Running too fast

[jagnut66]

Hi,
I'm hoping someone on here can offer some suggestions, as I'm running out of ideas.
I'm trying to get Sally, my four door, running right.
She fires up okay but then runs like the clappers, no matter how much I turn the mixture nut or what position I move the distributor to.
I did have an accuspark electronic set up in place but when that failed to adjust this out I swapped back to a standard points and condenser distrubutor and coil, which is what is on the engine now.
It doesn't matter whether the choke is in or out, she'll start without it, which I believe indicates she's running too rich but the mixture nut on the carb is wound right up.....
So I'm hoping someone on here has had this problem before and found the cause / a solution.....
If not I'll have to go to Facebook and try that group.
Thanks and best wishes,
Mike.

[59Elva]

Sounds similar to an earlier post. Not sure how to quote another post. See if this link works.
Bill B

viewtopic.php?p=720936#p720936

[Bill_qaz]

Piston stuck in dashpot or no oil
Throttle stuck open.
Massive induction leak pulling in air, does it have a servo?

[jagnut66]

Sounds similar to an earlier post. Not sure how to quote another post. See if this link works.
Bill B

Piston stuck in dashpot or no oil
Throttle stuck open.
Massive induction leak pulling in air, does it have a servo?

Thanks for replying. Your link worked fine Bill, a very similar theme, as you said. Read through the replies, food for thought.
There is no servo fitted and I don't believe the throttle to be stuck open.
That said, I will bear it in mind.
Massive induction leak? I hope not......
I have made a stainless heat shield, so I will check around where it is all clamped together.
I will be having another attempt to get it running this weekend, so we shall see if that yields any result.......
Best wishes,
Mike.

[Peted7202]

As Bill says check piston/needle stuck in dashpot. Remove carb bell housing and empty and flush dashpot. Check piston movement. Do a fall test whilst removed.

[svenedin]

I am presuming you know about the two screws that control the idle. One is the fast idle and affects the choke so that the idle speed is raised when the choke is pulled out. When the choke is pushed in fully (no choke) the fast idle screw should not be affecting the idle speed. The other is the normal idle screw and sets the idle speed when the choke is not in use. Both idle screws affect the idle by opening the throttle disc. As the throttle disc opens, more air rushes into the engine, this causes the piston to rise which lifts the needle attached to the piston and more fuel goes into the air and the engine runs faster. So in order for the engine to run too fast it must have both more air and more fuel in more or less the right ratio. If the piston is getting stuck in a raised position it will allow more fuel in but this will not necessarily make the engine run faster if there is no corresponding opening of the throttle disc. A stuck raised piston with the throttle disc correctly almost closed at idle would in fact make the mixture so rich the engine would probably just stall.

You say that the carburettor jet screw is all the way up but is it really? Did you slacken off the choke pinch bolt? If you don't do this the jet cannot go all the way up because it is fighting against the choke cable.


Go back to basics. Take the air filter off so that you can look inside the carburettor and see the throttle disc and jet. Slacken the pinch bolts on both choke and throttle cable. Now turn the mixture nut until the jet is level with the bridge. Turn the mixture nut down 2 full turns (this is the starting mixture setting). Check the throttle disc opens and closes. Check that the choke (fast idle) screw is not holding the throttle disc open. If necessary, turn the fast idle screw so that it is "just" not affecting the opening of the throttle disc. Do the piston lift test. Check the oil in dashpot, top up if necessary and then lift the piston with your finger and let go. It should fall with a soft metallic clunk. If it doesn't the piston is sticking.

Now start the engine. It should definitely need choke now, probably a lot of choke. Let it warm up. When up to temperature adjust the mixture by whatever is your preferred method. I like the Gunson Colortune followed by fine tuning with the lifting pin.

An air leak on the induction side will cause air to be drawn in when the engine is running and the engine will try to run faster but usually in these circumstances it will run very rough because the mixture is much too weak. I have had such a leak from a pin hole in a PCV diaphragm but that is not relevant here. It is worth checking carburettor to manifold gaskets, (either side of the spacer), inlet manifold gasket and manifold bolts. Also look for cracks in the inlet manifold.

Good luck!

Stephen

[jagnut66]

As Bill says check piston/needle stuck in dashpot. Remove carb bell housing and empty and flush dashpot. Check piston movement. Do a fall test whilst removed.

Agreed and already done. I also gave the piston a light sanding whilst I was refurbishing the carb, to ensure there was no rough edges and it all moves freely and smoothly.
Best wishes,
Mike.

[Bill_qaz]

Mike if you start it with no filter so you can see the carb piston do you see it lifting without you operating the throttle or better still with throttle and choke cables disconnected.
When you rebuilt the carb is the butterfly fitted correctly.
If you lift the piston and shine a torch does the butterfly appear closed.?

