CARB PROBLEM

[madmoggy]

Hi there ,weve just purchased a 69 ,2door as a none runner,after draining two and a half gallon of stale fuel from the tank and putting new fuel in we put a battery in and turned the engine over by hand first and made sure it was all free etc,new plugs ,turned the key and it fired right up,however it is running very rich and trying to adjust the mixture does nothing.
I removed the carb top and air cleaner ,the pison is tight ,I asume this should move freely,can I clean this with wd40 and some fine wet n dry paper? and do you think this may be causing my rich problem?
I just want to make sure the engine runs smoothly before I get stuck in to the rest of the car.
Any help greatly appreciated.

[Matt Tomkins]

the plunger should move up, then drop down again with a 'clunk'.
remove the plunger
Take the dashpot off (2 machine screws)
remove the big long spring
attempt to lift the plunger (and needle) out. take care not to bend the needle
if it won't lift out easily, remove the choke linkage (x head screw into jet) and remove the jet (might might be worth replacing both the needle and jet if any signs of wear/bending)
now the plunger should lift out.
undo the mixfture screw and remove the srping.
replace everything the reverse of the above and centre the jet following the instructions from the BMC manual.
then you can remove the jet again, put the spring in, replace the jet and ajust the mixture.
You would do well to put a small smear of copper gresase on threads on reassembly, and on the jet itself if it's sticky.

Hope this helps
Matt

[madmoggy]

Thanks Matt,the needle looks like someone has ten it out before with a pair of pliers(some marks on it)with this out the plunger is still tight ,can I take this out and clean it up? also I have a needle from another moggy carb can I swap the needles?
Regards Si

[Matt Tomkins]

just asked a freind of mine who is a carb expert. he says:


don't worry about it running rich so long as its running until its warmed up and the choke is fully in. wd40 is fine for cleaning, try taking out the damper - black screw thing on top of the carb. it should be a lot easier to lift then. the damper is why it is hard to lift.

if with the damper removed it is still stiff then remove the dashpot and plunger and clean with wd40

do not use wet and dry

cloth will do the job fine

i also advise taking the plunger out and emptying and cleaning out all the old damper fluid and replacing with 20w50 engine oil

it sounds like the choke is out or set far too rich, a sticky damper will make it run lean

[Matt Tomkins]

Thanks Matt,the needle looks like someone has ten it out before with a pair of pliers(some marks on it)with this out the plunger is still tight ,can I take this out and clean it up? also I have a needle from another moggy carb can I swap the needles?
Regards Si

swap both the needle and jet if possible.
that sounds like why it's sticking

[madmoggy]

Thik this may be a knackered carb then,the choke isnt even connected ,running badly rich even to the piont of black soot etc ,wont tickover even when run for a while using throttle to keep it going.

[Matt Tomkins]

probably savable with a good tune up etc.
where are you based?
I'm in oxford, and wouldn't mind helping if you're local

[madmoggy]

Cheers mate but Im in Devon thanks anyway.

[bmcecosse]

Certainly DO NOT use wet and dry! The piston will be sticking in the bell - so clean both with WD40 -in extremis - a little brasso is ok, but wash it away with WD40 before assembly. The piston must run easily in the bell - it won't be sticking in the jet assembly unless the needle is bent. You should check the code number on the shanks of the needles (and post up what they are please) before swapping - but the differences are likely to be 'minor' and it should be fine.

[mike.perry]

When you have serviced the carb check the needle in the spare carb and if it is in good condition and is an AN needle then it will be correct for your 1098.
To tune the carb, wind the mixture nut fully up, mark one flat with tippex or similar and wind the mixture nut down 2 turns or 12 flats, that should give you an approx. starting point. When the engine is hot and with the choke fully in, turn the nut up or down a flat at a time until you get the smoothest tickover. Adjust the slow running screw until you get the correct idle speed then adjust the fast idle screw so that it is just touching the choke cam lever

[bmcecosse]

Note that '6 flats' will only be = one turn..........

[JOWETTJAVELIN]

Dear God... wet and dry and pliers on a carb needle??? I know the S.U. is a simple thing but no carb should be subjected to this!

You won't necessarily have to buy a new carburrettor, just a rebuild kit. Remember also it's a very sensitive, precision built component.

[kennatt]

12 flats is the usual starting point.

[mike.perry]

Well spotted that man - post edited.

[Matt Tomkins]

a basic guide to stripdown. more to follow. might be easier to visualise with this http://www.youtube.com/watch?v=fuX30GsII10