I think I've had a breakthrough!

I had a quick play tonight after work and opened up the air correctors and it bought the idle back to a more normal range. I had set them at about 1/8 turn out and not changed them much as all the barrels other than one were pulling equally.

I had no idea these would have such an effect, I thought they were just there for adjusting the differences in air flow between barrels but I guess it was running so rich it was idling high......

At least now I can adjust my mixture screws and get the thing running properly.

Cheers:D

CAmeron,

Great to hear about your success. I have been following this thread because I sometimes have the same issues. How far out did you take the air correction screws? I too have mine pretty close to 1/8th.

Does anyone have a thought as what this means? Is there some other jet, etc. that should be changed if this has helped?

Rob,

I think I've got them out by about 1 whole turn now. I haven't yet put the synchrometer on the barrels and balanced them all again as I was pushed for time so I'm not sure if thats where they'll stay but its certainly made the idle drop.

I'm going to put my .60 idle jets back in on the weekend and have a good play with it then. Let us know how you go and I'll do the same. Oh and take your idle screws back to base as well, you'll have to probably keep it going with the throttle linkage but at least you'll know that you've got the right starting point.

Cheers

Cam,

Too rich will never raise the idle, only lower it. Sure, you can lower the idle by dialing out the air corrector jets so far that it leans out and will barely run, but you will know you've leaned too far when it doesn't have any throttle response. And watch out running lean, holed pistons and broken rings are at the end of that trail.

I have been following your story here and on Early S. I sincerely believe that your problem is the distributor. I think it's giving you too much advance at low RPM, which is why it won't idle. If I were in your situation, I would get a dial-back timing light so you can check the exact advance values, then prepare a map of the advance every 500 rpm from 0 all the way to 6000. Then compare that to the timing curve in the factory spec book. My belief is that you've got too much advance down low, which could be verified by dialing in a lot of retard for testing. Try it straight up, or five degrees retarded.

I read the part about you not being able to adjust the distributor. The distributor body has a radial notch in line with the #1 spark plug. Set the engine to #1 TDC with the Z1 mark opposite the notch in the fan housing. Verify that you are, in fact, at #1 TDC by poking something in the spark plug hole. Do not drop the something IN the spark plug hole, nor score the piston or otherwise do anything with the something that you wouldn't be proud to tell your mechanic. Got #1 TDC? Great. Remove the 13mm ATF nut from the distributor stud and pull the distributor out of the hole. Now put it back with the rotor pointing to the notch in the housing, with the distributor stud at exactly half way down the adjustment slot. Don't try to use a rev-limiting distributor for this, it is too funny-looking to aid in your diagnosis: find a straight one out of a later car or a VW. That is the correct timing alignment for #1 TDC straight up. Replace the nut and snug it up, do not tighten it.

With the timing straight up you should have enough retard for easy starting. Aim the timing light at the notch in the fan housing. You should see the Z1 mark illuminated. Now dial back five degrees of retard on the timing light. On our cars (you SC guys, keep quiet here) the distributor rotates in a clockwise direction as viewed from the rear of the car. That means that to retard the spark at #1, you turn the distributor clockwise, so that the #1 contact is further away from the normal position, and #1 has actually passed TDC and is starting down by the time the rotor gets around to touching the #1 terminal on the cap. With five degrees of retard on the light, the Z1 should be lined up with the notch. Now tighten the nut down, be careful not to strip it.

Next, throttle the engine up to every 500 rpm and dial in the advance until the Z1 mark is opposite the notch. Note the advance reading. Do NOT get your necktie or anything else (your ponytail or your grateful dead shirt, just kidding JW) entangled in the spinning fan while you are doing this.

With the map generated, you should have something that looks like this:

http://forums.pelicanparts.com/uploa...1135710624.jpg

Not that, exactly, because that is the curve for my 1966 normal, but you get the idea.

My guess is too much advance down low is bumping the idle up. Only testing will tell.

Good luck! See this thread for more: http://forums.pelicanparts.com/porsche-911-technical-forum/252299-before-there-bhkz-swb-engine-electrics.html

Great post John.

