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Bosch Impulse Starter Info AKA "IS" Suffix

This was an early and welcome option for starting larger engines like installations on the Rumley Oil Pull, Caterpillar. It was an impulse coupler that could be tripped manually. It retarded the spark, gave the mag a strong flip, and if all was well, the engine could be primed, barred over to or past top center, then started when the impulse was manually tripped. It can be a nasty surprise if one forgets to reset the impulse and gives the engine a mighty crank. Without the impulse engaged, we have a rich mixture and a full spark advance in place.  Always practice safe cranking and be sure the machine is out of gear.  These worked well when in repair. The problem with them today is that they have endured nearly 100 years of use and abuse, dirt, grit and lack of lubrication. These wre used with the DU.. and ZR series. When so equipped, the model would be followed by "IS" like a ZR4IS.





Beware of broken drive and rebound springs. Also of note is that the screws that hold the assembly together are standard 5MMx.8 metric thread.  The pin that holds the inner steel ring together is also metric in dimension. It is best replaced with a metric rollpin when the springs are replaced.



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