Rek
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| posted on 30/4/07 at 08:09 PM |
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SU Carbs and MGB GT
Apologies in advance for not going and asking on an MG forum but looking at a couple of them the people flame dumb questions like this. A friend
brought over his just bought MGB GT this evening. All seems great but it runs rich (Hunting and sooty exhaust). I believe the SU's have a mixture
(Yellow in the picture) and Idle Adjust (red in the picture), Is that correct?
Image deleted by owner
Also for the purposes of tuning is cylinder 1 at the front (Rad end) or rear of the engine, and does anyone know the timing settings (1800 N plate)
Lastly Should the battery really be here? I thought they were in the boot?
Image deleted by owner
Sorry these are really basic questions but I know Naff all about these. Does look nice though!!
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DIY Si
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| posted on 30/4/07 at 08:12 PM |
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The miture adjuster ison the bottom of the carb, where a funny pipe goes in. It's a hex nut thing. The adjusters you have there are for the idle
(red if I'm looking at it right) and the yellow is for syncing the carbs
The battery(ies) should be under the rear seats, but are a right ar$e to get at/get out.
[Edited on 30/4/07 by DIY Si]
Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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mookaloid
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| posted on 30/4/07 at 08:14 PM |
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I think the red is probably the idle adjust
I think the yellow is the throttle synch adjustment
The mixture is a big nut directly under the body of each carb - thee main jet protrudes from this and the fuel connection goes into it from the float
chamber
HTH
Chers
Mark
"That thing you're thinking - it wont be that."
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theconrodkid
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| posted on 30/4/07 at 08:15 PM |
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batteries (2x 6volt) are under the rear seats,the mixture adjustme nt is done by winding up the main jets,bottom of the carbs,its a bit of a pain to
get them balanced.
who cares who wins
pass the pork pies
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mookaloid
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| posted on 30/4/07 at 08:17 PM |
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must type quicker......
Also put some 3 in one oil in the damper pots at the top of each carb
Cheers
Mark
"That thing you're thinking - it wont be that."
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ditchlewis
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| posted on 30/4/07 at 08:25 PM |
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might be off the point or it might help...
had some SU's on a mini, it hunted badly and i could not set the mixture. turned out to be air leaking in from around the butterfly spindle.
needed a rebuild.
to check run the engin and spry WD40 on to the ends of the spindle, if the revs pick up then you have an air leak.
Ditch
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skydivepaul
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| posted on 30/4/07 at 08:33 PM |
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for the purposes of tuning No1 cylinder is usually next to the flywheel, in case of the MGG thats at the back of the engine
cheers
Paul
http://www.smartideasuk.com
http://www.smartmapping.co.uk
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Peteff
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| posted on 30/4/07 at 08:43 PM |
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We always used 20/50 engine oil in the dashpots, 3 in 1 let the dampers rise too quickly on ours. As per the others, those are balance and tickover
screws.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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mark chandler
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| posted on 30/4/07 at 08:45 PM |
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Red is idle, yellow is choke idle.
The mixture adjustment, unless really really old carbs will be through the damper hole (Black bolt thing on the top that you remove and fill with
light oil), you need a special tool.
You can tell if the mixture is about correct by either locating the damper lifting buttons (look under the carbs for smell rods 3/8" with
springs and Clips) or pull off filters so you can see the damper piston.
Next engine running lift the piston 1/4" up, idle should increase slightly then drop back, if it slows then the mixture is weak, if it rises
then its rich.
Regards Mark
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Rek
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| posted on 30/4/07 at 09:03 PM |
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Thanks all
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cs3tcr
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| posted on 1/5/07 at 04:51 AM |
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Those carbs appear to be the HIF type, ie the float bowl is in the bottom of the carb. The mixture adjustment is on the side of the carb body. Be
sure to sync the carbs, and make sure the ignition is up to snuff before messing with the mixture.
As for the brick, it should be below the rear seat squab.
The carbs the others have described are the HS type, which has a remote float bowl and has a large hex nut on the jet bearing to adjust the mixture.
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britishtrident
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| posted on 1/5/07 at 06:37 AM |
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cs3tcr is right most later UK spec MGBs had the the HIF type SU.
Before doing anything check the carb piston are rising and falling freely --- particularly that they fall on to the stop with a distinct
"click".
Also make sure the distibutor centrafugal advance is operating freely -- remove the rotor arm and put a single drop of oil down the single screw which
is revealed.
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Macbeast
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| posted on 1/5/07 at 07:12 AM |
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Cylinder numbering... any B engine I've ever dealt with, cylinder no 1 is at the front by the radiator.
