81 Sc Cis Problem? Or Valve Adjust?

[mb911]

I just got my motor running (3.0) ANd it seems to run good on 2 cylinders while the other four just kind of are there. I determined this from pulling spark plug wires when it was running. The deal is that I am not sure the CIS Is in good working order as I have never heard it run on a car and purchased it along with the engine supposedly in good working order. Ha Ha after new head studs 1 head new rings and a valve job here we are. My gut says take the valve covers off and check clearances. I am sure the cam timing is proper as it runs strong on the other 2 cylinders. Checked spark plug wires for OHMS and everything checks fine. The lambda brain does not seem to do anything hooked up or not. Just hoping someone could put me in the right direction.

Thanks
Ben
77 911 (3.0)
75 914-6 2.7

[mb911]

Must be valves but if any one has any Idea let me know
Ben

[kstylianos]

1) Check valve clearances. The valves could be WAY too loose and not opening at all. This would cause compression on 2 of 4 strokes rather than 1. There is no way the engine could run in 2 cylinders while the others are under comperssion 1/2 the time. I doubt this is your problem as you say you engine does run on 2 cylinders. Could be that the valves are adjusted too tight keeping the valves open all the time. Your engine could run on 2 cylinders like this, but be careful as you are in piston to valve contact territory depending on how off they are.

2) Check sparks to cylinders. Use a timing light and place the inductive pickup on each on the 6 wires to see if you can get a pulse on each wire. If you get a pulse, you know you are getting spark.

3) Check injectors. Pull the injectors one at a time, place in a jar, turn ignition to on and lift the arm in the air box slowly. You should see the injector squirt fuel.

Post your resulst......Mabye we can pinpoint a little further

[dean]

It could be a bunch of things. I am going to guess rich mixture. You really need pressure gauges to work on the CIS. Other wise your just guessing

[mb911]

Well this is what is going on with the running of the car. It starts up and pops and backfires for a few seconds then it will smooth out but not smooth like it should be. It is not running on all cylinders or at least not fully. I fealt each tube(header side) coming off each head and they are all warm but that could be heat transfer from each cylinder? the only other thing is that I installed an MSD box and maybe MSD installed the violet and green wires wrong like they did on si2t3m 's box and are giving me 35deg of advance but that doesn't seem to match up. I will try the fuel test and make sure that is working. What about a compression test will this tell me if the valves are adjusted properly?

Thanks
Ben

[kstylianos]

Originally posted by mb911
What about a compression test will this tell me if the valves are adjusted properly?

A compression will tell you if the valves are adjusted too tight (zero or very low compression). Too loose, will be hard to tell w/ a compression test.

Check valves, spark and fuel. Once those check out ok, start looking into timing, fuel pressure, etc....

Good luck....

[ruf-porsche]

You should remove all the spark plugs and perform a compression check on each cylinders. There is a reason why two cylinders are running strong and the other four are running weak. If the valves are too tight, a compression check may idicate low compression in those cylinders.

[mb911]

That is what I am leaning towards as The rear most cylinders on the car are the first ones you adjust in order to time the cams and need to be perfect in order to time properly. I am not concerned with low compression as with a high milage vehicle as this just had new rings and a valve job. That being said I am sure I must of rushed along with the other cylinders in order to be where I am now. I Thank you for your advice I think your right on the money and will let you all know as soon as I get to the test. If that isn't it I may just put carbs on and be done with the CIS all together. I do like the idea of the cis as My wife will be driving the car most the time( I can't seem to shake the 914-6) and I feel once working the cis must be very realible along with good fuel milage.

Thanks
Ben

[SteveF_911]

On a couple of occasions after rebuilding an engine I have had a mis fire.

Both times it was valve adjustment, I suspect a bit of crud get between the vale and seat.

I would re adjust your valves first, if the CIS was working before you stripped the engine, it should be Ok.

[mb911]

The big problem is I don't know if the CIS was working It was purchased with the engine in unknown condition just like the rest of the basket case from F2P our favorite pelicanite.
Thanks
Ben
I will check on those valves

[47silver]

check this site for testing the cis. i had problem last year and had six fouled spark plugs, due to points closing. i adjusted points at first and car would not start. tested spark by disconnecting a spark plug wire and putting a new plug in the end , ground the plug and have someone turn engine over. spark was perfect. hmmm, i replaced 3 of the plugs and the car started and ran on 3 cylinders. replaced them all and started immediately. recently i replaced the points with a pertronix and it runs great, a little warm (no oil cooler yet). check simple things first.

gary

[mb911]

I believe I have found the culprit. The valves seem to be adjusted wrong and will adjust to night. Some of the intake valves are hanging open. I double checked to make sure cams are in the right side and they are whoo! I will keep you all up to date.

Thanks
Ben

[mb911]

Ok here is the deal. I feel real stupid. 4 spark plug wires where in wrong location. Who would of thought that I teach at a local college and that I rebuild aircraft engines part time? I thank you for your help. And now time to crawl back into my shell and hide.

Ben