Popping Noise After Carb Rebuild at Idle

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LikeyMeYommy

XS650 Enthusiast
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Popping noise coming out of Left carb (see video) after carb kit rebuild. Added K & N air filter pods (Left pod has gas in it (WTF). Right pod is dry. Right carb is not popping). I realize now that I probably need to upsize my idle jets and my main jets if I’m going to run pods. Haven’t done that yet so I was surprised that this thing seems to be tuning best (highest RPM @ dead cal test) at about 2-1/2 to 2-3/4 turns fuel mix screw with the exception of this popping.

I’m going to take the carbs back off and double check the floats. Both carbs seem to be leaking a little bit from top of float bowl. I did put the new gaskets in <scratching head>.


No better way to feel like an invalid then taking up a new hobby and buying your first “fixer-upper”motorcycle 😄. I am loving it and learning a lot though and appreciate you dudes in the forum!!!
 
Your fuel screw settings are in the ballpark. The fuel in places it shouldn't be - description - indicates float valves not sealing, floats leaking or wrong adjustment though. Did the rebuild kit come with float valves? Are the floats set @ 25mm?

The popping symptom can be other things, but "flooding" causing the L cylinder to "load up" sounds like a good candidate.
 
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Those aftermarket rebuild kits can be pretty junky. My dealer quit using them because of too many returns with overflowing and leaking carbs. He only uses genuine Mikuni needle and seat assemblies now. The quality of those kit float needle and seat assemblies is hit and miss. The jet sizes included in those kits are often wrong as well.
 
5twins said:
Those aftermarket rebuild kits can be pretty junky. My dealer quit using them because of too many returns with overflowing and leaking carbs. He only uses genuine Mikuni needle and seat assemblies now. The quality of those kit float needle and seat assemblies is hit and miss. The jet sizes included in those kits are often wrong as well.
Click to expand...
Got from Mikes… sure you’ve seen them. I’m going to take them apart and check out the floats. I have a feeling I have a leaky float that is not “floating”. Where do you go to get your genuine Mikuni stuff?
 

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Yep if those are your float dimensions.

The original floats and the ones I linked will set @ 25mm.

Let us know how it turns-out
 
UPDATE: Finally got parts (and time). Went up 1 size from stock on main and idle jets. Also, got me a clear tube setup from ebay. Fluid level in left carb was 2mm low. Fluid level in my left carb (the popping noise culprit side) was 3.5mm low. Is this low enough to cause problems? In anycase, will ajust in the morning but I'm leaving the clear tube connected over night. Carbs are off the bike and fuel tubes still connected. I left fluid in the tubes. Want to see if my float needles are sealing well. Will check in the morning to see if the fluid level in my tubes drops.

One thing I noticed... if the carbs are not perfectly level, it easily affects the fluid levels. When checking fluid levels. Bike needs to be perfectly level (or in my case off of the bike and leveled on my bench)
 
xjwmx said:
I had this happen with non-Mikuni needles. Rubber tip expanded so much needle was firm and couldn't move up or down in seat!
Click to expand...

Yeah thanks for the info. Interesting! Crazy the differences between the genuine and non-genuine parts.

I have the all metal (no rubber tip) needle valve.

For those with the all metal float needles, in your experience are these valves sealing tight for the duration or do they leak over time? Mine seem to not be holding the fuel in the lines even overnight.
 
Perhaps a small amount of polishing compound on a q-tip to clean out the seat or use it like lapping compound with the needle. I’ve gone back to original parts that I cleaned that way many times because the newer stuff was junk!
 

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