It started with a pop

For you flat four Porsche 912 fanatics

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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

Yes the problem with a mechanical fuel pump and Solexs that have been left for a few weeks is that you can easily flatten the battery before you start the car.

I made the primer bulb mod about 4 or 5 years ago and it really transformed the ownership experience, as I now have a car that I can quickly start 99% of the time, rather than one that would only start 50% of the time if that.

Obviously you need to open the engine lid and prime the bulb for 10 - 20 seconds or so, but it's a good excuse to inspect the engine bay every trip.

If you use your car weekly, or have an electric fuel pump then it's not a problem.
If you only use your car once or twice a month and have a mechanical fuel pump, I would highly recommend it.

If you want to get oil pressure first, then you can do that before fully priming it!

I have read on the US forums about owners whose cars start but run on a few cylinders for a while until all the fuel passageways fill in the carburettors.
The advice I have seen is that this is because the carburettors are not fully primed.

I disagree as I find that even if I fully prime the carb bowls such that you cannot force any more fuel in with the priming bulb, the car generally starts on a less than four cylinders and takes 5 or 10 seconds of rough running to come onto song.

I keep meaning to try priming the carbs, letting them sit an hour, re-priming and seeing if this fixes the issue.

Still waiting for some final parts to arrive to get mine back on its wheels - so with the poor Xmas post might be after Christmas now :(
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 »

I bgt a primer bulb to fit to my 356 but ended up not using it.

I find that cranking and pumping the accelerator for no more than 10 seconds at a time is the answer. Normally about 3 goes if sitting for more than 3 weeks. I also think that a better charged battery seems to start sooner too. Andrew's comment about it not starting on all cylinders makes sense.

30 mins is very long for the carb not to fill but I have webers

Ron offers a more expensive solution to the bulb

https://precisionmatters.biz/auto-prime-primer-kit.php

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neilbardsley
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Re: It started with a pop

Post by neilbardsley »

https://r.tapatalk.com/shareLink/topic? ... source=app

Thread on 912bbs

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Timo
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Re: It started with a pop

Post by Timo »

I’m on Weber’s too Neil but I have exactly the same issue as Andrew, if I don’t drive my car every week or so the fuel drains back to the tank and evaporated from the carbs. Some times the car will start after a few attempts, (flooring the throttle a few times in between attempts), however if I’ve left the car sitting for a longer period of time it often won’t start at all and can easily flatten a fully charged battery. I have now established through max at revival cars that the issue lies with the mech fuel pump drying out and effectively becomes air locked. The answer in this case is to remove the pump and plunge it by hand until the fuel comes through, once the pump is bolted back on the car it starts pretty quickly.

I’m hoping the primer bulb may save having to perform this step if a large enough amount of fuel can be squirted through by hand.
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neilbardsley
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Re: It started with a pop

Post by neilbardsley »

What about changing the diaphragm on your fuel pump? Max has a lot more experience than me but I'm never heard of a vapour lock in the fuel pump before.

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Timo
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Re: It started with a pop

Post by Timo »

There’s nothing wrong with the diaphragm Neil, I’ve had the pump off and bench tested it.

It is a real issue I assure you and I’ve heard of many 912s suffering from the same thing after sitting for long periods. Once the fuel has disappeared from the lines/pump it needs to be re primed in order to get it going again.
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AndrewSlater
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Re: It started with a pop

Post by AndrewSlater »

Timo wrote:There’s nothing wrong with the diaphragm Neil, I’ve had the pump off and bench tested it.

It is a real issue I assure you and I’ve heard of many 912s suffering from the same thing after sitting for long periods. Once the fuel has disappeared from the lines/pump it needs to be re primed in order to get it going again.
Yes I agree, I encountered the problem with a freshly rebuilt fuel pump.
The priming bulb is an effective solution to this - so I would recommend trying it. It's not expensive and easy to implement.


As for my car, I've yet to take it out for it's first test drive, as I ran into a problem.
I had an exhaust leak between the main exhaust and the elbow to the tailpipe which I didn't spot at first.

I removed the rear bumper centre panel and used my trusty smoke machine to see where the leaks were.
Image

Turns out that the outlet pipes on the replacement exhaust I sourced are shorter than the original. As such there was no metal behind the whole length of the slot in the elbow.
Here's a photo of my old rusty elbow to show how far the slots go ( further than the output tubes ).
Image

I considered buying a new Dansk elbow ( that is very different in style to the original ones ) - but decided I wanted to keep the original style.

