Driving Symptoms - Solex 40 PII-4 carbs

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Michael Boyd
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Driving Symptoms - Solex 40 PII-4 carbs

#1 Post by Michael Boyd »

I have a 912 engine with rebuilt Solex 40 PII-4 carbs. From startup and after warming up, the engine idles quite well and as I put the car in motion and accelerate from a stationary position I often get a sneeze or pop (backfire). The car runs well until I find myself stopping for traffic signals when the car sometimes stalls as I decelerate before I get stopped or while stuck in traffic or waiting for a green light. As long as I get the transmission into neutral and keep the revs up, I can usually prevent it from stalling. I'm familiar with the worn throttle shaft and butterflies issues and the often referenced "difficulty with idle". Are my symptoms as described above, a driving example of worn throttle shaft/butterflies or do I have a some other problem which needs to be corrected? I would be grateful for the wisdom of the membership. I've told my mechanic that I don't believe he can "adjust" his way out of this problem.
Mike

Mike Horton
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#2 Post by Mike Horton »

Solid shaft (-'67), or split shaft (post '67 MY), and are you running 10% ethanol? Have you set the accelerator pump volumes?
Mike

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David Jones
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#3 Post by David Jones »

Two things that can be tried.. Check the ignition timing, if that is at least at 32 degrees BTDC and preferably 35 +/- 2 degrees then open up the mixture screws a half turn. It may be running a tad lean on idle. If that does not work then you just have to bite the bullet and do a full tune up. If the carbs are worn to the point of air leaking by the butterflies then usually you cannot get a good idle. You could also try a different mechanic. Where are you located that would help a lot on directing you to good help.
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Mike Horton
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#4 Post by Mike Horton »

"It may be running a tad lean on idle."

...where I was heading, David... the split shafts ran 55 idle fuel jets, and on the ethanol, were lean (smog tune in U.S. for '68 & '69)... I installed the solid shaft 57.5 idle jets, up here at 3300', and made progress...
Mike

Michael Boyd
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#5 Post by Michael Boyd »

Thanks Mike and David! I am running 10% ethanol and I have split-shaft Solexes. At the moment I'm not certain how the timing is set given some tuning by my mechanic. I also don't know what the jets sizes are at the moment. Carbs were rebuilt by a previous Porsche mechanic. Today after posting, my mechanic identified two spark plug wires with corroded connectors. After repairing, the engine ran much better and on a short test run, there was popping on acceleration still from stopped position but it never stalled on the test run. I can feel some play in the throttle shaft and I'm certain it's time to have the throttles and butterflies, etc done. Tomorrow I will order new set of wires, cap, rotor and plugs and try to get a longer test drive. I'm in Sarasota, Florida. Thanks again!

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Curt Dansby
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#6 Post by Curt Dansby »

Hi Michael
When you say re-built you mean kit- gaskets, needle valve etc- not sent to Bruce Smith or Carb Rescue for "Re-Hab"?

Curt

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Martin Benade
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#7 Post by Martin Benade »

Your timing might be a bit retarded from where it should be, that makes popping and sneezing more likely. Generally worn throttle bores cause a high idle if everything else is OK, because you cannot control the air leaking past the throttle plates.
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Michael Boyd
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#8 Post by Michael Boyd »

Martin, I will check the timing tomorrow and try a change to see if it addresses the popping and sneezing. Thanks for the info and suggestion.
Mike

Michael Boyd
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Re: Driving Symptoms - Solex 40 PII-4 carbs

#9 Post by Michael Boyd »

Curt, The carbs have just had the standard kit and I have now been in touch with Bruce to get the needed machining done. I think the discovery of the two bad plug wires may have corrected the stalling aspect of the overall problem and I do more traffic-intense test driving to confirm. Thanks...
Mike

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