The Official 356Talk Forum

Does the engine backfire when it looses power? Does it load up when it returns to idle?

If not, then probably just bad fuel. If it is backfiring, then the fuel is fine and you have ignition issues...

Franny

Have you checked the ignition Condenser? These can break down under load.

Harold,

David beat me to mention that you DON'T need 93 oct. gas; it'll run OK even w/87 oct.
When rebuilding fuel pumps correctly, you must compress the pushrod so the diaphragm will be in a flat position to
the body's face before snugging-up the 6-screws--also, the diaphragm hopefully is renewed, or still flexible; A stiff one won't do the job!
The throttle linkage adjustments start on the frontside of the fan shroud's bell-crank w/50mm ref.; Do you have a
shop manual?

The rest of the adjustments will be needed toward the throttle pedal and it's depressed to the wide open position, there should be a 6 x 45mm long stop bolt w/a a nut and washer to prevent overtravel and breakage!
Finally there should be a little slack @ idle so the carbs will not be held open slightly and prevent a high idle RPM.

Dick

People suggest the condensers ?
Back in the 70's 80's 3 years at a shop doing tune ups everyday (mostly VW) then my own shop for a few years,
I don't recall ever seeing a bad condenser.

More a general comment. We have here in Finland and probably at least in
other northern countries "alkylate fuel", check:

https://www.aspen.se/Guider/Guide_Engel ... ate_petrol_

The regular fuel 95E10 and 98E5 goes bad very quickly but this is great stuff.
Normal fuel have ethanol, 10% and 5% in it at least here.
When it's time to park my Porsche, I run the tank as empty as possible, then
fill some amount of alkylate fuel, run it thru the systems and no fuel related
problems next season.
Also chain saws, snowmobiles and such not so often used equipment start much
easier after a long standstill. Snowblowers and snowmobiles (my gear is old, no
fuel injection) usually run rich and after some use your clothes stink gas.
Not very pleasant, but this alkylate fuel don't stink. Highly recommended if
available. Here it cost about 0,60€ more per litre, 1,6€/l compared to 2,2€/l.
A small price compared to all the benefits.

Something else about running problems. My 356 had some misfires and backfires
specially at lower rpm, was running OK when cruising at 2700 - 3000. I bought
a 123 distributor and what a difference, all missing & backfiring is gone. Don't
look so original, but my car don't look very original so it does not matter.

Harold: Concur with fuel starvation. I had a similar problem with my '60 Normal w/Zeniths earlier this Spring and corrected it by raising the bowl lever by ~1.25 mm on the left carb (#3 & 4 cyl.).

Sled ran fine until I had to pull a grade or pass a slow mover. When I got up to 75-80 mph (3-4K) on the grade on my "test track" (Rte. 9 in CT) the car would bog down, loose power and I'd have to move over and slow to ~60. I checked bowl levels using both Pre Mat device and by removing the carb top and using a ruler. Found that bowl level for #3 & 4 carb was ~20 mm below top of bowl. Just outside the low side spec (18.5mm +/-1). Changed to thinner shims under bowl valve to raise bowl fuel level. That did the trick. Passed my test track gradient test without a stumble and had to back off at an honest 95 mph as I was running out of road.

Harold,

I forgot to mention: Adjusting the carb balance bank-to-bank, I do it during 2500-3000 RPM (if a Unisyn is used),
or the other. You'll do it more than once adjusting the vertical links; Then I adjust the mixture screws to suit the idle
smoothness as best as possible. However, if having Solex 40 PII carbs, the mix.screws are adjusted to suit the power
circuit of each if the compressions of all cylinders are reasonably matched to each other; Float levels, injections, & fuel pump
output not exceeding 2.8-3.0 PSI are set. Then set the idle w/the stop screws. Zenith carbs may need minor mix. screw. adjustments too, but single entry tops 'kinda' blends their power circuits which is easier to maintain.

Dick

As mentioned earlier, set the stop screw under the pedal.

Dick

Dick Weiss wrote:Harold,

David beat me to mention that you DON'T need 93 oct. gas; it'll run OK even w/87 oct.
When rebuilding fuel pumps correctly, you must compress the pushrod so the diaphragm will be in a flat position to
the body's face before snugging-up the 6-screws--also, the diaphragm hopefully is renewed, or still flexible; A stiff one won't do the job!
The throttle linkage adjustments start on the frontside of the fan shroud's bell-crank w/50mm ref.; Do you have a
shop manual?

The rest of the adjustments will be needed toward the throttle pedal and it's depressed to the wide open position, there should be a 6 x 45mm long stop bolt w/a a nut and washer to prevent overtravel and breakage!
Finally there should be a little slack @ idle so the carbs will not be held open slightly and prevent a high idle RPM.

Dick

Linkage has slack. Fuel pump rebuilt by Bruce at CFI just recently.

Franny Brodigan wrote:Does the engine backfire when it looses power? Does it load up when it returns to idle?

