No Throttle Power

[P J Quinn]

Hi
My Big7 has had an engine rebuild completed by experts in the field (new valves, valve guides, rings, bearings, timing chain etc). When rebuilt the car still wouldn't take the throttle. She would idle perfectly but wouldn't take the throttle unless the choke was on. I had the carburettor refurbished by one of our cherished suppliers but there is no improvement. Can someone please help. many thanks
P J

[Edgar Lowe]

Hi
My Big7 has had an engine rebuild completed by experts in the field (new valves, valve guides, rings, bearings, timing chain etc). When rebuilt the car still wouldn't take the throttle. She would idle perfectly but wouldn't take the throttle unless the choke was on. I had the carburettor refurbished by one of our cherished suppliers but there is no improvement. Can someone please help. many thanks
P J

Hi
It looks it's a fuel starvation which would allow it to run ok at low revs but not under heavy load, I had the same problem with a straight eight engine. Check there is nothing blocking the main jet in the carburettor.

[Bob Culver]

Is it the correct carb with correct venturi and jets? Hardly likely in this case but very stale fuel has the effect. After an engine rebuild there is the possibility of a gross valve timing error. The rocking point of the valves can be easily determined and should be slightly after tdc.

[Nick Salmon]

I was recently asked by a chap to have a look at his Big 7 - which he said was down on power. I took the air cleaner off and found the choke cable was connected too tightly and this resulted in the choke butterfly being permanently half closed. Released the cable and normal power was resumed.

["Slack Alice" Simon]

Its probably something to do with the fuel system, but also worth trying another condenser, which you can temporarily wire on the outside.

Simon

[Mike Costigan]

It certainly sounds like insufficient fuel; might be worth checking the fuelpump is functioning correctly.

[Bob Kneale]

Hi
My Big7 has had an engine rebuild completed by experts in the field (new valves, valve guides, rings, bearings, timing chain etc). When rebuilt the car still wouldn't take the throttle. She would idle perfectly but wouldn't take the throttle unless the choke was on. I had the carburettor refurbished by one of our cherished suppliers but there is no improvement. Can someone please help. many thanks
P J

Before you do anything drastic or complicated check that the carburettor is not leaking air at the inlet manifold joint. I've experienced this on sidedraught Zenith carbs, and the problem can be rectified by ensuring the flange is perfectly flat. Rubbing down the flange on a sheet of 'wet and dry' paper on a piece of plate glass or similar will soon indicate whether there is distortion present.
Also check whether the throttle spindle is sloppy and allowing air to leak in there.
Good luck
Bob

[P J Quinn]

Thanks for all the help guys

The butterfly spindle was refurbed. The fuel is fresh and the choke cable isn't keeping the butterfly open. She will rev when the choke is partially on. The engineer who built the engine had previously tried an A8 carburettor on before mine was refurbed and he told me it worked perfectly so it appears to be something in the carburettor.  Interestingly, my brother, who is a mechanic but not familiar with 7s thought she was sucking air prior to the rebuild.

[AustinWood]

Check for blocked main & compensating jets or blockages in the internal drilling. Blow through with an air line if possible.

[Zetomagneto]

Its probably something to do with the fuel system, but also worth trying another condenser, which you can temporarily wire on the outside.

Simon

Good point Simon, I found exactly this the other day with my Chummy, it would idle quite happily but as soon as given throttle it would die.Carb taken off, all cleaned, refitted, no difference, fitted a different condensor and all was fine