New 964 Cams in SC surging idle when cold after rebuild

[stealthn]

Hi,

I just got my SC fixed up for the next 30 years with a top end rebuild, new valve guides, rings, rod bearings and new 964 cams.
My mechanic took it for a boot and said it runs great but surges a bit at idle when cold, but idles fine when warm.

I've read about this before with the 79's (bigger ports) with 964 cams and SSI's, but I can't find the article.

My mechanics going to run through everything on the mixture, idle, air, etc. I just thought I would post here to see if anyone had the same issues.

Cheers, and looking forward to feeling the new cams in the ols girl

[edgarcia737]

Check the WUR. Hook the gauges up and see what pressures you are getting. I'm running 2.5 bar which is a bit lower than spec but it works for me.

I just finished a top overhaul which included JE 9.8:1 pistons, 964 cams along with SSI's and a Dansk Sport muffler. She running sooooooo sweet.

Ed Garcia
1977 Carrera 3.0

[stealthn]

Thanks,

I just spoke to my mechaninc and apprantly it does it hot or cold so I don't think it's the WUR. I will get the car tomorrow and take her for a drive to see if I can figure it out, and I'll ask them what they went through to troubleshoot.

Any more thoughts, anyone?....

Cheers

[aigel]

Surprised the mechanic didn't adjust the mixture, timing and idle all before sending you home with the new engine?

I had no hunting idle on mine but my mixture was all off when I installed my 964 cams and SSI (done at the same time).

George

[T77911S]

Originally Posted by aigel

Surprised the mechanic didn't adjust the mixture, timing and idle all before sending you home with the new engine?

I had no hunting idle on mine but my mixture was all off when I installed my 964 cams and SSI (done at the same time).

George

+1

may just be mixture since hot and cold are doing it.

[stealthn]

George, Was this on a 79?, As well what were the final numbers on afm, idle, etc?

Thanks so much

[Daviboy]

edgarcia,
This is weird I just posted on an issue starting with exactly the same set up apart from the Dansk, mine are custom headers and a 2 in 2 out Powerflow. I have not altered any CIS settings since re-build which is still as it was was when removed from the engine.

[stealthn]

In speaking with the mechanic, he has gone over idle, mixture and timing, but wants me to break in the engine first before a re-adjust. He said there is some resistance until the pistons/rings seat, then he can adjust in the final state.

I pick up the car tomorrow so I'll have a better feeling as to what the issue is, I'll post my findings.

Bob

[aigel]

Originally Posted by stealthn

George, Was this on a 79?, As well what were the final numbers on afm, idle, etc?

Thanks so much

Sorry stealthn, it has been too long for me to remember . I used my innovate afm meter to set it up. Idle was stock 950 and I was conservative on the mixture (richer side) as well as the advance (not many degrees over stock). I had an 81, so it is a little different with the lambda sensor.

George

[MotoSook]

BS on the adjustment after breakin. It can be tuned as is. Get it up to operating temp then make tuning adjustments. With new cams you'll need to adjust idle air bypass, mixture screw and timing. Even just an mixture screw adjust will be good for it n

[aigel]

Souk is right. There isn't any drag or resistance in an engine that is being broken in. At least none that would influence mixture, idle and ignition advance. I have built my share of engines and none ever needed re-tuning after the initial set up.

George

[stealthn]

Thanks guys, just picked it up and took it for a drive, it stalled 11 times. It was not up to temp yet, but what happens is when I slow for traffic light, and push in the clutch RPM drops to zero and doesn't recover/stalls. I tired coming up to a light slow in low RPM, but same thing.

I was able to keep it from stalling at a light by kepping the RPM's up to 1100, if I took it out of gear and let off the clutch it would surge between 650-950 RPM.

I called the shop and told them this is a BIG issue and it is not safe. I will be taking the car back. The wrench said he did adjust the air mixture screw and I assume he did the timing, but I wish I had true numbers to give him for advance, AFM, Idle, etc.

