tuning

[Alec]

Hello Phil,

I suggest that you start from scratch, take the piston and suction chamber off and clean both inside using solvent such as cellulose thinners or carburettor cleaner. (Don't use metal polish or any other abrasive). Make sure that the needle is not bent and that it is secure in the piston and that the shoulder of the needle is flush with the bottom of the piston.
Screw the jet adjusting nut up until the jet top is flush with the internal bridge in the carburettor, then adjust it down 12 flats (two full turns). Switch on the ignition and you should see fuel just below the jet top. The fuel pump should stop tickking once the level stabilises and there should be no fuel flowing out of the top of the jet. If all is OK so far, replace the piston\damper assembly, making sure that the damper cover fits snugly. Put a finger inside the carburettor and lift the piston and release it, it should slowly fall back and stop with a quiet but distinct click. If not then the jet needs centreing, and the carburettor will not work correctly, particularly at idle.

There is a lot of writing to describe what is quite a simple job and should take about 10 to 15 minutes. All else being correct, the jet setting of 12 flats should be near ideal and need little further adjustment (At idle the mixture will be correct whatever the needle fitted so the wrong needle will not be the reason). A more obscure fault could be a mismatch of jet and needle. The H(S)2 jet is a 0.090" and the fitting of a 0.100" jet will cause severe over richness.

Alec

[bmcecosse]

He's already done all that - and confirms it goes up and down as it should.  Sounds like the problem is not with the carb.

[Alec]

Hello BMCE,

yes I saw that later, but all the other basic setting up is relevant, especially the needle position in the piston and the float level check with the pump switched on. Black smoke is excess fuel, so is almost certainly carburettor related.

Alec

[mixerman]

Hello Phil,

I suggest that you start from scratch, take the piston and suction chamber off and clean both inside using solvent such as cellulose thinners or carburettor cleaner. (Don't use metal polish or any other abrasive). Make sure that the needle is not bent and that it is secure in the piston and that the shoulder of the needle is flush with the bottom of the piston.
Screw the jet adjusting nut up until the jet top is flush with the internal bridge in the carburettor, then adjust it down 12 flats (two full turns). Switch on the ignition and you should see fuel just below the jet top. The fuel pump should stop tickking once the level stabilises and there should be no fuel flowing out of the top of the jet. If all is OK so far, replace the piston\damper assembly, making sure that the damper cover fits snugly. Put a finger inside the carburettor and lift the piston and release it, it should slowly fall back and stop with a quiet but distinct click. If not then the jet needs centreing, and the carburettor will not work correctly, particularly at idle.

There is a lot of writing to describe what is quite a simple job and should take about 10 to 15 minutes. All else being correct, the jet setting of 12 flats should be near ideal and need little further adjustment (At idle the mixture will be correct whatever the needle fitted so the wrong needle will not be the reason). A more obscure fault could be a mismatch of jet and needle. The H(S)2 jet is a 0.090" and the fitting of a 0.100" jet will cause severe over richness.

Alec

alec,
thank u 4 your very detailed descripsion of what my problem is but i have done all that the only thing i can put my finger on is as u rev up the car the piston in the damper is not moving no revs it just cuts out is there anyway this can be checked in situ as i am going mad
thanks again phil

[Alec]

Hello Phil,
it should lift up as you open the throttle. Can you push the piston up all the way with your finger? What about if you remove the damper rod itself?
Did it run OK before or is the car new to you? If it's new, and this is a very long shot, one maintence check is to block the air holes in the piston and time how long the piston takes to drop. If those air holes are blocked the piston will not rise.
If the carburettor is pretty much OK mechanically, then look at if the engine itself is healthy, compression etc or even a partially blocked exhaust. I know it can't be fully blocked as you mention black smoke, but if gases can't get out they also can't get in.

Alec

[mixerman]

Hello Phil,
it should lift up as you open the throttle. Can you push the piston up all the way with your finger? What about if you remove the damper rod itself?
Did it run OK before or is the car new to you? If it's new, and this is a very long shot, one maintence check is to block the air holes in the piston and time how long the piston takes to drop. If those air holes are blocked the piston will not rise.
If the carburettor is pretty much OK mechanically, then look at if the engine itself is healthy, compression etc or even a partially blocked exhaust. I know it can't be fully blocked as you mention black smoke, but if gases can't get out they also can't get in.

Alec

the car is not new we have had it about 8 yrs u can push the piston all the way up the air holes are clear the only thing i have noticed is when u push the piston up when the damper rod is in the piston does not come all the way down as u look thu the butterfly opening their is a gap of about 1/16 of a inch if i take the damper out it falls very nearly flush with the bottom of the carb
phil

[rayofleamington]

Does it run without the damper?
All the damper should do is slow the piston rising up (to prevent kangaroo jerking in slow traffic) - it should not affect the piston coming down.

