Engine wont idle smoothly eek!

Airhead · Post by **Airhead** » Tue Dec 07, 2004 5:15 pm

Okay so I decided it would be a good idea to check the valve clearances, timing and carb synchronisation on my 912 as part of a service after taking it out of long term storage as a project..........only trouble is now it's less reliable than it was:rolleyes:

Perhaps I should have left it alone as it seemed to run fine but I was a bit concerned that the timing had seemingly been set to nearly 40 degrees total advance

Its running a 009 dizzy so that would be a fair bit of advance at idle and it used to idle a bit fast (1200 rpm).

The object of the exercise was to make sure that the timing wasn't dangerously over advanced, to get the tickover speed down to something more sensible, perhaps cure the fact that it wasn't always easy to start and to hopefully get a few more than the current 25mpg

Trouble is that although the carbs were dead easy to balance and set up they dont seem to stay that way one day it will idle at 1000rpm, sometimes back to 1200rpm and other times it will seemingly refuse to warm up and insist on a 650rpm tickover!

Since the idle circuit is all that can tuned I fear that the popping noise it occasionally makes through the carbs at 3500rpm on the motorway is not a good omen

Maybe its always been there but I didn't notice it before having only driven it for a week. I expect such noises when cold at tickover for the first few mins however.

I set the mixture at idle by winding the air screws all the way in and the out 1 full turn and then adjusting for best tickover when warm at idle. other than this the only carb setting I changed was to close all the air bypass screws as they seemed to balance fine without the need to adjust these. My understanding was that you use these to allow a little bit of air past one butterfly to balance in account for non even wear between the 2 in one carb but these carbs haven't had much use so seemed to balance okay as is.

It pulls through the gears lovely but I never seem to get the exact same tickover as the day I set it up and it's always harder to start than it used to be (hot or cold).

On a side note carb icing did cross my mind as a possible cause (it has stalled in a low gear once or twice) but I thought that the manifolds were short enough to be plenty warm on these cars.

Any ideas as to what is going on?

Airhead · Post by **Airhead** » Tue Dec 07, 2004 5:15 pm

Wow! long post........sorry just thinking out loud

hashman · Post by **hashman** » Tue Dec 07, 2004 11:31 pm

I remember reading some where that the advance springs in the distributor can have an effect on the idle. Getting new ones or adjusting the points on which they mount to so the springs are not so weak.
Just something to think about or investigate.

Barry · Post by **Barry** » Wed Dec 08, 2004 5:31 pm

I agree, make sure that your distributor is not fluctuating the advance around idle speed. I spent a lot of time and effort on the fuel side, only to find side to side play in dist. shaft plus a sticky advance/retard. Might be worth putting the timing light back on, get the car to idle and gently fluctuate the revs just enough to get the advance to kick in (don't welly it as this makes it easier for the advance/retard to re-set). See if the timing always returns to the same point.

Also then worth doing the same with a dwell meter (if you've got one): same process, the dwell might reduce by a degree or so but always be steady. Any jumps spell trouble! At least these checks are very visual, and can absolutely rule out ignition if fine.

lewis · Post by **lewis** » Wed Dec 08, 2004 5:57 pm

the 009 dizy requires an initial advance of 15 to 18 degrees at the crank and the starter motor has to work realy hard to overcome this,and is not really a porsche part more for hot VW's I changed mine to a 050 and it runs really sweet now. also heard of problems with number 3 cylinder using the 009.

lewis

Post by **Miggs** » Wed Dec 08, 2004 7:12 pm

if its 912 lose the 009 there bad for 12's

Airhead · Post by **Airhead** » Wed Dec 08, 2004 7:17 pm

Maybe the 009 isn't the ideal distributor but it's what came with the car so is what I have to work with for now.

However I dont think they are as bad as people make out since the VW has the same issue with the oil cooler being in the vicinity of number 3 cylinder why would the 009 exasperate the problem for the porsche but not the VW

It is a weakness anyway so if your car is having overheating problems then number 3 is bound to be the first one to pop a valve whether its a VW or a porsche flat 4 and whether it has a 009 fitted or not. Neither the 009 or the 050 have a retarded spark on number 3 cylinder either.

As for the initial advance......the 009 does have 8 degrees less internal advance than the 050 and a wider 2 stage curve. Set to 30 degrees of total advance at 3000 rpm the 009 would therefore fall back to around 8 degrees BTDC. However todays lower octane fuels mean that most experts recommend that you set your timing to no more than 30-32 degrees full advance instead of the factory recommended 37 (I suspec this is where the 15-18 degree figure comes from). So does the fact that the 009 has 8 degrees less advance than the factory dizzy or an 050 actually matter? Maybe the advance curve will give the engine different characteristics but I dont think running a 009 causes your engine to blow up or have starting problems as some would have you believe.

