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annoying misfire - advice sought

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Vortex O'Plinth
Posts: 785
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: annoying misfire - advice sought

Post by Vortex O'Plinth » Tue May 07, 2019 4:06 pm

If you pull the choke out does the engine speed at which the misfire starts, rise? If so, it's probably a fuel supply problem - could be dirt in the carburettor jet.
Last edited by Vortex O'Plinth on Tue May 07, 2019 6:59 pm, edited 1 time in total.
Nick

Pas d'elle yeux Rhône que nous.

Bud
Posts: 218
Joined: Fri Feb 12, 2016 9:06 pm

Re: annoying misfire - advice sought

Post by Bud » Tue May 07, 2019 4:56 pm

re: Ian's post

If you suspect ignition type problems, an old trick is to run the car in complete darkness and look for the "light show" as it will locate insulation failures and carbon trail arc overs most readily.

daimlersteve
Posts: 314
Joined: Wed Mar 09, 2016 11:20 am

Re: annoying misfire - advice sought

Post by daimlersteve » Fri May 10, 2019 5:39 am

Jez and Tony are right regarding carb feeds to cylinder #s . If the carb is rich at idle it will be rich further up the range ( if the needle is org. ) more likely to be electrical . some Plugs once fouled will not self clean up in that rich , now adjusted leaner cylinder use.
cheers , Steve

Marcus
Posts: 197
Joined: Tue Feb 16, 2016 9:06 am
Location: hong kong

Re: annoying misfire - advice sought

Post by Marcus » Mon May 13, 2019 6:16 pm

Thanks to everyone for their replies. Sadly Work and domestic chores have interfered with garage time so I have yet to follow up. I will post the answers when I have the problem resolved.

Ian Slade
Posts: 436
Joined: Sat Feb 13, 2016 9:54 am
Location: Akrotiri Cyprus

Re: annoying misfire - advice sought

Post by Ian Slade » Mon May 13, 2019 7:11 pm

The balancing and richness is controlled on the idle by adjusting the throttle stops and the diaphragm control, the accelerator is then set at about 2500- 3000 rpm balanced using a vacuum gage or bobble type thermometer adjusting the short rods to the carbs, when balance is achieved the richness can be adjusted again on the diaphram control( I found the Gunson Colour Tune spark plug replacement ideal but time consuming to get it right as it needs to be moved to different cylinders to get the best result.) 8 of them is the ideal but 4 gives a very good set up. The final tuning at medium rpm does compromise the idle set up but not much
Owner since the 70's, Genghis is slightly to my left.

KV8
Posts: 197
Joined: Sun Mar 06, 2016 7:05 pm
Location: Cambridgeshire

Re: annoying misfire - advice sought

Post by KV8 » Tue May 14, 2019 9:09 pm

Ian Slade wrote:
Mon May 13, 2019 7:11 pm
I found the Gunson Colour Tune spark plug replacement ideal but time consuming to get it right as it needs to be moved to different cylinders to get the best result.) 8 of them is the ideal but 4 gives a very good set up. The final tuning at medium rpm does compromise the idle set up but not much
I have considered this device for use on my other classic. However can not see how it can be used on DV8 engines where plug is at bottom of tube? Please explain?

Thanks

H

Ian Slade
Posts: 436
Joined: Sat Feb 13, 2016 9:54 am
Location: Akrotiri Cyprus

Re: annoying misfire - advice sought

Post by Ian Slade » Wed May 15, 2019 4:52 am

Actually they're brilliant, the light reflects off the tube and the whole tube glows, far easier to read than the exposed plug.
Owner since the 70's, Genghis is slightly to my left.

timmartin
Posts: 36
Joined: Wed Feb 17, 2016 1:37 pm
Location: Berkshire

Re: annoying misfire - advice sought

Post by timmartin » Wed May 15, 2019 9:48 am

...and the Colour-tune comes with a little extension which is easy to screw onto the plug and doesn’t get in the way.

The view of the spark igniting the mixture and the different colours of combustion are so clear that I have fascinated three generations of my family by showing them. At least, I think they were fascinated ... but they could certainly see it easily.

Don’t forget that the centre two cylinders on each bank (2 and 3) run leaner than the outside two (1 and 4) because of the imperfect design of the inlet manifold. This means that when 2 and 3 are set correctly (ie not too lean) then 1 and 4 have to be a bit too rich. This is why it has a reputation for being a “dirty” engine, and the oil gets sooty so quickly.
But don’t let that worry you, it has been so since before Daimler sold the first one, and we still love them.

The hardest bit is actually avoiding a mistake when deciding which carburettor supplies which inner cylinder, at least it is for me.
Tim
Blue 1964 SP250 in Berkshire

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