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 Posted: Mar 23, 2021 08:01AM
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Fixed needle or swinging needle? Sounds like you may have the fixed needle setup and the needles are not centered in the jet and are rubbing the jet as they try and fall to the lowest setting.

 Posted: Mar 22, 2021 03:00PM
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CA
Keep the parts of carb A from carb B - don't cross-mix them: the internal parts are matched to each other.

When you say the "dashpots are removed", do you mean the dampers - the black caps with the rod and the brass blob on the end?

The dashpot is the large chamber with the piston inside, held down with 2 or 3 screws. The piston test must be done with the dashpot properly screwed down.

What oil are you using in the dashpot dampers?

.

"Hang on a minute lads....I've got a great idea."

 Posted: Mar 22, 2021 02:35PM
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Well I have found the piston functions perfectly on both carbs, with dashpot removed, piston moves beautifully, the problem is arising when the dashpots are re-instated the pistons are both intermittently sticking during the downward travel, or deceleration is so slow. With the car running I can use my finger down the air ram and push the piston back to resting which will if I do it to both carbs return idle to about 1000rpm, adjusted the dizzy to lowest rpm when hot idle. The carbs don't seem to be drawing air in such that I can hear a roar sucking sound, but if I cover them they start to stall the motor so they are drawing the air in.. Tried carbon cleaner for the run on, checked plugs, they where black carbon coated, replaced with new ones, The part I don't understand with it is when its running, the motor revs up, maintains 3000rpm, at good constant rate, crazy oil pressure, thermostate kicks in, vacuum lines are all tight.. argghhhh I think I will just Take the Carbs off strip them down and start fresh...ohh, I never cross paired the dashpot and pistons in case anyone thinks that could be it... Thankyou to everyone who has responded, will update with final result...

 Posted: Mar 11, 2021 04:43AM
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CA
Quote:
Originally Posted by SPARKSnSPANNERS
Picking up a carbon cleaner tomorrow and will run through, I checked the dash pots, the centre plunger part, should that have a smooth resistance when reseating or should it feel free ? The oil was clear and even between the two. Timing in good, the car makes no difference with or without the air filter assembly attached. Can an Inlet manifold cause this symptom ? I don't hear vacuum or air squealing ?  

Thankyou for taking the time to respond.. Everybody.. 
With the damper removed (the thing you pull out to check the oil), it should drop quickly wiht a small but definite clunk. There is s spring inside the chamber to push the dashpot piston down.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Mar 10, 2021 06:04PM
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Picking up a carbon cleaner tomorrow and will run through, I checked the dash pots, the centre plunger part, should that have a smooth resistance when reseating or should it feel free ? The oil was clear and even between the two. Timing in good, the car makes no difference with or without the air filter assembly attached. Can an Inlet manifold cause this symptom ? I don't hear vacuum or air squealing ?  

Thankyou for taking the time to respond.. Everybody.. 

 Posted: Mar 10, 2021 10:44AM
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Quote:
Originally Posted by SPARKSnSPANNERS
I Have an issue that I am chasing, car has sat for two years but was occasionally fired up and seemed ok, then left for about 6 months untouched now when I start the car it runs and accelerates fine, revs straight up when hot ok course but when idle is now 1800-2000 rpm, when i try to turn the car off it continues very badly but continues to run and run and run, with all the idle removed from the carbs- Twin SU setup, i thought it was a fuel pump stripped it down no all good, then it was suggested a vacuum leak to break booster blocked that off..so currently the car requires a 4th gear switch off synchro-movement key off to kill it. I did over the period of not running found the choke cable became tight and wonder if I could have damaged the carbs with excess tension.  Carb expert of mech with any ideas please help, next step I think is pull the carbs of, but for the car to run, and run, I am assuming the fuel is from the carb bowls, ignition from carbon, plenty of air, so slightly baffled, I am hoping I am missing something very obvious.. The engine is a manual, engine number says block it from 1100s, rego says its 1275, head is the one with the extra bolts requiring rocker cover trimming. Then running twin SU carbs air filter saying cooper s.. Any Ideas Gratefully appreciated.. 
First thing to do is to find out why the idle is so high.
See if the issue is in the accelerator cable or the carb linkages.
You may have to disconnect the cable from the linkage to check this, it could be something as easy as a frayed accelerator cable or a choke linkage sticking causing the high idle.

If in doubt, flat out. Colin Mc Rae MBE 1968-2007.

Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.

 Posted: Mar 10, 2021 05:30AM
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CA
+1 to what Kermy suggests.
The first thing is to clear the engine of carbon. Run-on is a result of a too-hot combustion chamber that continues to ignite air/fuel mix after the ignition is switched off. If the fuel mixture is not right (e.g. sticking choke or there is a timing issue), incomplete combustion causes carbon to build up. When you run the engine, the carbon can heat up to glowing and act like spark plugs. If really bad, it can also alter the compression ratio.

Once you get it running better, determine why the problem occurred in the first place. Start with verifying the timing, including the timing advance at various rpms.

If timing is good, then look to the carbs.
 - Clean or replace the air filter(s).
 - Check the choke cable to ensure there is a tiny bit of slack at the carb when the knob is pushed fully in.
 - If that is good, make sure the linkage between the choke lever and the bottom of the main jets is free and operating smoothly - do the jets rise up to contact the adjustment stops - up to where the running mixture is set?
 - Check that the dashpot cores move smoothly and drop with a clunk. Remove the damper cores and lift each core and let it fall. They should drop all the way down to the bridge. If not, they may be dirty or your main jets need to be re-centred.  With that done, check the dashpot oil level and consistency.

The LAST resort would be to remove and clean the carbs. They would need re-tuning and re-balancing when you were done... in other words you problems would be more complicated.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Mar 10, 2021 05:29AM
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Drain off the old fuel for the lawn mower, and get a fresh tank of premium.

 Posted: Mar 9, 2021 06:47PM
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Run a can of carbon remover through the motor. Do the job at night so your neighbours don't complain about the smoke.

 Posted: Mar 9, 2021 02:35PM
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I Have an issue that I am chasing, car has sat for two years but was occasionally fired up and seemed ok, then left for about 6 months untouched now when I start the car it runs and accelerates fine, revs straight up when hot ok course but when idle is now 1800-2000 rpm, when i try to turn the car off it continues very badly but continues to run and run and run, with all the idle removed from the carbs- Twin SU setup, i thought it was a fuel pump stripped it down no all good, then it was suggested a vacuum leak to break booster blocked that off..so currently the car requires a 4th gear switch off synchro-movement key off to kill it. I did over the period of not running found the choke cable became tight and wonder if I could have damaged the carbs with excess tension.  Carb expert of mech with any ideas please help, next step I think is pull the carbs of, but for the car to run, and run, I am assuming the fuel is from the carb bowls, ignition from carbon, plenty of air, so slightly baffled, I am hoping I am missing something very obvious.. The engine is a manual, engine number says block it from 1100s, rego says its 1275, head is the one with the extra bolts requiring rocker cover trimming. Then running twin SU carbs air filter saying cooper s.. Any Ideas Gratefully appreciated..