4 replies to this topic

[mk=john]

Hi All
I recently had my Mk1mini cooper (twin carb HS2's) tuned, both ignition timing and carburettor.
The problem at the moment is that when the choke is fully in (warm engine), the engine revs increase/decrease, and this continues to cycle. It is quite noticable when the engine is at low idle. It isually takes around 20-30 seconds or so for the idle speed to increase/decrease noticably.

When the idle speed drops, the engine sometimes cuts out and I then need to apply a small amount of choke to keep it running at the traffic lights.

The tuner guy said that this could be the fuel pump not delivering the required fuel pressure to the carbs, or possibly a sticky or worn needle valve in the float chamber.

Does anyone have expreience of this, and what are the likely causes? Also, will adding a small amount of choke damage the engine?

Thanks

[Big_Adam]

choke just re-jimmys the fuel air mix and pops on some revs. so unless you runnning really reallllly rich there shouldn't be a problem. just means when you take you feet off the pedals your mini will keep going.

don;t know about the other stuff mind.

[bananaman]

If it doesn't do it with the choke out, it's not the fuel pump, you use more fuel on choke with it out.
You running an electric pump?
Possible that the idle screw settings on your carbs are not the same, or a sticking needle.
Whats your idle speed set to, maybe it's too low. I seem to remember a mate who had his set too low and the ignition systen used all the power from the dynamo not leaving enough to run the electric pump properly, hence no fuel and it cut out.
To be honest, it's been so long since I played with twin carbs I am just guessing.
You could try another tuner, see if he comes up with the same answer as the first.

Tony

[mk=john]

Hi
Thanks for the response. The fuel pump is the electric typw mounted on the rear subframe. This looks brand new as the car is reconditioned. However, the carbs are the original ones.

If I found the float chamber needlea are sticky, what is the best way to clean and lubricate them? What is the total process i need to go through if the needle valves are sticky?

Thanks

John

[THE STIG]

sounds like a air leak to me

this normmally causes the engine idle to be iratic

it is normally caused by the inlet manifold not sealing there are a number of reasons for this

the inlet manifold flanges are thicker than the exhaust manifold flanges

the inlet manifold is not tight

or there is a split in a breather pipe

or a few other just check its all tight

a easy check is to run the engine and spray wd40 on the manifold where bolts the the head if the revs

increase proves there is a air leak at the manifold

hope this helps