Your thoughts on a random misfire.

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mark rudder
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Your thoughts on a random misfire.

Post by mark rudder » Fri Aug 16, 2019 3:27 am

Hi all,

My Australian based GTE 6B is playing games. On cold startup it fires instantly, but often only runs on 5 cylinders.
Most times the other one comes in after 30 seconds or so & then all's good for the day.
But (there's always a but) on the odd occasion it doesn't come in. I have pulled the plugs & one random cylinder is
showing & smelling petrol wet. The problem shows on any cylinder on either bank. It has also had carbon fouled random
plugs cleaning them fixes them. My starting (cold ) procedure is half choke, 4-6 pumps turn key &, no accelerator
it runs, sometimes on 6 cyls!
Facts:
Standard Cologne, with good even compression, standard exhaust.
Weber DGAS, serviced, manual choke.
Lifters adjusted. Uses little oil. No oil on any plug.
Correct heat range plugs under 1000k's old (NGK BPR7ES).
When removed after an expressway run they indicate a little on the hot side still.
Good leads.
Factory Weber correct air cleaner.
9 degrees timing (on light)
Happy hot idle at 800 rpm.
Manual O/D box.
Uses no water, doesn't over heat.
Can occur one day or one week since last used.
Car is garaged.

It's REALLY annoying me. I even have a 7th plug to speed the changeover process.
If someone has an idea it's most welcome, I have pondered that I'm partly flooding it.


Mark from down under.
Current GTE 6B, Dolomite Sprint, Scirocco R. Past XJS (manual), V12 E-type (manual, convertible, lovely) 350 chev XJ6, TR6, TR4, Sprite, Midget, local Ford V8s, others... There's a pattern here.….

rebel alliance
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Your thoughts on a random misfire.

Post by rebel alliance » Fri Aug 16, 2019 6:26 am

Manual choke , why the six pumps ? Likely your flooding the engine before it even starts plus your washing the oil off the bores..i just give mine full choke turn the key till it starts then leave it on half choke till warm never touch the throttle



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Your thoughts on a random misfire.

Post by TrevorG » Fri Aug 16, 2019 9:48 am

Agree with reb, but the other first check......are you putting the plugs back in the same bore they came out? If not, could it be that simple? A plug breaking down....not in the normal way, but insulator giving up. Had it happen on the race bikes....difficult to start, but once hot it reseals and comes alive....bit like two stroke fouling.



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Your thoughts on a random misfire.

Post by DARK STAR » Sat Aug 17, 2019 8:37 pm

DGAS is auto choke, it needs ONE pump to pull the throttle linkage off the choke step (if you see what I mean, sorry, I can't think in english any more).
Did the factory really fit Webers to the 2,8, I thought they all had Pierburgs originally?
As Trevor says, verify if it is that same plug which is wet even if isn't the same cylinder.


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Post by rebel alliance » Sat Aug 17, 2019 9:41 pm

Can be Auto or Manual choke...this one is manual,no not factory fit on a 2.8 that was some other cheap carb



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Post by AJL Electronics » Sat Aug 17, 2019 9:43 pm

The factory method of starting is two pumps. It sets the autochoke and puts some neat fuel into the manifold. Six pumps is going to put far more than required, but it shouldn't cause a cold engine to flood.

I always fit BPR6ES plugs, so I be.ieve you have the wrong ones. Can't recall which way the heat designations run, but it could be that you are under heating the plugs which is why they are fouling.


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Post by DARK STAR » Sat Aug 17, 2019 10:02 pm

DGMS then :mrgreen:
Not sure Pierburgs were cheap, the service kits cost a fortune.
And are necessary.
They are certainly not the same quality as a Weber.


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Post by rebel alliance » Sat Aug 17, 2019 10:07 pm

He has a manual choke !...therefore not really any pumping required is there ?



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Post by mark rudder » Sun Aug 18, 2019 11:52 am

Hi all again.
TrevorG, wish it was that simple, the problem doesn't follow a plug movement.
AJL, the car had those plugs in it when purchased, it was running-on & they were heat stressed.
Counter intuitive to me but NGK's go colder as numbers go up, 7's recommended in the paperwork.
The Weber was retro fitted by a previous owner. Tried the starting methods suggested, they make
sense, started straight away, twice, still with a misfire that cleared within 30 seconds.
Thanks for the advice so far, anything else welcomed.


Mark from down under.
Current GTE 6B, Dolomite Sprint, Scirocco R. Past XJS (manual), V12 E-type (manual, convertible, lovely) 350 chev XJ6, TR6, TR4, Sprite, Midget, local Ford V8s, others... There's a pattern here.….

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Your thoughts on a random misfire.

Post by AJL Electronics » Sun Aug 18, 2019 6:18 pm

rebel alliance wrote:
Sat Aug 17, 2019 10:07 pm
He has a manual choke !...therefore not really any pumping required is there ?
So how does neat fuel get into the inlet manifold before cranking otherwise?


Yes, we can mend your Scimitar!
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