Fuel Starvation?? Cutting out at Speed- Help! Help me to Keep my Beloved Car

I have a daily driver 1800 auto clipper which is fitted with a weber carb of some sort…

It starts great from cold, and without tempting fate, runs great. Starting from hot if the car has been left for say 15 minutes or more is another matter. if I don't get the issue sorted, my better half who refuses to drive it until its fixed and is therefore wanting me to sell (we have a one year old daughter and with some justification doesn't want to get stranded out with her in the winter rain).

 I have worked out that the carb is flooding when the car is parked.

The fuel return line from the brand new fuel separator bowl is blanked off and when the car is parked, the pressure in the fuel system is causing the carb to flood. I reconnected the return line and the hot starting issue was instantly sorted. Result! No more flooding. But… at speed, the car cut out due to no fuel. I put a restrictor (looks like a carburettor jet) which I ordered from Webcon fuel systems in the return line and a test drive suggested all was well.

Success was short lived however because soon after joining the motorway this morning, it cut out again. Blanking the return from the fuel separator bowl meant that the car then ran perfectly well for the rest of the journey. But I know that starting from hot will be an issue again…

I find it really bizarre that the fuel is finding it easier to (I assume) head along a restricted return line as opposed to taking what I would imagine is a much easier route to the carburettor.

Am I barking up the wrong tree? Any ideas / solutions that you have will be greatly appreciated - I don't want to have to sell what is otherwise a great car but by the same token cant risk the missus and my daughter getting stuck…

Your help will be hugely appreciated.

apologies - I appear to have posted this in the wrong section - I have copied it to the fuel  section…

Just thought I'd give an update to this issue, which, without wanting to tempt fate, I seem to have sorted by fitting a new fuel reservoir / vapour separator. Quite why this has made a difference I don't know but it has.
The return line from this is still blanked off (as I believe is recommended for Weber carbs) and having taken the old one apart, it appears to be little more than a small pot for fuel to sit in.

However, since fitting, the car just needs a small throttle opening and she starts up just fine…

Another auto owner!

Cutting out at speed may be carb icing - mine used to do this (or at least did when it was running…but that's another story).

To cut a lot of troubleshooting short, make sure that the connections from the air inlet to the warm air deflector plate are all sound. In theory manifold vacuum (blue rigid hose) should pull open, against spring pressure, the flap just before the air input snorkel when the engine's at full chat. This allows in some air that's been warmed by the exhaust manifold which keeps the carb jets from getting blocked by atmospheric moisture that freezes in the airflow. On mine the crinkly foil tube joining the warm air deflector plate to the box with the flap in it had totally self-destructed: the flap worked fine, but it was only drawing in air from the bay, which was at the same temperature as everything else so didn't stop the icing. I replaced it with a short length of black silicone tubing and two jubilee clips and it got dramatically better!

The autos will always struggle when cruising at high speed because the engine's revving a lot faster than they're really intended for. When I took mine to Wörthersee the long runs on the autobahn really upset it as I was running at >4000rpm for hours at a stretch, I kept having to stop and let the carb warm back up! You may also find that engine bay heat is boiling the fuel in the lines before it gets to the carb, they're not a big fan of that either. Not really sure how it could be avoided other than by routing the lines more carefully.

Stone

Cheers Stone - I'll have a gander at the warm air bits n bobs to see if they're sound - I very much doubt it -  but, without wishing to tempt fate, all seems a-ok now

For a long while mine would only start to struggle if I exceeded the national speed limit (so about 4000rpm in 3rd…) or went up a steep hill, so it may just be that you're driving sensibly!

The time to find out it's not quite fixed is not when you're in the middle of overtaking… ask me how I know

I can relate to that - I get a bit of crud coming from the tank into the in line fuel filter…which I change every 2-3 months to keep ahead of the issue.

A while back, I had however forgotten to do and, without any warning whatsoever the car simply cut out in the overtaking lane of the M4 - thankfully, about 1/2 a mile earlier, I would've been in a tunnel on the M4, with no hardshoulder…

lesson learned…

It's worth removing the fuel tank sender and pickup (under the round cover that's under the rear seat base) and dangling a magnet on a bit of string into the fuel tank just in case there are any rust flakes in it from the filler neck going bad. Mine had been recently replaced when I bought it but there were some tiny bits clogging up the brown plastic perforated piece on the end of the fuel pickup so it was struggling when it needed to draw a lot of fuel for fast running.

RichieS said

Just thought I'd give an update to this issue, which, without wanting to tempt fate, I seem to have sorted by fitting a new fuel reservoir / vapour separator. Quite why this has made a difference I don't know but it has.
The return line from this is still blanked off (as I believe is recommended for Weber carbs) and having taken the old one apart, it appears to be little more than a small pot for fuel to sit in.

However, since fitting, the car just needs a small throttle opening and she starts up just fine…

Out of interest what did you use to blank the return pipe? Mine is doing the same thing cutting out at speed with a Webber carb. Might turn that

There's still a piece of fuel hose attached, about 3 inches. Into the open end I've screwed a very tight fitting bolt. Simple as that

Do the same to the other end and make sure it's not flapping about…

Good luck, let us know good you get on.