Need a bit of carb help

[JSeaman]

A bit of a cry for help - this is on a 1300 Ital enginee in a morris minor -

After a faulty SU pump I fitted a Facet electric pump and changed the points/condenser, plugs, dizzy cap and rotor arm. I can't get the carb set up quite right despite having gone though the Haynes manual process and doing some tweaking. Is anyone in the Alfreton/Derbyshire area willing to cast an eye over it and give me a lesson in carb tuning?!

[lambrettalad]

have you set the timing?

what does not quite right mean?

[JSeaman]

Yup timing is good, I can't get it to idle and run correctly. It's now kangarooing and previously it was feeling really flat.

Just about to check the fuel pressure because the Facet pump has been a pain so far and might be high

[JSeaman]

5 psi

That may be it - I'll try a pressure regulator first

[JSeaman]

The plot thickens, the ital. manual thinks 6psi minimum - everything I can find about minors says 2-4 psi, so either way it's wrong but if it's a 6 psi then the pump is not up to the job, anybody have any thoughts?

[daveyl]

Is the carb new to this engine? If so, maybe the jet is seized. And might be worth checking if the float needle isn't jammed.

[JSeaman]

Nope, the carb was on and running find before the fuel pump gave up

[bmcecosse]

Go back to the SU pump - the pump you have is not designed to suck fuel up from a low mounted tank.. However -i doubt that's the problem here.. Does the carb piston rise easily - and fall with a nice clunk - with the damper removed? What needle is in the carb? Is it a standard 1275 engine - or modified?

[JSeaman]

Thanks for the response - Standard engine so standard needle I assumed

Piston is moving freely

The pump is mounted by the tank so it is pushing as designed not pulling

[bmcecosse]

Hope it's well protected down there! What colour are the spark plugs - and have you optimised the Ign timing by advancing till it pinks - then back off v slightly?

[lambrettalad]

any leaks in the inlet manifold ?

[JSeaman]

The spark plugs were changed but they were black as soot so was super rich in the past

I haven't optimised ignition timing because mixture is too far out for that

No leaks at the inlet manifold

[bmcecosse]

Rich like that suggests either 'choke' stuck ON, or fuel level too high - possibly becuase of too high pressure from the pump...... Refit the SU pump.......

[JSeaman]

Choke mechanism is free and pulling it changes behaviour so I don't think it is stuck

The pump seems to be supply 1psi lower than the stock SU would

The old pump is junk so can't be put back on

[bmcecosse]

An SU pump is 'junk' ...? Can always be rebuilt - unless the coil has burned out??

[JSeaman]

It's junk when you take it apart and find bits are missing!

I don't understand why there are so many threads with people continually telling people to ditch electric pumps and go back to su - fear of the unknown perhaps? Either way I have an electric pump and would like to make that work

[bmcecosse]

The original SU pump is electric.....and has renowned reliabilty...that's all - no underhand motive I assure you! You can buy all the individual parts to rebuild an SU .....

[chickenjohn]

Yup timing is good, I can't get it to idle and run correctly. It's now kangarooing and previously it was feeling really flat.

Just about to check the fuel pressure because the Facet pump has been a pain so far and might be high

Can you post a few photos of the carb?? Your problems are not likely to be pump related if the fuel pump is working. It sounds to me like an air leak in the carb between the jet and cylinder head is causing a (possibly intermittent) weak mixture hence kangarooing and high idle speed. Carb jet may have then been over enriched to try and compensate and is thus causing sooty plugs. Check for manifold gasket/ carb - manifold gasket leaks. Check there are not openings in the inlet manifold or carb that should have a pipe on them ( depends on type of carb used, hence we need photos!).
Also, wiggle the throttle butterfly spindle to check for wear here- shows up as movement. another potential source of air leaks.

Or check for a blocked air filter. (Combination of problems).

cheers John

[JSeaman]

All sorted, I fitted an inline fuel pressure regulator and dropped it from 5psi to about 2.5 and it's perfect now

[bmcecosse]

Which is why we suggested the pump was wrong - but you were adamant it was correct.... There's a good reason why the SU pump is the one for the job.