carbs

[Hobbo]

Hi another problem with what I think is the carb. The engine starts perfectly fine with choke on, run till warm and the choke off, press on the accelerator and the engine dies to a stop, starts straight away no problem. Have had carb off to clean and blow out the jets, could not get main and compensating jets out for fear of damaging, blew through with plenty of air. Re-assembled carb put back on still the same problem, any help gratefully appreciated getting a bit downhearted with all the problems. Thanks Mike p.s. think timing o.k.

[Dave Wortley]

Have you a leak somewhere on the inlet manifold considering it works with choke engaged? Have you tried pulling choke out and pressing accelerator? Would be good if the jets came out then you can make sure they are clear.

[Barry Townsend]

Sounds to me like a partial blockage in the supply to the carb, to eliminate this if run the fuel pipe into a container and see what flow you get. It should be easy enough to put a bit of clear pipe on the end of the supply pipe after you’ve disconnected it from the carb. Some tanks get very mucky inside over the years. Hope this helps Jin

[Hobbo]

Many thanks for those two suggestions, will try with the choke pulled out when warm and pressing on the accelerator at the same time. Will also try to get the jets out to make sure they are clean, take off banjo connector to make sure clean petrol is flowing. Will let you know the results. Thanks Mike

[John Mason]

It sound like you may have a flat spot on the carb. After you have started the engine and it has warmed up try opening the carb up not with the accelerator pedal but with the linkage where it joins the carb. Do it very slowly and see if it will rev faster then. You may get a splutter to the engine but just shut it down and try again a few times and see it it will get past this flat spot. If it does get past and revs the engine it has proved it is a flat spot (air/petrol mix not quite right) This is corrected with the air mixture screw on the car. I am not familiar with big sevens so do not know what carb is fitted. If you are not familiar with setting up carbs this can be tricky and best left to somebody with the knowledge.

The Cornwall Austin Seven Club have a good thing on there site about carburettors for the Austin Big Seven.

John Mason

[Steve Jones]

Before any changes to the carburettor, I'd make sure you don't have an air leak at the manifold/carburettor joints. The problem you describe is typical. Whilst I have no knowledge of Big Sevens and no spares I do, probably, have a carburettor you could borrow. I'm only about 10 miles from you so worth a try once you're sure you haven't got an air leak.

Steve

[Hobbo]

Hi the carb I have got is a Zenith 30 VM4. I have looked at an exploded view on the internet and it seems I have some small washers missing I don't know whether this could be the problem. Tried with engine warm, choke pulled out accelerator slowly depressed a little better but misfired a lot then slowly died. Have seen service kits on the web but would not know where all the bits went. Exploded view numbers them but can't find what they are. Petrol very clean. Steve will send pm Thanks Mike

[Ian Williams]

Its running weak, either as a result of the jets still being blocked, or the wrong size, or as Steve suggested an air leak.

[Hobbo]

Hi have stripped off manifold, checked all surfaces are level with steel rule, gasket o.k., reassembled with the carb which has been reconditioned, problem still exists it will not rev it just dies. It has electronic ignition fitted don't know if there is a problem there. Getting at a bit of a loss as where to look next, Thanks Mike.

[AustinWood]

These symptoms sound like a blocked compensating jet or a blockage in the gallery it feeds.