Stil backfiring through carb

[AlMcL]

Hi All
Have reset points in fuel pump and centred carb needle,now have backfire throuh carb,wont rev up also exhaust downpipe glows red any ideas.Thanks Allan

[billlobban]

Ignition timing!

[AlMcL]

Cheers,Ihave set timming but still doing the same.

[katy]

Sounds like the mixture is way too lean.

[bmcecosse]

Amazing - because someone on the Mini forum has the same problem - I've only ever seen an exhaust glow red when running flat out on the rolling road! So - does the piston in the carb rise up easily with one finger - and does it fall back with a nice clunk ? What colour are the plugs ?

[AlMcL]

NOW IT DOES,AFTER RESETING NEEDLE

[bmcecosse]

And - is the problem still there ?

[Mogwai]

Firing order correct ? Plug leads round the wrong way will give these symptoms

[bmcecosse]

Including the 'red hot' manifold ??? I'm dying to hear what causes that!

[Mogwai]

swapping a couple of leads over can cause it as the unburnt fuel mix can be ignited on the exhaust stroke

[bmcecosse]

Surely no-one would run the engine for more than a few seconds on two cylinders............

[AlMcL]

all leads are on correctly even i would not mak that mistake

[bmcecosse]

Valve gaps correct ? Sticking valve ? Any chance of borrowing a compression tester - and running the compressions ?

[MarkyB]

Did you remove the carb when you centred the needle?

You may have disturbed the silt in the float chamber which then finds its way into the jet tube.
Not enough petrol can get through and the mixture is too weak.

Happened to me after laying the carb on its side during an engine rebuild.

[bmcecosse]

It can only 'back fire' through carb - if an inlet valve is held open when ignition takes place. Can happen with wide timed camshafts at low revs - but shouldn't be happening with a standard Minor engine. So - you need to investigate the valves........