rough start, rough running, carbon coating on sparkplugs

[nim205]

Just as I started enjoying my 1975 D-jet 450SE, after ironing out all the engine problems, the bitch started acting up again.

A week ago I parked it after a long ride (at that time everything was OK). Normally it cold starts perfectly with no gas. Today I had to depress and hold the accelerator to the floor for it to start, and then it ran very rough. around 3000 RPM it felt smoother, but when I let go the accelerator - the engine died. The exhaust smells of unburnt gasoline, and the spark plugs are covered black.

Any ideas where to look?

Thanks!

[oscar]

Dare I say it Nim but it sounds like the Manifold Pressure Sensor has a cracked diaphragm.  I think I remember you were looking for one ages ago and I can't remember whether you replaced it or not, but black plugs, unburnt fuel, serious flooding causing a stall, it sounds like the MPS is kaput.  Simply pull the vacuum line from it and suck on the vacuum port.  (or you can blow)  If it doesn't create a vacuum or you can blow air into the MPS then it's ratshit.   See how that checks out, I can't think of anything else.

BTW, if it is the MPS and you can't find any locally, I know 13B has a couple of spare 450 MPS's.

[nim205]

Oscar, I was looking for one in the past, and found three 

I'll replace it with one of the two spares ( hoping they are OK) and see what happens.

[nim205]

OK, I just returned from the car.

Even though it's Friday evening, and were supposed to go soon to my mother in law for Dinner (a big thing in Jewish family life that can get you in serious trouble if you're not ready on time), I had to go and see if it was indeed the MPS.

I fitted the wiring connector and hose on the new unit, sat behind the wheel, turned the key, and........... she started beautifully.

At first the idle was a bit rough (though nothing like before), and then it smoothed out like warm butter. What music to my ears! I haven't time to go for a spin, but it seems to be fixed.

So first of all - a big thank you to Oscar! Your trans global diagnostic skills saved my day!

Second, where can I get a good MPS? I would like to have at least one other spare.

[John Hubertz]

man, Mother in law too?  You DO have it rough!

[nim205]

Just returned from a 30 minute drive. The car runs perfectly!

We're going to visit my mother in Jerusalem today. Seeing that the old babe is back in shape (I'm referring to the car), I think I'll see how she makes the ascent. Report to follow.

[13B]

You have a PM.