Spit1500 Running Issues / Engine Cutout

[martinb]

Out for a short run in my Spit 1500 after not taking the car out for a few months.

No problem starting the car.  A couple of miles to the petrol station, ran smoothly, no issues.  A couple of miles later engine started "choking", intermittently at first then more frequently until eventually impossible to drive. Became particularly bad when putting load on the engine, such as accelerating up hill. Eventually had to get a tow home from RAC - fortunately wasn't far from home - as the engine wouldn't run for more than a minute or two.

Now trying to find the cause - any helps and tips?

Car will start and idle, and be happy for a few seconds or minutes before eventually cutting out.  Can also keep engine running at high revs for extended periods (minutes), but again, will eventually splutter and cough and cut out.

Fuel supply seems ok, chambers of carbs have plenty of fuel.

Inlet manifold has recently been refurbed, so has been removed and put back on (and not done any mileage since it was done).  May or may not be relevant?

Any relevance to the fact it started happening after refuelling (or just a coincidence)?

Planning on removing cleaning carbs as next step, but any further advice?

 

[RobPearce]

When you say the carbs have plenty of fuel, did you test this immediately after it cut out? The symptoms do sound rather like a fuel delivery problem - commonly vacuum build-up in the tank (due to a blocked breather) or a partial blockage somewhere.

That said, it's also possible you filled up with bad fuel.

You say the inlet manifold has been off - that presumably involved disconnecting some fuel hoses, so there's a possibility you got some rubber slivers in there, which can mess up the float valves.

Those are my initial thoughts.

[PeteStupps]

No offence intended but did you fill up with diesel?!

[martinb]

Quoted from RobPearce-

When you say the carbs have plenty of fuel, did you test this immediately after it cut out? 

That said, it's also possible you filled up with bad fuel.

You say the inlet manifold has been off - that presumably involved disconnecting some fuel hoses, so there's a possibility you got some rubber slivers in there, which can mess up the float valves.

Those are my initial thoughts.

Yes, checked the carbs immediately after it cut out.  I think it's unlikely it's bad fuel - it was from the local Shell station.  The fuel hoses were disconnected to remove/refit the manifold, so will double check for runner slivers.

Quoted from PeteStupps-

No offence intended but did you fill up with diesel?!

No offence taken!  It crossed my mind too (especially as my other car is a diesel), but it smells like petrol and the receipt from the fuel station definitely says unleaded.

[Velocita Rosso]

Also, manifold based,....if the manifold has not been reseated/re tightened up, you may be sucking in too much air.

[DP1164]

Just a thought. My Spitfire 1500 was cutting out under load. Checked the usual points all seemed OK. Float chambers full of fuel. Then checked fuel pump filter, 3/4 blocked. Cleaned fault cured.

Hope this helps

 

 

[RobPearce]

Quoted from DP1164-

Just a thought. My Spitfire 1500 was cutting out under load. Checked the usual points all seemed OK. Float chambers full of fuel. Then checked fuel pump filter, 3/4 blocked.

Ah, yes, that's a point I had overlooked!

The fuel pump (assumping you're still on an original-type mechanical one) "sucks" fuel from the tank in response to the camshaft. It pushes that fuel on by spring pressure. If you have a partial blockage that doesn't allow it to deliver enough fuel while running, it is possible for it to still fill the float chambers back up after the engine stops. Not a complete empty-to-full but enough to make a dry chamber look as if it's OK.

[martinb]

Quoted from DP1164-

Just a thought. My Spitfire 1500 was cutting out under load. Checked the usual points all seemed OK. Float chambers full of fuel. Then checked fuel pump filter, 3/4 blocked. Cleaned fault cured.

Hope this helps

 

 

Without wanting to sound a bit ignorant (!) - where would I find the fuel pump filter?

[DP1164]

On the top of the fuel pump you will see a screw/bolt that secures the filter housing, this where the fuel line from the tank attaches to the pump. Remove the screw/bolt and housing, you will then see the filter. Before taking of the housing make sure you stop the flow of fuel from the tank.

Apologies if I have simplified it to much

 

[martinb]

Thanks for the tips so far.

My fuel pump appears to be slightly different.  There is no screw on the top, but 6 screws attaching the top half to the lower half.  Have removed the screws and examined inside but no obvious filter in there.

Another thing I have done is remove the air filter to gain access to the carbs.  If I put my finger in the hole where the air filter would have been and gently try to lift the silver piston inside, there is about 1 or 2mm upward movement in the front one before encountering any resistance.  However in the rear (bulkhead) one there is significantly more free movement, maybe 5mm or more.  Is this a problem?

[martinb]

Have now removed the carbs after a few (short) runs of the engine - each time it spluttered to a stop.

Disconnecting the fuel hoses from the carb chambers there was sufficient pressure of fuel to the carbs that the fuelled spurted out as the hose disconnected - so it does look like fuel flow to the carbs is ok.

Removing the carbs there was a small puff of exhaust that came out of each manifold inlet when I released the bolts attaching the carbs to the manifold.  Normal?

Also, the inlets on the manifold felt damp with fuel.

Tomorrow I'll strip down and clean the carbs, assuming there are no other obvious things that come to mind from the above update.

[RobPearce]

The six bolts round the outside of the fuel pump are usually the ones holding the whole thing together and will reveal the diaphragm when undone. That's not required unless you're doing a full refurb. The original pumps sometimes had a glass bowl held by a clamp but more usually (certainly on the four cylinder cars) just a pressed tin top held down by a single central bolt, to give access to the gauze filter for servicing. If you don't have that then it may be a replacement pump.

The carb dashpots should behave the same. I would expect some resistance almost immediately. Have you checked the oil level in them? It sounds like the rear one is probably low, which will be slightly detrimental to acceleration and maybe to smooth idling but I wouldn't expect it to cause the engine to cut out.

[PeteStupps]

Obviously it's very hard to diagnose car problems from written descriptions, and we're all a bit biased towards things we've experienced before. With those caveats in mind:

I wondered if one or both of your jets might not be returning fully when you take the choke off, resulting in chronically rich mixture. Might explain wet inlet manifold, and the fact it runs ok for a while, then bogs down and dies.

This is a problem I had with shiny refurbished SU's on two different cars, and have heard of others suffering it too.

You probably won't be able to check it with the carbs off the car though. When you refit them, pull the choke fully out then push it back in, then reach under each carb and press the jets upward. If either of them move it indicates that they've been sticking. 

Pete

[martinb]

To close this thread off......

Carbs have been given a thorough clean and adjustment and at the same time fitted electronic ignition.  The combination of these has resolved the cutting out issue - but not entirely sure which of these was the original underlying culprit.

Thanks all for your input.