Out of options..engine keeps stuttering

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Thomas Sottile
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Re: Out of options..engine keeps stuttering

#46 Post by Thomas Sottile »

I think you need a fresh eye someone new to look at it. where are you located ?

Geoff Ver
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Re: Out of options..engine keeps stuttering

#47 Post by Geoff Ver »

Mike Wilson wrote: Fri Apr 12, 2019 4:25 pm When it shudders, is it what I would call a soft shudder like the fuel was shut off or it was starving for fuel or a sharp shudder, staccato-like, like you shut off the ignition? Fuel-related vs. electrical.

Have you run the engine in the dark and looked for bad wiring causing arcing?

Mike
Definitely a soft shudder..

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Re: Out of options..engine keeps stuttering

#48 Post by Geoff Ver »

David Jones wrote: Fri Apr 12, 2019 5:25 pm Geoff, whenever I have arrived at the stage you are at with a problem that I cannot resolve or pin point I find the best thing is to substitute known good parts and at this stage I would suspect the carbs, probably only one and probably only one throat. There are two ways to go. Run your carbs or distributor, coil or fuel pump on another car or borrow a known good part from another car and try it. Do it one at a time. I have one other thought, did you check that the throttle butterflies are tight and also the venturis or any of the other parts that can be removed are tight in their places. Compare one Zenith and base with the other and look for variances in them. Apart from the linkages they should be identical with identical jetting.
Good idea but not an option for me. Aren't any other 356jes around to test this.

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Re: Out of options..engine keeps stuttering

#49 Post by Geoff Ver »

Mike Wilson wrote: Fri Apr 12, 2019 5:46 pm I'm assuming Zenith carbs. Have you checked the float needle valves? There are some bad ones that hang up.

Mike
Yes, checked it. Can bigger jets help?

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Wes Bender
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Re: Out of options..engine keeps stuttering

#50 Post by Wes Bender »

Maybe, but by changing things rather than troubleshooting specifics, you'll be clouding the picture.
Some days it's just not worth chewing through the restraints.....

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David Jones
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Re: Out of options..engine keeps stuttering

#51 Post by David Jones »

Geoff. I would suggest that you take a ferry ride over the channel and visit Mike and Paul at PRS.
If I had known I would live this long I would have pushed the envelope a little harder.
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david meyers
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Re: Out of options..engine keeps stuttering

#52 Post by david meyers »

Greetings Geoff and others, while not to disagree with all the ideas/suggestions/things to try , ( as most of the veterans/posters here have forgotten more than I'll ever know) ...but I had a very similiar problem / symptoms ,
and before I ramble on with what was maybe the "perfect storm" of failures at the same time I had last year on my 64 C... don't think anybody has mentioned this possibility here....but I found out it was the damn Generator !
(and I first tried most of the suggestions mentioned in this tread )

If you have the book or access to it ..the356 "Technical and Restoration Guide" of the Registry , go to page 107, 108,109 and read what Larry Wapnik wrote from Vol.17 #4..
.if I wasn't such an old analog guy I would know how to post it here <smile> , but what he said in his article "Generator Removal and Replacement", got my attention , and after
installing one of Zim's Premium Generators.. bingo ! ..Now I get better milage, more power, less noise, more smoothness, better idle ,and better cooling..I have to agree with Larry ,
"you could say the generator housed in the 356 is very unique , and to be even stronger , you could say its the heart of the engine power plant, and if the generator breaks down physically ..."
well there is too much for my old fingers to type ...but check out your generator ...my car has never run better !

The "Perfect Storm " I mentioned was the old starter not disengaging, then taking out/frying the ignition switch , so after loosing a lot of my "DNA" I finally got a supposedly" rebuilt Bosche" installed , only to find out
that the term rebuilt to Bosche sometimes means get a rattle can of black paint... spray a little lipstick on that pig and ship her out ( all the black paint was coming off on my hands, etc during installation..ugh)
Well it would barely turn the engine ..and I had new battery, ground strap etc...Well, Dennis @ Zims admitted they have issues with the rebuilt Bosche units sometimes, and gave me a credit towards one of their
premium starters, which works / looks great..well then I had the roughness/shudder above idle ...Damn...happened to read the above mentioned article and started checking output, etc, voltage was all over the place
battery did not seem to be charging , so then a call to Zim's (thanks for the help Dennis) and I got one of their premium build generators, even added a new voltage regulator and wiring (determined to fix the weak link)

So I'm happy, car seems happy, even wife seems happy ...but the day is still young , and the "princess" still refers to every drive as a "test flight "
I can see she still has some doubt's...hmmm

cheers,
dm
David Meyers

It's never too late to have a happy childhood

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Martin Benade
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Re: Out of options..engine keeps stuttering

#53 Post by Martin Benade »

I think that comparison test of driving on left vs right carb sounds like an excellent one. If it is equal on both sides that pinpoints it to fuel pump delivery, or electrical. If only one side is bad, it is that carb or the ignition for those two cylinders only. Just trying to be clear, your understanding may be beyond this explanation.
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Geoff Ver
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Re: Out of options..engine keeps stuttering

#54 Post by Geoff Ver »

Hi all,

After weeks of testing without result I eventually borrowed a set of Zenith carbs, just to be absolutely sure the rebuild carbs weren’t the problem. But unfortunately they were the problem! After mounting the borrowed set and a quick tune I immediately noticed the difference. A smooth drive!
After these tests the rebuild carbs were checked again and we came to the conclusion that the Main jet, Air correction jet, Idling jet, Idling air jet and Pump jet were the wrong ones for this type of carb! Unfortunately these weren’t checked on the correct measurements and re-used when rebuilding the carbs. Really don’t know how the 356 has driven with these wrong carb parts in the past.

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Re: Out of options..engine keeps stuttering

#55 Post by Jeffrey Leeds »

Thanks for sharing the outcome of your problem. Happy Trails
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Geoff Fleming
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Re: Out of options..engine keeps stuttering

#56 Post by Geoff Fleming »

It was probably driven by someone who assumed the performance, or lack thereof, was normal for an old car. Many owners are surprised when they finally realize how great a well tuned engine is, after plodding along with sub-par mechanicals.

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Thomas Sottile
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Re: Out of options..engine keeps stuttering

#57 Post by Thomas Sottile »

Do a leak down test next

Dick Weiss
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Re: Out of options..engine keeps stuttering

#58 Post by Dick Weiss »

As I mentioned previously about the Zenith's injection nozzles "squirting" straight down.
make sure they do--I've had several which just "dribble" a small amount of fuel during
acceleration resulting the situation you're experiencing.
Also, i've had a couple of nozzles which weren't drilled properly--the holes didn't get fully
internally connected resulting in the situation above and finally--the nozzles can be clogged
due to"crusties" exist in the very very fine outlet which a fine wire can be used to poke it out
There are times that a carb cleaner won't break it down and an air gun won't do it, either!
However, soaking it in Stabil will eventually break down the crusties--especially strainer screens.

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Wes Bender
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Re: Out of options..engine keeps stuttering

#59 Post by Wes Bender »

That's good to know. I wasn't aware that Stabil could be a solvent too. Thanks, Dick.
Some days it's just not worth chewing through the restraints.....

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