Airhead · Post by **Airhead** » Wed Dec 08, 2004 7:27 pm

Here are the curves for a few dizzys that I dug up on the 912bbs for info I would credit the guy that produced them but forgotten who it was (thanks anyway)

All ignition systems are functioning correctly and I took pains to get the dwell angle bang on 50 deg (not easy with a set of points and feeler gauges......usually I settle for +-2 deg). Made sure the valve clearances were spot on before attempting to tune the carbs too.

I think the crux of it probably lies in the fact that I altered the position of the air bypass screws to all be closed. Some say you should close them, others say you should balance the lower throat to match the higher one at idle by opening them slightly. I assume this is to compensate for any uneven wear in the butterflies? Mine seemed to balance okay without the need to open them. Unless they have another function that I am not aware of.

lewis · Post by **lewis** » Wed Dec 08, 2004 10:08 pm

not really being an air cooled expert I can only act on advice given by different experts, Harry Pellow the maestrow, Duane Spence ect and they all go to great lengths to point out that a porsche engine is not a VW and that the 009 is a bad combination but if you are happy with it fair does.With the mileage that we all do now which in my case is nil untill I'm back on the road I can see your point of view.

lewis

Garfield · Post by **Garfield** » Thu Dec 09, 2004 2:55 pm

Anyone know where I can get new advance springs for an early 911 distributor (1969 911T)

gav p · Post by **gav p** » Thu Dec 09, 2004 3:32 pm

Airhead,

Not being a distributor expert I'm not sure whether the 009 would cause an uneven idle.. I'd have thought that it could only be the guilty component if it is worn or the mechanical advance is not working properly.

My 912 engine was very difficult to start when I first had it, and the problem was the carbs. The heat-sink spacers between the carbs and manifolds were missing, which meant that the carbs got too hot rather than too cold (never heard of icing being a problem on these cars).

The too-hot carbs result in the petrol evaporating from the float chambers when driving, so that when you pull up at the lights theres not enough petrol and the engine wont idle properly until the chamber fills up again.

On one occasion the engine stalled on the open road, as all the fuel must have evaporated. The same effect caused difficult starting, where the fuel evaporated when the engine was still hot after being shut down, leaving an empty float chamber - the car only started when fuel was pumped back in by cranking the engine over on the starter for 30 seconds...

If you have those spacers under your carbs though, this may not be relevant to you....

MdR · Post by **MdR** » Fri Dec 10, 2004 1:39 pm

I've never played with a 356 engine.
I've played with a few VWs and I've used the (Dave Darling on Pelican- I think) 009 float test.
Chuck your 009 into the nearest river/lake/sea, if it floats retrieve it for further testing.
I try to use a factory dizzy as they've a much better build quality.

Robster · Post by **Robster** » Fri Dec 10, 2004 5:47 pm

Good lord! 40 deg advance!, I'm surprised you didn't damage the engine!

30 deg advance should be the max.

Try the following -

1) set air bypass(s) to 1 turn out.
2) warm up the car, then adjust the timing, but check it at 3000 rpm, then you know the distributor has reached full advance.
3) assuming twin carbs, disconnect the throttle linkage and get it idling at @ 800 rpm. You need a good quality carb balancer to measure the airflow (one that doesn't cause too much restriction to air flow). make sure the throats nearest the trottle linkage on each carb flows the same air volume.
4) Doing each mixture screw in turn, back them all out by about 3 full turns, then one by one screw them in until the engine runs lean and starts popping out of the exhaust. back it out until the engine runs smoothly. On tothe next one...
5) you will have to keep adjusting the idle speed and comparing airflow on each barrel as you make adjustments.
5) Once that is done, then use your balancer to check each troat is flowing the same. This is when you can adjust the air-bypass screws, but they should all be flowing the same.
6) if you take time for the engine to react to each adjustment, with trial and error, you will get the carbs dialled in. Then re-attach throttle linkage.

The 009 should be fine on 356 or type 4 VW motors. The distributor cam has a profile that slightly retards the firing of the plug on cylinder 3, as the head on cylinder 3 runs slightly hotter than the others as it gets the least airflow from the fan.

I hope that helps!

best regards
Robster

Airhead · Post by **Airhead** » Wed Dec 15, 2004 10:17 am

Cheers, that is exactly what I tried next. It seemed to behave itself for a while but after lulling me into a false sense of security began misbehaving again. Doesn't always want to idle in traffic and misfiring getting more frequent............now working on the theory of something causing some fuel starvation as when it does stop it's a bitch to start again and the way in which it dies is very reminiscent of running out of fuel (i.e. nothng you can do with your right foot to keep it alive)