356 C Cab won't start when cold, what's going on??

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Dave Finburgh
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356 C Cab won't start when cold, what's going on??

#1 Post by Dave Finburgh »

I have had a recurring problem with my '65 C Cab. Seems like if the car sits for more than a few days, it just doesn't want to start. I know that the new ethanol fuels are not helping, but this problem is fairly recent...just in the last few months.( Yes, I have Stabil and Miracle oil in the tank and I have a separate electrical fuel pump, which is apparently working; although I turn this off once (if) the car starts).
My local 356 mechanic has tried everything, we even replaced the fuel tank, cleaned all the lines, re-built the carbs, replaced a faulty float in one carb, checked the electrical system ( apparently is ok)...and cleaned the gas cock at the reserve. My mechanic thinks it is was caused by the gas...even though this is a new problem?? Today, i couldn't get it to start again. After some advice from a well known 356 mechanic up north, I tried to crank it for numerous times, while pumping the gas pedal....no avail. ( except for possibly wearing down the battery nicely and who knows how much wear on the starter motor!!)
Here's the weird thing, while I have managed a few times in the past to get it started, and after much cranking and a few backfires, it runs great??? Unfortunately, today there was no way it was going to start. :(

Any ideas as to what's going on would be appreciated.

'65 C Cab 161176

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Alan Hall
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Re: 356 C Cab won't start when cold, what's going on??

#2 Post by Alan Hall »

If I am reading your question correctly, the car starts fine if it has sat a day or two but not if it sits longer. That sounds like an issue of the gas evaporating out of the carb, but you have an electric fuel pump which should fill the carb without a lot of cranking. Can you tell if the pump is filling the carb and then not pumping once the carb is full and the carb float valve has shut? If the carb is full (from the electric pump) before you start cranking, excessive pumping of the throttle could be flooding the engine, you might try cranking with the throttle held open (until it starts). You mention the carbs were rebuilt so I doubt a sticking float valve as they were probably replaced. If it works fine if it sits a day or two but not if it sits longer pretty much eliminates the problem being ignition related.

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Dave Finburgh
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Re: 356 C Cab won't start when cold, what's going on??

#3 Post by Dave Finburgh »

Alan, according to my mechanic, the car seems to start fine if it has sat for a day. I personally have not tried this. I do know that it won't start if I leave it for a couple of weeks. I don't know how to tell if the pump is filling the carb and stops pumping once the float valve has shut. If I hold the throttle all the way open, won't this also potentially flood the engine? It does seem like the carbs just aren't getting enough gas, but I cannot tell for sure ( I don't smell a lot of gas at the engine). Also, before the advice from the mechanic up north, I wouldn't really pump the pedal to try and start. I would let the electric pump run for about a minute and try and start it ( which it seemed to do before). Both ways seem to not work now??

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Doug McDonnell
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Re: 356 C Cab won't start when cold, what's going on??

#4 Post by Doug McDonnell »

Every 356 I have owned had a "sweet" starting procedure. Usually with gas in carb-say 20-30 seconds of electric priming- Gas pedal pushed to floor once, then hold 1/2 way to floor and crank ignition. When was your last complete tune up? I am assuming Zenith carbs correct?
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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Martin Benade
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Re: 356 C Cab won't start when cold, what's going on??

#5 Post by Martin Benade »

You should hear an electric pump "clicking" for about 40 seconds until the carbs are full, and then either stop completely or just click every several seconds. It that is fine, look into the carbs while you open the throttle a few times, after the pump stops, with the ignition off. You should see and hear the accelerator pump squirting fuel in. To start my car that has tired accelerator pumps, I have to pump the gas lots of times. It is worth a try, the worst that will happen is you will flood it. If it is flooded, cranking while you hold the pedal down should clear it. That will not flood it worse
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Dave Finburgh
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Re: 356 C Cab won't start when cold, what's going on??

