No Thermovalve - CIS

[echrisconnor]

Question, on cars with no thermovalve, what is to prevent the vacuum pressure at startup from leaning out the mixture too much? Should these cars just be set to have an even lower cold control pressure to accomodate for the vacuum system leaning things out at startup?

[Jubbie]

Not really sure. I assume you are talking about the aux air valve. From Jim's great CIS page: http://members.rennlist.com/jimwms/CIS/CIShome.html he says this about the cold start air valves:

Auxiliary Air Regulator :

Provides extra starting air (bypassing air around the throttle body) with a cold engine. The valve slowly closes with heat, provided by an internal resistor, and to a lesser degree, from heat from the engine itself. For part number 0 280 140 200 (from a 1976), the cold resistance of the heater is about 17 ohms. This device was added in '76.

Auxiliary Air Valve:

Provides bypass air around the throttle when the engine is first started. When the intake manifold vacuum reaches 5 - 6 inches, the valve closes. The closing is independent of engine heat. Part number 0 280 160 400 pulls in at ~8" vacuum. This regulator supplies air to the intake manifold during warm and hot starts when the auxiliary air regulator is closed. This was added in '76.

I put a Carrara 3.0 in the back of my 74. I took these two valves off and use my throttle for cold starts and have yet to have a problem on warm starts. I will let you know if I was wrong after this summer. I would think that the valve would work the same as lite pressure on the gas pedel during startup.

[Paulporsche]

Chris,
Your cold start temps are probably going to be much lower than Jubbie's, given your locations, for at least part of the year. Since the WUR is the only thing that affects your mixture setting, you may need to get a lower CCP than would normally be reqd for a stock engine. I am thinking this is the case for my car. I have been slowly experimenting w/ my WUR and the lower I get the CCP (further knocking in the plug) the better it starts/ warms up.

Have you checked mystery train's thread on AAR modification?

[echrisconnor]

Jubbie -- no the thermo valve is different. They started putting them on around '78 (I think). This device is an electrically actuated valve which cuts off vacuum to the WUR at startup. This allows the mixture to stay lean when starting, since high vacuum to the WUR leans the mixutre out.

You can see it listed in the top vacuum diagram as number 4

http://members.rennlist.com/jimwms/CIS/vaclines.html

Paul -- Like Jubbie, I've got a stripped down CIS system. I have no WUR or AAR and use the hand throttle to start. I think I'll try some plug knocking and pulling to see how that effects startup.

Thanks!

Chris

[Paulporsche]

Chris,
You must have a WUR. Otherwise, which plug are you knocking?

[echrisconnor]

Gad. I meant AAR or AAV. Of course, yes I have a WUR.

Apologies. Too many acronyms for early in day.

Chris