A small issue…

[DWW]

After a few months of storage with the occasional engine start, I had the opportunity to take her out for a short 3 mile drive and a re-fuel. On a couple of occasions when attempting to accelerate I got a hesitation and back fire, at the beginning I thought it may have been old fuel but it happened again after filling with fresh fuel. Where should I look fuel or ignition? Help would be appreciated.

[politeperson]

Have a quick look at the oil levels in the carbs.

You might be missing some.

[DWW]

That was the first thing that sprang to mind, checked it seemed ok but will top it up when I find that little bottle which I misplaced. Also will get the spark plugs out in case they need a clean as I have a slight misfire on idle fro one of the exhausts. Thanks for your reply.

[malcolm]

I'm no expert, but i wouldn't have thought that low oil in the dampers would cause a backfire. Sounds more electrical to me? I don't know what ignition system you're on, but I'd check the usual suspects like dizzie cap, rotor etc

[DWW]

Thanks will do and report back

[Jeremy]

I had similar problems after leaving mine for several weeks. It was extremely bad tempered, firing on 5 cylinders, spluttering. I changed the plugs, to no effect. I called Angus, who advised me to just take it out for a drive and it will probably clear itself. Which it did. I took it gently at first, and gradually it started behaving. After a blast down the M4 and back it was 100% again. Just sulking for lack of attention...these cars are such primadonnas.

[mgcjag]

Uh the old Italian tune up

[DWW]

Thanks Jeremy, sounds encouraging, will clean the sparkies as a matter of course and take it for a longish drive.

[44DHR]

Sometimes small issues can actually turn out to be small items causing the problem.
In September last year before I put the E Type away for winter, I had a similar annoying intermittent issue appear which I initially viewed as a misfire, but in reality the consequential misfire was really a starting issue. As the car gets started infrequently, sometimes the car would start and run perfectly and other times, I would roll the car out of the garage for it to misfire and not run correctly.
As I had believed it to be a misfire, I went through and replaced all the usuals - new plugs, distributor cap, rotor arm, leads, coil - I even sent the electronic ignition back for testing. Eventually, I realised it was not electrical, but fuel related, as initially it was cylinders 1 and 2 misbehaving, followed by also the next two cylinders of 3 and 4, so it could not be the ignition.
Having checked the fuel pump filter and delivery, plus the bulkhead and carburettor filters, plus stripped the carb to clear out all the jets, normal service was resumed - until I tried to start the car after a few days when the misfire reappeared.
To cut a long story short, eventually I traced it to the float bowl inlet needle valves being worn after my 20 years plus ownership of the car. Perhaps one of the smallest components on the car, yet these were either sticking in the valve bores or not sealing on the valve seats to give me incorrect float bowl levels and hence the misfire.
I do run triple Weber carburettors, but the principle of checking these on SU carburettors could well apply as such small items can cause major issues - and frustrations !
Old and new inlet needle valves :-





Cheers,
Dave

[paydase]

Apart from the obvious wear of the needle, it seems that the used bore is larger.
Is it an optical artefact?

[DWW]

Well any carb or fuel issues can be ruled out in my case as the car hardly did 2000 miles since it was restored. I haven’t had a chance to re-address the issue but will in the coming few days and report back.

[44DHR]

Hi Serge,
No, it must be an optical illusion as both the old and new have a bore of 6.5mm where the needle taper point slider fits.
Interestingly, with Webers there is a range of Needle valves of differing diameters in the seating area which are used depending on the fuel consumption rates and for fuels containing alcohols. I use 2.00 mm needles.
Another point made in the Weber literature is that the needle taper point and seat are finished and checked as a pair and are not interchangeable with respective parts of other valves. The needle valves can be damaged by engine vibrations and car motions if the float chamber is empty, so in the case of sports cars transported on trucks, they recommend that carburettor bowls should be filled with thin engine oil for proper protection.
A selection of Weber Needle valves :-



Cheers,
Dave

[DWW]

OK, gave the sparkles a clean, topped up SU oil where necessary, brought her home 25 miles down the M1, the drive was sweet everything worked fine.