Lancia Motor Club

Model Technical and Interest => Fulvia => Topic started by: Spider2 on 08 May, 2021, 02:35:31 PM

Title: 3000 rpm misfire
Post by: Spider2 on 08 May, 2021, 02:35:31 PM
I only bought the 1.3s sport in September last year. There is an annoying misfire at 3,000-3,200 rpm some of the time.
It is like a complete nanosecond loss of ignition. It could be fuel but it is so quick to both come and go I suspect ignition.
It has a 123 electronic ignition system set to no2 position. This is correct as per the instructions for this engine. However, the max advance this curve gives is 14 degrees at 3,000. Firstly, 14 degrees seems low for such a revving  engine and 3000 rpm is rather coincidental with the when the misfire occurs.
Plugs, leads, coil, cap are all new.
Anyone had a similar problem. I will strip and clean the carbs eventually. (Solex) but perhaps it is a faulty distributor?
PS. If I drive it like it was designed and not go below 4,000 rpm the engine never misfires!! The engine is good, it just does not like this rpm.

Title: Re: 3000 rpm misfire
Post by: dhla40 on 09 May, 2021, 06:54:15 AM
If you want to experiment you could try curve 5. Using an adjustable timing light you can set 14 at 1000rpm and max 28 at 4000rpm, as with all adjustments make sure you do not have plnking under load but I find this setting makes the engine more responsive. You might also consider enlarging the idle jets by 5.


Title: Re: 3000 rpm misfire
Post by: lancialulu on 09 May, 2021, 10:42:08 AM
The standard distributor give 14 deg crankshaft  dynamic advance at about 3200 rpm (level after). So with 10 deg static this is a total of 24 deg. I suspect something with the 123 in all honesty.

Idle jets also smooth the transition from idle circuit to main jet, but this occurs lower down around 2000 rpm from my experience.

Is it a misfire (back fire) or misfire due to lean mix. If the latter then the carbs are suspect and a good ultrasonic clean is recommended.

Title: Re: 3000 rpm misfire
Post by: AndyT72 on 09 May, 2021, 12:35:31 PM
Hello Simon

I had this exact issue on my Fulvia, with the 123 ignition. It would cut out for a nanosecond, seemingly at random, but normally under some load.  Many an electrician could not fault (and pre-123 it would fry points and battery)...but a call to Huib diagnosed. The 123 has a self protecting element when a current spike is introduced...he suggested looking at the voltage regulator. Sure enough, this was erratic, allowing charge up to 16v if i recall.  May not be the same for you, but an easy check.  A new regulator has cured.

Hope this helps.


Title: Re: 3000 rpm misfire
Post by: Charles Frodsham on 09 May, 2021, 03:31:12 PM
I have been chasing a similar issue with a 123 ignition system on my Flaminia. The description is very similar, and always at almost exactly 3000rpm. I have the standard Dynamo/regulator. I have got to the point where I am considering fitting the old dizzy back!

Top tip Andy....I will look at the regulator!

Title: Re: 3000 rpm misfire
Post by: Spider2 on 10 May, 2021, 07:39:12 PM
Hi All
Thanks for all the responses I now have new areas to trouble shoot.
It is definitely a nanosecond miss. No backfire and no spit so I really think it is ignition. I suspect the problem has been with the car for some time. Although the PO said he never experienced it I first felt it on the drive back from the auction!
The bills for the previous 12 months are: Spark plugs, coil, Ht leads, fuel pump, cap, points and condenser for old dizzy and finally a 123. Looks like someone was fault finding a miss????
I will fiddle with timing and try advance curve 5 and report back. However, I like AndyT72ís suggestion of a rogue regulator, just the sort of thing that would be impossible to find unless one was in the know.

Title: Re: 3000 rpm misfire
Post by: dhla40 on 11 May, 2021, 06:28:21 AM
Another thing I have found is that the fulvia is quite sensitive to plug gap. If using standard plugs at 0.6mm try dropping to 0.5mm and see if any better.


Title: Re: 3000 rpm misfire
Post by: Spider2 on 11 May, 2021, 10:00:26 AM
Thanks DHLA. I will try all these possible remedies one by one to find the culprit

Title: Re: 3000 rpm misfire
Post by: Spider2 on 11 May, 2021, 06:38:06 PM
Hi all
Went for a good hard drive to day. Switched the 123 to position 5. It pinked quite badly undeterred load and was down on power. Changed the static from 10 degrees to I guess about 6 or 7 and it now runs beautifully. Revs well and NO miss. All in all a great result. Why it misses on setting 2 (the one it is supposed to be on) is a mystery.
Thanks for all your suggestions.

Title: Re: 3000 rpm misfire
Post by: dhla40 on 12 May, 2021, 07:44:17 AM
Good to hear car is now running well, the pinking you had is because curve 5 has 24 degrees dynamic advance so using 10 static would give 34 max advance. I use 4 static to give 14 at idle and 28 max and always use adjustable timing light to check.


Title: Re: 3000 rpm misfire
Post by: Spider2 on 12 May, 2021, 11:49:55 AM
Hi Sean
Do not have a strobe but I have 10 degree static marked with indelible pen on the base of the distributor so it is fairly easy to eyeball a couple of degrees.
Such a relief to have it running right, I was not looking forward to stripping the carbs.
Where are you? I am in Kent but my wife and I have a couple of trips planned this summer. Could be fun to meet up if you are not one of the couple of Lancia owners in Scotland.