As far as I remember, timing is about 8 deg BTDC as seen on a strobe
"" The mixture adjustment, unless really really old carbs will be through the damper hole (Black bolt thing on the top that you remove and
fill with light oil), you need a special tool. " NO !! - This is damper to stop carb piston fluttering - nothing to do with mixture. But
yes- you should top up with oil and you don't need a special tool.
Also MGBs are notorious for overheating. That battery is not going to help in that position (and the heat won't do the battery much good
either). On earlier MBGs 2x 6V batteries should be under the rear seat but carriers may have rusted away. I think later ones had a 12V one somewhere.
I wouldn't be happy with the weight of the battery that far forward either. Handling and tyre wear must be affected to some extent.
It's odd if it's an N reg if it has chromium bumpers but these may have been retro-fitted.
There's usually an oil cooler in front of the radiator I think. (edit) oic, according to the pipework the oil cooler is probably right at the
front and doesn't show in the pic. But it won't work very well with the battery in that position either.
Before you start messing around, I would replace air filters, clagged-up ones would probably make it run rich
Anybody with an MGB should get the Haynes manual 
Hope your friend enjoys it
[Edited on 1/5/07 by Macbeast]
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02GF74
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| posted on 1/5/07 at 08:25 AM |
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red = this is idle speed
yellow = fast idle - it adjust the choke - the little screw is pushed by a cam.
I cannot tell if these are HS or HIF type SUs. For mixture adjustment:
HS = you raise or lower the jet by a nut.
HIF = these have a screw with a cross, more like two slots rather than philips tytpe - on the body of the carb; it is usually sealed to prevent you
messing as the jet height is set by the factor; the jet on these is on a bimetallic srtip to adjust for engine running temperature.
The battery is perfectly sited to obstruct air flowing to the radiator. 
There is a panel behind the main seats (roadster) where there are 2 compartments for two 6 V batteries connected in series. I am sure battery
technology has progressed sinced 1962 when the B first came out so you could fit one 12 V battery with the same capacity.
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britishtrident
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| posted on 1/5/07 at 09:31 AM |
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Carbs are the HIF type ---
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britishtrident
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| posted on 1/5/07 at 09:35 AM |
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quote:
Originally posted by skydivepaul
for the purposes of tuning No1 cylinder is usually next to the flywheel, in case of the MGG thats at the back of the engine
cheers
Paul
No it isn't No 1 cylinder is at the pulley end ie front.
This is very basic car mechanics - it hasn't changed in a 120 years.
[Edited on 1/5/07 by britishtrident]
[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]
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02GF74
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| posted on 1/5/07 at 10:51 AM |
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quote:
Originally posted by Macbeast
"" The mixture adjustment, unless really really old carbs will be through the damper hole (Black bolt thing on the top that you remove and
fill with light oil), you need a special tool. "
there is a procedure like this requiring a pecial tool for Stromberg carbs.
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Macbeast
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| posted on 1/5/07 at 11:00 AM |
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I didn't say that, I was quoting !!
Just spoke to my local friendly MG garage. Later MGBs had a 12V battery at the back, under the seat too.
Oh, and it's a legal requirement for all MGBs to have a copy of the Haynes manual on the back seat.
[Edited on 1/5/07 by Macbeast]
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flak monkey
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| posted on 1/5/07 at 11:48 AM |
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#1 cylinder is at the front of the engine! (Cambelt end)
Strombergs and SU's are very similar. Triumphs tended to be fitted with Strombergs and MGs with SU's (apparently)
David
Sera
http://www.motosera.com
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britishtrident
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| posted on 1/5/07 at 01:18 PM |
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quote:
Originally posted by Peteff
We always used 20/50 engine oil in the dashpots, 3 in 1 let the dampers rise too quickly on ours. As per the others, those are balance and tickover
screws.
20w/50 causes problems particularly in the winter -- either 10w/40 or auto trans fluid works best.
[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 1/5/07 at 01:21 PM |
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Ok --- just to cut through the confusion.
The carbs are SU HIF6
The mixture adjustment is by a large X head screw which is recessed into the the side carb body ---- it is 20 odd years since I adjusted the carbs
on a an MGB so I can't remember the exact location but istr a stubby screw ordinary driver is require --- nb not Phillips.
[I] What use our work, Bennet, if we cannot care for those we love? .
― From BBC TV/Amazon's Ripper Street.
[/I]
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DIY Si
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| posted on 1/5/07 at 02:48 PM |
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BT is correct they are HIF 6's. I looked at the pics and didn't read all the text, so assumed it was an early chrome bumber job. Mine has
HS's and just assumed yours were to! The mixture screw is one the forward facing edge of the carbs, about half way down the bottom. It is IIRC
angled away from the centre line of the car a bit, so should be a bit easier to get at on your car.
Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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