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SU CARB Overflow tubes

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Peter Mittler

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As some of you may know if you follow Skye's board my 81 MGB burned a couple of weeks ago. The final diagnosis seems to be that a float needle stuck and caused fuel to back flow into the two charcoal cannisters, whereupon it possibly filled the cannister and vapourized into a mist which was ignited by a spark from the ignition or possibly the heater fan motor which was on. Now I have purchased a 75 with the same carbs. Both overflow exits on the top of the float housing have no tube on them at all. This would mean any backflow goes onto a hot manifold. WHERE are these supposed to be 'tubed' to? I am not interested in any deja vue's and want to ensure the same problem does not re-occur. This car has only one canister and there is a open vertical stem on the canister which would apprear to be a place for a tube? I can post pics if it would assist. Others might like to check that there systems are correctly vented as well.
 
On my 70 B, the SU overflow outlets connect to two long tubes that go down below the engine and empty onto the ground. Then again, my B has little to no emissions equipment.
 
Plumbing the vents down to the ground doesn't sound like a bad idea to me. Emissions-testing people won't like the idea, but if you run them back under the car they won't see or worry about them.
 
I think venting the carbs overflow tubes under the car is a bad idea. I wouldn't do it. There is a hot exhaust pipe under there and every time you drag a muffler or other metal part on the road you get lots of sparks.
The charcoal can on my '73 B has three connections on top, one from the gas tank vent, one to the valve cover (the larger center one) and one to the over flow tubes on the carb float bowls. It also has a hose on the bottom of the canister that goes to the gulp valve.
None of this stuff affects horse power so if you don't have it, I would put it back on.
Good luck.
 
I would agree with Mark, If my car had a charcoal canister, I would do the same.
 
Think yours should look sorta like a doctor's stethescope: short rubber from each carb to a piece of metal tubing shaped like the part doctor put to ears going into 't' connector with single tub to below/behind exhaust...
...whatever you do, do it quickly or you'll be known by your insurance company as a 'double dipper'
 
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