rocketman
10-13-2004, 06:17 AM
Need options please on strange problem with my 78 R100/7
The last two days that I’ve ridden to work, a trip of approx. 20 miles with all but one mile on the slab, the bike ran fine on the way in but on my ride home in the afternoon when I got within a mile or two of home the bike would suddenly lose all power and start to back fire like crazy. What is strange is that it would idle just fine but if I gave it any throttle it wouldn’t go above 2000 RPM, then start to backfire and drop back to idle. Thinking it might be fuel related I dropped the bowls on both sides, fuel level was fine and equal both sides. Fuel was clean, no particulates and fuel flow was fine both sides. Just to be on the safe side I tossed the gas in the bowls and reinstalled them. Started the bike back up, it started fine and would idle smooth but as soon as I gave it gas, same thing, it would rise to 2000 or so RPM then back fire and shoot big clouds of black smoke and drop back to idle and it seemed to come mostly from the right side exhaust... I figured it might be related to spark even thought the current plugs had less than 2000 miles on them. So I put in some old spare plugs, and then the bike ran fine. When I got home I checked the plugs I had pulled, both where clean and dry, no cracking of insulation and same range I had used for the past 5 years. The next day the same thing happened at around the same point on the ride home, maybe a mile closer than the previous day. This time I changed the plugs first thing, doing one side at a time. Left plug change made no difference but when I changed the right side it ran fine. And what’s strange is that I used the plugs that had been in the bike the day before when it had lost power, so it doesn't seem to be the plugs themselves. I have a Dyna III on the /7 but other than that stock setup and the Dyna uses the mechanical advance. So I think it must be related either to the plug wire or coil for the right side, since if it was the Dyna III or the advance it should affect both sides. This seems like it might be related to operating temp. since the mornings have been cool, around mid 40’s to low 50’s and daytime temps in the mid to high 70’s. Both times the bike has been cool in the AM after getting to work, I can place my hands on the valve covers without discomfort but both times on the way home they have been rather hot to the touch. So, besides wire and coil is there anything else that comes to mind? Can wires or coils begin to fail when hot and why would changing a plug “solve" the problem, esp. using a plug that had "failed" before? Neither time did the bike sit long enough to cool down, it took all of ten minutes the first time and less than 5 the second time before it was running again. Far as I know both the wires and coils are original, bike has around 80+K miles. I wondering now if this is maybe related to a problem I’ve had with rough/erratic idle in the past on hot days esp. if caught in slow traffic, something I thought was due to junk in the tank (which really needs recoating, but I’ve just been to lazy to do it plus that’s two days of no riding!) getting into the bowls and clogging the main jets. Thinking back I realize that it often ran fine after it had cooled down some, though sometimes fresh gas has helped as well. Thoughts?
RM
The last two days that I’ve ridden to work, a trip of approx. 20 miles with all but one mile on the slab, the bike ran fine on the way in but on my ride home in the afternoon when I got within a mile or two of home the bike would suddenly lose all power and start to back fire like crazy. What is strange is that it would idle just fine but if I gave it any throttle it wouldn’t go above 2000 RPM, then start to backfire and drop back to idle. Thinking it might be fuel related I dropped the bowls on both sides, fuel level was fine and equal both sides. Fuel was clean, no particulates and fuel flow was fine both sides. Just to be on the safe side I tossed the gas in the bowls and reinstalled them. Started the bike back up, it started fine and would idle smooth but as soon as I gave it gas, same thing, it would rise to 2000 or so RPM then back fire and shoot big clouds of black smoke and drop back to idle and it seemed to come mostly from the right side exhaust... I figured it might be related to spark even thought the current plugs had less than 2000 miles on them. So I put in some old spare plugs, and then the bike ran fine. When I got home I checked the plugs I had pulled, both where clean and dry, no cracking of insulation and same range I had used for the past 5 years. The next day the same thing happened at around the same point on the ride home, maybe a mile closer than the previous day. This time I changed the plugs first thing, doing one side at a time. Left plug change made no difference but when I changed the right side it ran fine. And what’s strange is that I used the plugs that had been in the bike the day before when it had lost power, so it doesn't seem to be the plugs themselves. I have a Dyna III on the /7 but other than that stock setup and the Dyna uses the mechanical advance. So I think it must be related either to the plug wire or coil for the right side, since if it was the Dyna III or the advance it should affect both sides. This seems like it might be related to operating temp. since the mornings have been cool, around mid 40’s to low 50’s and daytime temps in the mid to high 70’s. Both times the bike has been cool in the AM after getting to work, I can place my hands on the valve covers without discomfort but both times on the way home they have been rather hot to the touch. So, besides wire and coil is there anything else that comes to mind? Can wires or coils begin to fail when hot and why would changing a plug “solve" the problem, esp. using a plug that had "failed" before? Neither time did the bike sit long enough to cool down, it took all of ten minutes the first time and less than 5 the second time before it was running again. Far as I know both the wires and coils are original, bike has around 80+K miles. I wondering now if this is maybe related to a problem I’ve had with rough/erratic idle in the past on hot days esp. if caught in slow traffic, something I thought was due to junk in the tank (which really needs recoating, but I’ve just been to lazy to do it plus that’s two days of no riding!) getting into the bowls and clogging the main jets. Thinking back I realize that it often ran fine after it had cooled down some, though sometimes fresh gas has helped as well. Thoughts?
RM