pacmyster

I might as well try this one out for my post on this bulletin board. I converted to the pre 73 exhaust setup. Reconfigured the oil lines to accomodate the the headers, purchased a 2 in 1 out muffler.. The works!!
I recall reading that the air fuel mixture needs to be richened up a bit to feel the full kick of the conversion. My question is could or should this be done by eyeballing it?? I beleive that the whole process consists of turning a screw one way or the other.. Any thoughts?? Can anyone walk me through it??
Thanks

Bill Verburg

There are 2 adjustable components on your CIS fi setup. 1) the air bypass, a regular slotted screw which is to the rear, accessible from the left side of the fi which regulates idle speed and 2) the fuel mixture control which is under a removeable rubber blanking plug on the top of the fuel distributor.
The tool for the air bypass is a regular flat bladed srewdriver(small). The tool for the mixture adjustment is a 2mm hex with a ~4" shank(i'm going by memory which is not so good sometimes, the official tool # is P377 I think).
First adjust idle to 850-900rpm (or to suit) then with out exerting too much downward pressure(which will stall the engine) turn, clockwise enrichens, cc leans. You are supposed to use a CO meter for 1-2% CO. Being an old f--- , I mean old hotrodder we always did it by ear for best idle.
Generally only small adjustments(no more than .5 turn on the mixture) should be required. if larger adjustments are necessary defects in other parts of the system should be suspected.

Bill Gregory

You can also use a dwell meter or a meter with duty cycle to set the mix on a CIS engine. You hook it up to a 3 pin test connection plug under the CDI Bosch box (positive goes to the pin with the green/white wire, the brown wire is negative, although I usually just run the ground clip to another part of the engine). Set the dwell meter to 4 cylinder, and the optimal reading will be 45 degrees. Or if you have duty cycle, then you're looking for 50%. In either case, if the reading is lower than 45 degrees dwell or 50% duty, the engine is running lean and conversely, rich.

PS. I think the tool is a 3mm hex

[ 02-06-2001: Message edited by: Bill Gregory ]

pacmyster

Thanks guys!!
Pete

RoninLB

BILL I love the idea of using the dwell meter.I have been using an inexpensive CO gas analyzer made in Britain called Gastester MK2.Although good for only inacurate results,I do find it useful after comparing it's reading to a good shop machine.It's accuracy is claimed at .5% Anyway,my 77 911s has a Permatune unit.I don't understand how the dwell reading is related to the fuel/air mix.I now assume that his system is DME.I can't imagine how this dwell test can be used on my system........I do enjoy your approach to all these problems in this forum.

Bill Gregory

Damn! Time to fall on my sword. You can use the dwell meter or duty cycle meter ONLY on the 1980-1983 911SC with an O2 sensor. For the other years, you need to use a CO2 measuring device, unless you're an old hotrodder.

My apologies for any confusion I caused.

[ 03-06-2001: Message edited by: Bill Gregory ]

pacmyster

This whole thing has got me very confused...
Does anyone want to lend their 2 cents worth over here?????

911 BBS

[ 04-06-2001: Message edited by: pacmyster ]

Bill Gregory

Pete,

If you want to adjust your CIS mixture so it's richer, the right way to do it on your engine is with a CO2 analyzer (Sorry if I confused you about using a dwell meter). You actually adjust the mixture through the fuel distributor.

Just behind the air intake on the top right side of the engine is the fuel distributor, with a bunch of lines going into it, which includes the lines that feed the fuel injectors. Just to the left of this, on the fuel distributor, is probably a plug. It could be a screw, or it could be a break off fitting. That needs to come out to give you access to the hex bolt that adjusts the mixture. You need a 3mm long hex wrench which is about 4" long to get down to the fitting. Or, take it to your trusted mechanical wiz with CO2 analyzer.

Does that help?

PS. We've assumed you have CIS fuel injection. You don't, per chance, have carbs do you?

[ 05-06-2001: Message edited by: Bill Gregory ]

pacmyster

Bill,
Sorry if I've confused you... I understand how to perform the task and I'm not sporting Webers... I posted a link to another string that tackles the question of which is better, rich or lean. There seems to be disention among the ranks..
Pete

rickc

I have installed an air fuel mixture meter and had some success in adjusting the richness by monitoring the fuel mixture as I drive. You have to install an O2 sensor, but that is easy to do if your running a test pipe that already has the fitting. Most of the stock catalytics have an o2 sensor fitting already installed.You can even install the meter in the engine bay and look at it occasionally if you are concerned about cluttering the dash. I like this meter because it gives you feedback about the condition of your mixture under load.

aquabat911

did you build the air/fuel meter yourself(pelican parts board) or did you buy one off the shelf? I know K&N once made them but I can't find anyone that sells them anymore. If it is off the shelf, how do you initially calibrate the unit. thanks in advance,