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Running on!

Posted: Sun Apr 16, 2017 6:57 pm
by bigstraight6
My Mk2 2000 on Stromberg carbs is driving so well but runs on when the ignition is turned off, an issue which is very frustrating. I'm running on NGK BP6ES plugs, is there a hotter running plug I could use? I can't stress enough how well the car is driving apart from this running on performance.

I've also been told that the Stromberg carbs (which I took apart and rebuilt with new diaphragms and needles) are not that good and replacing with SU carbs would be a good move? Or perhaps I'm missing something obvious!.....

Re: Running on!

Posted: Sun Apr 16, 2017 8:58 pm
by Dazzer
Strombergs are good and react faster than SUs. The running on can be minimised by slowing down the tickover. Cheers Dazzer

Re: Running on!

Posted: Mon Apr 17, 2017 6:42 am
by Clifford Pope
Plug heat range terminology is confusing. As I understand it, a hotter-running plug means one that gets hotter, not one that can stand hotter combustion. So if you want to lower the temperature of the plug tip so that it doesn't provide a hot-spot for triggering running-on, you need a cooler plug not a hotter.

Combustion temperatures increase as you advance the ignition timing nearer to the knocking point. It's always said to be good to run the ignition as far advanced as possible just short of knocking, but the penalty is any red-hot carbon or the plug tips will tend to trigger running-on.
I found the 2000 engine especially sensitive to pinking and running-on. I read that unleaded petrol runs hotter than the old 4-star, which some engines are more sensitive to.

I did sometimes convince myself that letting the engine idle for a short while before switching off reduced the tendency.

Re: Running on!

Posted: Mon Apr 17, 2017 8:03 am
by bigstraight6
Thanks for the replies, mentioning fuel I don't think old cars like the grade of petrol
we have today, I use Castrol valvemaster plus additive as it's an octane booster. I will certainly have a play with the idle speed settings to hopefully sort the problem.....

Re: Running on!

Posted: Mon Apr 17, 2017 7:32 pm
by Mike Stevens
I've found that running the mixture a little bit on the rich side can help with running on.


Re: Running on!

Posted: Wed Apr 19, 2017 8:16 am
by pete lewis
my mk2 has SU of which i have a avid hate of them , take apart both makes and lay out the component parts and compare the engineering in both its easy to see which is designed and which is a load of meccano ,

both can do a good job but stroms are far better in trouble free and economical terms ,, there are less needle specs available for Stroms if you need to play around with aftermarket must have filters.

fuel addatives are made for guys to buy , its not needed just use a 97-99ron fuel and keep the ££s in your pocket, you will find the addative will add to your problems not solve them.

i ran a emission test dept for our trucks and in the 70-80 lots of things changed , we did some tests on addatives as a way or reducing and in most tests the HC and C0 had increased vs plain fuel . the later products may be better but they are not needed in our cars

if you get problem with correct timing correct idle speeds correct mixtures then you could add a anti run on valve in the manifold to open when you switch off , the additional air weakens and it wont run on

some GT6 had this added just an idea


Re: Running on!

Posted: Tue Apr 25, 2017 7:37 am
by Clifford Pope
I wonder if pressing the brake pedal would have the same effect, causing the manifold to draw in air from the servo?