75 S to R Homage

[Bruce M]

Did you also swap the manifolds or just the carbs?

If a quick shot of ezi-start down that barrel gets it firing, then you know the is a fuel/air issue. Otherwise (considering the compression) it seem to be spark.

[haasad]

Hi yes, bought new manifolds , made flanges to close any poss air leak through old CIS notch and tried the easy start/ carb cleaner/ mapp gas tricks looking for leaks. I have just discovered that the 2 k resistance across the caps insn't repeatable consistently ...but on cylinders that are firing perfectly. I need to take alan uk up on his offer of some other beru caps to try on those . I make up my own leads from solid cored 7 mm wire never had an issue with them before and its all spotless with no sign of arcing. I'm pretty sure its sparks too though

[Alan @ CanfordClassics]

Hi Andy shall we arrange a time and we can pop over? Bob is down here a lot so I could also bring him. 3 heads better than one? I also have some new snap on equipment that could help?

Alan

[911hillclimber]

A bit of 'Bob' will do it I think.
If he visits, please pass my regards to him.

I moved the carbs and found the fault stayed with the cylinder, but I did not move the manifolds. My leak was on the head/manifold interfaces.....

Sounds like sparks to me.
You have changed the plugs? (or at least moved them to see if the fault follows the plug?'

I certainly know how 'distracting' this can be Andy. I spent 1.5 years with a 5.5/6 911 engine.

Look forward to hearing what the fault was as Bob will sniff it out. Doubt he needs anything from Snap On!

Graham.(with a hard to start 911 engine...you are not alone...)

[haasad]

Alan, that would be excellent I'll call you tommorrow, its a right pain.

Andy

[haasad]

Alan, that would be excellent I'll call you tommorrow, its a right pain.

Andy

[haasad]

An update...Less frustrated and tired I went through the cam timing ( just in case) and initially thought I'd made an error but both cams are within a knats of 5.4 mm lift. Next I carried out a simple pressurisation of the "problem" cylinder. I do get some audible leakage past the rings but they are not bedded in yet and I gave it 100 psi, the intake and exhaust are silent. So I'm confident in saying there are no mechanical issues especially given the excellent compression.

Next I removed all the plug caps and checked the lot for continuity and resistance. A new cap is continuous and gives about 2 k ohms resistance. I know this because I fitted two new caps to the "problem number 3 cylinder" and used them as reference. So I discovered of the 12 caps.. 5 had zero continuity......Not sure this is the main issue since I did have the new caps on no 3 cylinder. I'm now going to change all those caps and test the leads independantly . 1 step at a time .....

[911hillclimber]

Yep, change just one thing at a time if you can.
No valve hiss at 100 psi!
Good going. You are good at lapping then!
Look forward to you spotting the solution.
Keep at it!
G.

[haasad]

So new caps all round, new leads too with more "period" end caps to the dizzy. I also pressure tested the inlet manifold to head with a sneaky little tool I made and a pushbike track pump...pics later...Ran it up .....lazy number 3.....So decided to say sod it and drove it 10 miles to the garage for fuel . Its certainly got 6 under load. I think I may have the wrong plug ratings NGK BPR6ES ...What are others using ? These may be too hot and constantly fouling ...its a possibility?

[haasad]

So new caps all round, new leads too with more "period" end caps to the dizzy. I also pressure tested the inlet manifold to head with a sneaky little tool I made and a pushbike track pump...pics later...Ran it up .....lazy number 3.....So decided to say sod it and drove it 10 miles to the garage for fuel . Its certainly got 6 under load. I think I may have the wrong plug ratings NGK BPR6ES ...What are others using ? These may be too hot and constantly fouling ...its a possibility?

[haasad]

double post

[911hillclimber]

I went through 3 grades of plugs and the best ones were those used as stock 3.2!

If the grade was wrong then other plugs would go foul too?

If you think this is so, move #3 plug(s) to the other side of the engine and see if # 3 is still out.
When you say # 3 is out do you mean the exhaust outlet is stone cold compared to the other hot 5, or is it partly running?

6 cylinders under load? Could it be timing, but I would have thought fuel as a lot is going in under load?
Have you had a colour tune on # 3 at tick-over? black is no combustion, yellow is too rich. The correct petrol-blue burn is quite hard to achieve. Not much difference between all 3 states.

One factor that woke my lazy cylinder up was the points being too small a gap, 8 thou and not 16.
I'm sure you have done all that.

What about running the engine as a 6 plug engine then if on 5 try the other 6.
If 3 is totally lazy then both leads have to be duff, not likely I would have thought.

If it is any compensation, I've had a frustrating day with domestic appliances, new showers that are unstable delivering warm water....

[haasad]

I'm pretty sure its running at least when loaded but not as hot as the others. The headers are wrapped so color up when hot, no3 is still very white compared to the brown others, also if its just been ticking over I can hold no 3 header comfortably.. It is running too fat all round at low rpm and with typical plug fouling. I noticed I have R resistor plugs today I'll change then out for a set of BP5ES . I've done all the lead swapping etc . An annoying thing is that the motor is dry... well except for the rear crankshaft oil seal which has sprung a leak...have a good weekend with the DIY...

I'm off to Thruxton for the HSCC meeting

[911hillclimber]

I'm off to Thruxton for the HSCC meeting

That's unfair!

My #6 problem was cool rather than cold or hot compared to the other 5.
All plugs are black now when idling for some time, so rich on tick-over possibly right at speed.

Plugs come out of the 911's 3.2 a perfect light biscuit, but it has done 120K miles or so and never been remotely apart other than plugs, a dizzy cap, valve clearance check this Xmas (all were 4 thou...) and the alternator.
What an engine, but on stock Bosche ECU etc.

Enjoy the roundy stuff, too far to travel this weekend.

[haasad]

MOT passed...... first time no issues......... The car is booked for an ignition and carb tune on 20th of this month...can't wait. Sadly won't make the great unveiling but hope to show the thing in the flesh to some of you at the various events going forward this year.....Hopefully we'll get some decent weather soon

Can't believe this thread is finally drawing to a close