Carb problem

[Tony Griffiths]

Zenith 30VM downdraft carb (similar to that on a Nippy). The Ulster was running really well when it slowed and would not rev, only tick over. Checked that the fuel pump was working and fuel getting through. Removed the float bowl and the three jets, which were all clear. Blew the jets out anyway - and the holes in the bowl. Reassembled - and it revved cleanly. Has anyone had a similar problem or knows what the cause of this sudden-tickover situation might be?

[Tiger]

My advice would be check the ignition system

[Tony Griffiths]

My advice would be check the ignition system

Ran over that, too (especially with the previous problems) but a good fat spark at the plugs and from the coil, etc.

["Slack Alice" Simon]

Condenser starting to fail / earth intermittent to same?

[Howard Wright]

Hi Tony

I had a similar problem some time ago. It turned out to be a ‘floater’ in the fuel line. Tickover was fine but any draw on fuel would pull the offending bit of grit up the pipe and block the filter on the carb. The problem was that it was intermittent and happened just after I got a distance from home. Advice… blow through all the fuel lines.

Cheers

Howard

[Tony Griffiths]

Hi Tony

I had a similar problem some time ago. It turned out to be a ‘floater’ in the fuel line.  Tickover was fine but any draw on fuel would pull the offending bit of grit up the pipe and block the filter on the carb. The problem was that it was intermittent and happened just after I got a distance from home.  Advice… blow through all the fuel lines.

Cheers

Howard

Thanks Howard - that's a very good idea.

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Condenser starting to fail / earth intermittent to same?

Thanks. I've had lots of interesting condenser problems, so I carry a spare with wires fitted with clips, ready to try (plus, of course, a complete distributor and a bag of electrical bits and pieces).

[dickie65]

Hi Tony,
Were you running at high speed then got a sudden loss of power and misfire ?
I have had the above symptons which cleared after ticking over for a short while.
In my case I found out that it was the carb icing up.
I strapped a digital thermometer probe to the carb and went for a drive and all became clear as the temperature plummeted, I actually managed to stop and open the bonnet to find the outside of the carb covered in frost.
It might be worth trying a carb with a slightly larger choke and jets.
The Nippy manifold has a hotspot and it still got frosted up.
My car would repeat its misfire trick at the same distance along the road from home give or take 100 yards.
Now running a semi downdraft SU with no problems

I hope this might give you additional ideas.

Cheers Richard

[andrew34ruby]

Hi Tony,
Were you running at high speed then got a sudden loss of power and misfire ?
I have had the above symptoms which cleared after ticking over for a short while.
In my case I found out that it was the carb icing up.

Carb icing can be quite amazing, has to be seen to be believed. It happens on cold days but especially on cold damp days. Never mind a bit of frost on the outside of the carb, I have seen cars where the intake of the carb is a large ball of ice.

Not ice this time, but a cortina that a friend was foxed by had a dead fly floating around in the float chamber.