I'm frustrated! I've been trying to sort out a couple of driveability issues with my '82 Maxim 400:
1) Abrupt throttle tip in. Especially noticeable when cruising along in 5th or trying to ride slowly in lower gears. I'm either accelerating or decelerating. Nothing in between. I THINK that this is related to pilot screw adjustment...
2) stumble / misfire / bucking between ~4000 - 7000 RPM with heavy or full throttle. I can hear the carbs roaring while the exhaust gets loud and spluttery (that is a technical term isn't it?). The bike runs strong above 7000 RPM to 10,000 RPM or smoothly at any RPM with light throttle. I can't reproduce the misfire in neutral, I must have a load on the engine for it to occur. For example, climbing a grade of any sort at 100 kph in 5th gear (~5200 RPM) results in loosing speed with the throttle held steady, as expected. If I open the throttle, very gently, I might be able to maintain speed. But if I try to accelerate, it starts to miss and gets worse the more I open the throttle. If I rev the engine out in lower gears it will pull through the misfire and I can maintain the higher RPM's with the engine running smoothly.
What I've done:
- Cleaned carbs (to get bike initially running)
- Replaced mufflers with universal fit ones without crossover pipe (factory were shot)
- run strong fuel system cleaner (no change)
- running Shell Gold gasoline (91 octane but with no alcohol)
- Ultrasonically cleaned carbs (no change, but I'm not positive I got it spotless)
- Adjusted pilot screws and synced carbs
- Tested needles in every clip position, returned to middle (3 of 5) slot
- Rebuilt sparkplug wires and cleaned all connections I encountered
- Exchanged new NGK DR8ES-L sparkplugs for used Champion RA6HC sparkplugs (THIS made a noticeable difference reducing the misfire / stumble and narrowing the RPM band affected)
- Cursed and muttered
I don't know if the stumble is ignition related, carburation, or a combination of both. I probably should check and adjust valve clearances as well. And I'm obviously frustrated by my inability to resolve this misfire.
Any thoughts or words of wisdom would be appreciated!
Thanks,
Dave
1) Abrupt throttle tip in. Especially noticeable when cruising along in 5th or trying to ride slowly in lower gears. I'm either accelerating or decelerating. Nothing in between. I THINK that this is related to pilot screw adjustment...
2) stumble / misfire / bucking between ~4000 - 7000 RPM with heavy or full throttle. I can hear the carbs roaring while the exhaust gets loud and spluttery (that is a technical term isn't it?). The bike runs strong above 7000 RPM to 10,000 RPM or smoothly at any RPM with light throttle. I can't reproduce the misfire in neutral, I must have a load on the engine for it to occur. For example, climbing a grade of any sort at 100 kph in 5th gear (~5200 RPM) results in loosing speed with the throttle held steady, as expected. If I open the throttle, very gently, I might be able to maintain speed. But if I try to accelerate, it starts to miss and gets worse the more I open the throttle. If I rev the engine out in lower gears it will pull through the misfire and I can maintain the higher RPM's with the engine running smoothly.
What I've done:
- Cleaned carbs (to get bike initially running)
- Replaced mufflers with universal fit ones without crossover pipe (factory were shot)
- run strong fuel system cleaner (no change)
- running Shell Gold gasoline (91 octane but with no alcohol)
- Ultrasonically cleaned carbs (no change, but I'm not positive I got it spotless)
- Adjusted pilot screws and synced carbs
- Tested needles in every clip position, returned to middle (3 of 5) slot
- Rebuilt sparkplug wires and cleaned all connections I encountered
- Exchanged new NGK DR8ES-L sparkplugs for used Champion RA6HC sparkplugs (THIS made a noticeable difference reducing the misfire / stumble and narrowing the RPM band affected)
- Cursed and muttered
I don't know if the stumble is ignition related, carburation, or a combination of both. I probably should check and adjust valve clearances as well. And I'm obviously frustrated by my inability to resolve this misfire.
Any thoughts or words of wisdom would be appreciated!
Thanks,
Dave