prowlindowlin
CB750 Member
Hello All,
I'm new to the forum, but extremely happy to see it alive and active. I recently acquired an 81 750F from a "collector". Very clean and well maintained bike. 11,xxx miles. Bike is nearly what i would consider to be 8 or 9 out of 10. However, the bike has a somewhat consistent sputter/pop/backfire that ranges in intensity on deceleration or at low RPM. It only occurs on the right side of the bike (cylinder 3 or 4). Its not deafening, but it is consistent and slightly concerning.
I've also found that if i let off the throttle completely for a second or two, even after releasing at low speed, the moment i open the throttle at all, it will cause a semi intense pop. This happens pretty consistently. Or, if i leave my hand very light on the throttle, barely opening the butterfly, that a more smooth consistent pop will occur. I've only heard it backfire loud maybe once. I'm hesitant to keep riding it for fear of making the problem worse. I haven't looked too far into it, however I have gone through most of the basics of the bike and everything is in very clean condition. No missing parts from the bike, even the less desirable ones (spawn of satan? lol). I've checked carb synchronization and found that it needed no adjustment. Im not an expert but all carbs were surprisingly synced up, despite previous owner saying he had never synced the carb (i don't think he rode it a lot).
Im looking for any advice or experience with a similar issue. Im going to look closer at the intake boots on the airbox and carb to see if i can find a leak. Also, ive heard that exhaust leaks can cause backfiring or popping by letting air into the exhaust causing the late combustion. On the right header right before the muffler, there is an very small hole (maybe between 1/16" dia). It looks like it was manufactured like that. The left header has it too however it appears plugged with something. Could this be enough to cause the backfire? I'm considering plugging it with a small dab of high heat JB weld, but before doing that I wanted to see if I can gain any wisdom.
Thanks in advance
Pat
I'm new to the forum, but extremely happy to see it alive and active. I recently acquired an 81 750F from a "collector". Very clean and well maintained bike. 11,xxx miles. Bike is nearly what i would consider to be 8 or 9 out of 10. However, the bike has a somewhat consistent sputter/pop/backfire that ranges in intensity on deceleration or at low RPM. It only occurs on the right side of the bike (cylinder 3 or 4). Its not deafening, but it is consistent and slightly concerning.
I've also found that if i let off the throttle completely for a second or two, even after releasing at low speed, the moment i open the throttle at all, it will cause a semi intense pop. This happens pretty consistently. Or, if i leave my hand very light on the throttle, barely opening the butterfly, that a more smooth consistent pop will occur. I've only heard it backfire loud maybe once. I'm hesitant to keep riding it for fear of making the problem worse. I haven't looked too far into it, however I have gone through most of the basics of the bike and everything is in very clean condition. No missing parts from the bike, even the less desirable ones (spawn of satan? lol). I've checked carb synchronization and found that it needed no adjustment. Im not an expert but all carbs were surprisingly synced up, despite previous owner saying he had never synced the carb (i don't think he rode it a lot).
Im looking for any advice or experience with a similar issue. Im going to look closer at the intake boots on the airbox and carb to see if i can find a leak. Also, ive heard that exhaust leaks can cause backfiring or popping by letting air into the exhaust causing the late combustion. On the right header right before the muffler, there is an very small hole (maybe between 1/16" dia). It looks like it was manufactured like that. The left header has it too however it appears plugged with something. Could this be enough to cause the backfire? I'm considering plugging it with a small dab of high heat JB weld, but before doing that I wanted to see if I can gain any wisdom.
Thanks in advance
Pat
the bike starts way better with no choke necessary. Idles super strong and consistent at 1000rpm with no dying at stop signs. I really am surprised the issue was as simple as some dirty jets. i noticed especially the low speed jets i was able to remove (1, 2, and 4) were noticeably blocked up around the bottom of the jet with some of them almost appearing completely gummed up on the sides.
