Nater_Potater
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- Joined
- Apr 7, 2013
- Messages
- 1,342
Lately, the old girl has picked up the nasty habit of crapping-out at the end of my favorite morning commute side-road blast. Assumed ignition-related as one cylinder would drop out, but would clear out after returning to a "normal" speed (65 mph). "Assumed" ignition, since we're running a single Mikuni, which shouldn't cause only one cylinder to die. However, switching the petcocks to "Reserve" seemed to help.
Then, the dropped cylinder transitioned to an annoying off-on-off-on as if the kill switch was being repeatedly pushed and released. Again, it would clear up after 15-20 seconds of steady cruise. Pulled the fuel tank. Pushed and pulled all the associated wiring and connectors; checked the points; messed around with the ballast, hoping to get it to fail; tugged on the points lead-in wire while the engine idled, hoping to have it die, to no avail.
A couple days later, we we're even able to maintain a constant speed, forcing us of the side of the road. Gave it a quick once-over; nothing out of the ordinary. No dripping fuel, plug wires tight on both ends. Fired up, and headed on into work.
The final straw was having the engine run so rough that it wouldn't idle at the stop-light near work, then died while on the last stretch. I had to push her into work (yes, I had an audience).
The trip home:
Pulled the float bowl off to find it almost empty. Hm-m-m... Pulling the float arm revealed a pretty healthy dimple where it contacts the spring-loaded, non-Viton-tipped needle. That, and the seat's through-hole looked to be awfully small. Guess what? I'm running a used carb that appears to have been originally off of a two-stroke, meaning snowmobile, meaning fuel pump, meaning a 1.5mm hole. In other words, about the same size as the main jet (240/1.4mm). Let me guess; gravity won't feed fuel as fast a a fuel pump. Ya think? Digging through the Mikuni manual, pressure-fed carbs use 1.5mm seat, while a gravity-fed carb runs 3.0mm.
Seat next to the main jet:
After "massaging":
As for why it wasn't refilling the float bowl, I can only surmise it was from the notch that has since been smoothed out. This last weekend's ride seemed to prove that out, as she never skipped a beat over the 225 mile ride.
Now, (if you're still awake) you're probably wondering what the hell this has to do with the clutch? Up until swapping over to the Barnett clutch plates clutch-slippage-part-enter-your-number-here-t22376.html, I've never been able to stay on the loud pedal long enough for this to happen. 'Funny how one thing can lead to another. What next?
Nathan
Then, the dropped cylinder transitioned to an annoying off-on-off-on as if the kill switch was being repeatedly pushed and released. Again, it would clear up after 15-20 seconds of steady cruise. Pulled the fuel tank. Pushed and pulled all the associated wiring and connectors; checked the points; messed around with the ballast, hoping to get it to fail; tugged on the points lead-in wire while the engine idled, hoping to have it die, to no avail.
A couple days later, we we're even able to maintain a constant speed, forcing us of the side of the road. Gave it a quick once-over; nothing out of the ordinary. No dripping fuel, plug wires tight on both ends. Fired up, and headed on into work.
The final straw was having the engine run so rough that it wouldn't idle at the stop-light near work, then died while on the last stretch. I had to push her into work (yes, I had an audience).
The trip home:
Pulled the float bowl off to find it almost empty. Hm-m-m... Pulling the float arm revealed a pretty healthy dimple where it contacts the spring-loaded, non-Viton-tipped needle. That, and the seat's through-hole looked to be awfully small. Guess what? I'm running a used carb that appears to have been originally off of a two-stroke, meaning snowmobile, meaning fuel pump, meaning a 1.5mm hole. In other words, about the same size as the main jet (240/1.4mm). Let me guess; gravity won't feed fuel as fast a a fuel pump. Ya think? Digging through the Mikuni manual, pressure-fed carbs use 1.5mm seat, while a gravity-fed carb runs 3.0mm.
Seat next to the main jet:
After "massaging":
As for why it wasn't refilling the float bowl, I can only surmise it was from the notch that has since been smoothed out. This last weekend's ride seemed to prove that out, as she never skipped a beat over the 225 mile ride.
Now, (if you're still awake) you're probably wondering what the hell this has to do with the clutch? Up until swapping over to the Barnett clutch plates clutch-slippage-part-enter-your-number-here-t22376.html, I've never been able to stay on the loud pedal long enough for this to happen. 'Funny how one thing can lead to another. What next?
Nathan