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S1 rear cyclinder missfiring when cold
https://ukbeg.com/forum/viewtopic.php?f=8&t=20847		 Page 1 of 1
Author:  jelly9 [ 16 Oct 2015 14:05 ]
Post subject:  S1 rear cyclinder missfiring when cold
Hi All,

My S1 is misfiring only on the rear cylinder when cold, once its warmed up there is no misfiring and it runs great?

Work done so far:

1.Test: idles with just the front plug lead connected and revs, but died when i did the same test on the rear cylinder.

2. New plugs : Fault still there.

3. New plug leads : a little better but fault still there.

4. Checked the coil and its inside spec just. coil measured Primary at 3.0 for, should be with in 2.5-3.1. and Secondary was just over 10,200 should be with in 10,000 - 12,500.

Looking at changing the coil next but before i do is there any think less i should check for ?

thanks for any help.
Author:  pash [ 16 Oct 2015 15:35 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
Where are you?

I can lend you a coil to try.

But the wasted spark system is shared between the cylinders so if one cylinder sparks, the other should. The none common elements are:

* upstream of the cam positioning sensor, and this is the rotor cut outs
* downstream of the spark, and this is your non-common mechanicals (carb and inlet are shared)

Is the CPS rotor damaged?
Have you dropped a valve?
Have you broken a ring?
Have you scuffed the piston and welded the rings in?
Is the exhaust header broken on the rear cylinder?
Is the exhaust gasket 'no more'?

I'm sure :maz: will know what the cause is...
Author:  jelly9 [ 16 Oct 2015 15:59 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
Thanks for the info. i'm in poole Dorset but now i'm thinking the coil is OK

Is the CPS rotor damaged? : looks OK

Have you dropped a valve? : No runs fine once its warm

Have you broken a ring? : Maybe

Have you scuffed the piston and welded the rings in? : Maybe

Is the exhaust header broken on the rear cylinder? : Looks OK

Is the exhaust gasket 'no more'? : They should be OK only just changed them 100 miles or so ago.


Going to check the plug gaps tonight as I've over looked this, as it's a resistive system I'm thinking if the gap is to big on the rear, the overall resistance on the rear will be higher and the wild spark system may just default to the front as the resistance will be less.
Author:  jelly9 [ 20 Oct 2015 11:18 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
Decreased the plug gap on the rear head and its working fine, but now the rear plug gap is under the book spec?

Weird, does this point to a problem somewhere else? :askmaz:
Author:  pash [ 20 Oct 2015 11:31 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
Points to a dielectric strength issue.

Paschen's Law shows that the breakdown voltage requirement is higher with:
* increased air gap
* increased pressure
* lower temperature

And you have confirmed this:
* reduction in air gap gets rid of the misfire
* it misfires on the rear when it sparks on the compression stroke
* only misfires when cold
Author:  rik [ 20 Oct 2015 11:49 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
Go 'single-fire', 'wasted-spark' is a nonsense. :old:
Author:  pash [ 20 Oct 2015 12:33 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
rik wrote:
Go 'single-fire', 'wasted-spark' is a nonsense. :old:

What single fire do you have Rik?
Author:  rik [ 20 Oct 2015 13:30 ]
Post subject:  Re: S1 rear cyclinder missfiring when cold
pash wrote:
rik wrote:
Go 'single-fire', 'wasted-spark' is a nonsense. :old:

What single fire do you have Rik?

Crane FireBall Hi-4 Powerlink :mrgreen:
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