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Stuttering under load

PostPosted: Wed Sep 11, 2019 10:19 am
by andyhay
Hi all

My plus 2 had some work done recently and wasn’t used for 2-3 months. Now I have it back it is stuttering under load from 4000 rpm and beyond. I changed the spark plugs ( the old ones were black when removed) and now the stuttering starts at 5500 rpm. Otherwise the car is driving perfectly. Could it be the coil on the way out? The car has electronic ignition and has a Bosch MEC 717. The only other thing I’ve noticed that has changed recently is the ignition light is coming on more than it used to. It comes on at idle and I don’t think it did that previously.

Any suggestions for possible causes would be much appreciated.

Thanks

Andy

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 10:44 am
by 69S4
Last time I had similar symptoms it was the rotor arm playing up.

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 10:58 am
by types26/36
andyhay wrote:My plus 2 had some work done recently and wasn’t used for 2-3 months
Andy

Have you used fresh petrol as fuel does degrade with time.

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 11:22 am
by andyhay
Yes - have refilled with fresh fuel. That was my first thought. Have also done around 100 km and problem persists.

Andy

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 2:10 pm
by grassyknoll
Dirt in the fuel filters?

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 4:12 pm
by Matt Elan
What plugs are you using? I'm currently using NGK B7ES in my Plus 2 with Vegantune'd engine. It was originally on B6ES, which caused poor starting and various misfires depending on use, and would foul at low revs and when cold. With the slightly hotter 7s the car was transformed, revving cleanly from cold and behaving itself hot or cold. Also don't buy cheap plugs from popular internet sites - there are a lot of counterfeits out there which are rubbish. Buy them from a reputable source....

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 5:13 pm
by types26/36
Matt Elan wrote: I'm currently using NGK B7ES in my Plus 2 with Vegantune'd engine. It was originally on B6ES, With the slightly hotter 7s the car was transformed,.

Matt,
I think you have that slightly wrong, with NGK plugs the higher the number ......the colder the plug.
Champion plug numbers work the other way round.

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 10:49 pm
by andyhay
Thanks all for the suggestions

Plugs are new NGK B6ES

I suspect not dirt in the fuel filters because it improved with new spark plugs - still a possibility .

Could be the Rotor Arm - Is this straightforward to inspect or one for the experts?

Regards

Andy

Re: Stuttering under load

PostPosted: Wed Sep 11, 2019 11:32 pm
by SENC
andyhay wrote:Thanks all for the suggestions

Plugs are new NGK B6ES

I suspect not dirt in the fuel filters because it improved with new spark plugs - still a possibility .

Could be the Rotor Arm - Is this straightforward to inspect or one for the experts?

Regards

Andy


Get a good quality one not a cheapo...
http://www.distributordoctor.com/red-rotor-arms.html

Re: Stuttering under load

PostPosted: Thu Sep 12, 2019 8:04 am
by grassyknoll
I had a stumble and poor running at higher revs recently, it was a faulty fuel regulator, I wasnt getting enough fuel due to low/fluctuating pressure, would run fine pootling around, only a problem when running over 5000 rpm.

That said, I changed plugs to a spare set of iridium, expecting it to be a disaster only to find perfect starting, so spark is just as valid a point...

As always with lovely older cars, probably a combination of many things, fustrating when you fix it but can't put your finger on exactly why !
So many variables !

Re: Stuttering under load

PostPosted: Thu Sep 12, 2019 11:54 am
by denicholls2
5,000 RPM is a bit high, but 4,000 is likely within the progression region of the Webers. I'd start by making sure the jets are clean based on my experience with lean stumble on this region on my Europa.

In my case, the symptom was stuttering at a steady state 65-70 mph in high gear. Step on it and it goes away (because you're no longer in progression then.) I went to richer jets, but in your case if it used to run fine they may just be gummed up.

Modern fuel is a handful. It is definitely NOT the improved model, and most of its ill manners manifest after sitting. Varnish builds up through evaporation at a pretty amazing rate.

Re: Stuttering under load

PostPosted: Thu Sep 12, 2019 12:04 pm
by Grizzly
I actually run NGK BP5ES 's in my 2 seater, i don't drive it aggressively so the 5's stop the plugs carboning up and they last two or three times longer than 7's. For me i know my afr is in the right ball park so i just kept going for a hotter until the colour of the plug went a nice light tan (the difference in smoothness when cruising is profound when you have the right temp plugs in) if you have too cold a plug you get soot on it even if the afr is good.