It started with a pop

For you flat four Porsche 912 fanatics

Moderators: Miggs, KS

User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

Thanks to Matt for his helpful explanation and PMs.

To answer your questions which may help others.

'What does your afr and colortune tell you?' - If I set the AFR much above 15:1 with the Knecht air filter boxes off, the car does pop back through the carbs. The colortune shows the combustion going off blue to more of a white colour - so this seems to confirm.

I set the AFR to about 14:1 without the Knecht air filter boxes and the car rarely pops - so that seems the max I can tolerate at idle.
At this setting the idle is very stable and can be set to a steady 900rpm quite easily.
However with this setting once the Knechts go back on the AFR drops to around 12.5 to 13:1 - which feels a bit rich to me at idle.
It still idles well with them on but obviously the rpm rises so I need to adjust it back down a little.
This is a little problematic as at this point you can't tell whether the carbs are still balanced side to side ( unless I remove the air filters again to check ).

So the Knechts richen things up significantly on fitment.
At this point the colortune is more blue than white, and my Gunson gaster gives me around 5% or so CO.

I think my plan is to tune the AFR closer to 14:1 with the Knechts on, and then monitor the AFR under different conditions on a run.

Should I be able to buy any petrol any time soon, I will let you know how I get on.
If I can't buy any more fuel then its all a little bit academic :wink:

Thanks again
Andrew
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
neilbardsley
Nurse, I think I need some assistance
Posts: 7690
Joined: Mon Apr 16, 2012 4:31 pm

Re: It started with a pop

Post by neilbardsley »

According to this your aim is about right for 10% ethonal. However, when I had my 356 RR Ben didn't use afr at idle because he said the engine wasn't blowing hard enough. Sorry I can't remember what he used

Image

Sent from my M2004J19C using Tapatalk
“A REMINDER. I would be grateful if those members who have borrowed bits from me in emergencies (e.g starter motor, oil cooler, etc) would return them and/or contact me”. – Chris Turner RIP
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

Hi Neil,

thanks for info.

My plan is to try and use Esso Synergy 99+ E0 going forward but set it on the safe side of E0 in case I do need to use a mix of E10 in the near future.
If I have to move entirely to E10 use I will go around the buoy again, but expect to do that again in a few more hundreds of miles as the rebuild settles in.

Garages don't tend to be able to get accurate AFR readings at idle from a probe due to the air contamination due to the light exhaust load.
If you stuff a rag in the exhaust also you get a better reading but generally still a bit on the lean side.

I have fitted a O2 sensor bung at the exhaust elbow and the readings seem stable and accurate against a CO gauge - so hopefully I can set it more accurately.

The issue is finding somewhere to start and then see what AFRs I get at all other operating conditions and iterate to best compromise.

Just need to find some time and fuel to proceed. :)
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

During the week or so of madness when petrol seemed to be unobtanium, I managed to make some more tweaks.

Firstly I reset my float levels to nominally 57-58mm as per Matts suggestion.
I also bought some replacement nitrile rubber square section to replace the seals on my air base plates that had gone rock hard with time.
I found 5.5mm square seemed to work well.

My airboxes had always had their gaskets missing - it hadn't really bothered me as they only seem to seal air on the outside of the air filter.
Regardless the replacement seals are now available but seem expensive, so again I made new ones from nitrile section.
At this point I noticed that as my air boxes were being tightened directly onto the filters, the metal section of the air filters had slightly deformed from many attempts at tightening.

I ordered some new Mann filters to replace my old Meyle ones.
Image

Interestingly the Manns ones have a metal insert on both sides of the paper element - so arguably better made.
Whether they are quite as free flowing that might be a different matter.
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

Today I was finally able to take the car out for some runs to check the AFR in different scenarios.
Image

The plan was to perform a few runs changing some of the jetting to see what worked best.
I had ordered some larger idle jets a while back so started with those 60s fitted.

Firstly I took the car out with my Innovate LM2 running whilst filming the gauge and tacho in case I needed to review it.
The first impressions was that the car ran really well although my warm idle was a little high.
During 1500-3000rpm there was still a small hesitation at times , but much better than my previous runs, so am thinking the float level is much happier.

Interestingly during the points were it hesitates a bit the AFR was too rich 10.5:1 and lower ( I was expecting the opposite ).

I brought the car back and swapped the idle jets back to the more standard 57.5.
This has improved matters although there are still times when it hesitates ( although less noticeable ).
To be fair I think this is the best I have ever had the car running.

As I was driving around, I noticed the AFR start to climb followed by a smell of fuel.
Soon the car wasn't running on all cylinders and I had to pull over.

