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MG MGB Technical - Carb float

After sitting for five months over winter, I started the MGB up. It's running very rough, and I suspect it is possibly a sunken carb float. Is there a way to check if it is a bad float without removing the carbs and opening them up?
I will likely check the spark plugs first to see if any are extremely gummed up, or black, which would indicate the car is running rich.
I know one of the floats was replaced a few years ago; it was the front one, I believe.
The car is a 1977, but I installed twin SU's on it about 11 years ago. By the way, that made a huge difference in the way the car performed, and I highly recommend it.
Let me know if you have any thoughts on checking the floats.
Thanks,
Randy
Ithaca, NY
1977 MGB, Tahiti Blue/Tan
Twin SU carbs, electronic ignition
Randall Olson

HIF or HS?
R. K. Marcks

After siting idle I would first remove and clean the dashpots and ensure they drop easily and refill the carb dampers + ensure the chokes drop back when choke released.


(noted electronic ignition - so that rules out points ! but cleaning/checking the plugs is a good idea)

R.
richard boobier

These are HIF carbs, with the float accessible from below the carb body.
Randy
Randall Olson

If the float has sunk, shouldn't fuel be coming out of the overflow?
John Bilham

You would probably have to remove the overflow hose from the carb ports to see the overflow as otherwise it has to wend its way all through the emissions control plumbing.

Just been pondering this on HSs. Looking at those, the top of the jet is quite a bit lower than the overflow port on top of the lid. I've had a tiny seep on first one carb then the other, so slow that the pump was clicking once a minute or less frequently. So why does excess fuel come out of the overflow and not bubble up the jet and run into the engine? I can imagine it would if the float were fully sunk so fuel was gushing into the float chamber, but not with a seepage that small.
Paul Hunt

A small seep will come out the jet with engine running, but you'd not notice much if it's been tuned to accomodate it. A sudden leak could be picked up with a keen ear. With the engine off the needle is in the way mostly, and so choses path of least resistance: the overflow. If you lift the pistons manually (or left the pump on ages) you might see a bit pool up around the mostly closed butterfly.
Roadwarrior

Try tapping the side of each carburetor with a wrench. Usually, this will free up a stuck float. RAY
rjm RAY

I think if you had a 'seep' that allowed more in to the float chamber than the engine was using at idle you would know about it pretty quickly from the frequency of pump clicking with the ignition on but the engine stopped.

But that still doesn't explain why very small seeps as described come out of the overflow at all. In fact 'overflow' is a misnomer, it's primarily a vent. If it wasn't there the fuel level would never rise in the float chamber to shut off the float valve, and the pump would pump fuel straight out of the jet.
Paul Hunt

"You would probably have to remove the overflow hose from the carb ports to see the overflow as otherwise it has to wend its way all through the emissions control plumbing."

My 1977 'Europeanised' ex-US car has twin SUs with none of the above plumbing, hence my comment.

However, do I assume that even with twin SUs fitted the US requires that emissions control equipment is retained?
John Bilham

The US doesn't allow for any modifications to the fuel or emission system on any car whatsoever. Even installing a pair of SU carburetors isn't allowed on pollution controlled vehicles. My '67B, having come with no emission controls besides a PCV valve, is exempt. RAY
rjm RAY

From what I've read in the past USA requirements vary from state to state. There have been a huge number of past posts in various places from people there removing air pumps to save power, charcoal canisters and everything else to save space, and fitting single or twin SUs or Webers in place of the Zenith.

Emissions kit started there in 1968 with air injection, then vapour collection (charcoal canister) in 1970 and 71. That was on twin HSs, and HIFs in 72. The single Zenith didn't come in until 75.
Paul Hunt

Ray,
I grew up in Tustin, CA and remember my dad having an old 50's Ford straight six in his van which had to have a PVC drilled and hooked up before he could get a tag. He didn't like the idea of them drilling holes in his valve cover.
Also, in the early 80's when we sold Fiats and other sports cars in Birmingham, the Fiat came in a 49 state model and a California version with less power. California would not allow previous year model cars to be sold New, after the smog laws changed, so Fiat sold them to other states at reduced costs. We got several and didn't tell the customer they were different from the car next to it, only that they were made for California. There was a noticeable difference in performance.
Cleve Crews

Currently, most counties in California require emission testing every two years for any car newer than '74. As Paul mentioned, states vary wildly in their emission applications. When I moved here in '95, my '67B just missed the cutoff date and I was required to remove my Weber DCOE carburetor and install the original SU HS4s. By that time, my Lucas 25D4 was long gone and I was running a Mallory dual point distributor. Fortunately, the smog station attendant was unfamiliar with MGBs so he never realized that the car had the wrong distributor installed. Once the car passed smog, all the performance items went back on. Here in Mendocino county, emission testing is only required when you first register the car. We're what is referred to an a nonconforming county, as we have more trees than people.RAY
rjm RAY

Interesting - there are similar rules here in France, but they apply to virtually any changes from the manufacturer's original mechanical specification.
John Bilham

Guys,
I just came in from the garage, after removing the carbs. Sure enough, the rear float was half full of fuel.
The spark plugs were as black as coal, too. Cleaned them up, but will likely buy new ones tomorrow.
As for the emissions discussion, I removed all of it on the MGB years ago. They don't check in NY state, apparently. But, from the others posts it's a strictly enforced law in CA, where I spend time in the winter. I guess I won't be taking the MGB there (or the Jaguar, which also has SUs that were not originally installed).
Anyway, I should have the new float early next week, so the B should be ready for the road...if the winter ever stops! It's supposed to snow tomorrow.
Thanks for the help,
Randy
Ithaca, NY
Randall Olson

Ray,
You live in a beautiful place!
Back in the 60's there was a wine for sale in CA called "Nappa Sanoma, Mendocino Premium Table Wine". Their commercials depicted people trying to say the name in the store.
Hey it worked! I remembered the name 50 years later.

Randy,
Take your cars there. As long as you are a visitor they don't care.
Cleve Crews

" there are similar rules here in France, but they apply to virtually any changes from the manufacturer's original mechanical specification."

I knew someone who wanted to transfer a V8 conversion to France. He said the only way he could do it was if they crash-tested it first!
Paul Hunt

Paul,
I've heard similar government request from
other countries.
Think of all the old cars in France. Imagine if they told the owners they would have to crash test their Delage before it could be driven on the road.

Cleve Crews

This thread was discussed between 31/03/2015 and 04/04/2015

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