Special getting closer...

[911hillclimber]

I'm not having much luck with all this am I?

Started the engine about an hour ago.

Started after the pump had filled the floats and eventually fired.

Guess what?

It has the bangs and pops back.
Cannot believe it.

Shelsley Walsh will be run in my very trusty 911. Mind you, any hillclimb in the wet in the Lola is a bit miserable, so not too sorry.

So: Where are we with all this?

The PMO's are a very nice bit of kit, and I have no regrets at all buying them. They are v nice.

The tweeks I've made to the car this week are similarly good, just WHY are the bangs back.

I must now think the engine or one cylinder is fooked.

My plan is to pop the lower rocker cover off tomorrow and check the vale clearances incase one is tight (clutching at straws) and then a leak-down test.
I will also book the car into HiTech for a roller session as Mick sorted the webers.

I am getting 6'' blue flames from the same engine side as before. Totally different carbs in fab condition and here I am again. Must be the engine.

[markmws]

Really sorry to hear that Graham- I can imagine how frustrated you must feeling right now

I fitted your old Webers to my 914/6 tonight , and had I had a charged battery to hand , would have tried firing it up

Hopefully I will get it running tomorrow , and let you know how they perform on my engine - might possibly give some clues as to your problem ??

Good luck in the 911- as you say , at least you'll be dry (er) !!

Mark

[jwhillracer]

Hi Graham,

What a pain! But logically, the trip to the rolling road sorted your problem last time, and didn't pick up any engine problems. If the problems then were deeper than carburation, tuning the carbs wouldn't have solved it. Presumably the only thing you have changed is the carbs, so hopefully another RR session will get you sorted.

Best of luck,

Jonathan

[MikeB]

Just to be clear, Graham, flames and pops out of the exhaust or the carb ?

[911hillclimber]

It is all out of the exhaust.
The induction side sound fab, really good, not a spit in the air.

The PMO's are much better made than i thought (these are the first ones I've ever actually seen)

When it fired I accidentally gave the connecting bar a bit of a stab down, about 1/3 throttle and the engine sure does pick up. This has obviously freed the induction over the 40's.

Isn't it simply very odd that totally different carbs and the return of the issue on the very same side?

I hope you are right Jonathan, but somehow i suspect the engine is done for on one cylinder, BUT, if there was a bent valve ot whatever the thing would not run as smoothly as it does, rev so freely etc?

On tick-over you can feel the hit-n-miss fireing with your (gloved) hand close to the silencer outlets. The other (good) side is even and you can feel the regular firing beat. The other is missing a beat randomly.

It gets worse as it warms. (just as before)

Mike:

I was told by another 911 owner (2 litreS) that he had the same prob as those webers (2 dead chokes at tickover).
He tracked it down to a lead blanking slug missing in one of the float chambers. There is a cross-drilling that is blanked off using a lead slug. It then allows the fuel to follow the least line of resistance to the one float chamber. Might be the same or a red herring.



Certainly testing my determination now this car.

I really wonder why I bothered, I really do.

[MikeB]

If you stick a syncrometer on the 3 inlets on the side that is popping you might see which barrel is missing.

You have to start suspecting an exhaust valve all the same, sorry that your probs are continuing Graham.

Mine did 100yds in the first sprint (luckily there was an expert witness on hand to confirm I wasn't abusing it !!), discovered a loose rocker and a worn exhaust lobe, just bolting it all back up again with a replacement cam, so you're not alone.

[911hillclimber]

bloody cars.

The webers had 2 dead chokes on tick-over/slow speed circuit.
The two plugs on the one bank were dry, so no fuel.

These PMO's are perfect condition, like new so there are no probs there, the 3 plugs on the offending side are all firing as deposits are on the plugs.

How can the prob come back with a carb change yet the rolling road man dialed the bangs out on the carbs, BUT they were returning at Prescott!

Just maybe a valve is tight and is being held off enough to allow the firing stroke to get out and into the headers every now and then.

Perplexing.

[Gary71]

Graham,
I've been trying to dial out some running issues on my car recently, popping, banging and a partial misfire at low revs/throttle openings.

To try and narrow it down I pulled the plug leads off in turn whilst it was running and found that the spitting back through the carb was primarily from no. 5 cylinder as it stopped when I disconnected that lead. Clearly it was then missing, but no more noise.

I am starting to suspect valve seating as well, but spent some time playing with the idle mixture screw on that cylinder.