Cam, as I mentioned earlier, sending the dizzy away to be re-mapped (and rebuilt if necessary) for your new engine specs and Aussie fuel is well worth the trouble.

John(s)

The dizzy has been sent away and remapped. I gave them all of the info on the car including the type of petrol I use (98) They removed the vacuum advance that was not connected anyway. It came back with a sticker on the side that said 10 degrees BTDC but I have timed the engine from 5 degrees ATDC to 10 BTDC and it didn't seem to make any difference to the idle. Advance at 6000 is currently about 35 and I am running about 3-4 degrees BTDC at present. I might try to map the advance curve through the range but it does seem to advance OK.
I reset the dizzy exactly as you have described.

Cheers

Well is sounds like the dizzy is safe then... are you running electronic ignition?

Did you check out your fuel pressure? If it was fine before the changes to the carbs, then it's probably still okay. Double check the needles. I'm interested to know if it's pulling the same air on all barrels. I'd basically work on getting it all equal and tunes, and then use the hand throttle to keep in running smoothly.

Cam, Who did your distributor? How much was it? Thank you!

Aloha Jon

It was done by Performance Ignition in Melbourne Australia! About $200 Australian was the cost. No one doing dizzy's in Hawaii?

John I've still got the original CDI and points since I took out the pertronix.

Cheers

Ok I have only had the chance for a quick play today and that was spent resetting the timing as the points gap was closing up making it miss a little.

I have another question though from John Cramer's post above. Even if the air correctors are out a turn or so, can't you then adjust the mixture screws to get the correct mixture setting without risking running lean?

Cheers

Cam, once you set the points gap with a feeler gauge, be sure to tighten the screw nice and tight, but be careful, it's easy to strip.

Cam: if the engine is running too fast at idle, there is only one cause, and that is that somehow, whether past the throttle plates or another way, the engine is getting too much air. A fat, or lean idle mixture is not used to set the idle, it's the throttle position. If you have the throttle plates open, and then use a fat mixture to slow the engine down, the mixture will be wrong in the rest of the operating range.

It seems to me to be a correlation problem. Get yourself an STE sycnrhometer such as the fine one available from our host. The first thing is to make sure the linkage is set with zero preload. Of course, the best way to do this is to remove it all: throttle link, cross-links, side links. Basically you want two independent carbs for setting the idle. Next, check the throttle linkages for any binding or play, or anything that could cause them to NOT seal the bores when you are at idle. I would even go so far as to remove the carbs and verify that you can't see daylight around the throttle plates, and check the clearance when the throttle is at the stop with a feeler gauge, just to assure yourself.

It's a simple matter of putting the air corrector screws in the same position on each carb, dialing the idle speed adjustments all the way out, or remove the screws entirely so that the linkage hits the stop, start the engine and measure the airflow. You should get a reading of between 3 and 5 Kg/hour for each throat, and the air corrector screws can be used to dial this reading down, and set it equal between them all.

Good luck!

Oh crap....the fun continues.....Took the car out to warm it up to start playing with the carbs and it started breaking down again. What the ..I just gapped the points again yesterday as they had closed up a little.

Pulled the dizzy again and the gap was fine. Ok then lets get past this I thought and put the Pertronix back in. Can't get more than about 5 degrees advance, dizzy at far end of slot, same problem as before as one tooth's adjustment sends the dizzy off to the other side of the slot.

Anyway now I'm seeing the timing mark moving around through a range of about 5 degrees at steady speed particularly with a few revs. Call me crazy but this should not be happening with a newly rebuilt dizzy should it?

Arghhh where will it end??!! Perhaps they stuffed up the dizzy rebuild?

Cam,

I am one of the few people who doesn't think a Pertronix is necessary, insofar as the point wear you get with a CDI is negligible. With only 420 mA of current in the wire from the points to the CDI, you just don't get the same wear of the points that you do with the old-style SWB "kettering" battery-coil-condenser ignition. So for consistency purposes, I would advise you to put the Pertronix aside until the breakup issue is resolved.