This is a mechanic that I trust, to an extent and he knows he stuff, but my safety is more important.

Any more thoughts or real numbers would really help.

Thanks

[MotoSook]

A good mechanic isn't always a good CIS tuner. Plenty of good shops and good techs out there can fix just about anything and fail at CIS.

If he just turned the idle mixture screw and nothing else, he's asking for trouble.

He has to check and make sure everything is inplace and all hoses connected. Not know how much he changed the idle mixture screw, I'd say he has to start as if it is all out of whack. He's going to have to spend a good bit of time timing this thing. I hope it's part of his fee (already paid for or agree upon for the rebuild).

[stealthn]

Agreed, but this one knows CIS.

Update so I took it back to the shop after work, and we checked all the hoses and connections, now warm it would have issues starting.
The mechanic then increased idle to 1050 RPM to prevent stalling, then adjusted the mixture to lean it out a little (about 1/16 of a turn), then he checked timing and adjusted it about 2 degrees.
He then set idle back to normal and the car seemed much better. I took it for a rat around the block and it was very close to correct, but not perfect.

He said to keep driving for a while, and when everything "finds its' place" he will adjust again.

It's not perfect but very close. I know people have different opinions on breaking in, but I do agree with his thinking on this; CIS is very finicky with not much in the way of help such as O2 sensors or computers (in my year) and introducing something new to the mix (the 964 cams) along with all the new parts requires the engine to seat, find it median mark, then you can adjust from there. Everyone may think different, but I like this thinking.

Anyway thank you for all your help and once I get a few miles on her, we'll get it adjusted perfect and I can post the exact match.

Cheers,

Bob

[aigel]

Bob,

What did he set the mixture at?

I don't think it is a matter of opinion. It is a fact that there is nothing getting seated in your engine that would affect your fuel injection system and timing settings. Your engine should run like a well oiled machine on the trip home after a rebuild. It should run better and have more power than before you dropped it off. There was no required re-adjustment of the system after factory delivery either .... If you do not trust Souk's and my opinion you should go ask in the engine rebuild forum.

It is good that you are patient, but don't let the mechanic string you along long enough where it is not his responsibility any more to get the engine running right. I sincerely hope you'll get this resolved soon so you can enjoy your new flat six.

George

[stealthn]

George,

Your post comes off as kind of defensive?

I didn't say I don't trust anyone...

I'm not sure what the final AFM was set at I'll ask. Like I said the engine is very close I'll check the AFM after I get it up to good temp on a long drive.

I appreciate everyone's advice and I take it under consideration the same way I take a Porsche certified mechanic that has built hundreds of engines, runs his own shop and whom I've know for years. Everyone gets their input then I make the choice.

Bob

[aigel]

Bob,

Just trying to help as I think this thing is time sensitive. Not trying to argue or get defensive. Sounds like you are sure he's going to make it right - that's something that wasn't that obvious before you were starting to defend your mechanic.

Good Luck and keep us posted!

Cheers, George

[jsoderbe]

Hi Bob, you forgot the most important thing: How does it feel? Can you feel any difference?

I have my 964 cams on the way here now, and I can't wait to get them in the car.

Thanks,

Johan

[aigel]

Johan,

I did 964 cams and SSI at the same time. It was a very noticeable difference. My car would walk away from any chipped but otherwise stock 3.2 on the track (straights).

George

[Peter Seow]

Originally Posted by aigel

Johan,

I did 964 cams and SSI at the same time. It was a very noticeable difference. My car would walk away from any chipped but otherwise stock 3.2 on the track (straights).

George

If i am getting this right?

I have a euro 83 sc if i can the cams for 964 cam alone, will get more more power using the same CIS system?

What adustment did you need to do? Do i need to get an adustable WUR?

I am taking off my engine this week am keen to hear about the 964 cams, shoukd change it any other things needed?