If not, then probably just bad fuel. If it is backfiring, then the fuel is fine and you have ignition issues...

Franny

At Idle: From cold it fires right up and at warm up during idle I don’t notice much back fire right now.

Driving: I don’t know that I would call it loading up but, really any acceleration seems to make it feel like it’s stumbling or losing power. Even missing. It will backfire some. Strange that it starts and idles so well.

I don’t have any wear on the distributor. It’s tight. The cap rotor and wires have all been replaced now with new stoddard Bosch parts. Points gap was checked. No wear or burned spots on those. Condenser I have not changed. Maybe that will be the next thing and some additional coil tests?

Dick Weiss wrote:Harold,

I forgot to mention: Adjusting the carb balance bank-to-bank, I do it during 2500-3000 RPM (if a Unisyn is used),
or the other. You'll do it more than once adjusting the vertical links; Then I adjust the mixture screws to suit the idle
smoothness as best as possible. However, if having Solex 40 PII carbs, the mix.screws are adjusted to suit the power
circuit of each if the compressions of all cylinders are reasonably matched to each other; Float levels, injections, & fuel pump
output not exceeding 2.8-3.0 PSI are set. Then set the idle w/the stop screws. Zenith carbs may need minor mix. screw. adjustments too, but single entry tops 'kinda' blends their power circuits which is easier to maintain.

Dick

As mentioned earlier, set the stop screw under the pedal.

Dick

Pedal stop screw is checked and good. I’ll put the balance at 3k on the list of checks.

Harold Singh wrote:

Franny Brodigan wrote:Does the engine backfire when it looses power? Does it load up when it returns to idle?

If not, then probably just bad fuel. If it is backfiring, then the fuel is fine and you have ignition issues...

Franny

At Idle: From cold it fires right up and at warm up during idle I don’t notice much back fire right now.

Driving: I don’t know that I would call it loading up but, really any acceleration seems to make it feel like it’s stumbling or losing power. Even missing. It will backfire some. Strange that it starts and idles so well.

I don’t have any wear on the distributor. It’s tight. The cap rotor and wires have all been replaced now with new stoddard Bosch parts. Points gap was checked. No wear or burned spots on those. Condenser I have not changed. Maybe that will be the next thing and some additional coil tests?

Harold - That is what I was getting to. If the car is running lean under load (from your history), it is probably a fuel related issue, but it would need to be common to both sides (like bad gas, not one carb out of tune). If it is rich under load and backfiring a bit, then it is probably electrical, but, again something common to all four cylinders. The first thing I would look at is the condenser. Throw on a known good part and see if that is it. I had these exact symptoms out driving one day and a new condenser and 10 min and I was back on the road again (yes they do go bad and can be bad from new). As a rule, I don't change them anymore during an electrical tuneup as new parts seem to have a high failure rate (for me). If the condenser is known good, then take a look at the coil or other electrical connections.

Just try to box this in and think - is it common to all cylinders, or just one side? What do I hear out of the tailpipes, what out of the carbs? All these issues have a specific tell. Folks will tell you what worked for them but listen to the car. It will tell you who to believe. A bad/fouled spark plug and a bad coil have very different tells but are both electrical.

Listen, postulate, test, eliminate, repeat.

You'll get it!

Franny

Martin Bruechle wrote:People suggest the condensers ?
Back in the 70's 80's 3 years at a shop doing tune ups everyday (mostly VW) then my own shop for a few years,
I don't recall ever seeing a bad condenser.

There are a number of more recent threads on this emergent problem Martin. The replacement ones available these days are rather more fickle than the ones 30 years ago. I have had two fail and others have had similar problems. An easy item to check.

viewtopic.php?f=1&t=36845
viewtopic.php?f=1&t=31632
viewtopic.php?f=1&t=44775&start=15

Mervyn Hyde wrote:

Martin Bruechle wrote:People suggest the condensers ?
Back in the 70's 80's 3 years at a shop doing tune ups everyday (mostly VW) then my own shop for a few years,
I don't recall ever seeing a bad condenser.

There are a number of more recent threads on this emergent problem Martin. The replacement ones available these days are rather more fickle than the ones 30 years ago. I have had two fail and others have had similar problems. An easy item to check.

viewtopic.php?f=1&t=36845
viewtopic.php?f=1&t=31632
viewtopic.php?f=1&t=44775&start=15

Will a VW condenser work for a quick check today or should I order a Porsche one only? Maybe the standard gb-125 mentioned?

Not any discernible difference between any of the capacitors used on all distributors except for packaging. They all perform the same function across the world. Total globalization of a product. Lucky for you the VW one is a direct replacement quite often in fitment. Lucas not quite so convenient.

David Jones wrote:Not any discernible difference between any of the capacitors used on all distributors except for packaging. They all perform the same function across the world. Total globalization of a product. Lucky for you the VW one is a direct replacement quite often in fitment. Lucas not quite so convenient.

Awesome!

Thanks!