Morris Minor Owners Club

My 1098 Convertible has been sat in the garage for 9 months and after replacing the exhaust and air filter I have hit a problem starting her up. The engine fires almost immediately (so no probs with damp, battery, spark, etc) and the revs shoot through the roof! the carb piston is topped up and moves freely and the throttle spring is strong and visibly closes the butterfly OK. removing the throttle and choke cables makes no difference. She runs on leaded.
Any ideas folks?

was it running ok before you put it away?

Sounds like the idle speed screw has been adjusted from "slow", through "fast-idle" and along to the little-known "Jet" setting. Best to get that checked out...

IIRC, the screw works on a cam, so that could have seized on, maybe?

visibly closes the butterfly OK.

have you checked by rasing the throttle slide and observing the butterfly moving? Or was it by watching the linkage on the outside.
Theres a slim chance that the butterfly isn't moving relative to the exterior linkgage - should be easy to check tho.

If the butterfly is shutting off properly, then have you got an air leak?

I have seen the butterfly moving. It shuts fully when the engine is stationary.
The car was running with no problems before.
The throttle lever on the car moves smoothly.

Where could the air leak be? Bearing in mind the fuel supply is up wind from the butterfly, any leak around the manifold would remove the fuel from the system surely?

Are you sure the butterfly shuts fully? I can't see an engine
revving high if the butterfly IS closed. Has the throttle cable
OUTER sheath been pulled out of its housing at the engine
end so that it prevents full closure of the butterfly? Do you
have a late car with the breather pipe going to the CARB instead
of the air filter?

Are you sure the butterfly shuts fully

No, it's very difficult to see inside there in a dingy garage, holding a inspection lamp with one hand, the carb piston up with the other hand and wiggling the butterfly with my third hand

Has the throttle cable OUTER sheath been pulled out of its housing

I tried starting with no cables attatched and there was no difference.

Do you have a late car with the breather pipe going to the CARB instead of the air filter?

No, it connects into the filter housing.

OK Petee, bet it ISN't closing then. If you tried with the throttle
cable disconnected then check that the outer sheath of the
choke cable has not been lifted out of its socket so that it is
effectively open by about a quarter of an inch when you think that
it is closed. Easy to check, with both choke and throttle unoperated
you should have a small amount of free play when you operate
the choke before it starts to open the butterfly.

Looking through the carb with the air filter removed and the float piston raised the butterfly is clearly visible. It is shut - that is to say nothing else is visible beyond it, no dark crescents above and below.
The throttle and choke cams move smoothly, the piston moves smoothly and rests at the base of its travel, the throttle spring is intact. Removing the throttle and choke cables has no effect on reducing the revs. Even if the butterfly was sticking in the fully open position as a result of gumming-up it doesn't explain how it got there with no accelerator cable attached. Or how it got back to the idle position when it was switched off.

Thinking back now the (it's hard because I drove another Minor for hunderds of miles in that time) the last time I drove the car was back from it's MOT. It did seem to have an artificially high tickover which appeared to rise over the 20 miles or so that I drove it. With a new air filter I would expect it to be a bit higher still but not sky high - unless whatever is causing it to rise is due to time rather than anything else like vibration.

Doesn't sound like anything too obvious, but I side with Willie that maybe the butterfly isn't fully closing.
Does the tickover screw make contact with the choke cam when the choke is off (normally it should't)
You could try running it with the tickover screw completely removed, but if that doesn't help I expect it'll then be time to remove the 2 nuts and take the carb completely off for a good look at it.
Ray.

but I side with Willie that maybe the butterfly isn't fully closing.

I can see how this would raise the tickover but we're not talking 1000-1500rpm, the revs are climbing up to 5000 rpm or more (best audible guess). Surely this would require a fully open butterfly and or a weak spring?

the throttle spring is strong and visibly closes the butterfly OK.

I am with Willie and Ray if the above is correct the revs cannot go that high have you checked manually that the spring has pulled it back or does it just look like it.

The problem I have is looking at the carb action when starting the thing up. I can't be in the car and under the bonnet at the same time. As soon as the engine fires I have to be there to switch the thing off when I really need to be looking down the throat of the carb to see what's going on.

Get some help.........

(sorry thats really obvious.......)

I can't be in the car and under the bonnet at the same time

very true - I've been there dozens of times myself and where there's a will there's a way.

A button press solenoid will do the starting part. Failing that, there's always the option to use a jump lead to the starter.

A couple of twisted wires (or a switch) connected into the coil low tension between coil and dizzy will do the engine off part.
The points just earth the coil feed - therefore your twisted wires shouldn't be a problem - if it shorts to ground, it's just like closed points.


For looking down the carb with engine running, you want good lighting. And I would also recommend goggles - if it backfires for any reason you don't want to use a braille keybord to write the next response.(not that I ever follow my safety rules)

It's worth a looksee, but if it's going to take more than a few minutes to hotwire an off switch, you may as well have the carb off for a very close look at it.

or get some "willing" volenteer to start/stop the car for you.......

Well Petee, I reckon you are going to have to remove the carb
so that you can have a clear look at the butterfly and see what
is amiss because if the butterfly was closing properly you could
not possibly rev as high as you say because not enough mixture
could enter the engine to cause the problem. the butterfly is
held in position by two screws, are they both still there? Check the
butterfly spindle bearing surfaces ( I once reconned a carb which
included fitting bearings to the butterfly spindle. I got it wrong and
suffered overrevving). After all, removing the carb complete is
an easy job provided you have a new gasket ready.

Well you were right Ray & Willie. The problem was down to me not checking the throttle return spring was in the right place. It was hooked round the cam/lever thing but not in the widget especially designed for it. As a result it was fouling the last 1/4" of movement. Amazing that such a small amount could cause the revs to climb so high.

I've now driven her round the block and she's fine. Despite her best efforts to kill me with exhaust fumes in the garage and a brake pedal that sunk to the floor for the first two attempts at slowing .

Thanks for all the help.

oh dear! was there just air in the system?

my brake pedal has done that a couple of times also.

I've put it down to the cylinders sticking in the out position when i last used the car, and with it standing for a while the fluid flows back to the master cylinder. So when you first push the brake pedal it simply pushes fluid back into the cylinders and the pedal feels really light.

I fixed the problem by (a) adjusting the shoes so the cylinders dont have to travel so far and (b) cleaning the cylinders using brake fluid.