CIS Trouble

Superman · 03-24-2002, 07:31 AM

While I'm at church this morning perhaps the pagans on the board can discuss my CIS problem. I cleaned but did not adjust my CIS system while rebuilding my engine. Now, in order to get it to idle after startup, I have to richen the mixture. Initial richening was about 1.0 to 1.25 revolutions of the 3mm adjusting tool. Quite a bit, I'd say. Then after warmup, some of that initial richening can be backed off. In the meantime, the popoff valve has gotten a real good workout with all the intake popping and bangs. The engine makes decent power, for a new engine with only about an hour of running so far, but it certainly does not have the fat bottom end I was expecting with the 20/21 cams.

I figured, and still figure, that there should have been no need, or little need to adjust the mixture. Air/fuel ratio should be the same with or without the different cams. So, I am thinking I have an intake leak somewhere, though I was sure everything was tight. Intake leaks have never been easy for me to find. Comments welcome.

In the meantime, I'll pray for you.

Doug Zielke · 03-24-2002, 09:01 AM

No, Super, I think *we* should pray for *you*, or rather your engine.

Anyway, I like the intake leak theory.
John Walker likes to waft a little oxygen from an un-lit torch around all the fittings. And some like to use brake cleaner from a spray can. The engine idle will rise when aany of the above hits the leaking suction.

Don't call in a priest just yet......you'll find it!

Early_S_Man · 03-24-2002, 10:19 AM

This pagan can't help much witrh the CIS! But, I do wonder about the ignition advance curve ...

I know that there are those that seem fearful about revving a newly-assembled engine to 6000 rpm to check the timing ... but the factory did it in their run-in procedure, after warm-up, of course!

Still waiting to hear what cured the missing spark problem ...

Tyson Schmidt · 03-24-2002, 12:26 PM

Superman, with a fresh and tight engine, you are developing more manifold vacuum at idle. Also, your new cam profile affects this as well. These two, along with ignition timing, can wreak havoc with you fuel mixture on a CIS car. I'm not at all surprized that the mixture is now off.
You will need to set timing, then mixture, then timing again, then check mixture again, until they both stabilize. They are very dependant on one another on these cars. Trying to do it without a CO sniffer is nearly impossible.
I'm not saying you don't have a vacuum leak, however. That's very possible. But with manifold vacuum now being very different than before due to the engine changes you made, the sensor plate height is now also very different than before, and must be adjusted.

Tyson Schmidt · 03-24-2002, 12:29 PM

Oh, and don't forget to make sure your frequency valve is operating.

Superman · 03-24-2002, 02:55 PM

Warren, as near as I can tell, the ignition system got tired of my verbal criticism and just started working. When I declared no spark, I'm pretty sure I was right. Timing was set at the usual spot, which is where it's at now. Fuel was happening but the engine was not alive, except for the occasional BANG. A few times I ran the starter while staring straight into my timning light. Nothing. Then all of a sudden she started up. Ran very poorly except for the first couple of seconds after start. I ran back and pushed up on the sensor plate quickly beofre it died once, and thyis smoothed everything...made it run. I adjusted muxture...again just over a full turn (these things are usually pretty sensitive...a full turn is WAY, WAY OFF if nothing has changed).

Warrren I also did test advance (I put a 25 degree mark on my pulley as part of the rebuild) and it does in fact advance up to there. Close anyway.

I'll continue to fiddle with mixture, but the problem is that during cold running, the mixture has to be richened (compared to before) and then after warmup, this thing will surge and die unless I lean the mixture back.

Here's one more symptom. The oxygen sensor duty cycle, measured at the test connector next to the CDI unit, stays at a steady reading of 89 (dwell). Typically this has been a steady 45 or a wavering meter, centering on 45. Perhaps this is my frequency valve. I wrote the 89 reading off as a dead O2 sensor (I used a fair bit of silicon grease throughout this rebuild, which may have killed my O2 sensor). I'm not too excited, a dead O2 sensor is just about as good as a live one for my car. But again, this car's fuel system is supposed to get along fine without that device.

Superman · 03-24-2002, 05:44 PM

Tyson (or anybody), my frequency valve is not buzzing. Aren't these things supposed to buzz? Runs better but still not right.

Of course until I find this gremlin it'll be hard to tell, but I do not feel the bottom end this is supposed to have with the 20/21 grind cams. Power is still around 4000 rpm and up.

Early_S_Man · 03-25-2002, 10:19 AM

Jim,

I suspect your frequency valve not pulsing is related to your earlier notation about the OXS sensor duty cycle being 89% and not vaying!

Perhaps it is time to get a Gunston gas tester ... while you adapt the '73 exhaust system to the car ... ???

Tyson Schmidt · 03-25-2002, 05:56 PM

If your frequency valve isn't buzzing, then that would account for the mixture being so far off. Check the relay under the seat. With the car running, remove the relay. If there is no change in how it runs then replace the relay. Make sure there is power to the relay. I believe it gets power from the same circuit as the dome light, so check the fuse. If the frequency valve is operating, duty cycle should be 60%.

john walker's workshop · 03-26-2002, 07:05 AM

you may have forgetten to plug in the lambda connection on the rear shock crossmember near the top of the left shock.