Very weird running problem

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Jim Liberty
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Re: Very weird running problem

#61 Post by Jim Liberty »

CJ. I have both, one from Zims (VW), and the SC Cab. and one from Neutech, looks stock, but larger dia., on the '63 Coupe. That is the one that failed. Leonard T. sells it, and machines the stand to fit. BTW, I get all my pistons, jugs, and con. rods, etc. from him. A delight to do business with, and superior parts.
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Mike Wilson
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Re: Very weird running problem

#62 Post by Mike Wilson »

Late to the discussion and I haven't seen it mentioned (unless I missed it)...has the distributor cap been replaced? A good friend of mine was experiencing problems with his '59 coupe and it turned out to be a broken center contact on the cap. It would run a bit uneven and when going up a hill, it would stumble like you were running out of fuel. The stumble was caused because the engine was under load and not getting enough spark.
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C J Murray
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Re: Very weird running problem

#63 Post by C J Murray »

I think it was on a rolling road today but I have not heard anything.
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Jason McCandless
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Re: Very weird running problem

#64 Post by Jason McCandless »

subscribed...

Great reading through this thread, everyone has given me a number of issues to check/double check in my starting issue, so thank you.

Was a definitive solution ever found?

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Steve Carroll
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Re: Very weird running problem

#65 Post by Steve Carroll »

Jason McCandless wrote:subscribed...

Great reading through this thread, everyone has given me a number of issues to check/double check in my starting issue, so thank you.

Was a definitive solution ever found?
New 356 owner here. I also experienced the weirdness described in the first post: Initially, the engine would barely run, and only at high RPMs with lots of throttle, but wouldn't idle. After fiddling with ignition components enough to hold a rough idle, I started to pull plug wires from the distributor, one at a time, to see which cylinder(s) was dead. Starting with #2, I killed the engine. The weird part: After restarting and pulling the plug wire for #3 (but close enough for the spark to jump), the engine started running much smoother, but would get rough as I reinserted the plug wire back into the cap. Eventually, with a new coil, cap, points, and condenser, I could get it to idle fairly well but with backfiring. One other observation that may be relevant: After running for a little while, the plug wires become "stuck" in the distributor cap. I have to pull really hard to get them out.

I'm guessing that I still need to verify generator and regulator functions as mentioned earlier in this thread. Any other suggestions would be welcome.

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Harlan Halsey
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Re: Very weird running problem

#66 Post by Harlan Halsey »

Seems to me that the only thing likely to change on crossing the pond is the fuel

But I see that the last post on the problem was 2 years ago...by C J Murray. So, was there any satisfactory solution??

Andy Prill mechanic-ed on a European based T1 coupe driven by Richard Miller several years running at the Monterey Historics. One year they holed a piston and Andy got a new one from Leonard and installed it in the pits. Andy has got a good reputation in England these days, and might have an opinion on running the same car on both sides of the pond.

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Re: Very weird running problem

#67 Post by Thomas Sottile »

have you checked the plug wires a ship voyage means a lot of humility.

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Martin Benade
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Re: Very weird running problem

#68 Post by Martin Benade »

Steve, I have seen that where a somewhat fouled plug will fire better with the spark jumping an extra gap, meaning the wire pulled partly out. Some spark plugs have an extra gap internally for this, to slightly "intensify" the spark. I cannot explain it, but I believe this is real.
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Steve Carroll
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Re: Very weird running problem

#69 Post by Steve Carroll »

Martin Benade wrote:Steve, I have seen that where a somewhat fouled plug will fire better with the spark jumping an extra gap, meaning the wire pulled partly out. Some spark plugs have an extra gap internally for this, to slightly "intensify" the spark. I cannot explain it, but I believe this is real.
Interesting. I would not have believed it if I hadn't seen it with my own eyes. Thanks for confirming that.

