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T-Series & Prewar Forum

Setting the SU carbs

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Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
I rebuilt the carbs on my TF last year or so ago with all new gaskets, seals, springs, spindles, etc. All went well and they work fine but I couldn't stop a slight weepage of fuel from the base. I tried both Viton and PTFE seals as advised on this forum, and others, but to no avail - they still leaked. As a last resort I bought the Burlen Superdry seal kit, which is more than just a set of rubber seals, there are a whole of other parts to replace as well. So have reassembled the carbs on my test rig with the new seals and they seem completely leak tight. At the same time I took the opportunity to reset the fuel levels. This has seemed more of a struggle than usual - I normally use the meniscus method, but just couldn't get it to work right for me this time. The problem is exacerbated by the fact that the jets sit rather low in the upper jet bearing, and always have. In fact they sit 3mm (1/8"winking smiley below the top of it. Rather than count the number of flats on the jet adjusting nut I set both carbs with the jets droped the exact same amount using a micrometer. The WSM method of setting the floats requires a round bar of 3/8", but I found that if I used this the fuel was level with the top of the jet, which is not ideal, so I set them with a round bar of 7/16" instead, taking the fuel level just below the top of the jet (which is what I would have been aiming for with the meniscus method). However, I still find it odd that the jets sit so low below the top of the upper jet bearing and the bridge (with the jet adjusting nut well up its thread range) - its as if the jets were 1/8" / 3mm shorter than they should be. Does anyone have an explanation for this?
Dave H

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LaVerne Avatar
LaVerne LaVerne Downey
Fruita, Colorado, USA   USA
1954 MG TF "Green Hornet"
1969 MG MGB
Over the last dozen years or so, there have been a number of cases where owners could not lean out the carbs to acceptable levels at idle. I think the consensus was that the washers supplied in the rebuild kits by Burlen are thicker than the originals and do not allow the jets to rise to the correct seated position.

Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Indeed so LaVerne, I've even reported that one here myself, but they only make a smidgen of difference - but what I am concerned about is why the jets are so short (3mm / 0.125"winking smiley. Is it because a common jet being used for a range of carbs, some of which it fits better than others.
Dave H

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perfectpitch Avatar
perfectpitch Charles Windsor (Disabled)
Disabled Account, Antarctica   ATA
I would never buy anything from Burlen. Mitches post reads like an advert direct from Burlen. Never heard of Super dry kit and Burlen is peddling such trach these days I would never give them any money on a kit nobody really needs.

Mitchman2 Avatar
Mitchman2 Mitchell Andrus
Mills River, North Carolina, USA   USA
In reply to # 3514742 by perfectpitch I would never buy anything from Burlen. Mitches post reads like an advert direct from Burlen. Never heard of Super dry kit and Burlen is peddling such trach these days I would never give them any money on a kit nobody really needs.

All I know is, 2 sets of cork seals in the TD's carbs weeped and stank up the garage and the new seals are tight.... so far. It could easily be that the "O" rings offered by Moss work just as well for far less money. If (when) the seals in the A start to weep, I'll try the Moss "O" rings. One thing I know for sure I will NEVER install seals make from tree bark again.

On to the next crisis.



Buy a man a plane ticket and he flies for a day,
push a man out of an airplane and he'll fly for the rest of his life.

'30 Model A Ford
'48 MGTC
'58 MGA
'58 MGA

perfectpitch Avatar
perfectpitch Charles Windsor (Disabled)
Disabled Account, Antarctica   ATA
Mitch, surprised you did not try the teflon o-rings everybody been talking about the last few years. Only mod you need make is to polish the jet tube so smooth slide inside the o-rings. The teflon is pretty hard and don;t seem like it should work, but it does, unless you got nicks or scrapes or wear in just the wrong place of carb body.

Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Tried them, and polished the jet tube, but they leaked.
Dave H

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Mitchman2 Avatar
Mitchman2 Mitchell Andrus
Mills River, North Carolina, USA   USA
In reply to # 3514830 by Buckdendave Tried them, and polished the jet tube, but they leaked.
Dave H

Dave, "them"... meaning Teflon?



Buy a man a plane ticket and he flies for a day,
push a man out of an airplane and he'll fly for the rest of his life.

'30 Model A Ford
'48 MGTC
'58 MGA
'58 MGA

Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Yes, Teflon. Bought the size and type specified on here, but didn't work for me. Because its a fairly inelastic material I imagine dimensions are critical, and not compatible with my carbs. For some others Teflon seems to work fine. Fuel leaks under the bonnet / hood make me nervous.
Dave H

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ddubois Avatar
ddubois Gold Member Dave DuBois
Bremerton, WA, USA   USA
Dave - I have been using the teflon 'O' rings for many years in our TD. The trick is to use two at each position - a single teflon 'O' ring will not work and will leak fuel like nobodies business.
Cheers,



Dave DuBois
1953 MGTD
1966 MGB
http://homepages.donobi.net/sufuelpumps/


Member Services:
SU fuel pump restoration and conversion to solid state. Information and technical articles on SU fuel pumps.
Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Yes, thanks Dave - I did use two Teflon seals in each position and they were the exact same size as specified on here, but they just didn't work for me. All I can assume is that there was a dimensional discrepancy somewhere because so many people have recommended them. Anyway the Burlen kit works well when the Teflon doesn't. Do you know why the jet tubes are so short and not flush with the top of the upper jet support bearing or the bridge? There seems no good reason for it, and lack of adjustment range as a consequence.
Dave H

Nr Tewkesbury, Gloucestershire, UK   GBR
1954 MG TF
1968 MG MGC
Dave, have you though about asking Burlen?
Eddie

Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Yes, maybe I will.
Dave H

ddubois Avatar
ddubois Gold Member Dave DuBois
Bremerton, WA, USA   USA
Quote: Do you know why the jet tubes are so short and not flush with the top of the upper jet support bearing or the bridge?
Don't know - as far as I remember (shorter and shorter as the years go by) the original jet tubes are still in the carburetors in our TD - Maybe Burlen is saving money by cutting the tube short by a mm on each oneconfused smiley
Cheers,



Dave DuBois
1953 MGTD
1966 MGB
http://homepages.donobi.net/sufuelpumps/


Member Services:
SU fuel pump restoration and conversion to solid state. Information and technical articles on SU fuel pumps.
Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
I've asked them - if I get a good answer I'll post it.
Dave H

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