Winding it in (lean) eventually made it pop out of the exhaust, winding it back out made it spit through the carb. I eventually found a position where it did neither, 1/4 turn either way would change it.

Now it runs much cleaner and doesn't spit, but the setting for that cylinder is totally different from the others so I feel I'm masking some other issue by changing the mixture.

Maybe this is how it was dialled out on the rollers, but is now back with a new (and evenly set) pair of carbs?

Just my thoughts for the morning!

[911hillclimber]

Thanks for this insight Gary.

It sounds the way to go.
I'll get the 911 redy for the race and have a go at the mixture after finding which cylinder is the offending blight'a!

Mike how has my old webers is bolting them to his 911 engine and if that runs right then it is clearly the engine and i think a valve.

Sure hope the heads don't have to come off.

[Gary71]

a bent valve ot whatever the thing would not run as smoothly as it does, rev so freely etc?

Glenn75s engine had half a dozen bent valves when he finally stripped it trying to get to the bottom of why it wouldn't idle properly, it ran pretty much ok at higher revs. As does mine...

I really wonder why I bothered, I really do.

...because it's a great idea and looks bloody fantastic!

[chris68]

Just a thought, have you compared compression test figures of each cylinder? It would show up any cylinder with a bent valve that wasn't seating properly.

I wondered also if it could be a cam timing issue but that would affect the whole bank. Could it be a faulty spark plug or lead? Are you running with a CDI system? Does the problem dissappear with conventional coil, points and condenser. Is it worth double checking plug gaps and checking for signs of tracking? Sorry if I'm suggesting stuff you've already considered.

I've just been going through the process of jetting, swopping bushes and adjusting the webers on my 2.0S motor (after rebuilding it). Thought I was going mad chasing my tail for a while, but it's running ok now. I'm not quite in your league but happy to lend a hand, bounce ideas if ever you need it.

Stick at it, if it were easy everyone would be doing it!

Regards,
Chris (Lichfield / Burton area)

[911hillclimber]

Another afternoon chasing ghosts on this thing.

followed Gary's ideas.
1
With the engine stone cold, I dropped the exhaust side cover off and checked the valve clearances. All @ perfect setting (I have one of those special curled feeler gauges)
Started it.
Removed each lead off the 6,5,4 cylinders and it seemed to go away with 4 off...so put my spare lead in. Bangs as usual.
Now quite warm i took the 456 plugs out (again!) and 4&5 were 'cold' and 6 was 'hot'! Ah! no sparks on those then?

4 and 5 cannot have been firing? No signs of deposits etc either.

Changed the cap and rotor to the ones that came with the engine. (other ones are new). Pops and bangs galore.

Removed the plugs...and all 3 are hot!

Did Gary's plug-off trick and removing any of them made zero difference, bangs galore no matter what.

could this be the electronic ignition (new from Aldon)is not triggering?

So, closed the garage door and came up here to type this.
Utterly naffed off and a perfect finish to a really cr&p week at work!

This engine ran points in this dizzy. I have the bits and a capacitor, and I'm very very tempted to re-fit them and see what happens.

A compression test is needed next incase the/a valve is bent but the clearance is correct, but somehow i find it hard to accept it is something like this. Also, i think the cam on this 4/5/6 side must be ok as the last power run @ 234 bhp on 40's is not too bad?
Additionally, Terry who last ran the engine is arrow straight and would have told me if there had been an incident with the engine.

Chris: thank you for the suggestions!

So:

Points, and if no different Aldon bits back in and:
Rolling Road at Hi-Tech in 2 weeks time and hopefully Loton Park hillclimb.

The 911 is all ready to give the usual service.

Gary:

This Frankenstien of a car is a joke next to the 911, and it will take a lot for me to connect to it now.

Just so bloody dissapointing and embarrassing too.

[MikeB]

Graham,

Have you followed the PMO set up guide ?

If you got the engine from Terry, and it ran correctly for him, then you can assume that the cam timing is correct.

So if you have spent the time sorting out the carbs as PMO suggest, and the engine hasn't been tampered with, then it I'd tend it to be a valve issue.

[911hillclimber]

PMo set=up guide?

Never knew there was one.

Will take a look.

I'll have to make a leak-down tester, spark plug/tube/welder/pipe/40psi in a spare wheel!

and have a listen....

[MikeB]

Look in the Support section on the PMO site