Very weird running problem

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C J Murray
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Re: Very weird running problem

#16 Post by C J Murray »

david pettengell wrote:(if Trump lets me in)
I just talked to him and he said "you're in".
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paul yanacopoulos-gross
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Re: Very weird running problem

#17 Post by paul yanacopoulos-gross »

My speedster ran beautifully in Europe. When I brought her over to the states I had all sorts of issues, compression was off, backfiring, loss of power, exhaust fumes. I rebuilt the carbs, changed the plugs, rebuilt the ignition coil. It took about a year of fiddling to get it right.
Or almost as I lost a cylinder and then had the engine totally rebuilt. Now I'm up on power and she runs sweet.

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Greg Bryan
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Re: Very weird running problem

#18 Post by Greg Bryan »

I've read here that the 123 units are very susceptible to low battery voltage - that's the most likely variable after a long storage period if nothing else changed. I'd throw another distributor in and throw the 123 unit ...
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Re: Very weird running problem

#19 Post by David Pettengell »

I was guessing that.... bugger they are expensive too

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Brian R Adams
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Re: Very weird running problem

#20 Post by Brian R Adams »

david pettengell wrote: My current thoughts are definitely ignition related, could be lack of voltage from ignition switch to coil. I have changed coils and made no difference or something wrong with the distributor causing a weak spark.
I recently had a similar mysterious spark issue, described in this thread:

viewtopic.php?f=1&t=41867

I had replaced the very old coil and the condenser, and it turned out to be my BR 18 distributor's paper insulator between the points spring and the distributor wall had broken down over time, so that it was bleeding to ground intermittently. The problem was solved 100% after I replaced all the various insulator parts associated with the points spring and the terminal screw (an inexpensive kit from Partsklassic, which Brad Ripley had pointed me to):

https://www.partsklassik.com/p-31-distr ... -br18.aspx

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Jim Liberty
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Re: Very weird running problem

#21 Post by Jim Liberty »

CJ., all, my two cents, and I'm not as much an expert as most of you. I use only original Porsche (Bosch) distributors in my cars. The units that came with that particular model. I do have an 031 in my big bore S-90. That said, I always have John Jenkins curve mine to match carbs and cam. He usually sets the advance to come on at 1200 RPM. As to the science of these devices, I am no expert, but before John J. got involved, I had a lot of problems with idle.
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C J Murray
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Re: Very weird running problem

#22 Post by C J Murray »

For most 356 engines the stock distributor works great. The 123 has advantages but it does require consistently good voltage and the charging system along with old wiring is a weak point on a 356.
'57 Speedster
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Re: Very weird running problem

#23 Post by David Jones »

What is the threshold voltage failure point on the 123? Is it a similar failure as the pertronix at about 5.2 volts but with the drawback that once failed it is dead in the water? Sounds like a fatal flaw.
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Re: Very weird running problem

#24 Post by David Pettengell »

So, I checked... voltage at the coil (from ignition switch via fuse 1) is varying between 3 and 4 volts. Does this give us a smoking gun?

My wiring has been hacked about so much on the past I am not entirely surprised, only thing is I am guessing fitting a new loom is no small job?

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Re: Very weird running problem

#25 Post by Neil Bardsley »

Have you charged the battery? As someone has said since it has been sitting on a ship for ages a full charge of the battery should help. Have a look at the bushes on your dyno and see how many volts you are getting from there. A new wiring loom isn't cheap. What voltage are you getting across the battery, then the ignition switch etc. There is a good electrics chap near me if you need someone but PRS are also very good.

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Re: Very weird running problem

#26 Post by David Pettengell »

charged the battery many times since it has been back and swapped for my 6v Optima. Problem with these cars is that I have to work away a lot of the time to pay for the buggers so I can't check the other voltages until the weekend.

Funnily enough I had a charging problem on the way back from Hershey. When I got the car back to blighty I changed the brushes and it solved it, charging light went out and the voltage increased at the battery when the engine was revved.

I also have a right hand indicator problem (left works, right doesn't) and that works from fuse 1 from memory. Maybe I have an electrical issue between the ignition switch and fuse 1?

I will look at this at the weekend but she is going off to PRS next Tuesday anyhow. Even if this is fixed they can tune her up and admire CJ's handiwork.

