It started with a pop

[AndrewSlater]

Hi Ben, thanks for the kind comments.

I had seen the Precision Matters Auto Prime Kit and from all accounts it works well - albeit a bit pricey.
I wonder if it subtly alters the throttle response as you are adding a counterweight to the linkages.
Would it subtly alter the idle ( depending upon whether it was full of fuel or empty )?


My plan of getting a test run and then a 50 or so mile run before a first change of the oil has gone out of the window until lockdown ends and I am 'allowed' to drive it.

So I am just playing a waiting game at the moment. In fact I have even started to tidy my workshop - that's how bad it is.

[neilbardsley]

Thank Andrew. Tool returned in better condition than I sent it. Would you like to borrow anything else

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[AndrewSlater]

Thank Andrew. Tool returned in better condition than I sent it. Would you like to borrow anything else

Ha ha - thanks for letting me know it got back safely and many thanks again for the loan.
Let me know if I can repay the favour in the future.

No sign yet of any slackening of the lockdown restrictions - so no test drive yet.

[AndrewSlater]

I can't believe I started this back last September, but got delayed testing the car due to lockdown rules.
In the meantime I had decided to fix the leaking velux windows in my workshop, which resulted in a scaffolding tower that blocked my car in.
With the scaffolding finally down, it was time to get the car out and give it it's first run.



The original plan was to put 50 or so miles on the clock keeping the revs below 3500rpm and then change the oil.
Plenty to test ( and go wrong ). The engine rebuild, the full flow filter kit, the gearbox strip and gasket replacement, the new clutch, clutch cable as well as the new throttle linkage bushes etc etc.

Took the car for a few tentative local laps to check all seemed good - and all seemed fine, so off for an extended drive.

61 miles later all below 3500rpm and all was mainly good.

Firstly the new soundproofing does seem to have quietened things down quite a lot in the cabin.
Although that's great it does make it difficult to compare how the engine now sounds compared with previously - definately more muted now.
The clutch and gearbox seem pretty smooth and quiet - the new clutch release bearing is definately quieter than the old one.
No pops or bangs so the exhaust seems to be properly sealed and behaving itself.
Performance wise - difficult to say at the moment due to limited rev range - but I don't expect any performance gain, I'm just hoping that the new pistons seal well to prevent the oil fouling I was getting previously on the plugs.

One hiccup was that the idle was not always returning to a low value so it was time to check the carb balancing again.
When I rebuilt the engine I managed to drop my synchrometer and break it so I had missed out this step.

Luckily I recently got a replacement from Tim ( goodtogo ) so it was time to make some use of it.



It soon became apparent I had two problems.
Firstly with the accelerator rods removed from the carbs it became apparent there was a small difference between the left and right bank, quickly sorted with the idle screw.
The second problem was that during the rebuild I had put new accelerator rods on as my old ones were a bit worse for wear, but the new ones were slightly raising the idle when fitted ( more so on one side than the other ). With the synchrometer it's easy to diagnose and fix, so after a small modification to each rod, the idle was unaltered when the rods were fitted.

Spurred on, it was time for another 30 mile test drive, (this time raising my rpm limit to 4000 rpm), and confirmed that the idle problem was fixed - all good - yeah!

I'll probably put a few more miles on it before changing the oil ( I'm guessing the full flow oil filter buys me a few more miles ).

So in summary really pleased it all seems good.

[neilbardsley]

Congratulations!

How close is your front rear cylinder balance? I have webers and had to use the air bypass.

I've been thinking about changing the oil in my new engine but the builder said to put 1k on it but I like your idea more.

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[AndrewSlater]

The front to back balance seems the same both sides with the front cylinders reading about 3.5 at idle with the rears about 3.8 or so. That's balanced to within 7% or so, so not a bad start. Obviously that percentage reduces as the revs climb. The only option to match it further is to starting bending the butterfly shafts on my solid shaft solexes, which is easy to get wrong. I suspect I will leave it alone for the moment and see how things pan out.

As for the oil, the Maestro recommends a full oil change at 50 miles, but then he is talking about cars that didn't have full flow oil filtration. As mine now does I suspect the filter will catch any debris first time around, whereas previously it would have gone through the bearings probably at least 7 times before being filtered. As you would expect most wear at the beginning it makes sense to change the oil and filter early I think.

The best oil to use is obviously subject to much debate.

I previously used Millers running in oil on my 911 rebuild but that didn't work very well as the oil is so thin and watery it easily finds its way out of an air cooled engine (most of mine tracked into the exhaust )
This time I went for Westway classic car running in oil which is high in ZDDP to protect your cams and bearings etc. I believe there are other additives to help with piston ring bedding - so time will tell how that pans out.

