Squirrel Power: Saving a Suzuki FA50

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The PEI (Pointless Electronic Ignition, or more commonly known as a CDI) is a simple box of semiconductors that collects and discharges voltage for the ignition system.  The advantage of PEI ignitions is there are no mechanical parts to fail, so these systems generally run forever with no maintenance required.  However the PEI regulator does occasionally fail and with all other possibilities exhausted, we turned to the little black box.  Suzuki does have a service tool for the electrical system, but a home mechanic can still test the PEI unit’s effectiveness with a simple multimeter.  Just check the resistance between each of the four terminals and see if it matches the service manual spec.  Ours did not, confirming our suspicions.  Suzuki no longer sells parts for the FA50 and PEI boxes are long since out of stock.  One aftermarket company does make them, but they looked nothing like what we had on our bike.  Instead, we went to eBay and found a used PEI for $30 shipped and crossed our fingers that it would work.

The two PEIs look identical, but the difference is one works and one does not.  Surprisingly, the one that looks older and more abused is the functioning PEI.   

We cleaned the contacts of the plug and installed the new CDI, then checked for spark again…SUCCESS!!!  We added some gas, primed the carb, and, without so much as a spray of starting fluid, the old bike coughed into life on the first kick.  It pissed out a bunch of oil (the pump works even when the engine doesn’t run and there were many dry fire attempts hunting down the lost spark), but once it cleared out and warmed up, it ran surprisingly well.  We made a few quick adjustments to the idle and gave our FA50 a run around the block.  This thing is fun!  It may not be fast and a lot of stuff still didn’t work (like the speedo) but, this motor sings and revs nicely.  We were getting thumbs up within the first five minutes (to be fair this was the hipster neighborhood of town, so there may be some bias for old bikes like this).  Even with no exhaust whatsoever, the bike isn’t overly loud and if anything the noise helps people notice you, which is very handy for not getting run over.

However the celebrations were short lived.  The bike ran great for the first few minutes, but when we stopped to grab our helmet and go for a longer ride, the motor began to bog and would eventually quit altogether.  After trying to kick it to life again, the exhaust would barf out raw fuel.  This was clearly a sunk float flooding the engine.  When we pulled the carb out for inspection, we noticed the float would slosh when we shook it.  The float is supposed to be airtight (so it can float obviously) so sloshing is a sign of a leak.  This would explain why the float would slowly sink and then flood the engine.  Replacement floats are pretty much impossible to find, so instead we just bought an entire carburetor.

The new carb on the right is a direct fit replacement for the Mikuni carb Suzuki fitted 34 years ago.  The new carb is a Chinese knockoff and it shows: there is casting flash all over the body, which is clearly made of an inferior alloy, and the float inside is plastic.  Installing the new carb means replacing the throttle and choke cable ends, which are both sized differently.  Fortunately, the new carb includes both.  The fitment isn’t perfect, but it does the job.  We also had to buy a new intake gasket to go with the new carb.  Once adjusted, this carb works perfectly and is a good replacement for the Mikuni part.  The float in the original carb is brass and we will attempt to repair it at a later point, as the old carb is definitely higher quality and has a larger venturi, so it should flow more air, important if we plan to modify this engine further.  For now, the knockoff carb is doing the job.

With a functional engine, we moved onto some other maintenance that needed to be done to ride the Suzuki safely and reliably.  First, we drained the oil from the transmission and driveline.  The FA50 uses a single speed slipper clutch, with the chain and driveline all built and encased in the swingarm.  The old oil was very black and in dire need of replacement.  We then refilled the driveline with exactly 500 mL of 10W-30 oil.

Changing the transmission oil was easy.  Old oil out, half a liter of new oil in.  We also had to replace the damaged screws for the rear fender.  Check out the coilover rear shock.  While it is adequate for 170lbs of nerd, we may upgrade it in the future.  It’s a fairly common size, so there are actually aftermarket upgrades available.

Next, we checked the brakes.  The Suzuki uses mechanical drum brakes front and rear, both actuated by hand levers.  Since the FA50 was supposed to be more familiar to bicycle riders than motorcyclists, the brakes are set up like a pedal bike.  With a fully automatic clutch and one-speed transmission, this is possible.  The rear brake felt fine and the indicator on the shoes showed plenty of life left.  The front needed some adjusting, but the shoes were also good.  Unfortunately, the adjuster for the front brakes was frozen solid.  Even with lots of penetrating oil, it refused to budge.  We will live with slightly spongy front brakes for now and replace the cable at a later date.  We lubed both brake cables and the throttle cable to help prevent stuck or broken cables in the future.

The dead speedo was an easy repair.  Turns out the speedo cable had just come unscrewed and fallen out.  Once we popped it back in, the speedo worked perfectly.  We found the top speed to be around 25 MPH, given a full block to accelerate and we could just barely touch 30 when going downhill.

While the magneto based electrical system does not require a battery, the FA50 comes with one anyway.  Presumably this is to ensure the rider still has lights and turn signals if the bike stalls or runs out of gas.  The battery does have another purpos as it is actually used as a voltage regulator.  With the magneto charging system, voltage isn’t always supplied at a steady rate, since the magneto’s output is directly proportional to engine RPM.  So the battery supplements the magneto when the motor is idling or accelerating.  Since losing your brake light when stopping is really dangerous, we decided to replace the battery.  The system is all 6V and the battery is tiny, about half the size of a soda can.  The battery in our bike was so old it was bone dry.  The 6V electrics are an annoyance as it heavily restricts the parts we can use.  We’ll stick with the 6V system for now, but if we can find a 12V magneto that fits, we’ll be upgrading to 12V.