10 replies to this topic

[CharlieNZ]

I got my '78 1275GT a couple of years ago, it came with a Weber DCD but I couldn't get it to pick up nicely, so replaced with a HIF44. I also put electronic ignition on it when I got it, Pertronix I think. A-series, not A+.

 

It has started running very rough recently. It starts easily, but only seems to be running on three most of the time.

 

When I take the plug leads off 1 and 4, revs drop and it's even lumpier. But when I do the same for 2 and 3 there's much less difference, if any.

 

I did a compression test and they are all pretty much the same, just below 180.

 

I've also tried swapping to an old distributor cap I had, and I've tried swapping leads around with zero effect.

 

Any suggestions on what I should try/test next? Would be really appreciated.

[Rapidmini59]

Hi dude
Start with the basics.
Have you tried new spark plugs? (as you could have a duff intermitent spark plug).

Do you have a healthy spark on each of the plugs?. Should be a nice blue colour.

How clean are the contact points in the distributor cap? Should be shiny and not have white deposits on them.

What condition is the end of the rotor in? It should be shiny? Being brass the contact end normaly gets black from dirt deposits.

Are you running a fuel pump,regulator and fuel filter? Are the filters for fuel clear of debris-it starts fine but lacks smooth pickup so could be debris in the filters- basically when you start the engine it has fuel in the carb, so will start fine but as you rev it movement of the debris could block the internal hole not allowing fuel to flow properly.

Keep me posted dude
Regards
Rapidmini59

[Alpenflitzer]

Troubleshooting   Backfiring and bad ignition

Possible causes:

 

1. The engine may be running too hot.
   The fix: Check and repair cooling system.
2. The fuel pressure regulator may be operating at low pressure.
   The fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
3. The ignition timing may be set wrong.
   The fix: Adjust ignition timing.
4. Ignition system problem.
   The fix: Check and –if necessary -replace distributor , ignition wires and spark plugs. Measure if ignition leads to the sparks if they have a more or less  equal resistance (Ohm)
5. The fuel filter may be partially clogged.
   The fuel pump may have a problem, the pump itself or the wires in the back are faulty.
6. Possible internal engine problems.
   The fix: Check compression to determine engine condition.

[Mark G]

Might be worth checking the intake manifold for leaks using starter fluid as well as all the above.

[CharlieNZ]

Thanks everyone, those are some really helpful comments. The contacts in the distributor cap and the on the rotor arm are clean.

 

There was a spark from 2 and 3, but not the same strength as from 1 and 4. At least, I seemed to get less of a jolt when I pulled the caps off those plugs compared to the others! I think plugs and leads need closer investigation.

 

The point about intake leaks is a good one - I guess it's possible that the intake gasket has failed.

 

I won't get to it until next week now but you've certainly given me something to think about

[panky]

Hate to say it but it's the same symptoms as when my head gasket went between cylinders 2 and 3

[CharlieNZ]

Hate to say it but it's the same symptoms as when my head gasket went between cylinders 2 and 3

That's why I did the compression test. Is it possible that it is still head gasket, even with the decent consistent figures I got?

[panky]

Oops sorry I missed that bit, if the gasket had failed then there would be a noticeable drop on one or more cylinders. Work your way through the other suggestions and you will nail it eventually.

[gazza82]

Is there play/sideways movement on the distributor shaft?

 

If you can swap out one lead and see if that improves things ... if you swap lead 2 with lead 4 for example does the spark on 4 drop? If it does it may be the leads or connections. If you have the carbon leads rather than copper, the carbon breaks up over time.

[CharlieNZ]

New leads and distributor cap clarified the situation. It started running very evenly, but only on 3. So I swapped the plugs for 2 and 3 around and the misfire moved with the plug. Bought new plugs but didn't have time to fit them as I had to pick up my daughter.

 

So it was a bad plug compounded with poor leads.

 

First suggestion in the first reply was bang on, thanks Rapidmini59! This forum really is the best...

[Rapidmini59]

Hi charlieNZ
Your most welcome.
Glad to help and wish you luck for the future of your mini hobby.
Regards
Rapidmini59