Cabrio carb

[Mickaleen]

I hv a Ford 2ltr Dohc carburettor engine which is not ticking over very well, its hunting to a point of stalling. The Carburetor is a 2v tldm. I have taken the following steps to try and fix this....
1).* Replaced the inlet manifold gasket.
2).* Checked the electric fuel pump by disconnecting the pipe from the carburetor.
3).* Taking the carburetor apart and cleaning using compressed air and replacing the various gaskets and diaphragms.
4).* Checking the vacuum where vacuum connections are, manifold, brake servo, engine and carburetor.
5).* Replaced the spark plugs.
6).* The insulation block was also checked for cracks.
7).* New gaskets used either side of the insulation block
The engine has only completed 76000 miles.
Lastly having carried out the work the mixture screw does nothing, screw it in or out makes no difference to the tick over, it remains hunting.
Out on the road under load it accelerates really well but will not tick over but remains hunting.
Can anyone help me please.

[dogoncrazy]

Re: Cabrio carb

Are you sure that the carb's float valve isn't sticking causing it to flood?

[greyV8pete]

Re: Cabrio carb

Check and clean the EGR valve / crankcase breather system? Also as per above, check that the float isn't holed and sinking. Remove it and give it a shake. You will hear any fuel sloshing around inside if it is holed. Peter.

[Mickaleen]

Re: Cabrio carb

Hi,
Thank you for your replies both of the suggestions were part of carburetor cleaning nothing wrong there.

[greyV8pete]

Re: Cabrio carb

Check wiring connections to and serviceability of the idle cut off valve. If thats failed the idle valve will stay shut. Usually wont run below a fast tickover but may just cause your symptoms if the carb is set rich enough. Peter.

If you need parts Gower & Lee are very helpful:

http://www.gowerlee.dircon.co.uk/TLDMtype.html

[Mickaleen]

Re: Cabrio carb

Hi Peter,
The wiring was also checked. Cut off valve is functioning correctly.

[greyV8pete]

Re: Cabrio carb

And is the 12v supply from the ignition switch ok too? Clutching at straws here. Peter.

[Mickaleen]

Re: Cabrio carb

Hi Peter,
Yes the electrical system is fine. I appreciate your help.
I am at a loss as to what to next, a new carburetor I suspect.

[greyV8pete]

Re: Cabrio carb

A carb wouldn't suddenly fail unless ...... I fitted a recon exchange carb for my classic once and during a club tour in France it had the same symptoms at yours. The idle jet had a speck of dirt in it which kept making it idle poorly and backfire on overrun, a classic weak mixture symptom. So as I had already cleaned the idle jet I assumed (incorrectly) that it couldn't be the same problem so in Castellane, suspecting an air leak, I fitted a new inlet manifold gasket in a car park, much to the entertainment of the locals. Fine for 20 miles and then a recurrence of the fault. The actual cause was again a blocked idle jet! The reason was that the recon carb had only been stripped to replace the usual parts, jets spindle bearing etc. The blockage was caused by small specks of scale that were flaking off the walls of the drilled fuel ways in the carb body that supplied fuel to the jets. Through having stood on a shelf for a while and then being subjected to the heat of a lot of mountain passes in the south of France the scale started to fall off. The idle jet being the smallest became blocked, whereas the main jets being huge in an old classic were ok.

Soo initially remove all the jets and give it a good blast through with a high pressure air line. If that doesn't do the trick I would look for somewhere that has ultrasonic cleaning equipment. Its used to clean fuel injectors on moderns so search for them first. Ideally you need to carefully drill out any small lead plugs so you can look right down the fuel ways. Of course you need to use a flat ended punch to fit new lead balls afterwards. Hope this is helpful. Peter.

[dogoncrazy]

Re: Cabrio carb

Seal /gasket between servo and brake master cylinder. Sometimes gets left out when working in this area and will cause poor running.
Had you being working on the vehicle prior to the problem and if so on what?
Like Peter I also experienced partial idle jet blockage on Cortina GT years ago. Took me ages to find and was the remains of a small insect causing all the issues

[Mickaleen]

Re: Cabrio carb

Hi,
The carburetor has been blown through with compressed air as mentioned earlier in this thread a total of three times to no avail. Every fuel way, every jet, main and secondary blown through with compressed air.
I don't have the facilities to drill out plugs accurately not a job I would under take.
Thank you both.

[greyV8pete]

Re: Cabrio carb

The fact that the mixture screw doesn't do anything is suspicious. Which suggests too rich from other jets or no idle fuel supply. So I would want to be sure that there isnt anything in the fuel gallery supplying that. Silicone sealant is a no no with fuel as it swells up and blocks things. Also is the float level correct? Another thought is the automatic choke working correctly. Is it pulling off smoothly or sticking closed / fully rich? Peter.

[Mickaleen]

Re: Cabrio carb

Hi Peter,
I don't know what else to say. I think there is a restriction some where in the carburetor, all that has been suggested has been carried out.
I have read on this forum similar problems with this carburetor which was only cured by replacement.
I think I may be following this route.

[greyV8pete]

Re: Cabrio carb

You wrote in your first post
“Lastly having carried out the work the mixture screw does nothing”
Do you mean that the mixture screw did nothing after the strip down or despite the strip down and clean?


Has the hunting gradually become worse or did it start suddenly? Have you done any other engine or distributor work recently? Has the vacuum advance unit in the distributor failed. The diaphragms can fail after long service giving a weak mixture which the mixture screw cant cope with? Put a vacuum pump directly on the units vac connection and see if moves the contact breaker plate and if it holds its position.


Is there any chance that the primary and secondary progression jets and emulsion tubes have been swapped around somehow in error?


Another thought is to check that the secondary throttle flap is closed at tickover and maladjustment or failure of the operating diaphragm unit isn’t letting it stay open? Also check the secondary throttle plate is opening at the correct time relative to the primary. The workshop manual should give you all the settings.


As a final thought have a look at the gaskets for the power valve and accelerator pump valve. I seem to remember that on my Sierra (different carb) the sort of triangular shaped ones can be fitted either way up. Could this have happened and is maybe blocking a fuel hole?


Also check the accelerator pump bleed back / non return valve isnt stuck open. Also check that you can see a jet of fuel squirt into the carb barrel when the throttle is opened quickly.


Keep chipping away. Its got to be something simple that is causing the problem! Peter.

[Mickaleen]

Re: Cabrio carb

Hi Peter,
I'll answer your questions as layed out...
1). Mixture screw does nothing.
2). Hunting became worse.
3). No vacuum advance ( e c u)
4). Diaphragms replaced.
5). No breaker plate. ( e c u)
6). Primary&secondary emulsion tubes original and in original places.
7). Secondary throttle flap closed at tick over.
8). Power valve & accelerator valve gaskets replaced.
I have this after noon bought a new after market fuel pump. The pressure of the Ford pump may be suspect, only way for me to check this is with a new fuel pump. The pressure should be about 2 psi according to Webcon. Webcon suggested the carburetor may not be getting enough fuel could be starvation.