stops. And god forbid that you pull up and put her on the side stand without turn the petrol off.
1961 A7 since 1976
1960 A10 Gold Flash Super Profile Bike
1958 Matchless G80 Project
1952 Norton Model 7 Plunger (becoming a project)

Offline AdrianJ

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Re: Carburetter studs?
« Reply #36 on: 15.04. 2019 22:35 »
Sorry Angus, too far away  - West Yorkshire.
I think the float chamber has quite large capacity and if you over tickle it you have to wait a while for it to get back to the right level.
Good luck with it.
Adrian.
'53 Plunger Flash, Steib S500.


Online ironhead

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Re: Carburetter studs?
« Reply #37 on: 17.04. 2019 05:34 »
ironhead don't you have to deepen the seat for the slide to sit into *conf2*

G'day Berger.
No, as you are only taking off .020" from each side of the hole. There's still seating area left. If & when I have to take it off I'll try & figure out how to post a picture.
PS It hasn't swallowed a slide yet. *eek*
SA

Offline berger

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Re: Carburetter studs?
« Reply #38 on: 17.04. 2019 13:28 »
ironhead just wondered because dad bored out some rocket three carbs for bike mechanic when I was a young un, I can remember him having to recut the slide seats because Mr mechanic hadn't realised the slides wouldn't seat with the amount that was bored out. I don't know how much he asked him to take out though so it seems a little is ok a lot and you create another job.

Online ironhead

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Re: Carburetter studs?
« Reply #39 on: 18.04. 2019 12:47 »
berger , yes I only took a small amount. There is still about a 1mm seat.  From memory some Spanish 2 strokes from the 70's used Amal 27mm, that's what gave me the idea in the first place. maybe your dads mechanic tried to go to 28. ( the slide is only 30mm.)
I've seen tridents with Keihin's about that size. Also I'm pretty sure  *eek* *eek* ( have to check) but 928 930 & 932 carb bodys are the same size. they just bore em bigger. I really only did this to see if it worked, I swapped a 350 single for a 500 & had to get the bike back on the road asap. that was about 5 years ago & still going.
Does at least 100k per week. ( probably swallow a slide tomorrow now that if said that) *shh*   
SA