[jagnut66]

An air leak on the induction side will cause air to be drawn in when the engine is running and the engine will try to run faster but usually in these circumstances it will run very rough because the mixture is much too weak. I have had such a leak from a pin hole in a PCV diaphragm but that is not relevant here. It is worth checking carburettor to manifold gaskets, (either side of the spacer), inlet manifold gasket and manifold bolts. Also look for cracks in the inlet manifold.

Thought I'd touch base with your reply, so you know I'm not ignoring anyone. I inspected and cleaned the plugs yesterday, they were black, though not thickly soiled, which I believe is an indication of running rich.
I can't see any visible sign of (air) gaps in between the carb gaskets.
The manifold is new, two part (separate inlet and exhaust) Maniflow system. I don't think it has developed any faults (cracks) since fitting.
I'm about to try your 'back to basics' advice regarding pinch bolts.

is the butterfly fitted correctly

I have looked at this and have compaired it to my spare HS2's, it seems okay and they all open and close the same (freely, no sticking), with a minimal gap left, allowing the engine to idle when the car is stationary. It is, of course, the speed of that idle that I wish to reduce.
Best wishes,
Mike.

[Bill_qaz]

You haven't got a worn spindle or bushing.
If the idle is high with cables detached and idle screw backed of, its got to be pulling air to increase speed.

[svenedin]

You haven't got a worn spindle or bushing.
If the idle is high with cables detached and idle screw backed of, its got to be pulling air to increase speed.

Yes and that is a known issue with these carburettors. To run fast there must be fuel and air in roughly the right proportion. If the leak is way in front of the jet, such as a manifold gasket it tends to make the mixture very weak and the engine does try to run faster but runs extremely rough because that air is not rushing past the jet drawing in extra fuel.

Stephen

[jagnut66]

Latest posts above noted with thanks, I have now adjusted the mixture with the choke cable slackened off completely, with the result that the choke knob now needs to be pulled out fully. When pushed in I can now say it is completely 'off'.
If this makes no difference, or not enough, then I shall replace the manifold to engine gasket, as advised as a possibility above, and try again.
I also found an older post, so old that 'bmcecosse' contributed to it.
However, it is relevant to what we are trying to resolve, so included a link below, for anyone referencing this post in future.
Best wishes,
Mike.
viewtopic.php?t=46560

[svenedin]

Latest posts above noted with thanks, I have now adjusted the mixture with the choke cable slackened off completely, with the result that the choke knob now needs to be pulled out fully. When pushed in I can now say it is completely 'off'.
If this makes no difference, or not enough, then I shall replace the manifold to engine gasket, as advised as a possibility above, and try again.
I also found an older post, so old that 'bmcecosse' contributed to it.
However, it is relevant to what we are trying to resolve, so included a link below, for anyone referencing this post in future.
Best wishes,
Mike.
viewtopic.php?t=46560

Yes exactly. I tried to explain that in my long post. Perhaps it wasn't very clear.

Stephen

[jagnut66]

Yes exactly. I tried to explain that in my long post. Perhaps it wasn't very clear.

Sorry Stephen, I should have made it clearer myself that it was following your 'back to basics' guidance that prompted me to go back over this.
Everyones advice / experiences are relevant here, as sometimes doing these things solo, then coming up against a string of problems can tie you in knots mentally.
That's when it's time to 'phone a friend'......
Anyway, the upshot is that, whilst it does attempt to slow things down now, taking excessive choke out of the equation has left the 'ongoing' fast running lumpy.......
In this respect I have now followed the next piece of advice and replaced the exhaust manifold to engine gasket with a new one I had in my drawer of spares.

As a side note here, if someone is having a (classic car spares) clearout and offers you the lot (or your pick of it) always say yes!!
Donations to the cause are always gratefully received!

Too late to attempt to start her now, I shall do that tomorrow, wish me luck.....
Best wishes,
Mike.

[svenedin]

Yes exactly. I tried to explain that in my long post. Perhaps it wasn't very clear.

Sorry Stephen, I should have made it clearer myself that it was following your 'back to basics' guidance that prompted me to go back over this.
Everyones advice / experiences are relevant here, as sometimes doing these things solo, then coming up against a string of problems can tie you in knots mentally.
That's when it's time to 'phone a friend'......
Anyway, the upshot is that, whilst it does attempt to slow things down now, taking excessive choke out of the equation has left the 'ongoing' fast running lumpy.......
In this respect I have now followed the next piece of advice and replaced the exhaust manifold to engine gasket with a new one I had in my drawer of spares.

As a side note here, if someone is having a (classic car spares) clearout and offers you the lot (or your pick of it) always say yes!!
Donations to the cause are always gratefully received!

Too late to attempt to start her now, I shall do that tomorrow, wish me luck.....
Best wishes,
Mike.

Good luck!

It's a strange one this. I'll be very interested to hear what the culprit was.

Stephen