[Alec]

Hello Phil,
if the car ran OK before then what happened for it to run so badly?
If you take the damper out, as you say, can you push the piston down any further? From what you're saying it sounds as though the piston can't fall freely all the way and that the jet centreing is called into question?

Alec

[bmcecosse]

I asked ages ago if it fell with a clunk !!

[mixerman]

Hello Phil,
if the car ran OK before then what happened for it to run so badly?
If you take the damper out, as you say, can you push the piston down any further? From what you're saying it sounds as though the piston can't fall freely all the way and that the jet centreing is called into question?

Alec

the piston falls freely and the jet is central but on trying to start it for about 10 min i have noticed the coil is to hot to touch is this normal? phil

[bmcecosse]

Well no ! It should get warm, but never too hot to touch. Seems there must be a short in the ignition circuit - drawing too much current.

[Scotland]

By screwing the jet adjuster up or down should make all the difference. What if anything happens when you try lifting the piston using the small button just below the bell chamber? If there is no difference I would suggest the piston is stuck and it may be worth removing the 3 screws that hold the piston housing to the body of the carb to see if there is anything obstructing the piston.

Contacting your local club to try and borrow another carb would be my first thought though. If all else fails trying to get one on EBay.

Alternatively you can get SU service kits, but when you start taking out the jets etc it is a real minefield, probably best left to a specialist.

May sound daft but you have got 3 in 1 oil in the damper pot and not 20/50?

Good luck with it - hope you sort it soon

[bmcecosse]

It's easy to overhaul an SU - don't be put off too easily !

[mixerman]

By screwing the jet adjuster up or down should make all the difference. What if anything happens when you try lifting the piston using the small button just below the bell chamber? If there is no difference I would suggest the piston is stuck and it may be worth removing the 3 screws that hold the piston housing to the body of the carb to see if there is anything obstructing the piston.

Contacting your local club to try and borrow another carb would be my first thought though. If all else fails trying to get one on EBay.

Alternatively you can get SU service kits, but when you start taking out the jets etc it is a real minefield, probably best left to a specialist.

May sound daft but you have got 3 in 1 oil in the damper pot and not 20/50?

Good luck with it - hope you sort it soon

thank u 4 your reply the piston is falling with a nice clunk so i know it is not the needle/jet assembly the piston inside the bell housing bit it seems ok i have asked on this thread and somebody is so kindly going to take a working carb of one of is minors and send it to me so i can make sure it is the carb or not
thanks phil

[bmcecosse]

I still think this is not carb related - check over all the ignition system.

[mixerman]

I still think this is not carb related - check over all the ignition system.

I have put new points/plugs/dizzy/condenser/timing is bang on each plugs is sparking fine the only thing is as i said on a previous thead the coil does get VERY hot but it still sparks at the plugs
phil

[bmcecosse]

Did you manage to get the compression check ? For a crude home check - turn the engine on the handle (ign off) - do all 4 feel the same - same resistance ? You could try advancing the ignition timing until it 'kicks' against the starter - this of course is too far - so now ease it back until it stops kicking. If there is fuel, compression and spark - it must go !

[turbominor]

i said on a previous thead the coil does get VERY hot

dont worry about the coil.. mine get so hot it hurts to touch..

this will be made worse if you have left the ignition on while you are tinkering.

Back to the black smoke/rich running/possible headgasket etc

Are the plugs all the same colour? if they are all jet black it would point to carb/mixture. If they are different say 2 jet black could be head gasket leaking oil in?

On the subject of compression, are all the valves opening and closing properly?

[mixerman]

i said on a previous thead the coil does get VERY hot

dont worry about the coil.. mine get so hot it hurts to touch..

this will be made worse if you have left the ignition on while you are tinkering.

Back to the black smoke/rich running/possible headgasket etc

Are the plugs all the same colour? if they are all jet black it would point to carb/mixture. If they are different say 2 jet black could be head gasket leaking oil in?

On the subject of compression, are all the valves opening and closing properly?

thank-u 4 your reply
all the valves are working fine i cannot see it being head gasket as 4 a few seconds the engine with rev up as normal then it dies and back to normal if u have read all my theads problems i have the plugs are black and sooty but i cannot tune it as the engine does not run long enough i keep moving the tuning nut a flat at a time but to no good i am still convinced it is the carb if i am wrong i will eat the spare wheel
phil

[bmcecosse]

Is there maybe a load of junk in the float bowl - gets sucked towards the jet when it runs - falls back when it stops. I assume the fuel pump is working ok - but test it by pumping some fuel into a bottle. It should pump frantically producing an almost continuous stream. If not - it could be the filter blocked/fuel pipe blocked or kinked/ or just dirty points.