After much thought it was out with the welder to reduce the slot lengths.
Image

After a bit of a battle ( I am the world's worst welder ) I finally had an elbow with shorter slots - all good.

With the exhaust refitted and once again using my smoke machine I have no leaks - hurrah!

All just in time for lockdown - so no test drive yet :(
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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soulsonicboy
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Re: It started with a pop

Post by soulsonicboy »

I've been following your thread with great interest for a while Andrew, it's truly remarkable your can-do attitude and getting stuck in, and with such skilled precision! Very impressive.

On the topic of cold starting problems, I had those too with my 66 912, which is very similar to yours, with Solexes too. It was fine when using the car regularly, but if left for any more than a week or so it would require at a lot of cranking to get the carbs re-filled and start firing. I went to the expense of buying the Precision Matters Auto Prime Kit, as it seems such an ingenious piece of engineering (and hidden behind away to keep the engine looking stock original) However, with the intention of fitting it this winter while the car was laid up, I started using ethanol free unleaded (Esso Supreme Unleaded) just before the summer, and I was astonished at the impact that had. I could leave the car 2-3 weeks and she would start almost instantly. No more repeated long cranking. I was amazed. It must be the ethanol that causes the fuel to evaporate so quickly in the carb bowls.

So after my very welcome discovery, I thought I wouldn't bother fitting the Auto Prime Kit, and just stick with ethanol free fuel. However, I've just frustratingly found out that Esso have now added my local area (NW England) to the growing list of where they declare their Supreme Unleaded is not ethanol free - their website now updated to everywhere except "Devon, Cornwall, Teeside, Scotland and NW England"

If you're lucky enough to live outside these 5 areas, I highly recommend you give it a try!

Cheers

Ben
1966 912 Aga Blue
jwhillracer
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Re: It started with a pop

Post by jwhillracer »

Don't give up on the Esso Supreme. I queried it with an ex-Esso research engineer who competes with us. They have changed the labelling to cover themselves, but as of last year at any rate, Supreme still ought to be ethanol free.

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Mike Smith
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Re: It started with a pop

Post by Mike Smith »

Fit an Electric Fuel Pump

You can insert it into the system anywhere that takes your fancy

You can pump through the existing Mechanical pump (Late Pumps)

Just remember the rule on ALL Pumps - Keep the suction to a minimum

If you want to be a little more fancy add a switch and just use it for priming

Mine has been operating off the Ignition circuit for 30 years

PRS (of course) can supply a suitable pump (6 or12v)
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Re: It started with a pop

Post by robs912 »

Mike
I've been thinking about doing this on my 912 purely to use for priming.
Once it's been primed will the mechanical pump draw the fuel through the electric pump ok?
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Rob
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Re: It started with a pop

Post by Mike Smith »

Certainly with the Pump that I have fitted - it will

As for what pump I have on there - I cannot remember and I cannot get to my car currently - (I am having an enormous sort out at home and everything is jammed into the garages)

Leave it a couple of days and I will come back to you
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Re: It started with a pop

Post by Mike Smith »

OK -I have thought about it a bit more (while pulling out sundry phone wiring)

6v 356
The pump that I used and the one that we supply is 12v
My 356 is 6v and the 12v pump delivers fuel at the correct Fuel Pressure for Solex and Zenith carbs when used on 6v

912`s and 12 v 356`s
If you are going to use it on a 912 (which, of course is 12v) or a 12v-356 - you MUST remember to turn it off when the carbs are filled or it will deliver too much pressure and flood the motor.
You will know when the carbs. are filled the pump note changes

If you think that you may forget to switch it off, then use a button that you have to hold in manually until the carbs. are full, or if you want the clever way link it into the starter wiring so it only pumps when you are turning the key.
However a button is simple and can easily be tucked away under the dash
Mike at P.R.S.
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Re: It started with a pop

Post by robs912 »

I was thinking about a momentary toggle switch or push button just to prime the carbs as you mentioned.
PM me if you like when you find out pump details.
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Rob
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Re: It started with a pop

Post by Mike Smith »

The pump that I used and the one that we supply is 12v
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