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Engine popping- help troubleshoot my troubleshooting

  • Thread starter Thread starter Cdhickey
  • Start date Start date
C

Cdhickey

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My 650 (new to me) starts and runs very well, but I have noticed some popping on deceleration. After a longer run last night, I also noticed the popping continued at idle. This may have been present before but I just hadn't noticed, or it may be a new occurrence. It seems to be coming mainly from the left side of the bike, if that matters.

My my understanding is that popping is generally the result of running lean. Here's my proposed plan of attack:

1) Check the vacuum line running to the fuel petcock to ensure it is not leaking. I had my tank off last week and noticed that the petcock is leaking so a new one is on the way. It also appears that the vacuum line is not original and was kinked, and there are no hose clamps installed. Would a leak in this line cause lean running?

2) Check for air leaks by spraying carb cleaner around the intake boots.

Do you have any other easy or obvious first checks? If these fail, I'm guessing I'm heading into idle mixture and carb troubleshooting.

Thanks for your help!
 
start with those
i see its a 81 650
is it stock or does it have pods and a pipe on it
does the poping happen only on deceleration and going down hill??
or is it poping and stuttering while you are accelerating??
 
I'm pretty sure one of the first questions one of our "diagnosticians" will ask is are you running the stock intake/exhaust?
 
Yes leaks in the vacuum line will make a lean condition and popping. What year bike? I assume you have CV carbs? Have you rebuilt the carbs yet? Done the valve adjustments? replaced intake manifold orings? What condition are the manifolds in? What exhaust are you running? What air cleaner configuration..pods or stock???Share every detail about how long youve had the bike and what you have done AND AND how you did it. We love to help but we need a crystal clear report to be able to make a somewhat educated response. It all makes a difference.
 
Thanks guys.

The exhaust, air cleaner and intake manifolds are all stock as best I can tell and appear to be in reasonably good condition- no obvious holes, damage, rust, etc. I have only had the bike for a few weeks so my maintenance to date has been minimal- replaced choke and tach cables, repaired my headlight and verified that I need a new fuel petcock. I have not yet done a full carb job and valve adjustment, although that is my plan for the immediate future- hopefully early in the fall when it starts to cool down. For now, I'm trying to take inventory of what needs to be done, prioritize, and ride as much as possible!

edit: also, it is a 1981. BS carbs.
 
Priority on a bike I know absolutely nothing of its previous maintenance are valves and carb rebuilding. Without those 2 as a minimum, you can get all sorts of symptoms that you think just cant be the carbs or valves...but they are. Valves are top priority because you smoke them and your into a helll of a lot of money and down time rebuilding the entire top end.
 
Fair enough! I guess the valve job just got bumped up my list!
 
Note that on the right side of Cliffs website home page youll see some rebuild tutorrials..chose the CV one.
 
You don't need hose clamps on the vacuum line, should be a tight fit, the fuel line maybe, if you use a rubber fuel line from an auto parts store, yeah gonna need the clamps. Use the fuel line made for the bike, just the spring clamp is all it needs. Here are couple more things to check for the popping, Exhaust gaskets and any where the exhaust pipes connect. Also look for rust spots on the exhaust specially the under side and the nooks and crannies, could be a pin hole or a bunch of holes, that can cause the popping as well. Do the other maintenance stuff first valves, petcock, vacuum line, carb boots, carb rebuild, and make sure the air box has a good tight seal as well. We having fun yet!? lol
 
When my petcock failed it leaked fuel down vacuum line into #2 cylinder fouling plug at low throttle settings, thereby dumping gas into left side exhaust where it popped when caught up to #1's exhaust. Try the new petcock first, but understand that these things run really lean in stock form, and clogged carbs/ other maintenance neglects aggravate issues.
 
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