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Posted by: shane Oct 7 2021, 06:25 PM

Trying to get a better cold idle and air fuel mix. I have a 74’ 1.8 L-jet that idles around 500rpm and runs rich for a couple minutes. After that the idle comes up to normal and it doesn’t smell rich (no black smoke on rev). No vacuum leaks, auxiliary air valve works, good fuel pressure, timing and points dwell is set. Had the cold start valve and injectors cleaned and tested (Mr Injector) new injector seals and intake gaskets, tested harness and connections. New seals and base gasket on oil fill and cap. Was thinking my CHT is at about 2700 ohms before starting and 200 ohms after is warms up. Maybe just getting a CHT that is more around 2k to start with would lean it up a bit and shorten the time that it runs rich? Idk if a bit leaner would raise the idle thought? After it’s warmed up it idles at 1k rpm. I turned it up a bit to offset the low idle when cold. Any help would be appreciated

Posted by: tvdinnerbythepool Oct 7 2021, 06:59 PM

I just replaced my CHT with a 914Rubber part that is 2.4K ohm around 68F FYI

Posted by: shane Oct 7 2021, 10:50 PM

Thanks for the heads up, I was reading a thread on here that someone was mentioning a few different brands and their values. But I can’t find it again, if I remember correctly they said the URO CHT was like 2k to 200 ohms.

Posted by: tvdinnerbythepool Oct 8 2021, 10:04 AM

I just tested my URO and it was 2.35K at same temp (68F)
Pretty close to the 914Rubber model and both fresh units.
Hope that helps....

Posted by: shane Oct 8 2021, 12:01 PM

It does thanks, well my old cht is at 2.73k in my 60ish degree garage so I’m thinking a new one would be a step in the right direction (leaner). And maybe it would be more responsive and drop it’s ohms a bit faster too. Either way for $20 bucks it’s worth a shoot. Thanks

Posted by: Dustin Oct 8 2021, 12:59 PM

You can use parallel resistance instead of a new sensor.

Posted by: shane Oct 8 2021, 08:43 PM

Wouldn’t my low side ohms be to low then?

Posted by: tvdinnerbythepool Oct 8 2021, 09:33 PM

@http://www.914world.com/bbs2/index.php?showuser=15518 You got it. There are threads on here about modding a 13mm deep socket for installation/removal. I glued the washer on so it didn't fall off during install. Pain in the ass to find the threads getting it in but if I can do it, Lol!

Posted by: Dustin Oct 9 2021, 01:26 PM

If you put 15525 ohms parallel with your 2700 ohm CHT the resulting cold ohms will be 2300 ohms

The resulting hot ohms will be 197.5 ohms.

15525 isn't a standard value.

It might be cool to put a potentiometer there to see if you can trim it to get the result you want. I doubt the low side will be too low.

I've always heard that these cars run better rich.

I'm not sure what you're trying to accomplish really. 99% of the time your car is probably going to be running right as it sits. When you're driving it.

I did this quick and didnt put any thought in to it. So... I could be wrong.

Posted by: sholman5 Oct 9 2021, 07:19 PM

914 rubber sells the 012. Just bought a replacement for mine. Mine was measuring 1759 at 82 degrees. ambient air temp and 70 ohms hot 15 mins at idle.

Posted by: shane Oct 10 2021, 04:03 PM

Thanks for all the info on this it runs a little to rich and low idle for the first few minutes then seems perfect after that. But I went back to the beginning and tested my cht again and it would only read anything if I messed with the wire. So I’m just going to replace it with the right one for my year then if needed and a resistor in parallel if I need to do anything else and that’s it I’m done. Thanks again