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Harlan Halsey
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Re: Very weird running problem

#70 Post by Harlan Halsey »

That is an old trick. The reason a fouled plug doesn't fire is because the voltage bleeds off before it gets high enough to jump the gap. Putting an air gap in the line prevents this. When the charge jumps the air gap, it also jumps the plug gap if the fouling is light. Sometimes firing the plug this way results in clearing enough of the fouling that the problem is cured.

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Re: Very weird running problem

#71 Post by Steve Carroll »

Aahh, I see. So, currently I can start the engine and it will idle, but as I increase the revs it backfires frequently. I'm interpreting this as a low voltage issue from either the generator or regulator, since I've already replaced the coil, points, condenser, cap, and rotor. I realize that I can measure the voltage but my car is at a shop away from home and I just haven't done it yet. That sound like a good next step? If it's the regulator, how do you guys feel about the new substitutes as opposed to buying used?

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Re: Very weird running problem

#72 Post by Thomas Sottile »

You do not need much voltage to run a 356 after it starts so I would rule out a generator problem try changing the plug wires or a least test them.

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Re: Very weird running problem

#73 Post by Martin Benade »

Backfiring like that can occur if the timing is retarded from where it should be. My car did that for months after a 25 year hibernation, I think the intake valves were sticking and leaking just a tiny bit, causing it to make almost more of a sneeze that an actual backfire. It did it under light load, not when really pulling. Lots of 356s will do that just a couple of times after a cold start, when there is nothing wrong at all.
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Re: Very weird running problem

#74 Post by David Jones »

Steve, it sounds like you have a plugged idle jet or two. Pull the jets and also blow out the passages. What carbs are you running and what are the rest of the engine specs? Always useful to know what we are dealing with and also where are you? There may be someone close by who can help.
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Steve Carroll
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Re: Very weird running problem

#75 Post by Steve Carroll »

Thanks for the suggestions. They are really appreciated.

A bit of background: This car had sat for several years with minimal use until recently, when it was purchased by an acquaintance who then sold it to me. He indicated that he cleaned out the fuel system and carbs as you would anticipate being necessary after a long idle period. When the car arrived, it ran pretty well. After a day or two of sitting, it became hard to start and wouldn't run other than at high RPM with lots of pedal. I noted that the only exhaust port that was hot was #4 -- the other three exhaust ports were still cool after running for a minute or so. (!!!) I suspected fuel residues had come loose and had probably plugged the carbs -- they are Zeniths. However, both carbs were getting fuel, and all four spray bars were squirting when I'd move the throttle linkage.

One thing that made me leery of the plugged carb theory was that there was no change in starting characteristics after squirting starter fluid down the carbs. In any case, I pulled both carbs and blew out the jets and ports to the extent that I could without a complete disassembly. After re-installing the carbs, there was no change in the starting behavior.

I then shifted my attention to the distributor. Several posts on this site have found the condenser to be faulty, so I replaced it with a new one. Since the distributor is a 009 (I know that's not what I should have and will replace it with a BR18), I had to rotate the distributor to mount the new condenser, so I confirmed static timing before locking the distributor position. To my surprise, the engine started and would idle just enough for me to get to the back of the car and pull plug wires in search of the dead hole(s). That's when I discovered the air-gap-spark phenomenon, and now the car will start and idle but backfires every few seconds when running at anything higher than idle. One sure sign of improvement: All four exhaust ports are now hotter than blazes after running for a minute or so. Next, I replaced the coil, cap, and rotor thinking those may be suspect, but honestly didn't see much improvement after that. However, I'm still suspicious of an electrical gremlin as opposed to fuel, and leaning down that path.

I have ordered a set of plug wires so will check that off the list in a week or so. Now that I can maintain an idle, I'll re-time it with a proper timing light. I also need to double-check valve clearances. I realize that syncing the carbs is part of a proper tune-up but that's new territory for me.

By the way, the car is a 1960 Cab with a 1963 S90 engine. I'm near Portland, Oregon. Thanks again for your help.

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