Now, the points gap should not "close up" in normal operation. The points are held to the advance cover plate with a small cheese-head screw and the gap is set by inserting a feeler gauge in the points gap with the points "open"-- with one of the bumps on the distributor shaft touching the phenolic rubbing block at its highest point. Once you have it set, and verified that you haven't got the gap set too wide because the feeler gauge is cocked to one side, you must tighten the screw so the points don't move. It will require a fair amount of torque, but not so much that the screwhead strips or, heaven forbid, the three threads in the advance cover plate rip out.

Once set, the gap shouldn't change at all, even over tens of thousands of miles.

You can fairly easily check whether the distributor was properly rebuilt. Pull it out and check the shaft for axial (up and down) play-- should be no more than about 1/16 of an inch, and radial play, which could cause teetering of the rotor -- should be virtually none. Verify that the advance mechanism moves smoothly and returns to normal when you release the rotor. Make sure the advance is lubricated with a goodly amount of Bosch Distributor Grease but do NOT get any lubricant on the points.

Reinstall the distributor so that when the rotor is pointing to #1, it's pointing toward the right rear corner of the car, as you face the engine. This will allow you to dial the distributor clockwise and anti-clockwise sufficient to set the advance at idle. It should NOT be running out of range.

I am somewhat suspicious of the "10 degrees" that came on the distributor when you got it back-- does that mean that 10 degress is the initial timing setting? That would NOT be correct for an S distributor.

Good luck and keep us posted on this Antipodean mystery!

Cam, from the factory workshop manual p. L40a:

6000 RPM 30 BTDC
2800-4400 rpm 23-29 BTDC
2000 RPM 10 BTDC-18 BTDC
1000 RPM 4ABDC- 2BTDC
Vehicle Stopped Max 4 ABDC

John,

Yes the dizzy came back with a sticker that said 10 degress BTDC which I would assume is the initial setting. Very little play in the shaft and new spacers and roll pin.

Hopefully I'll get more play time tonight. Are you sure on 30 degrees for a '72/73 S motor? I thought they could run around 36.

Thanks for your continued help here.

this is what I use with low comp pistons. At 10 advance engine starts and runs great w/ vac disconnected . It's not even close to detonation on low test gas. I'm not cheap at all.. i'm just real positive.

This dizzy is cheap brand new.









http://forums.pelicanparts.com/uploa...1157357942.jpg

From 72/73 P Tech Spec bk





http://forums.pelicanparts.com/uploa...1157360600.jpg

Cameron it sounds like a vacumm leak. I recently rebuilt my 2.7 7 when it came to the timing i had the same problem as you with the dizzy being hard to the right against the bolt to get my timing spot on i just left it there,it works fine.Where did you get your webers rebuilt as i have to get mine done?

And now for tonights instalment:rolleyes:

Bede when I said I had my carbs rebuilt, I meant changing the venturis, jets, emulsion tubes etc and putting a kit through them. When my mechanic checked them over he said the shafts were fine. I had no problems before I had them apart, but the specs were more for a T engine and I wanted the extra horses.!!

Unfortunately I pulled the carbs apart and sent the dizzy off to be reconditioned at the same time, hence not knowing where the problem is coming from.

Tonight I moved the dizzy one tooth clockwise as I couldn't get as much advance as I wanted. As before it means the dizzy is clocked over to the opposite side now but I can get anywhere from TDC to mucho advance-o.

I set the timing at 10degrees BTDC and went through the rev range and here's where its at.

Mine
1000rpm - 10 degrees
1500rpm - 20 degrees
2000rpm - 25 degrees 4000rpm - 30 degrees
6000rpm - 30 degrees


These are rough as I only have a basic timing light and marked off 10 degree increments on the pulley wheel with some white out. As before the timing only gets hung up when the engine is warm. Still getting a few degrees of timing fluctuation with a few revs.

I think I might pull the dizzy tomorrow if I get the chance and put the points back in and do it all again but you would imagine the result would be the same.

So what do you reckon guys?

No time to play tonight but BUMP for input.....!