It started with a pop

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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

The rivet pulled through although it did leave a small annular sliver of metal that I found in the fuel pump.
I suspect the new one will fail in the same way.
I've reported it to the supplier again but not had a further reply yet.

I will dig out the old ( good one ) to see how they used to be made in the good old days.
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
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Re: It started with a pop

Post by neilbardsley »

Could you solder that? Or is it moving too much and will break?

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AndrewSlater
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Re: It started with a pop

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I think Ian called it, when you look closely from the side you see that the base plate is not perpendicular to the arm - it's quite crooked as the riveting process has deformed the plate. So two problems with it really.

Image

I don't really want to start trying to fix new parts that I've payed good money for. I expect new parts to be fit for purpose.
I could reuse the old diaphragm but that defeats the purpose of rebuilding the pump - its the first part in the kit that wears out.

As for solder I wouldn't use that - very poor mechanical strength - Nasa wire wrapped Apollo rather than soldered it for a reason. :wink:

Still awaiting a response from the supplier :(
Have sent the photo of the bent part.
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 )
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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

The supplier had checked their stock and sent me the best looking diaphragm they have.

Image

This one looks better, the disc plate is flat with no deformations and the rivet looks a lot less stressed and clean.
The manufacturer can clearly make a decent one when they try :roll:

Hopefully I'll get a chance to fit it tomorrow so I can move 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 )
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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

Whilst waiting for my second replacement diaphragm, I'd bought some new brake pads.

I've tried OEM: so-so, EBC Greenstuff: Not a lot different to OEM, and EBC Redstuff on the 911: Better than OEM, so I thought I would try out Yellowstuff.

Image

Who knows how these will behave but I will keep you posted.


As for the fuel pump saga, so I went around the buoy again.
Rebuild fuel pump - tick.
Reconfigure fuel lines to fit a pressure gauge - tick.
Refit P78 tool to double check float level with new fuel pump. - tick
Change the idle jets from size 57.5 to size 55 to try to increase AFR at light idle loads. - tick
Change the main jets from 122.5 to 130 to try to reduce AFR at WOT. - tick

Now check the fuel pressure - approx 3.2psi - spot on.
Check the float levels are still good - tick.

Check AFR at idle with new jets AFR a little over 15:1 suggesting the reduced idle jets have altered idle mixture - richen up idle screws to get closer to 14:7.1

So how does it run -well a couple of carb spits after first start but all gone after 60 seconds or so. I suspect these are a lean condition whilst the carburettor fuels properly.

Time for a drive and hope the fuel pump holds out!

When cold there is still the lightest of hesitation getting from say 1.5K to 2.5K, but once warmed up seems better.

At WOT the AFR seems to hold around a much better 12.5:1 ( max power ).
Idle sits somewhere around 14.5:1 on average.

Light throttle still seems a bit rich with readings often in the 11:1 to 12:1 range but possibly a little better than before.

Here is the new AFR distribution over my standard test roads.

Image

Whereas previously I seemed to have two peaks either side of 14.7:1, the bulk of the spread seems to be between 12:1 and 15:1.
In my mind I should have moved the previously lean WOT peak to the other side of 14.7:1, and have pulled the idling circuit peak down a smidge.

I may take the car out again and get some more data but it seems to drive pretty well, so will keep with this setup for a while.
It would be interesting to see what the car did if I was to reduce the idle jets from 55 to say 52, maybe I should gamble another £40 on an extra set of jets.
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
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Re: It started with a pop

Post by neilbardsley »

My understanding with idle jets is that it doesn't so much affect your lean/rich mix but when the main circuit comes in?

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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

neilbardsley wrote:My understanding with idle jets is that it doesn't so much affect your lean/rich mix but when the main circuit comes in?

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Strangely there don't seem to be any charts with any of this on.
There is one that is occasionally posted on the US Porsche sites but I'm not convinced it relates to Solex carbs, more Webers.

I'm pretty confident that the idle jet in conjunction with the idle air bleed, set the mixture for conditions between idling and power.
The bottom discharge port has adjustment ( via the idle mixture screw ), to set your mixture at idle - as this is the dominant port with the butterfly almost closed.

The other discharge ports come into play as the butterfly moves from idle towards full power. On solid shaft Solex you have three discharge ports ( + the idle one ), on later split shafts you get extra holes. The only adjustment you have here ( other than the accelerator pump ) is the setting of idle jet and idle air bleed.

I guess a secondary effect of changing the idle jets is that it will slightly the move the transition point, at which the main circuit contributes more than the idle circuit. However I expect the change is very subtle unless you have very large idle jets.

I'd really love to understand this more - but there really is little information out there as to how everything interacts - definitely a black art.

I suspect with my car the very slight hesitation at times when transitioning from low to partial throttle is down to the accelerator pump settings.
It's set to 0.35cc / 2 strokes which seems to be what everyone suggests, but might try taking it a little lower. This would account for it richening up on partial throttle application, but I would expect this effect to be short-lived, 2-3 seconds, but it does seem to stay rich for longer.
I probably need to do some more runs, but with more steady state throttle to rule out the accelerator pumps.

To be fair this is the best the car has ever run in my ownership and is probably 95%+ the way there, just would be nice to know what few more percent I can get - I like a challenge!
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 )
RobFrost
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Re: It started with a pop

Post by RobFrost »

AndrewSlater wrote:...as the butterfly moves from idle towards full power...
My tentative understanding is that the movement of engine speed from idle to high revs is equal to the butterfly in importance, in determining which jet is dominant. In particular, it is the rate of flow of air that governs jet dominance, and that is a product of engine speed and butterfly position.

Qualify that slightly, (on Webers at least), by the fact that when the butterfly is in the fully closed position I think its edge actually covers off one of the jets.
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1988 3.2 Carrera backdate, Black
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neilbardsley
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Re: It started with a pop

Post by neilbardsley »

RobFrost wrote:
AndrewSlater wrote:...as the butterfly moves from idle towards full power...
My tentative understanding is that the movement of engine speed from idle to high revs is equal to the butterfly in importance, in determining which jet is dominant. In particular, it is the rate of flow of air that governs jet dominance, and that is a product of engine speed and butterfly position.

Qualify that slightly, (on Webers at least), by the fact that when the butterfly is in the fully closed position I think its edge actually covers off one of the jets.
Agreed with that but when I was on the RR the chap said something about the idle jet having an impact too

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robs912
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Re: It started with a pop

Post by robs912 »

Hi Andrew
When tuning my carbs with an afr meter I found it really helpful to completely disconnect the accelerator pumps and go for a drive to get them dialled in. Although I'm running webers but should be able to do the same on the solex carbs.
Rob
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