cold blooded 1975 911 Porsche

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Old 12-07-07, 09:43 PM
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cold blooded 1975 911 Porsche

HI,
I've worked on my 911 on and off for 10 years and have never been able to solve the cold start behavior it exhibits. There aren't any dealers any where near me and I can't get the local foreign mechanic to take a look at it. So here I am, asking this question. Is it normal to have to wait 3 to 5 minutes for the engine to warm up to the point where the manual choke isn't necessary. In other words, if I try to take off driving right after I start it, and come to the first stop sign, as soon as I let out the clutch the engine will sputter and die if I don't rev the engine or pull on the manual hand accelerator (choke). After about 3 to 5 minutes, depending on the temperature outside, the engine will warm up and no longer exhibit this problem. There is a cold start valve that I could replace but I don't think that is the problem.

This is kind of a shot in the dark so I thought I would post and see if anyone has any knowledge with this sort of thing.

-Derick
 
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Old 12-07-07, 10:10 PM
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It's easier to talk in generalities. An engine would normally take about that long to warm up. For that period of time an engine would require a richer fuel air mixture (provided either by manual choke or automatic choke or computer controlled injectors).

In fuel injected engines a sensor driven computer controls the injectors to provide that richer mixture.

Some engines, because of design, require less time to warm up than others. Things like head configuration and amount of water jacket for cooling, etc. can have an effect on it. Others may run a richer mixture after warmup and that may impact how long the cold running stage would require additional fuel to the mix.

In terms of your 911, you may not be maximized during your cold run period, but all engines have to deal with it.

Hope this helps,

Bob
 
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Old 12-07-07, 10:37 PM
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Yep

Thanks Bob.
I agree that in general an engine like this does have a considerably longer warm-up time when compared to todays standards, however it just seems a bit longer than it should/could be. I'm hoping that some one may know of a way to shorten the warm up time, other than only driving it on 90+ degree days . Specific knowledge of this engine is probably required. I could provide lots of details on the engine, but I'm not sure it would help if you don't already have some familiarity with it. However its essentially just a 6cyc version of a VW horizontally opposed air/oil cooled 4cyc.

-Derick
 
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Old 12-08-07, 11:44 AM
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That's about the case, Derick. I imagine it's hard to find Porsche people with vehicles of that vintage working on that problem. You probably want to keep it original, otherwise retrofitting with an electric choke might be an option.

I don't believe todays engines actually warmup in shorter times since most operate at lower combustion temperatures to accommodate emission standards. But their driveablility is much better because of the controls built into the vehicles to handle it. I do know, from experience, the boxers in the Beetles were very slow to warm up.

You mentioned a faulty cold start valve. Is that an air flow restriction valve, possibly thermostatically controlled?

Have you ran across anyone with a Porsche from those years with a similar problem?

Wish I could give you a specific fix to help you out, sorry. I don't know if there are Porsche car enthusiasts forum that have some specialists or experienced hands in that area.

Bob
 

Last edited by marbobj; 12-08-07 at 01:28 PM.
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Old 12-08-07, 03:28 PM
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You may want to head over to thePelican Parts Porsche forums.

I don't believe you'll find larger concentration of Porsche mechanics anywhere. Good place to buy parts too.
 
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