I remember seeing the Harrys garage video where he gets his Lamborghini Espada V12 engine rebuilt by Iain Tyrell. He states that they buy the cheapest oil they can from the supermarket and use it for 500 miles, claiming the worse the oil the better it runs in. Not quite sure I would do that on such an expensive engine.

Previous to the test run there was a very slight oil weep from one of the push rod tubes, but that seems to have sealed nicely on the test run.
I'm hoping there will be no leaks on either the engine or gearbox from now on - fingers crossed.

[neilbardsley]

There is a very good book by Richard Mitchell 'Which Oil'! He has a 912

Summary is

10/40 is about right for 616 engines. He has a much more involved formula for calculating the right weight to use

Use a synthetic oil

If the synthetic means B2/A2 standards. It lubrication properties are better than a mineral oil with zdpp

Look for a higher base oil number



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[bjmullan]

Glad you got the car out for a drive There is so much salt on the roads here, so my car remains in the garage

[Kneeslider]

Yay, congratulations on all the work turning out well. When you talk about the vertical threaded throttle rods which attach to the carb bell cranks, I had quite a time with them when setting my engine up for the first time.

I found that the key to good adjustment was to use the vertical threaded rod which lives in front of the fan housing (where you can't see it) to put the centre of the vertical ball end of the bell crank 50mm away from the fan housing. I cut a small bit of wood to the exact length so I can do it by feel behind the fan housing.

I think that I found that tip on the Registry forums.

Start setting up by using the Unisyn and with the vertical rods to each carb disconnected. Get all 4 carb throats pulling the same by adjusting the idle stops and (if you have split shafts) the screws between the throats of each carb.

With that done, adjust the lengths of the vertical adjusting rods till they just pop on, and you should be done.

Then you know you should be getting full throttle and consistent idle. If the bell crank behind the fan housing isn't set to 50mm there could be the chance that you can't get the throttle open all the way.

There's way too much adjustment in all that for my liking! A cheap and simple cable would suffice for any other manufacturer but not Porsche!

Its almost like an aircraft engine throttle linkage. They are just as bad!

[AndrewSlater]

Not put too many miles on the car in the last few months but time for an update.

I continued to drive the car, upping the self imposed rev limit by 500 rpm every 50 or so miles.
After 300 miles or so I was able to use full revs and my view was that the engine pulled really well past 300 miles and a look at the plugs showed no signs of any oil fuelling - so hopefully that is sorted.

Once I had the full rpm range to play with it soon became apparent that the engine was much happier above 3000rpm than below, but the car has always been like this in my 9+ years tenure.

My plan was to put some more miles on the clock and then go back to the valve clearances etc once I had gotten to 500 miles on the rebuild but then a strange thing happened.

I was sorting away a lot of my car parts when I came across a P78 clone tool that I had never seen before. Obviously one came with the car when I bought it but I hadn't spotted it hidden away and so bought a Biecker engineering one. As I stored the newly found one away with my Biecker one I noticed a difference.



The S4 line on the Biecker gauge on the right ( the setting I've been using for the last 9 or so years for the P40-II carb ) sat way above the marking on the other tool.
After a bit of research it appears Biecker made at least one batch with incorrect markings.

The minimum line on a P78 tool is normally 54mm from the jet centreline.
This one was 61+mm away ( 7+mm too high ).

Now this might explain why I always thought the car ran a bit rich and that the acceleration up to the main jet transition wasn't great.

I checked the float levels again and the floats were exactly where I had previously set them, so I'm guessing 7+mm too high.

I managed to adjust the right hand carb down but the left one wouldn't adjust - time to get the car back in the workshop for a thorough check.

Anybody got a P78 tool that they could measure to tell me what level they set to above the jet centreline?

[hashman]

Andrew
You could try a check on floats by this method, only costs a straw.

Technical and Restoration Guide, Volume 2 Pg. 163. Jerry Kiliany Writes: I use a McDonald's straw cut to 50mm and make a mark at 29mm and adjust the level to this mark. The mark is the point to adjust to at the top of the carb vent hole. I chose a McDonald's straw because the diameter of the straw is critical, too small and it falls into the bowl, too large and it rubs the side of the vent hole.
I have used this on a friends car and it appeared to work but I have almost no experience with Solex carbs. The materials are readily available.

[AndrewSlater]

Thanks for the quote - had seen that on the 912bbs site. There is also a caveat that the vent tubes on Solex can vary in height across variants and more so with gasket variation.

Having the P78 allows very accurate measurement - I just need to know what the general consensus is as to where I should set to.
As such I'd be interested to know the where the line is drawn on other members gauges.

I'm quite a way into tuning the engine again but can easily try out different float heights if the 54mm I now have is wrong.

