I have an 05' superhawk with 16500 miles on it. I got it in june of 08 with 3500 miles and its had this noise since i got it but now its getting worse. When warming up and first few miles of driving especially at lower rpms, It makes a deep loud thud popping noise. when im next to it i can hear it all over and when im ridding it it feels like compression pop under my chest in the gas tank/air box area..... I thought it was that cct issue but reading other threads that seems to be more of a rattle which i dont have. I did just checked the valves on it at 16k and they were in spec.

O btw yesterday was the first rain of the season and i was ridding and lost the rear cylinder... that was so much fun.... pretty sure water got under the spark plug boot but not sure... trying to diag both complaints this afternoon

 

Sounds like it could be related to the pair system, if you can't figure it out you can always swing by and I can give you a hand with the diag.

 

There is also the issue of tank vent line placement.. In the stock location in the rain water pools up and blocks it causing fuel starvation issues.

 

You know i forgot to mention one other important detail... I disabled the PAIR when i did my valve adustment, flipping the reed valve stopper. I also removed the three evap valves and canister.

Lazn are u refering to the small diameter vent tube or the large diameter vent tube... I no longer have the charcoal canister so both are vented to atmosphere down at the chin spoiler. What did u do to fix this, just move it? and is it possible that it would only starve one cylinder... because the front one was firing ok

 

Well these things are kind of hard to trouble shoot on line but you might have a vacuum leak or missed a line somewhere.

The small diameter hose is the vent line, the larger line is a drain if you over fill the tank (you can see the opening for it when you open the gas cap)

Like I said, I'm just down the road from you and can either come by or you can swing by here if you can't get the problem figured out.

 

sounds like carb backfires to me... the thudding as you call it. The dropping one cylinder when wet is a hole different problem most likely. I don't think it would be venting issues as that can keep the bike from running at all. If it is though pretty easy to diagnose lift the lid on the tank and if it goes away that is the problem.

As far as the thudding it can indicate a lean condition, on my superhawk it only would do it on the lower rpms, I have since rejetted my bike and no longer have carb backfires. Something to look into.

 

Thanks 8541Hawk I got it together and running so ill let u know if i didnt fix it...

Cornadp when u rejet did u use a jet kit and replaced them all or did u just replace one jet

 

Which is why I'm thinking a missed vacuum line in the Ca emissions removal.
Did you plug all the lines or did you go by the procedure which recommends leaving one line open to atmosphere (which is not the right way to do it) ?

 

I used a jet kit, a little more to it then swapping a jet or two. I would check all connections to the intake first, its free to do that. If everything checks out jet kits are about $90. There are plenty of threads on jetting.

 

It sounds like I had a similar problem a while back, When I was riding at any speed and the RPM's were around 2500-3700 I would hear a thud under the tank, after taking the tank off i discovered that I had a backfire though the carbs. I tried to tune the carb my self and then ended up taking it to a shop to get the carbs reworked.