Having been in the motorcycle repair industry just shy of 35 years, we’ve certainly seen the occasional Bultaco. This past summer alone, however, we’ve had 5 come through our doors for service. With that in mind, we decided it was time to write about one of these special motorcycles.
Bultaco was a Spanish manufacturer that built motorcycles from 1958 until 1983. The Bultaco logo, pictured to the right, features a thumbs up and is said to be inspired by a rider signaling assurance to his pit crew that “all was well”. In this article, we’re going to discuss our work on a 1977 Bultaco Frontera MK9 Model 143, a single-cylinder 360CC two-cycle.
One of the unique features of this motorcycle is the small storage area on top of the fuel tank. Held closed by a small rubber strap (similar to a battery strap), this storage compartment is the perfect place for spark plugs and a tool kit. We tried a few of our phones to see if they’d fit, but they were each slightly too big for the space.
This Frontera was brought to us with the two main goals of getting running again and replacing the crank seals. Secondarily, we were to also change the fluids and replace the grips and center stand spring. Once on the bench, we began our work by addressing the crank seals first. We prioritized this because with bad crank seals, we aren’t able to get a motorcycle to run properly, or possibly even at all.
On a two-cycle of this age, it’s common for the crank seals to be bad as the rubber gets brittle and/or sticks to the crank, resulting in a tear after the crank is spun for the first time after after sitting for a period of time. On many two-cycles, splitting the cases is required to replace the crank seals. However, on this particular model, both seals can be replaced without splitting the cases or removing the motor. This is possible via a round inspection panel, pictured below, that can be unbolted, that allows direct access to the crank seals.
With new seals installed, we were able to move forward with getting it running. The next step in this process was to clean and reinstall the carburetor. We filled the bike up with non-ethanol fuel (ethanol will eat up the fiberglass tank) and gave it a few kicks. With no luck—not even a measly pop—we knew we needed to next check for spark.
After the customer gave approval, we decided that upgrading the points and condenser system to a more modern CDI ignition system was the best path forward. Hugh’s Bultaco Classic Motorcycles out of Craryville, NY, was of great help in sourcing the CDI as well as various other parts, such as bulbs and a manifold.
After receiving the CDI and installing it, we set the timing. A few kicks later, the Frontera was running! As to be expected with a two-stroke, it filled the shop with thick smoke. After a few carburetor, idle, and air/fuel mixture adjustments, it wasn’t just running, but running well!
Have a project you’re interested in having us work on? Call (740) 747-2299 during normal business hours!