It took me a while to realise but the newly rebuilt fuel pump had decided to develop a fault.
Luckily as I have a hand prime bulb fitted I was able to refill the float bowls which allowed me to drive a further 300 yards.
A few stops for manual fuel pumping and I finally got home!

Oh well something else to investigate - but I think I am getting closer to getting the jetting correct.
If anything when the car is at WOT the AFR could be a little richer and closer to 12.5:1
I think the idle circuit is possibly a little rich with part throttle dropping me below 12:1.

Once I have investigated and fixed the fuel pump ( I could always put my old one back on ), I'll try to dial it in a little better.
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
hot66
Moderator
Posts: 18221
Joined: Tue Nov 11, 2003 4:17 pm
Location: North Yorkshire

Re: It started with a pop

Post by hot66 »

I have duel lambda / afr readout.. they’re great for this kind of stuff. What afr are you aiming for at the top end of the revs/ load ?
James

1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster

Its not how fast you go, but how you go fast ;)
RobFrost
Put a fork in me, I'm done!
Posts: 1917
Joined: Thu Jul 08, 2021 8:18 am
Location: Lichfield

Re: It started with a pop

Post by RobFrost »

AndrewSlater wrote:During the week or so of madness when petrol seemed to be unobtanium, I managed to make some more tweaks.

Firstly I reset my float levels to nominally 57-58mm as per Matts suggestion.
I also bought some replacement nitrile rubber square section to replace the seals on my air base plates that had gone rock hard with time.
I found 5.5mm square seemed to work well.

My airboxes had always had their gaskets missing - it hadn't really bothered me as they only seem to seal air on the outside of the air filter.
Regardless the replacement seals are now available but seem expensive, so again I made new ones from nitrile section.
At this point I noticed that as my air boxes were being tightened directly onto the filters, the metal section of the air filters had slightly deformed from many attempts at tightening.

I ordered some new Mann filters to replace my old Meyle ones.
Image

Interestingly the Manns ones have a metal insert on both sides of the paper element - so arguably better made.
Whether they are quite as free flowing that might be a different matter.
You can judge how free flowing they are by how little they richen the mix.

Sent from my SM-G988B using Tapatalk
1970 911T, Signal orange (Restoration thread)
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

RobFrost wrote:You can judge how free flowing they are by how little they richen the mix.
Yes the combination of Mahles/Knecht airbox always richened the AFR up quite a bit.
The car would idle quite nicely with them on but would always spit and pop a lot more with them off.

Counterintuitively the Manns seem to be better flowing ( they don't look like they should be ).
hot66 wrote:I have duel lambda / afr readout.. they’re great for this kind of stuff. What afr are you aiming for at the top end of the revs/ load ?
I though at the top end I would want to shoot for around 12:1 AFR, but under full WOT I seem to be more 12.5 to 13.5 so possibly not quite making full power.
More interestingly is that from WOT to lift off/coast the AFR increases to 18:1+, so not sure if this is a problem or not.

Looking at the distribution of AFR across 13 minutes or so of varied traffic I get this distribution.

Image
I would say the majority of the sub 11:1 AFR readings are at partial throttle 1500-3000rpm.
The majority of 15:1+ readings are on lift off / coast.

I'm wondering if the spread is a little wide or not.
In order to reduce the spread I'm thinking I could try dropping the idle jets from 57.5 to 55, and increase the mains from 122.5 to 130.

To be fair I don't think the numbers are that bad and the car drives really well ( well it did until the fuel pump died ) but feel there is always scope for some more improvement.

Any suggestions before I try again are much appreciated.
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
hot66
Moderator
Posts: 18221
Joined: Tue Nov 11, 2003 4:17 pm
Location: North Yorkshire

Re: It started with a pop

Post by hot66 »

im not sure what the ideal is for the carb'd 4 pots .. but with my MFI I'm aiming for about 13.5 AFR at full load / 7000 rpm. On the engine dyno my afr plot for 1800- 6500rpm starts around 11.5 through to 12.8 as the revs rise ( this was a BS motorsport graph when tuned on teh dyno for max safe horsepower ). I have an idle too rich though as its in teh 10's

I'm currently trying to get to the bottom of a problem where mine starts going lean around 7100 rpm ( goes to 14 for soem reason ) so have spent a few hours now watching my afr meters as I 'tune' it up and down a local road I have.

Point being, you seem to be aiming slightly richer than me ? At my afr levels it still smells fumey
James

1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster

Its not how fast you go, but how you go fast ;)
RobFrost
Put a fork in me, I'm done!
Posts: 1917
Joined: Thu Jul 08, 2021 8:18 am
Location: Lichfield

Re: It started with a pop

Post by RobFrost »

AndrewSlater wrote: More interestingly is that from WOT to lift off/coast the AFR increases to 18:1+, so not sure if this is a problem or not.
Assuming you're on Webers, all I can add is to make sure you get some good long readings at constant throttle, constant revs, so that you can isolate the jets from the effects of the enrichment pump.
1970 911T, Signal orange (Restoration thread)
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

I have to admit I'm no expert at this, but would expect that you want to aim for 12.6:1 for max power at WOT.
With an E5 fuel that 12.6 is probably slightly lower again.

