Bultaco Maintenance - 1

1973 Bultaco Model 98 "Sherpina"

After my friend (Sponge) Bob suffered a DNF at the CATRA Vintage Trial, due to a faulty condenser, I decided it's time to move my condenser up to the frame. I should've done this back when I rebuilt the bike. Luckily my bike never suffered the same problem as (Sponge) Bob's borrowed Bultaco. The job wasn't that difficult and took less than an hour to complete.


The photo above shows the new location of the condenser, attached to the frame.

Tools Required: 13mm socket, 3/8" drive ratchet, 13mm wrench, T-handle allen key, 27mm impact socket, 1/2" impact driver, flywheel puller (and wrenches), flat-blade screwdriver, Phillips screwdriver, 10mm wrench, center punch, ball-peen hammer, 3/8" drill, 1/8" drill bit, wire stripper/crimper, 8mm wrench.


Here you can see the Radio Shack electrical junction block installed in place of the stock junction block. I replaced this in 2004 when I restored my Bultaco. The stock junction block was badly corroded and some of the screws were stripped. While I do not like using butt-splice connections, this bike does not see much regular use. The yellow wire is attached to the lighting coil, in case I ever want to add lights.

Additional Parts Required: Butt-splice wire connector, screw and a nylock nut.

Process: Remove kick-start lever, ignition cover and ignition/lighting coil (hint: if your ignition timing is spot-on, punch mark the backing plate and side case to use as timing marks). Disconnect the condenser wire from the points and remove the condenser from the backing plate. Reinstall the ignition/lighting coil and slip the flywheel onto the shaft. Remove the tank and find a spot on the frame, near the coil, to install the condenser. Mark the spot, center punch and drill a 1/8" hole through the frame. Rub the paint to expose the bare metal where the condenser contacts the frame. Attach the condenser with the screw and nylock nut. I like to use nylock nuts because they have less chance of vibrating loose. The stock junction block accepted bare wire ends, which would only require removing the connector and stripping 1/4" of insulation from the wire. The Radio Shack junction block uses screws which are too large for the connector on the condenser. I removed the connector, stripped back 1/4" of insulation and installed a new butt-splice wire connector. Then I wired the condenser into the primary side of the ignition coil.


Above is the complete ignition system showing the junction block, relocated condenser and ignition coil.

After relocating the condenser I checked ignition timing and point gap. Sherpa T timing is supposed to be 2.5mm to 2.7mm BTDC. I don't remember what the Alpina timing is, but it is different. The point gap was within specification, but timing was around 3.5mm, so I retarded the timing to 2.7mm. Additionally I changed the sparkplug from an Autolite 64 to an Autolite 65. This is a one-step hotter plug which, hopefully, will prevent the plug fouling I experienced at the CATRA Vintage Trial. Finally I put everything back together... well, almost. It was time to clean and re-oil the air filter. Also noticed the rear brake was hanging up, so I'll need to pull the rear wheel and take a look at that.

Sept. 17, 2007 - Update: Over the weekend I cleaned and re-oiled the air filter. Also took the rear wheel off and fixed the back brake using a small amount of Lubriplate the grease the brake shoe cam. I was concerned that I might have difficulty starting the Bultaco after making multiple changes (condenser move, ignition timing and spark plug heat range) to the ignition system. To my surprise, after tickling the carburetor and giving two slow-speed priming kicks, it fired up on the first full kick. After adjusting the carburetor air screw and idle speed I warmed up the engine then took it for a few laps around my backyard practice trap. As I suspected the power is a bit sluggish compared to when the timing was set at 3.5mm. However the engine tends to rev out further and idles along nicely at crawling speed. First gear works really well in my practice trap. Before the motor would top out climbing the hills in first gear. I'm still thinking about installing a one-tooth smaller countershaft sprocket, but I really should ride it in a trial before making any more changes. Also considering replacing the primary and secondary silencers with a motocross silencer I have for my GasGas enduro bike. The Bultaco is not horribly loud, but I'd like to see if I can make this silencer work. It's aluminum and would reduce overall weight by replacing two heavy steel silencers. Additionally I could repack this silencer making the Bultaco, hopefully, quieter. Screw it! I don't have the time to do a one-off custom fabrication. I'll just braze up the hole in my primary (middle) silencer and use radiator hose over the joint between the header pipe and primary silencer.