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Can not adjust mixture on Bosch injected car


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So my car (1987 HCi) is running quite rich. Smoke machine has been used, and no vacuum leaks found. This is a federal car with Bosch K-Jet.

Tonight, I hooked up a Gunson exhaust analyzer. Hoooo boy. Factory range for acceptable CO is 0.3 up to 1.3.

My car was averaging a reading of 3.5! And yes, that's some eye burning exhaust.

So I took the airbox off to perform the adjustment. Done this many times before on DeLoreans which are also K-Jet.

Somebody has been in there before, as the factory metal plug had been drilled out, and there was a properly fitting stopper in place.

I pulled out the stopper, put my 3 mm Allen wrench in, and went to turn the screw to lean it out. It seemed to turn a little, but then the wrench slipped. Thought maybe I didn't have it into the screw quite right, but after feeling around with the wrench, I did.

At this point, I became suspicious. I got a magnifying glass, and a flashlight, and looked into the adjustment hole. Whatever clown drilled out the factory metal plug also managed to drill into and mangle the adjustment screw. No size Allen wrench (and I tried a few) will fit into and be able to turn it.

So, I literally can not adjust the mixture because the screw is mangled.

Considering how rich the car is running, I really have no intention of leaving it more than double the acceptable C/O.

My thought process is this: Disconnect all of the fuel hoses from the mixture unit, unbolt the top half from the bottom half (so I don't have to pull the whole thing), remove the mangled adjustment screw, and replace it with a good one. Provided I can find one of these screw, I understand they're a bizarre shape and thread.

Thoughts? What would you do in this situation?

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I guess you won't have the choice, you'll need to pull it out. You could unscrew the whole distributor from the pressure plate assy.

Cheapo option would be to grind a slot across the allen head to use a flat screwdriver.

If you are able to remove the adjusting screw and you need to re-use (and if there is enough space) you could drill in the head, tap and fit another small allen screw on top. I know...sounds crazy. Gluing it in could also be enough, you probably already know there is not a lot of running torque on this screw.

Take pictures, I'm interested in seeing the exact setup.


Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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  • 4 years later...

i also need to adjust my mixture but the manuel does not say how to remove the plug. my k-jet guy in Australia said drill it out

does anyone know if this is removable?

or do i have no choice but to drill it out? 


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