1986 F1B with 20,000k on the dial. I've been experiencing symptoms which include running on 1-cylinder (rear cylinder is cutting out.) It's exhibited this issue in both cold and hot running conditions (40ºF-95ºF). Initial feedback was to replace the ignition pickup wires which are prone to deterioration due to engine oil exposure. While they were a bit tired, the insulation was not cracked, but the wires were upgraded with aircraft grade wire and coated with high temperature epoxy. While this was probably necessary in the long run, it didn’t fix the issue. Fast forward 16 months and most of electrics have been replaced including:
1) keyed ignition switch (modern)
2) on-off rocker switch (NOS)
3) high-low beam switch (modern)
4) coils (Dyna)
5) ignition pickups (NOS)
6) pickup wires (second time)
7) DMC electronic ignition
8) Rectifier
Fuel tank has been drained twice and both carbs were inspected and cleaned. Original vacuum operated petcocks were replaced with newer style gravity feed types. When rear cylinder was cutting out, the situation was replicated on a dyno, and starting fluid was sprayed into the rear carb to see if it might indicate a fuel starvation issue. That didn’t help. Since installing the new electronics, the bike is also charging consistently around 14V with no fluctuation.
When the bike runs on only 1-cylinder it feels like an ignition problem, because it will sometimes sputter back onto both cylinders. It doesn’t happen at any particular time because it happens at low speeds/low RPM’s, in addition to high speed/high RPM’s.
However, when it completely dies it feels like it might be fuel related, because it bogs down to the point of stalling. The only way to keep it running is to give it massive amounts of throttle, which doesn’t always work. When this happens, it will usually start right up after sitting for a few minutes.
Something I have noticed is that the fuel tank seems to be building up a lot of pressure. When I take off the gas cap, it makes a loud sucking noise and emits a light spray of gas. I haven’t tried running it without the check valve which is fairly new. I have had stalling issues on more modern Ducati’s directly related to faulty check valves. However, this is the second check valve in place.
I also experienced a strange incident last weekend while stopping at a gas station. I was about to leave and noticed a loud, high pitch whining noise, which sounded like it was coming from the gas tank area. Oddly enough it sounded like what a modern fuel pump sounds like when it’s failing. It lasted for about 15 seconds and was loud enough for my friend to hear who was standing 10 feet away with his helmet on. I know these aren’t fitted with a fuel pumps but the sound was similar to what I’ve heard on modern bikes with pumps on their way out. At that point, it started up fine and didn’t cause me any grief until I got closer to home. I wondered if the noise was the gas tank straining under excess pressure. That made me begin to think that maybe the vent on the top of the tank might be clogged. I’m also not sure if the stock gas caps have a vent like more modern rubberband bikes.
Lastly, the shop who works on it (who I trust implicity) had gotten feedback that fuel can sometimes vaporize in the rear fuel line because of its proximity to the exhaust. That was rerouted a bit with heat shielding wrapped around it.
That’s all I can think of right at the moment. Any help is greatly appreciated and I apologize to those board member’s who I might have reached out to directly.
Thanks in advance-
Gary Herman
Nyack, NY
Brandx52@optonline.net