Doodlebug of Doom: Saving a Superpowered Minibike


Our original coil is on the left, the new ARC sourced coil on the right.  The coil incorporates the spark plug boot as well as a hot wire connection for the power switch.
The coil fits against the magneto.  Remove the fan housing and you’ll find the coil and magneto.  The coil is only held on with two bolts, though you do have to set the gap between it and the magneto.  This is a bit of a pain since the magneto will attract the coil.  You want a fairly small gap, but enough clearance to prevent contact (which will destroy the coil).  We also noticed the magnet for the coil had a lot of surface rust on it, so we hit it with some sandpaper to give us better continuity.

With the coil in place, we now had spark.  Hooray!  After quickly priming the carb, the engine roared into life.  And I do mean ROARED.  This is the wildest sounding engine I’ve played with in a long time.  And it will literally be six inches below my ass.  Alright, time to drop the motor back in.


The exhaust doesn’t do much more than make sure the smelly, hot gases go out the back and not onto your leg.  The “muffler” really doesn’t do all that much muffling.  But hey, who needs backpressure?

The motor slotted right into its home (we decided to use the original gas tank for our test running as the mounts for the large tank needed some re-engineering).  We unplugged the factory kill switch and rewired the pre-installed handlebar kill switch (we added some bullet terminals to both so we could easily switch between the two for riding and engine-out maintenance),  Then we ran into a couple problems.


During the diagnosis phase, we used the OEM gas tank.  Using it made engine pulls a lot easier.  We will need to add some more substantial mounts with vibration isolation to the oversize fuel tank before we feel comfortable riding with it.

Problem 1: The upgraded carburetor that feeds this engine was not meant for a Doodlebug and the throttle linkage is a bit wonky and jerry rigged together.  We noticed the cable would jam and not fully close!  Before we can even hope to ride this thing, we need to make sure the throttle shuts completely.  Stopping this beast is already going to be tough, it’ll be a lot tougher if the engine is still at part throttle when we do!


A quick and dirty edit in MS Paint shows our throttle problem.  The bike came with a bracket for the throttle cable that put the cable in a direction that wasn't conducive to opening the throttle.  Basically, pulling the throttle would cause the cable to try to shut more!  However if we can get the cable to pull from the bottom, this will cause the throttle blade to rotate.  All we need is a way of making the cable pull around one of those open holes.
Our idea  required running to hardware store (which we did on our trusty FA50 moped, because why the hell not?  It’s what we bought it for after all.).  We picked up an M3 bolt and a few assorted nuts and washers to try and make a valley to capture the cable and give it something to pivot around.  

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