Juddering at 60mph

[Tea]

One of our cars drives fairly well, but when we get to around 55 - 60mph it starts to 'judder' and 'kangaroo'. The engine is a 1098cc.
It used to be fine, but started to do this a little while back. The engine steady mounts are in good condition and secure as is the steady bar, so am pretty sure the engine isn't moving around.

What might be causing this?

[chesney]

Gearbox steady cable of incorrect tightness?

[bmcecosse]

Wheel balance ?

[Tea]

We had our wheels balanced a couple of years ago and I'm sure they mentioned something about a couple of the wheels being buckled. They told us which should go on the back to avoid any issues. Maybe that could be the fault?
I'll take a look at the gearbox steady cable once the weather has cleared.

[Tea]

The steady cable looks/ feels fairly tight. There is a bit of movement, but possibly not enough.

[chesney]

If it's too tight, it could be a source of problems.
Its role is only to stop the engine moving forward, and the fan ploughing into the radiator under braking, it should not be very tight.

[kennatt]

when you say kangarooing.do you mean missing?surging? or just a general vibration,could be a fueling problem,not enough at the higher speed but OK at lower demand.Pump or carb, fuel starvation.Tank vent blocked have you got an inline filter:-?

[bmcecosse]

Does it do the same at that same speed in 3rd gear ??

[Tea]

More surging. Definitely not just vibrations. It has got an inline filter, came with the car. I'm guessing I should get rid of it?
Not sure I could reach 60mph in 3rd gear ;) but no, I have no problems in 1st, 2nd or 3rd gears, only when reaching 'high' speeds in 4th.

The pump seems fine. Ticks away quite happily and the points are cleans.

Should I start with scrapping the inline filter?

[bmcecosse]

Yes! And it should get to 60 in 3rd..... Maybe a compression check would be worthwhile. What colour are the plugs after a good run?

[kennatt]

Try taking the filler cap off and see if that helps,and throw the filter away. see what happens and report back.

[Tea]

The plugs are a light brown, so running a good mixture. I'll do a compression test tomorrow as I don't have one at home.
Sorry for my ignorance, but the filler cap for what? I'll check the pipe I have is long enough without the filter and, if so, take it off tomorrow before going out. If not, I'll order a new pipe and replace once it has arrived and let you know what happens.

I noticed today that when applying the accelerator you can hear what sounds like a rush of air or a suction sound coming from around the carburettor. A little like the flushing of a plane toilet, but nowhere near as loud. Only noticeable if you have your ear relatively close to it. Is this normal? Can't say I've noticed it before, but also can't say that I've listened to my carburettor before...

Thanks for all the suggestions. I really do appreciate it.

[bmcecosse]

Oil filler cap..... Rushing sound..... is the vacuum advance tube connected between carb and dizzy - and not leaking? What state is the air filter element - plastered with oil ? Try running without the paper element in place to see if it goes any better. Also -check the carb piston rises and falls easily - and put some oil in the little damper chamber.

[Tea]

I thought the oil would come out the top if removed when the engine was running?

The filter element is relatively new and clean. I will try running it without though and see if there is an improvement. Carb piston moves freely, and I topped up the damper oil a couple weeks ago. The vacuum advance has the potential of being a problem as it came off an engine that has been sitting for 20 or so years. Our friend that we took it from had tested it and said it seemed to be working well, so have no reason to think otherwise.
Is it safe to run the engine for extended periods without the an air filter element?

Tomorrow I will do away with the inline filter and have a run to see if it makes a difference. Then try without the air filter element and report back.

[bmcecosse]

Yes - run without air filter - unless you live in a 'dust bowl'.....unlikely with all this rain!

[kennatt]

petrol filler cap,to eliminate a blocked vent which would prevent full supply on high demand,due to vacuum in tank.

[bmcecosse]

Yes - but also the oil filler cap to check for plume of smoke/fume when revving up the hot engine....

[Tea]

The pipe we have is too short, so will be ordering a new one today.

However the surging seems to have stopped. The only extra thing that I did was reset the points gaps as one had closed a little and another was too open. I suppose that could have altered it??

Anyhow, many thanks for the help. I'll keep driving around and see how it goes and put the new pipe on once it gets here. If the problem comes back I'll be back for more help

[bmcecosse]

You have two sets of points?? Or - are you talking valve gaps..... ?

[taupe]

Twin contact set on some SU pumps

T