One carb dumping fuel when cold

[UKPhilTR7]

Recently my little girl has started having trouble when starting from cold, or as cold as it can be in Sydney in spring

When I start her from cold, she is rough and often cuts out no matter how much choke or gas I give her. She can cut out at least 4 times. During this she dumps fuel out of the front carb overflow pipe. The dump of fuel is around one to two foot on the garage floor.

After a minute or so running (or trying) she runs fine. She runs nice and smooth at around 800rpm with no more fuel dumps. When I start her the next day all is OK, so it only happens say when I leave her for a week and then run her.

First I thought that it might be that I was giving her too much choke, but less choke just starves her and she cuts out and if it was the choke both carbs would have the issue.

So now I am thinking the float and even the needle.

Has anyone come across this before or know what I can look at?

[saabfast]

I have had similar when the needle valve was not shutting off on one carb and fuel was pouring from the overflow pipe. Not sure if it stopped when warm or not. I had to change the needle valve to a new one (and old one from a spare carb did not work either). It may be that yours is just not closing fully and sufficient fuel is being used when warm but not with a slow cold idle? the only other part affecting it really is the fuel pump and if that has not been touched it is difficult to see that being the problem.

[busheytrader]

I had the same issue with fuel flowing out of the front carb overflow pipe. It was the smell that first drew me to it. Upon taking off the fuel bowl lid, there was a clear ridge around the needle valve preventing it from sealing properly. Replacing it sorted out the leak. As the rear one had a light ridge I replaced that as well. It took about 5 minutes per carb IIRC.

[Rubberbiscuit-1]

A bunch of years ago I used what were called Gross Jets in my TR6's Zeniths. They are all in one, self contained float valve assembly utilizing two steel balls along with a seat for each ball that totally controlled fuel flow into the bowl. In the day they were considered the cat's nuts. Still available?

[Hasbeen]

I had this problem first after fitting a new fuel pump.

In Oz at least you can not buy a dedicated fuel pump, set up for the 7, just a generic pump, that must have the thickness of spacers between it & the block adjusted to give something very near, but not above the required 2 PSI fuel pressure.

I have also had a float partially fill with fuel by osmosis & sink a little, which raises the float level. I fixed this by drilling a small hole in the float, getting the fuel out, then plugging the hole with a bit of match stick, shaped suitably & lightly driven into the hole & trimmed.

Surprisingly this never let fuel in again, & is still running over 12years later.

I have the newer needles in my float bowl, which have a rubber tip. This seals better, doesn't seem to wear, but will still suffer from gumming up, if the car is used occasionally, & the fuel allowed to evaporate to dry too often. More a warm Ozzy problem than a cold climate problem. I suspect this may be your problem.

My suggestion. Check for above problems, &/or a bit of dirt above the needle & seat, then DRIVE THE DAMN THING MORE OFTEN.

Note to self, follow the above advice yourself.

Hasbeen

[supercass]

A hole in the diaphragm in the original fit fuel pump can also cause this problem.
supercass

[UKPhilTR7]

The pump was new not so long ago so I think it is time to take to bowl apart. I have had a look and the new needle valves do not cost much at all as I will do the both of them in one go. From what I am hearing it seems to be this as I will look at the float when it is all apart.

[Hasbeen]

Have you checked the fuel pressure since replacing the pump.

Over 2 PSI, almost guaranteed with the pumps supplied in Oz, unless you have gone to considerable effort to set it, will give you flooding. particularly with the front carb, which has a higher fuel level.

Hasbeen

[UKPhilTR7]

I thought about that Hasbben, but this has only just started to happen, within the last two weeks and the pump I have on now has been there at least seven years.

[dursleyman]

Burlen do this stay up float kit which also means you can actually adjust the float level to the recommended setting and know the float won't leak and sink.

[UKPhilTR7]

Cheers Russ I had a look and they have some good thing as as some good prices. There did seem to be two types though the.75 and .90. Which do we use for ours.

[UKPhilTR7]

Over the weekend I replaced the fuel pipes from the pump to the crabs, the little ones. I have started her up twice and there has been no fuel leak from the front carb overflow pipe. The old rubber pipes were solid, but could changing them really stop fuel leak? I have a pair of float needles on order and will change them, but can it really be fixed.

[busheytrader]

Maybe a bit of crud between the needle valve and it's seat were dislodged?

[dursleyman]

Cheers Russ I had a look and they have some good thing as as some good prices. There did seem to be two types though the.75 and .90. Which do we use for ours.

Sorry just spotted the question about needle valve sizes, I went for the bigger ones because I may want to use them in some 2" SU carbs on the new Sprint engine I am building, fully balanced, ported head, fast road cam etc. The smaller ones should be fine for a standard TR7 engine.

[UKPhilTR7]

No worries thanks for the reply. I have since changed the float needles and the dumping of fuel from this front carb appears to of stopped. I had a bit of an issue taking them out as not much space, however all is good now.