Car only runs with choke pulled out

[Craigcass]

Hi all

 

I've started having trouble with the spitfire, everything has been ok until yesterday. When out driving I have to keep the choke out in order to stop it from cutting out when coming to junctions etc even though it's warmed up sufficiently as it won't idle properly (when pushing the choke back in it wants to stall/cut out) as if it is not getting enough fuel. 

 

Today coming home from work after driving down the A19 (60mph) for 20 minutes (so should be warmed up) and then driving on 'normal' 30mph roads I still have to have the choke pulled out in order for it to keep running, and when driving it judders, it doesn't misfire, but feels like it's not getting fuel, I got home and now it won't start no matter what position the choke is in. Whenever I tried to push the choke back in (thinking perhaps too much fuel is causing this it immediately cuts out) as if it's not getting enough fuel.

 

I've checked the spark plugs, they were slightly sooty, probably from having to run with the choke pulled out in order to keep it running put not enough to create a bad spark. I checked the inline fuel filter and this looked clear, I've checked the float chamber for debris and all looked ok, I checked inside the carb where the needle sits and there's fuel visible in the jets. I haven't adjusted anything on the carbs as they've been fine.

 

The car will now not start, any ideas on what to check or possible reasons for being only able to run/idle with the choke pulled out even when the car is warmed up.

 

Thanks,

 

Craig

[RobPearce]

It could be many things.

If the plugs are sooty after a run - not just a bit of idling as they'll always be sooty from that - then it suggests the mixture is actually rich, so the choke is hiding the problem, not fixing it. That in turn suggests probably not a fuel pump problem. It could be a problem on one carb only, such as a sticking float valve or a defective waxstat if fitted, though in that case I'd expect two plugs to be sooty and the other two not.

It could be a valve problem. Try a compression test.

Of course it could also be an ignition problem - weak spark sometimes causes misfires that go away if you richen up a bit. That's a bit harder to diagnose but if it's not had an ignition service for a while I'd say change the points, condenser, rotor arm and cap.

[Craigcass]

Thanks for the info, having found some time today I found the culprit to be my jets sticking open, I put some penetrating spray on the jet stems when fully open and on the linkages for good measure and everything seems to be running fine again.

Thanks again

Craig Cass

[PeteStupps]

That's quite a common problem Craig. Mine took ages to properly sort out - I thought they were fixed but one was often not fully returning, meaning the car intermittently ran like a sick dog. Are your carbs relatively new or had a recent refurb? 

The eventual solution for me was to slightly re-shape the lever arm which is screwed into the jet assembly. The repro item was not at quite the right angle so applied too much sideways force, resulting in the jet binding. This wasn't evident when the carbs were off the car, so eluded my first thorough investigation. 

Pete