Author Topic: Vacuum leaks at injectors M189 6-piston injection pump  (Read 3178 times)


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Vacuum leaks at injectors M189 6-piston injection pump
« on: July 16, 2015, 18:15:21 »
So I have managed to get the 1965 300SE to run on gasoline and it is backfiring at idle through the intake.  It is not because the plugs are wired incorrectly.

What I have discovered is that if I spray carb cleaner at the injector block for the first two injectors both the backfire stops and the idle increases and sounds really nice.  So I know I have a vacuum leak that is in the bakelite blocks (or missing gaskets) for the first two injectors.  I also know that the block for the second two injectors was replaced at some point with a machined aluminum block.  And the bakelite block for the third pair of injectors has stress cracks (as does the bakelite block for the fist set).  I haven't checked to see if there are vacuum leaks at either of those two sets of injector blocks. 

SO MY QUESTION TO YOU M189 people is...   What do you do about cracked bakelite blocks?  I think I can source a couple used ones, or I can fill/epoxy the ones I have, and of course order new gaskets for all of them.   But I'm wondering how other people have dealt with this as I'm sure it has come up before.   Keep in mind that this is a 6-plunger injector pump, not the 2 plunger pump that would have the distribution blocks that are a slightly different setup.

I case you didn't see (hear) the video (sound quality is poor) you can hear the backfiring in this short video.

Hoping for suggestions on how to deal with the vacuum leaks and cracked bakelite blocks.

Scott Allen
'67 250 SL (early)
Altadena, California