316 "twitchy" problem

[Ilt17]

Hello all,

I own a '77 316 and am embarassed with a weird problem since last week-end. Being unable to find out myself what it's all about since 3 days, I might request your knowledge on E21 to get some clue :

- The motor starts and keep running, but the rpm counter "oscillates", isn't stable at all around 1000 rpm (-> ignition ?)
- Once on the road and giving gas, the motor starts to shut fastly, about 2-3 times per second, irregularly.
- There have been heavy smoke 2 times, but it's not recurring, doesn't happen everytime the motor runs.

I thought about the electrical fuel pump and put a new one, giving absolutely no changes. The original mechanical pump was still on the motor, also tried this one, but doesn't help.
I also replaced the coil, no changes either.
Unmouting the Delco shows nothing particular.
Might it be some dirt in the carburettor (Weber twin) arrived through fuel ?

I am a bit upset with this problem, and am in a big hurry for a TSD rally taking place this week-end.

If anyone has got a clue or already experienced this kind of problem, any help would be very much appreciated.



Thomas

[Jeroen]

I hope our carb specialist Peter pops by soon. To get some more info: did this start all of a sudden, or slowly built up? Any changes done, recently? Even a MOT with adjustment may have messed things up of course. Did you inspect the rubber gasket at the base of the carb (between carb and intake manifold)? Check by spraying some brake cleaner for example, also check on the gaskets from the manifold to the head. Engine keeps running on all 4 cylinders even when oscillating?

[Reck]

A couple of easy things to check...

Fuel filter clogged?

Dizzy rotor cap and/or arm worn out?

[Ilt17]

Hi Jeroen, Reck,

Well I learned some things meanwhile which could prove critical in this case, I got a call from my father who could have a closer look today at the car (I work far away from home during week unfortunately), I already knew that previous owners might have done some dodgy work under the bonnet but it might be more serious than expected...
So I learned today that I had an E30 electrical ignition, I don't know if my father knew it before but he didn't tell me anyway (and I'm still not really proficient to find this out myself, it was big surprise to me, shame on me haha). This would be fine if the control unit wasn't higgledy-piggledy connected, not in a reliable way, and was also exposed to water, oops. We had already seen and repaired a few cable connections which would have bring problems for sure, but still hadn't find out those ones.
So he managed to get a new one today and will install it correctly as soon as possible, we'll see if this solve the problem.
Otherwise, fuel filter is fine, carb rubber gasket is new and the car runs fine while stopped, giving big gas and the motor says how he likes it (well only with the rpm counter not stable at idle) only once the car is in motion, the previously described problems occur.
I hope this could be only an ignition unit and connections problem, which we could solve for this week end. We'll see when I get news from home and will let you know.

btw what is an MOT ? I had never read that.

Thanks for replies,

Thomas

[Jeroen]

MOT=keuring

keep us posted sir!

[stefankj]

Check your ground connections

[Ilt17]

Hi,

Yes, as Stefan just said, it might well be a ground connection problem. I just got reassuring news telling that with a new ignition control unit properly connected to ground all seems to work as properly, looking forward to give a long " " session friday to see if everything is now allright, I hope so but am confident.

I'll try to post the car in the owner's gallery next week.

Thanks again for replies,

Thomas

[Ilt17]

EPILOGUE : it was indeed the ignition unit which hads been badly linked to ground, now all is in order and I could run de 600 Km TSD rally last week-end without a single problem, fantastic.

Thank you for your replies,

Thomas