1978 k-jet wur and air valve operations. - PeachParts Mercedes-Benz Forum

rwd4evr · #1 05-03-2019, 11:56 PM

I'm preparing to go drifting with my 450SLC Ttommorrow and got to wondering. I've had a bit of an eratic idle speed usually when it's cold(all the time except at an event once it's all nice and heat soaked and settled 190-205 ish) with no thermostat valve. It has the outer piece and a freeze plug in the bypass port. I'm wondering if I can completely take the WUR and air valve out of the equation and deal with it being a ***** when I'm starting it cold. It's seems down on power like it rich sometimes and the WUR is the one that came on the car after it's long slumber in the bushes. Not doing it tonight but I'd love to eradicate any variables. I've heard the WUR actually does change mixture under different vacuum conditions.
Thoughts ?

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JKMorahan · #2 05-04-2019, 08:55 PM

The dual chamber WUR with a vacuum line is the version designed for turbos and flexible engine demands requiring WOT enrichment, as it both adjusts for cold/warm running and also loading as read by manifold pressure.
The single chamber one without the vacuum line is meant for simpler setups and low demand engines and only adjusts for cold/warm running using a simple bimetal system alone.

If you had the simpler WUR and cold running issues I'd suggest you wouldn't get a performance loss if you bin it, when warm running the engine as it is no longer influenced by this WUR.
With the dual chamber WUR however I suggest you lose some warm running horsepower due to WOT enrichment if you go and bin it rather than replace it for some cold running issues.

okyoureabeast · #3 05-05-2019, 02:15 AM

Won't help immediately with your idle, but there are modern fuel rail upgrades for the kjet system.

These guys have a kit that you can install in leui of the original CIS one.

https://kjetkillers.pl/pl/p/Zestaw-wtryskowy-piggyback-EFI-Mercedes-V8-m117-/77

Page is in Polish so use a translator.

This guy can rebuild the WUR kit for you http://www.k-jet.biz/

rwd4evr · #4 05-05-2019, 02:29 AM

I have the vacuum assisted version. I actually bought the one from a 911 turbo thinking about converting my m117 or m110 to turbo with it.

R-3350 · #5 05-07-2019, 09:26 AM

the thermo valve likes to stick with corrosion over time. pull it and polish the piston and bore to get the idle to stabilize. as for the wur don't remove it since it modulates the control pressure based on coolant temp manifold pressure and baro pressure. you can make it easily field adjustable by replacing the diaphragm pin with a machine screw but don't forget to put a non hardening sealer on the screw before install. your control pressures are something i might be interested in checking out as well id have to look up what the spec is for an early 450 but off the top of my head its somewhere between 25 and 32 psi lower pressure make for a richer mixture. and finally check the mixture at each individual cylinder with an ir temp gun they can be trimmed with the tiny allen screws on the bottom of the fuel dizzy. all that should help net a bit more power and throttle response.

rwd4evr · #6 05-07-2019, 03:03 PM

The issue I have is just that I want it running at full temp setting as low as 140 degrees. I have done some more reading and I realize that it is controlling control pressure besides while warming up through vacuum input. O
I have an 061 WUR in my car and I've never tested it. I suppose I probably should.

rwd4evr · #7 05-07-2019, 03:11 PM

Also could you elaborate more on the process of making it adjustable? I'm very competent at modifying things but I've only seen the service available to have it done. I have a new 438140112 Porsche turbo wur that I would like to make adjustable for future projects.

Frank Reiner · #8 05-07-2019, 04:56 PM

rwd:

A method of making the Control Pressure (CP) adjustable (in the downward/rich direction) is to bridge the outgoing line (top of FD) to the return line (adjacent to main pressure regulator in base of FD). By including a needle valve in the bridge line the CP may be reduced, and the mixture made richer.
Consider installing a wide-band O2 sensor, and ideally, a recorder, so that you can see what the mixture ratio is.

rwd4evr · #9 05-07-2019, 05:59 PM

Yeah definitely wide band if I'm monkeying around in that rube Goldberg carburetor. I think a needle would vary pressure over high or low fuel consumption situations. I know the WUR is modified with a Allen bolt and locknut to move the innards in relation to the housing but I've never had one apart to see how they did it.

rwd4evr · #10 05-07-2019, 06:01 PM

I'd still like to be able to throw a switch to start up in "cold " control pressure then get it out of the equation. Maybe I'll pull a bad one apart.