my frankenstein car has problems

[outlaw912]

So, before I get into it, here is a little background on my crazy car.

1969 912 body, with a 71T 2.2L motor. 2.7 Crank, S cams, 73.5 CIS injection. Busch headers, Manta exhaust.

Been having problems with cold starts recently. I installed two AFR gauges to monitor the mixture in both headers. Whoa, what an eye opener. Mixture goes way lean at WOT, so I richened it up. Now the needle is pinned at 12:1 at idle and just a hint over stoich @ wot. The mixture should be rich under throttle right? Also the left side headers show a leaner reading the the right.

I have a microswitch for the cold start valve which is activated at idle, maybe thats the source of the richer mixture at idle?

Regardless, today I replaced the cap, points and rotor, thinking that might have been contributing to my starting issues. While checking my timing I noticed that at 6000RPM the mark was jumping all over the place, left and right. Distributor seems solid (no play in bushings).

Help

[Grady Clay]

outlaw912,

“1969 912 body, with a 71T 2.2L motor. 2.7 Crank, S cams, 73.5 CIS injection. Busch headers, Manta exhaust.”

Hopefully the “S cams” are ’74-’77 911S CIS cams. If ’67-’73 S cams – well….


”Been having problems with cold starts recently. I installed two AFR gauges to monitor the mixture in both headers. Whoa, what an eye opener. Mixture goes way lean at WOT, so I richened it up. Now the needle is pinned at 12:1 at idle and just a hint over stoich @ wot. The mixture should be rich under throttle right? Also the left side headers show a leaner reading the the right.”

That would be VERY unusual with CIS.

”I have a microswitch for the cold start valve which is activated at idle, maybe thats the source of the richer mixture at idle?

Regardless, today I replaced the cap, points and rotor, thinking that might have been contributing to my starting issues. While checking my timing I noticed that at 6000RPM the mark was jumping all over the place, left and right. Distributor seems solid (no play in bushings).”

I would pull the distributor and do a through cleaning/lube “rebuild” with new points also.

Sounds like it might be worthwhile to start from scratch. Measure the cylinder leak and cranking compression, adjust the valves and check cam timing, investigate for intake leak, check nozzle flow on all six simultaneously, check for nozzle leak, condition of wires and plug connectors, NEW sparkplugs (BP7ES), sticking sensor plate and more. I would put the pressure gauge on and leave it in place for a few days and note pressures under all different conditions.

Was the fuel tank changed in this conversion? CIS is very intolerant of air in the fuel – I suspect if you have the original tank, you found this out with low fuel level.

Best,
Grady

[HarryD]

If I am not mistaken, CIS fuel distributors are matched to the engine displacement (among other factors). A 73.5 CIS is sized for 2.4L cylinders and may not be able to flow enough fuel at WOT due to internal restrictions. This may explain your lean reading sat WOT. Without knowing your true displacement, you can only guess at your problems.

I have a microswitch for the cold start valve which is activated at idle, maybe thats the source of the richer mixture at idle?

Sorry but it is not supposed to be on at idle at all times. The microswitch on the throttle plate is for operating the cold start injector (the injector on the throtle body). When I start my car, first I pull up the black throttle handle next to my seat and crank the car. The hand throttle opens the throttle plate slightly which closes the micro switch. The microswitch gets it's powerfrom the Starter circuit and when I crank the car, it activates the cold start valve to richen the mixture only while I crank.

[outlaw912]

The cams are 2.7L s cams. Displacement is 2.2L

Planning on pulling out the distributor this weekend and doing a cleaning, hopefully this will rectify the timing issue.

Should I adjust the throttle with the adjustment screw on the housing or somewhere else??

I'll keep you all updated

[outlaw912]

So, fixed my distributor issue I think, Rotor wasn't seated all the way.....

Seems to fire at the right time now.