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79 XS1100 Special Vacuum Advance Issues?
Thanks in advance for any help or advice.
I have a 79 XS1100 Special and it is having some problems. When I am accelerating out of a lower RPM situation such as 35-40 in 5th gear the bike will start to spit, sputter, pop and it seems to miss to the point where I have little to no acceleration.
If I downshift into 4th I will have some acceleration but the problem will persist. I have found that I can temporarily solve this problem by pulling in the clutch and shifting to other gears to release the clutch only until I feel it start to engage, re-shift into an appropriate gear for my speed and then the bike will pull out of the fit and run normally. I can tell before shifting back to an appropriate gear if it is running right by pulling back the throttle and hearing the engine rev. The problem is only slightly noticeable with the clutch pulled and no load during a fit and will only pop and sputter when the clutch is released and the bike has a load in gear.
This problem can happen in any gear, not just 5th but never neutral. Alot of the time it appears in 3rd but I believe that is because I have the 2nd gear problem so it is normal for me to start at a lower speed for 3rd because of having to skip 2nd.
I have just had the carbs cleaned and synched by a professional and the bike seems to be running excellent until it goes into a fit.
I believe my problem may be the vacuum or mechanical advance. Or possibly the pickup coil I suppose? I would appreciate any advice on how to test these things before I try to replace them. As you all know they are hard to find parts and are priced higher than gold.
I unhooked the vacuum hose coming from the advance unit and plugged the carb intake that I pulled it from and took it for a ride today and for the first time it seemed to ride well for about 100 miles and then the problem came back seemingly worse.
I hooked the vacuum line back to the carb, took it back out and the problem was still happened intermittently and still seemingly worse.
I would like to think that maybe the 100 miles of good running was a coincidence but for the last month of last years motorcycle season, and the last two weeks since I got the bike back from the mechanic, I couldn't drive it more than a couple blocks without the problem happening.
The problem started before the mechanic touched it, and still persists after. When it runs good, it runs great...excellent acceleration, no popping or backfiring ever, smooth idle.
I have tested for spark, compression, air leaks in the intake boots. I read that if you put your petcock on PRIME then essentially you bypass the octy. I am not entirely sure that is true but I tried that and still the problem persists. I have rode with my gas tank open, still the problem persists.
What would you expect the bike to run like with the vacuum line coming from the advance unit unhooked and "hanging" while you plug the carb hole it came out of to prevent air leaks?
Sorry for making this so long, I wanted to be thorough.
Any help would be greatly appreciated,
Mike
I have a 79 XS1100 Special and it is having some problems. When I am accelerating out of a lower RPM situation such as 35-40 in 5th gear the bike will start to spit, sputter, pop and it seems to miss to the point where I have little to no acceleration.
If I downshift into 4th I will have some acceleration but the problem will persist. I have found that I can temporarily solve this problem by pulling in the clutch and shifting to other gears to release the clutch only until I feel it start to engage, re-shift into an appropriate gear for my speed and then the bike will pull out of the fit and run normally. I can tell before shifting back to an appropriate gear if it is running right by pulling back the throttle and hearing the engine rev. The problem is only slightly noticeable with the clutch pulled and no load during a fit and will only pop and sputter when the clutch is released and the bike has a load in gear.
This problem can happen in any gear, not just 5th but never neutral. Alot of the time it appears in 3rd but I believe that is because I have the 2nd gear problem so it is normal for me to start at a lower speed for 3rd because of having to skip 2nd.
I have just had the carbs cleaned and synched by a professional and the bike seems to be running excellent until it goes into a fit.
I believe my problem may be the vacuum or mechanical advance. Or possibly the pickup coil I suppose? I would appreciate any advice on how to test these things before I try to replace them. As you all know they are hard to find parts and are priced higher than gold.
I unhooked the vacuum hose coming from the advance unit and plugged the carb intake that I pulled it from and took it for a ride today and for the first time it seemed to ride well for about 100 miles and then the problem came back seemingly worse.
I hooked the vacuum line back to the carb, took it back out and the problem was still happened intermittently and still seemingly worse.
I would like to think that maybe the 100 miles of good running was a coincidence but for the last month of last years motorcycle season, and the last two weeks since I got the bike back from the mechanic, I couldn't drive it more than a couple blocks without the problem happening.
The problem started before the mechanic touched it, and still persists after. When it runs good, it runs great...excellent acceleration, no popping or backfiring ever, smooth idle.
I have tested for spark, compression, air leaks in the intake boots. I read that if you put your petcock on PRIME then essentially you bypass the octy. I am not entirely sure that is true but I tried that and still the problem persists. I have rode with my gas tank open, still the problem persists.
What would you expect the bike to run like with the vacuum line coming from the advance unit unhooked and "hanging" while you plug the carb hole it came out of to prevent air leaks?
Sorry for making this so long, I wanted to be thorough.
Any help would be greatly appreciated,
Mike
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