MGB & GT Forum
Vent line for SU carbs
Posted by gofastandfalldown
gofastandfalldown
Glen Horne
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Topic Creator (OP)
Oct 1, 2014 03:39 PM
Joined 11 years ago
1,148 Posts
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My problem of the day.....
There is a vent fitting on each of my SU carbs that doesn't connect to anything. It seems to me that these are vent lines, but if there was a float failure, raw gas would then blow all over the hot engine. Should there be a drain hose or something connected to these fittings?
There is a vent fitting on each of my SU carbs that doesn't connect to anything. It seems to me that these are vent lines, but if there was a float failure, raw gas would then blow all over the hot engine. Should there be a drain hose or something connected to these fittings?
Oct 1, 2014 04:20 PM
Top Contributor
Joined 17 years ago
11,922 Posts
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HS4 had their own tube connection routed down the side of the engine to the ground.
Later carbs had a collection tube to charcoal canister.
I suggest;
ASAP, rubber hose/tube combination, collect overflows together and run the line across the firewall to the RH side of transmission and down.
"It is a mistake to try to look too far ahead. The chain of destiny can only be grasped one link at a time."
Sir Winston Churchill
---------------------------------------------------------------
"It all starts in your mind's eye, then it goes to your heart
and finally to your very soul."
G.S.George PHD
Later carbs had a collection tube to charcoal canister.
I suggest;
ASAP, rubber hose/tube combination, collect overflows together and run the line across the firewall to the RH side of transmission and down.
"It is a mistake to try to look too far ahead. The chain of destiny can only be grasped one link at a time."
Sir Winston Churchill
---------------------------------------------------------------
"It all starts in your mind's eye, then it goes to your heart
and finally to your very soul."
G.S.George PHD
Georgetown, TX, USA
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Oct 1, 2014 04:38 PM
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Joined 12 years ago
3,502 Posts
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Here is a picture of the '70 evaporative loss system available on the GJ engine.
If you don't have the metal piping, it could be fabricated. From the flexible hose (which originally would have been plain rubber, I used the braided covered hose) it goes to another metal pipe that runs above the heater and terminates at the charcoal (adsorbtion) canister.
If you don't have the metal piping, it could be fabricated. From the flexible hose (which originally would have been plain rubber, I used the braided covered hose) it goes to another metal pipe that runs above the heater and terminates at the charcoal (adsorbtion) canister.
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dbraun99 LLC no longer offers Carburetor Bench Services on SU Carburetors. See www.dbraun99.com for helpful pictures of carburetor rebuilds.
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Oct 1, 2014 07:13 PM
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Joined 13 years ago
32,640 Posts
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And see #5 here (also currently running). I've actually extended my overflow pipes such that any overflow goes to ground on the other side of the block. Of course where you live may have legislated that you can no longer 'dump to ground'.
Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Lots more as I did a nut and bolt rebuild; finished 2015. Tartan Red.
GT: December '78. VW Golf guards, flush fit front and rear valances. Torana XU1 vents, frenched indicators & Mk1 rear lights. 'Worked' Rover V8 with Monsoon ECU for EFI. GM4L60E, Lokar tiptronic & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.
Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Lots more as I did a nut and bolt rebuild; finished 2015. Tartan Red.
GT: December '78. VW Golf guards, flush fit front and rear valances. Torana XU1 vents, frenched indicators & Mk1 rear lights. 'Worked' Rover V8 with Monsoon ECU for EFI. GM4L60E, Lokar tiptronic & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.
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Oct 1, 2014 08:08 PM
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Joined 18 years ago
24,294 Posts
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Usually the loss is small. But the vapor generation is large enough to tell you within seconds as you are driving that there is an issue you need to attend to RSN! (Real Soon Now). Usually it requires an extremely technical light rapping of a screwdriver handle (or a handy stick of most any kind) to the float bowl lid to dislodge a stuck float valve.
If it vents to the evap or otherplace, you might not realize it for quite awhile.
1973 Pale Primrose Roadster. A nice 10-footer!
SUs, Datsun 5-speed
If it vents to the evap or otherplace, you might not realize it for quite awhile.
1973 Pale Primrose Roadster. A nice 10-footer!
SUs, Datsun 5-speed
Oct 2, 2014 01:22 AM
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Joined 13 years ago
2,298 Posts
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Nice looking engines.
The steel webbed piece that connects to the crossover tube to the carbon canister is a good spot for a short piece of clear tubing. I use it to visually make sure there is no carb vent overflow. If there is a flooding floatbowl you see the fuel flowing toward the carbon canister.
In my case I usually open the hood before starting and turn the key on and watch it as the pump clicks until it stops when the bowls are full.
Kind regards
Mark
The steel webbed piece that connects to the crossover tube to the carbon canister is a good spot for a short piece of clear tubing. I use it to visually make sure there is no carb vent overflow. If there is a flooding floatbowl you see the fuel flowing toward the carbon canister.
In my case I usually open the hood before starting and turn the key on and watch it as the pump clicks until it stops when the bowls are full.
Kind regards
Mark
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