#6 Post by Dave Finburgh »

Doug, yes Zenith carbs. Haven't done a tune up for about six months, but would this explain the car running well once it starts? The starting problem is the issue.
Martin, I will try this and see what happens. Thanks.
BTW, would an accelerator pump problem also show up under normal driving? Poor acceleration etc.,??

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Doug McDonnell
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Re: 356 C Cab won't start when cold, what's going on??

#7 Post by Doug McDonnell »

If your carbs were just overhauled then accelerator pumps should be fine and correct quantity injected.
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: 356 C Cab won't start when cold, what's going on??

#8 Post by Geoff Fleming »

Accelerator pump injection absolutely critical for cold starting...all four nozzles should be seen injecting raw fuel when the carb arms are activated. Don't assume they are working, with the engine off and air filters removed, look down the throats of each carb while pushing the throttle arm down to full stop.

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David Jones
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Re: 356 C Cab won't start when cold, what's going on??

#9 Post by David Jones »

I have found that some of the replacement accelerator pumps on Zeniths are not as good as I would like and some have not worked worth a damn even when new. They can also fail if they dry out and if the car sits for a while you will never get enough gas pumped into the throats to get the car to fire up. As Geoff noted all four nozzles should be squirting approximately the same amounts. With a dry set of carbs doing a first run I have resorted to pouring approximately a shot glass quantity of fuel into each carb shared between each throat and that is usually enough to get the engine to cough into life and run it for enough time for the fuel pump to fill the bowls. It takes a lot more raw fuel than one would think to make the engine fire up.
My diagnosis from afar is a possible weak fuel pump and accelerator pump diaphragms that are not pumping very well resulting in too little fuel being injected to start the fire.
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Doug McDonnell
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Re: 356 C Cab won't start when cold, what's going on??

#10 Post by Doug McDonnell »

You are correct Geoff I was "assuming" carbs were rebuilt correctly and pump volumes were set correctly. And we all know what " assume" makes U and me:>) And Dave you mentioned you have Stabil in your gas. How old is the gas?
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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John Lindstrom
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Re: 356 C Cab won't start when cold, what's going on??

#11 Post by John Lindstrom »

Your ignition switch, the key rotates too far, cutting out the current to the coil. Or maybe not. Are you getting good spark at the plugs?

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Re: 356 C Cab won't start when cold, what's going on??

#12 Post by Geoff Fleming »

Oh, I've assumed a lot in the past and always ended up learning the hard way!

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Dave Finburgh
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Re: 356 C Cab won't start when cold, what's going on??

#13 Post by Dave Finburgh »

Thanks for all the replies so far.
The gas is actually pretty fresh. We replaced it all about three weeks ago when I replaced the gas tank.
I will definitely ask my local mechanic if they can look at the accelerator pumps in the carb.
Would the car run well once started if the accelerator pumps weren’t working well? Like I said before, If I can get the car started...big if, it has run well once started.

Also, according to my mechanic, there is good spark at the plugs.

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Doug McDonnell
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Re: 356 C Cab won't start when cold, what's going on??

#14 Post by Doug McDonnell »

If as John said it is the ignition switch turning too far and deactivating power to the coil then a hot wire from B+ on Voltage regulator to + on coil and car should start right up. Worth checking.
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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Sebastian Gaeta
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Re: 356 C Cab won't start when cold, what's going on??

#15 Post by Sebastian Gaeta »

John Lindstrom wrote:Your ignition switch, the key rotates too far, cutting out the current to the coil. Or maybe not. Are you getting good spark at the plugs?

I have found that 98.3% of “carburetor” ploblems are ignition.
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Registry #8339

'65 C coupe
'64 C cab

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2014 Boxster 981
2005 997 C2 Cab
1967 Karmann Ghia Convertible
1966 VW Single Cab
1966 Ducati Cafe Racer
1964 Karmann Ghia Coupe
1963 Beetle

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