Would a vacuum leak cause staring problems?

Hey All

Fairly new to Landies so be nice!

Since getting my 1973 S3 petrol, I've put on new plugs, leads rotor and cap, changed the points for a 'SimonBBC' electronic set-up along with a new standard coil from same, cleaned up the earths from the negative battery pole and the starter to chassis point, put in a new battery,
and topped up all the fluids.

Unfortunately I did all of this in one hit, and now have an annoying intermittent starting problem!

Typical!

Basically when it happens the symptoms are the same as a dodgy earth - starter turns as if the battery is really low, two or three laboured turns and 'DONK'. Every time it happens I remove the battery, charge it, put it back, check all connections, fiddle with a few bits, and get the same.

Usually after an hour or so of cocking around with the basic stuff it turns over and fires really well and runs perfectly. Starts first time for a day or so as long as it's started regularly. If left for more than a day or two though - same thing - RH RH RH DONK.

Today I got a little ****y with it and took everything to bits again,. put it all togaether and got the same. Then I notices the rigid small bore vacuum pipe from the Webber carb to the diaphragm(sp?) had about 2 inches of flex rubber pipe between the end of the metall pipe wich met the diaphram(sp?). I pulled this off to take a look and it appears this metal pipe hat broken at some point, and a previous keeper had 'mended' it by joining the two ends with rubber pipe.

I 'sealed' both ends with insulation tape and bugger me, it started.

Does this sound like the cause? Or have I lucked out again in the lottery of 'fiddling with stuff 'till it works'?

Grateful for any comments - apologies for the essay!

Jof

Does sound like an electrical fault in the starter circuit. Might be worth bypassing the starter solenoid with an old screwdriver to eliminate it from your enquiries but it could be a poor earth (check the strap from the starter motor to the chassis) or worn bushes in the starter motor itself. Are the connectors swaged or soldered to the cables 'cos swaged ones can go intermittent.
Or it could be the battery - what voltage does it show when charged?

Sorry - my ignorance is about to shine through here.

Do you mean bridge the solenoid contacts with the screwdriver therefore elimonating it from the circuit?

Have already cleaned up the starter to chassis earth - hopefully eliminating it from the list.

I gurss the main reason I suspected the vac pipe is that I've dome a lot of diddling inh the distributor area and thought I may have loosened something.

I'll try the solenoid thing and report back - though as it's recently started, I'll give it a day or two to rear its head again. Ta for the reply - most helpful.

Just to confirm though, would the vac pipe issue cause this type of behaviour?

Can't see how the vacuum leak could make it turn over slower. Surely an electronic fault.

It could be a sticky solenoid so shorting out the contacts should eliminate it as a problem. Check the solenoid low current circuit as well - a poor earth here would cause these symptoms.

If bridging the soleniod doesn't work, From the earth braiding on the engine, take a lead from that to the -ive pole of the battery. Might have a high resistant between the earth braiding on the chassis and the -ive pole of battery.
Just an idea

Jof said:

Just to confirm though, would the vac pipe issue cause this type of behaviour?

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not usually.

but in referance to your "- RH RH RH DONK."
when it does its "donk", is it stopping turning over pretty suddenly?

reason i ask, is cos if ignition timing is too far advanced, it sometimes causes this to happen.
however, if turned off and tried again, usually you get the rh rh rh donk again.
with the vac pipe disconnected, the carb wont be pulling a suction at the dizzy, so wont be advancing in this way.

personally, i would be checking the battery voltage while cranking to eliminate a duff battery from the equation. if/when its proven good, would be lookin for bad connections, inc starter brushes, then ignition timing.

how have you set the timing?

em... haven't set the timing at all. Sadly wouldn't know where to start

nrgserv said:

not usually.

but in referance to your "- RH RH RH DONK."
when it does its "donk", is it stopping turning over pretty suddenly?

how have you set the timing?

Click to expand...

Jof said:

em... haven't set the timing at all. Sadly wouldn't know where to start

Click to expand...

ah.
and the first question?

yep stops turning suddenly

As I haven't touched the timing since fitting the electronic kit, would it be worth retarding the dizzy by a few degrees to see if that helps?

with out reading all the posts on this, yes the vacume pipe does affect starting. the small bore pipe controls the air flow for advance and retard,and a lot of problems occure when working on the distributor. and the main 1 which always seems to get by unoticed is the spring in side the disistributor,which do break have you checked the spring, which is fastened to the plate underneath the points.

the springs for the centrifungal advance and wont really matter unless its missing or snapped.
how does the electronic pickup receive its signal?
best thing you could do is buy a strobe light, retard the dizzy so it will start, then adjust the dizzy so the timing mark on the crank pulley matches the pointer.
this can also tell if the centrifugal advance works, and the vacuum advance.

edit
is it the lucas dizzy or ducellier?

It's a Lucas 25D

so it should have the vernier adjustment screw on the vacuum advance.
(should have A-R on casting, advance and retard)
need to know how your electronic timing replaces the points?

There's a magnetic ring that goes over the cam, and a module that sits under the dizzy cap which I presume measures the speed of the ring passing by it. Got it from 'SimonBBC' after reading a lot of positive reviews

so would I be right in thinking I can retard the timing using the wheel rather than loosening the dizzy and twisting?

Sooo - cheeky request time then...

Anyone near Taunton in Somerset fancy a few beers in exchange for an hour under my bonnet with their timing strobe?

Jof said:

so would I be right in thinking I can retard the timing using the wheel rather than loosening the dizzy and twisting?

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yes on the original setup. dont know on yours now.
wouldnt know how to set the timing on the electronic without the instructions.

Jof said:

Sooo - cheeky request time then...

Anyone near Taunton in Somerset fancy a few beers in exchange for an hour under my bonnet with their timing strobe?

Click to expand...

kinda rules me out then!