My car is running original Solex solid shafts, with standard jetting other than the mains and idle jets that I am playing with.

Rob is right in that it is good to be able to separate your AFR data out against conditions.
I had videoed my runs but found that with the bright sunlight it was difficult to see the AFR readings at times.
I could try to log RPM from the LM2 but I've experimented with this before and its pretty flaky on RPM.


As for the fuel pump, the central rivet across the diaphragm appears to have failed.
That would explain a lot, as the fuel would not maintain sufficient pressure but did start to pump fuel across the diaphragm through the rivet hole, which I could smell.

Image
Have already sent an email to Roger Bray letting them know of the failure on the rebuild kit - see how I get on.
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

Fair play to Roger Bray - had a prompt email response thanking me for the feedback. They sell lots of these kits and say this is the first failure they have heard of. A new kit will be in the post today - so add that to the jobs list.
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

One of the other tasks I undertook whilst awaiting fuel was investigating my shock absorber setup.
I'd watched a video of someone installing Koni Classic shocks to his '67 911 and was surprised when he claimed they were supplied with the incorrect bump stops for the SWB cars. Apparently the rears are supplied with an 9 bump stack but that SWB cars should only have 8 fitted, the later LWB cars take 8.

This made me wonder whether my Koni Classics were correctly installed.
I'd always felt that if I hit a pot hole or speed bump the car would jolt more than I would expect - maybe this could be the reason.

Another thing I had read was that the shocks aren't always supplied with the rebound setting the same.
Must admit, I'd never checked the number of bump stops or how the rebound was set, I'd just fit them as supplied :roll: .

So whilst the carbs were off the and the rear suspension readily accessible I dropped one of the rear shocks.
Bump stops = 9 - bugger!
Rebound setting checked - fully soft - that's good.

Quite a bit of the bump stop rubber had found its way onto the piston of the insert so I am guessing I had hit the bump stop on quite a few occasions.
I find it quite annoy that a set of shocks bought specifically for a SWB car were supplied with no notes suggestion that they need to be modified.

Image

So I hack sawed off a bump stop, and then repeated on the other side.

Now as I have also lowered my car an inch or so from standard height I expect that I had even less play on my bump stops.

Deciding that this was a good find, I decided to check the front rebound setting and bump stop scenario.
At the fronts the standard bump stop was fitted along with the extra one Koni supply.
Now some people suggest removing the extra one when a car is lowered and as its approximately the same height as the extent to which I had lowered the car - I decided to remove that also. Again there was quite a bit of bump stop rubber on the piston of the strut so I suspect it had been hitting quite often.

I also felt that possibly the rebound on the fronts was a little on the low side, so decided to dial in 25% on the fronts.

Needless to say as part of the drive around checking the AFRs the ride seemed a lot more compliant than previously, and when I hit a pothole or two it no longer jolts. Seems a good improvement.

Morale of story: if you are fitting Koni Classics count your bump stops!
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
User avatar
AndrewSlater
I luv DDK!
Posts: 968
Joined: Wed Nov 30, 2011 3:35 pm

Re: It started with a pop

Post by AndrewSlater »

Again fair play to Roger Bray, my replacement fuel pump kit arrived today.

Looking at the new diaphragm, to my eyes, it doesn't look like it is rivetted together at all well.
You can see fractures / tears around the edge of the rivet and the disc is deformed from the riveting process.
Image
The more you zoom in the more you can see
Image

What does anyone else think?
The engineer in me thinks it will probably fail the same as the last - so not too keen to fit it to find out.
Am I being paranoid or unreasonable to expect it to be better quality?
1966 Porsche 912 Slate Grey, red interior - first owner owned for 41 years
1974 Porsche 911 2.7 (The Manhattan project) viewtopic.php?f=28&t=51455
1973 VW 914 1.7 Olympic Blue - ( gone to a good home )
Nine One One
Put a fork in me, I'm done!
Posts: 1619
Joined: Fri Mar 01, 2013 11:45 am
Location: Kernow - good old Cornwall

Re: It started with a pop

Post by Nine One One »

Does not look brilliant, it is as if the rivet is too small, or not centralised and, extra pressure has been used to try and compensate for it, which has pushed it all to one side.

Where did the remains of the rivet head end up on the one that failed?
Post Reply