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C J Murray
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Re: Very weird running problem

#27 Post by C J Murray »

Hello Mate! This is good news. It is very similar to the problem I faced some years ago when I rebuilt the engine of my friend Walt Weir. This was extra risky because we travel to Holidays together and if it would break I guess I would be obligated to hand him my car and the title and find Jean and I standing by the side of the road. Anyway, Walt's car was very hard to tune when I was breaking in the engine. It was not responding definitively to jetting changes and ran inconsistently. Removing the Pertronix made things better but I instructed Walt and his son to work on all the wiring and fuse box to increase voltage as a winter project, problem solved!

The number 1 problem with 356s, other than rust, is the charging system and the condition of our 50 year old wiring. You cannot have a strong running engine without strong voltage. I don't have the specs in front of me but the as new spec is almost a minimum number. A points distributor is a crude device that requires regular maintenance and wears but it will tolerate low voltage and still run. Only at very low voltage when the coil can no longer function will the car stop. When Jean and I left Park City towards Reno with no charging we drove 464 miles before the engine sputtered very badly and we pulled down a ramp to a gas station. No way would we get that far with a Pertronix or 123 or any electronic ignition. I love the 123 but when I travel I always bring a points distributor with the clamp in the correct position to drop in just in case. I also bring a good battery charger so that we can charge the battery in the hotel at night until we get to where I could fix the charging system.

Guys, if your car has a running problem you must confirm that the fuel and voltage is in good supply and clean.

I hope Mike doesn't find a connecting rod hanging out of the case to embarrass me. :P
'57 Speedster
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Doug McDonnell
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Re: Very weird running problem

#28 Post by Doug McDonnell »

At the least knowing this voltage drop will make it easier for PRS to sort out!
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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Re: Very weird running problem

#29 Post by David Jones »

If you suspect voltage drop issues at the coil try connecting a jumper wire from B+ on the regulator direct to coil +.
This should eliminate any and all voltage drop as you are getting 6 volts direct from the solenoid terminal with engine off and direct from the generator once the engine is above idle. If you have less than 6 volts at the coil at this time you have a major issue.
If I had known I would live this long I would have pushed the envelope a little harder.
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C J Murray
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Re: Very weird running problem

#30 Post by C J Murray »

Here is what I wrote to Mike yesterday morning as background on Dave's car...
Hi Mike,
The engine is a C but had early A Normal crank and rods when it was disassembled so Dave went to a Scat and Carrillo rods. Shasta 86mm pistons and cylinders were used with relatively tight piston to head clearance to promote turbulence and combustion. The cam is what Jacques Lefriant calls a stock SC but which in reality has stock lift and lobe centers but has 10* more duration. Call it a mild street performance cam that should not cause any running issues. The heads received only a standard rebuild without modifications. It has 40IDFs with 32mm venturis that were with the car when I got it as was the 123 distributor. I did connect the vacuum advance during the rebuild.

After reinstalling the engine I drove the car quite a bit and it showed some erratic behavior which was traced to a rusty gas tank. The tank was replaced, the fuel pump was cleaned, and the carbs were cleaned along with replacement of the needles and seats just in case. Dave reports to me that the carb float bowls have remained clear when he has lifted the tops but there is a strong possibility that rust silt has migrated from the fuel lines. I think that a fuel pump rebuild would be a good idea to check for rust as well as confirming that the bowls are clean.

There were a lot of slow starting problems that Dave had before I worked on the engine. A Porsche repair shop near his house here charged him quite a bit of money for a starter and flywheel replacement and I think some "tuning". That work accomplished nothing. At some point I suspected the ignition switch was not working properly and Dave sourced a replacement which helped. Keep in mind that the wiring is also suspect and that something might be going on there. I am not sure about the actual voltage at the coil.

The plugs that I would use in the engine are NGK B6HS. My engines sometimes have interference problems with extended tip plugs that caused reduced or closed gaps.

The car did run very well and very consistently before it crossed The Pond and had been driven quite a bit so I am hoping for the best. I am hoping that some fuel or ignition fault will be found that is easily rectified. Thank you for your efforts.

I had asked Dave to forward you my emails with my previous rambling suggestions in case they may help.

Cliff Murray
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car
'63 Cabriolet "Norm"
'67 911 S Original Owner
'03 Ferrari 575M
'09 Smart Passion

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