Pelican Parts Forums - How to setup CIS with no gauges

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Originally Posted by JFairman (Post 9506984)

Use the WUR you mentioned.
The TPS on later CIS only disables the lambda emissions system that leans out the CIS somewhere around 2/3 throttle open on up so it effectively richens the mixture a little bit according to throttle position.

CIS is a 100% mechanical fuel injection system. Electrical devices like a throttle position sensor have no effect on the actual fuel injection system pressures.

while you are correct, the early CIS systems had a mechanical throttle position sensor to adjust fuel pressure for enrichment. It was eliminated in 1975 in favor of the vacuum actuated unit the OP has. This Web site has a lot of good info: 911 CIS Primer - Index

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Mechanical CIS is controlled by system fuel pressure which should remain constant all the time and hydraulic control pressure changes in the fuel head.
You have the mechanical air flow sensor plate pushing the control plunger upwards in it's cylinder with fuel metering slits in the side as the engine revs up and sucks in more air and hydraulic control pressure pushing down on the top of the control plunger keeping it from going all the way up in it's cylinder exposing too much of the fuel metering slits and flooding the motor with wayyyy too much fuel.

Nice description.

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With todays E10 fuel in the USA the original non ethanol tolerant o-rings in the fuel head are going to break down and start to leak. This is going to eventually happen and it's just a matter of time before the motor starts running rough or miss on one or more cylinders at low rpms from leaking rubber o-rings installed on the outside of the fuel head control plunger cylinder.
There's one large o-ring in the bottom of the inside of the control plunger cylinder too.

After market ethanol tolerant rubber fuel head o-rings and rubber diaphragms used in aluminum fuel heads are available in fuel head rebuild kits from a couple places. One place that has them is Welcome to salvox! - salvox

Sometimes they sell on ebay for little bit lower prices than directly from their website so an ebay search may save some $.

Good to know.