Cold Start Problem 2.7 1975

CARRERIC · 11-20-2002, 05:40 PM

Hi guys. My car fires up immediately on cold start using hand throttle. I have to continue using hand throttle while driving for about thirty minutes, and completely warm up or it will stall. If it stalls it's difficult to start again. I don't think it is the WUR. The idle will also surge up and down while at a stopped at a light.

Any ideas or comments

Eric

Sunroof · 11-20-2002, 07:08 PM

Yep, sounds like mixture to me. If the idle searches it would be good to try and adjust the mixture as it could be too lean. One small click at a time for adjustment (clockwise-rich, counterclockwise-lean). I had the same problem.

Bob
73.5T

jk911 · 11-20-2002, 08:10 PM

I had the exact same problem with my '75 911 CIS. It sounds like your deceleration valve has died. its that funny pear shaped bass object directly behind the throttle body.

bigchillcar · bigchillcar's Garage

I need to weigh in on this thread. I have a '74 2.7 currently having some cold start trouble. Mine starts right up with the hand throttle all the way up too. No problem starting, but have to baby the hand throttle until really really warm or the idle just drops to under 500. Don't think it will die, just sounds like it would...cd player always stops playing to let me know...

I've wondered about the WUR and have recently heard mention of the decelleration valve as well from Doug Clauder or maybe my mixture is the problem. I really don't know the proper way to set it or the idle, but figure I better start learning fast. The car drives great when warm. Found my rev-limiter tonight around 6500!

Ryan

crashr · 11-20-2002, 09:11 PM

I have a 75 911S that I recently purchased. When I got it I noticed that the idle speed was way to high... Could this have been a (incorrect) correction for the same problem?

What does WUR stand for? What is it?
How does the deceleration valve work?

Superman · 11-21-2002, 07:31 AM

I'm going to disagree. It may be mixture, it may be decel valve, it may be WUR, but the device that is supposed to keep your idle up during cold operation (by allowing additional air into your engine as though the throttle were slightly open), is the Auxilliary Air Regulator. On my engine, it is attached to the intake runner between #5 and #6 cylinder head. It has an electrical plug on it and two large hoses. Disconnect the hoses and, with a flashlight and mirrir, check to see that air passes through, from one hose to the other. While cold. Once warmed up, that opening should be closed.

At least, this is all true of the CIS systems I have dealt with. YMMV.

Sunroof · 11-21-2002, 08:39 AM

I do not have on my 73.5 (first CIS) a thermotime switch nor air regulator (pump) as in the update models, so I could be 25 degrees to port on this one. I do know that when I had the same problem (great on cold start, but problem after warm up) it took fiddling with the mixture to get the problem solved.

A heads up on the mixture screw though.............when I put the allen wrench (t-handle) down into the adjustment screw and turned, nothing happened. It did turn out that someone put loctite on the screw to set the mixture PERMANENTLY. I had to remove the air cover and hold the sensor plate with one hand (firmly up) to get the adjustment tool into the screw slot and turn hard. I finally loosened it up with PB Blaster.

My mechanic tested the decel valve by taking the hose off where it connects at the base of the distributor and "blew or sucked on it" to check the movement of the mechanism. Strange heh! But that show he could tell if it was functioniong properly.

Their is a K-tronic tune-up and info guide that I have seen around for about $20 that may be well worth the investment.

It may be worth having the fuel pressures set on the WUR first, then move to the mxture adjustment and you air valve.

Regards
Bob

CARRERIC · 11-21-2002, 10:50 AM

The valve stem on the the top of my decelerator valve has a nipple cover on it and the hose is missing. Does anybody now where the hose goes to and why it would ahve been removed and covered? Any diagrams?

jk911 · 11-21-2002, 02:43 PM

See that's your problem. The deceleration valve was faulty so someone tried to inactivate it by blocking it.

You should replace it with a new one. Its not expensive and its relatively easy to replace.

It solved my surging problem instantly. My revs use to shoot up and down like crazy before I replaced it.

Review some of my old posts and you should find some diagrams
also check this site out.
http://members.rennlist.com/jimwms/CIShome.html

jk911 · 11-21-2002, 02:48 PM

Oh yeah , Superman,
1975 models didn't come with an Auxilliary Air Regulator. Only the deceleration valve is used.

CARRERIC · 11-21-2002, 05:15 PM

JK911, THANKS FOR THE INFO. WOULD YOU HAVE THE VACUM LINE AND EMISSION CONTROL DIAGRAM ON HAND? I TRIED SEARCHING THE POSTS. EACH YEAR IS A LITTLE DIFFERENT.

47silver · 47silver's Garage

we put a new hose on ours. the bottom connects to a small post that is located about 2 inches to the passenger side and 4 inches 6 inches down from the top of the valve. i could not see it but was able to feel the connection. i removed the air filter cover and it was a little easier. incidently i think that the hose is 5 mm diameter. it is #64.

jim sims from nm posted this for me.

Parts catalog lists it as vacuum hose C4.5 mm (ID) x 10 mm (OD) x 520 mm long; Porsche Part no. 999.181.167.50 sold by the meter. I've used Pelican Part no. VH-5-10 as a replacement for the OEM size. Jim

CARRERIC · 11-30-2002, 01:01 AM

47 Silver, Thanks for the diagram and part number. They are a big help.

Rouxzy · 11-30-2002, 03:31 AM

The purpose for the decel valve is mostly emissions. It is there so when you let off the throttle the rpm's decline gradually. I did encounter the same problem with my '77. It wasn't the decel valve, it turned out to be a vac leak. Check all your hoses for cracks and such. Just a thought.