I'll post an update shortly as to where I have got to.

[wildtexas]

Andrew, I suspect your too high and rich at 61mm on the Bieker gauge.

There was a long discussion on this on 912bbs with plenty of input including our own, good Ashley James.

I have a Bieker gauge which I also found was too high @ 60.25mm. I have remarked mine at 58mm and that seems to be where my car is happy. Ashley also measured his carb at 58mm and Paula Golus came up with that measurement too but runs a mm or so lower. Fuel dependent perhaps?

If you're struggling to get the fuel levels low enough then you may need a thicker washer beneath your needle valve. Also check you fuel float pivot for straightness whilst you're in there.

I use the straw method as a quick and dirty check to make sure both carbs are even and where I want them but only after setting correctly with a gauge.

Ashley likes his levels lower, I believe, but my car protested.

Hope this helps. Matt

[AndrewSlater]

Thanks for the info Matt, I had seen a post stating the 54mm height but not seen the ones discussing 58mm ( any pointers to where that is - can't seem to find it within a search ).

At 54mm the fuel level seems to be just below the port on the side with the screw removed, at 61mm its much higher and the fuel pours straight out - which is a bit of a clue that the 61mm was too high.

I've been going around the buoy again on all aspects of tuning and have tweaked plenty of things in the process.

On putting the car back in the workshop I first double checked the valve adjustments.

Cylinder 1 and 2 were a little tight on inlets and cylinder 4 was fractionally wide on both inlet and outlet.
I had hoped to find cylinder 1 and 3 inlets a bit tight to account for the fractionally less air draw on these two cylinders.
I reset the valves and also retested the carb balancing, possibly a small improvement on cylinder 1.

I've also checked that the timing on my 031 distributor is still at 32 degrees at 3000rpm - which is where I last set it.
Dwell is a constant 50.7 degrees across the rpm range ( spec if 50 degrees +/- 3 )

I also rechecked my fuel pump pressure at it is still 2.9psi as per when I rebuilt it nearly a decade ago.
I recently bought a spare second hand pump, so have rebuilt that and fitted it.
It is providing a nice 3.2psi ( so I'm now bang on middle of the 2.9-3.5psi spec )

At some point the float level in the left carb changed significantly to the point that when I stopped the engine I got the dreaded gurgle of fuel in the bores.
I'm guessing my adjustments had taken effect and then it had suddenly moved to a much too high a float.

At this point it was time to remove the carbs to fix the float height issue.

On inspection the only issue I could find was that the adjustment screw had bent the adjuster arm a little and as such there was a bit of friction in the adjuster.

I decided to give both carbs a strip down, and boiled them in a lemon juice to bring them back to shiny.
On the problematic carb I also changed the float valve over for a new one although I don't think the one fitted was a problem.

I set the float levels to 54mm using a bench setup with the correct 3.2psi pressure.

On putting it all back together I decided to fit a wideband O2 sensor to a spare tailpipe union that I had, so I could at least try to tune the carbs with hopefully some accurate figures. My plan was also to try a a few different combination of jets to see what worked best.

And just to add to the overload of information, I fitted my Colortune plug to cylinder 4 to 'see' if the combustion seemed to stack up with the numbers.

Now my first question is that all the articles I have read about tuning the carbs seem to have been written before the availability of wideband O2 sensors, and all the talk is of cylinder balancing and setting the tune for maximum rpm at idle.
All this seems to be done with the airboxes off - but from years of doing this before I always find that the car runs very differently once you put the airboxes back on.

My AFR meter shows a significant decrease in AFR once the airboxes go on.

So the questions I have never been able to answer is how do you balance the carbs with the airboxes on, and what would be a good AFR starting point for a 900rpm idle?

[wildtexas]

Andrew, I'll find a link for you on the discussion.

What does your afr and colortune tell you?

I find getting the valves, timing, dwell, float levels and sync right will make your car happy. When you can get a steady idle at 800-850 with minimal rocking of the engine you are very close.

Don't forget that even if you get the carbs synced and droplinks balanced at idle they can get out of shape at higher rpm. That is where having the cross shaft correctly positioned and adjusted comes in.

I check my carb balance at 3000rpm also with the synchrometer.

I find that at idle my car needs to be in the 12.5afr range, leaner and it starts grumbling and spitting back, maybe about 5%co2 if your using that. I'd love to have a permanent afr to tell me the score underload.

With respect to air filters on and off, are you saying your car richens up when the filters go back on?

Try pulling the plug leads one by one whilst watching the rpm drop. As you've just rebuilt your engine you'd expect them to be even.

It is a dance for sure. Matt

Ps you may need your idle lower to stop the timing advancing and causing your idle to race and hang up higher.