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Hello Chaps,

Wonder if you can point me in the right direction? My MK2 3.8 runs with twin SU carbs that were rebuilt 10,000 miles ago and not had a problem with them until now. Car starts perfectly and runs and idles well when cold either on or off the electric choke but once the engine is hot it will stall rather than tick over. When driving its fine problem is only tickover, new SU pump of correct pressure fitted as the old one was original and becoming less reliable and 123 ignition distributor fitted as well as new leads and plugs, no change.

Thanks in advance.

Regards

Goss

I had a old Range rover years back , that would cut out when hot , turned out to be the HT lead to the coil , are you using copper leads ?

I have exactly the same issues. I've put it down to fuel vapourisation and am considering driving around with the bonnet open

I had a old Range rover years back , that would cut out when hot , turned out to be the HT lead to the coil , are you using copper leads ?

I have replaced all leads with copper ones and the coil too.

Hi Goss

Can you give us a little more info. Do you mean it won't idle when you take your foot off the pedal and the revs fall back (when hot) - or that it won't idle from start up when hot. Was any work done on the car before the problem started - was it a sudden or progressive fault etc. Any further description would be helpful.

If it was an HT issue I would have thought that it wouldn't run when hot - period.

Robbie

I have exactly the same issues. I've put it down to fuel vapourisation and am considering driving around with the bonnet open

I have been using the car since 1999 and its only started doing this in the last 18 months, prior to this issue it has always been great with no difference in performance/temperature whatsoever. I may remove the carbs and give them a good clean and balance, I noticed when I changed the plugs that 1,2 &3 were richer than 4,5 & 6.

Goss

Hi Goss

Can you give us a little more info. Do you mean it won't idle when you take your foot off the pedal and the revs fall back (when hot) - or that it won't idle from start up when hot. Was any work done on the car before the problem started - was it a sudden or progressive fault etc. Any further description would be helpful.

If it was an HT issue I would have thought that it wouldn't run when hot - period.

Robbie

Hello Robbie,

It was a sudden fault but after being laid up over a winter. The car starts perfectly from cold with fast idle when the aux carb is on then runs and idles perfectly without the aux carb until the engine reaches normal working temperature then it idles at 300 rpm and stalls. When hot it is hard to start too which is uncomfortable with the stalling. In summary hot idle and starting is the issue.

Regards

Goss

Mixture over rich caused by carburettor (s) losing tune, auto choke still passing extra fuel when it has apparently shut off (more likely), or valve clearances closed up.

It does sound like carburation. I would start by checking things like dashpot oil level and viscosity, jet alignment and freedom of movement for pistons, correct adjustment and operation of throttle linkage, idle screw positions - and as you say, balancing and mixture adjustment. Phils suggestion of a leaky choke shut off also sounds plausible.

Let us know how you get on.

Robbie

Your tickover speed of 300rpm seems a bit low to me so if the distributor is working ok and nothing has happened to the operation of the valves (and timing) then the carburation/fuelling is likely to have had something happen to it. So need to check the supply is ok then look at the carb settings (having ensured no sticking aux carb or float chambers needle valves etc).

Thanks for your replies, hope to get some time this weekend to have a look at it as I need to be ready for Goodwood Revival!

Will keep you posted.

Goss

I have exactly the same issues. I've put it down to fuel vapourisation and am considering driving around with the bonnet open

I have been using the car since 1999 and its only started doing this in the last 18 months, prior to this issue it has always been great with no difference in performance/temperature whatsoever. I may remove the carbs and give them a good clean and balance, I noticed when I changed the plugs that 1,2 &3 were richer than 4,5 & 6.

Goss

Mine is a fairly recent problem too. I have only owned this Mk2 for just over a year but at first it stalled all the time due to rich running. Now it's only when hot. I have had the entire carburation and ignition system renewed and updated with 123 ignition and a Malpassi Filter King. The last company to have the car (for several months) was CMC who assure me everything is perfectly set up but it still hates being hot. It also has a new electric fan which comes on at the minimum setting and I run on premium unleaded but neither makes any difference. Otherwise all is spot on. I have bypassed the otter switch so the AED is not a factor.
Is fuel vapourisation a common fault on these cars as I don't think there's much more that can be done with the carbs?

Back in the sixties I never experienced any problems relating to vaporisation. You could remove both dash pots and pistons, switch on the ignition and check the fuel level, sometimes a gentle tap of the float chamber allows the delrin fuel control valve to settle and fully close off the fuel supply when the float chamber is full. Mop out any surplus fuel that may have accumulated and check that the fuel is visible down the needle tube, from memory it should be about an eighth of an inch down. On the other hand it could be flooding slightly.
You may need to remove the float chamber lid to adjust the fuel level or even consider replacement valves.

Prior to above , with the engine hot and at idle RPM , a very simple test is to very carefully lift the piston with a figure tip, if there is a rise in RPM then clearly it is too rich, alternatively if the engine dies then the mixture is too weak.

Gosh,this subject takes me back a bit ! I think the SU is a great carburettor and exceptionally reliable at that. I have recently been given four SU's which I may eventually fit to my carburetted V12 . The standard fit is Stromberg's but they have never been my favourite

Do let us know how you get on

PS to above, do you know where the piston lift pins are, just under the dash pot

Also consider the possibility of an intake vacuum leak - manifold, carburettor mounting, vacuum advance connections, butterfly spindles etc.

Robbie