[gerdawg]

I'm posting this over here as there doesn't seem to be much input from the vstar forums on other sites. Just the same two people answering most threads.

I've included a youtube video of the problem. Does anyone know what is making this sound? It's easily reproducible by just lightly giving throttle then backing off. If you give throttle and hold it happens but a lot less frequently. It also happens at idle with no throttle advance. Any help pinpointing what the sound is coming form near the carbs would be helpful.

As a side note we took off the AIS this weekend and the back firing is less. The other thing I noticed is that gas is pooling in the rear cylinder intake boot and it tends to "spurt" out a bit of fuel mist when that sound goes off. It almost looks like there is a backfire going on, the float is stuck or the coil isn't producing spark and not burning the gas?

 

[Buford]

First, make sure you don't have any leaks around the boots that attach the carbs to the engine. A leak will cause things like idle hunting around, lean and then rich conditions and backfiring/popping. Once you have the leaks sorted and you still have the problem you may need to sync your carbs. You'll have to research the sync process.

 

[SmokenJoe]

Almost like an electrical crack.

 

[toby]

Due to the fact that it happens at the exact same points of throttle/rpm, and gas pooling and spitting out, betting on it being a leak in the boot, crack or not tight to the carb in combo with carbs out of sych and/or floats sticking, pin hole in diaphragms, and possible timing off, something in those areas.
But as Joe said electrical arc? Since it happens at the same rpm point every time would mean the loose connection is rattle from vibration right at that point. That still does not explain gas puddling and spiting out?

 

[gerdawg]

Thanks for the input guys.

So...a little more information from me on this:

I've had the bike apart a few times and am pretty sure that the boots are snug into the intake and the that the filter is secured to the airbox pretty well. It doesn't appear to be leaking air that I can tell at this point.

We did try to sync the carbs using a digital manometer and that left us scratching our heads even more. While syncing the carbs the front cylinder was originally pulling most of the vacuum while the rear cylinder wasn't favored on the scale. The carbs were adjusted so that at idle the manometer read 0 meaning both sides were pulling the same equal volume of air.

HOWEVER...when given throttle input the manometer jumps back to higher vacuum reading in the front cylinder. No i'm not a pro by any means with a manometer but I figured that with the carbs being synced at idle that no matter where you are on the throttle the butterflies should be pulling in and out the same cfm for airflow if synced and the reader should remain at 0 but this isn't the case.

Further information is even with the airbox off of the bike and looking straight down the intake boot of the carbs when revved the back cylinder (which after pulling the plugs shows gas on them) is pooling the gas while the front cylinder is dry as a bone. I'd believe if it were an issue with the air seals that both of the boots would display gas in the intake boots while there is nothing attached to them but that is also not the case.

At this point I debate if there is a float that is intermittently sticking and/or open past the 12mm allowance, missing spark on that cylinder that causes the gas not to ignite (though I'd think the un-burnt fuel would be thrown out in the exhaust stroke), or a stuck intake valve where on the compression stroke the fuel still in the intake it being ignited and is blowing back into the rear carb.

We haven't yet checked timing and that seems to be a real PITA on this bike as I believe we have to take it apart in order to verify where the gears are lined up. (Or is there an easier way?)

This also doesn't seem to be the same RPM that this happens at. It can just reproduce the issue easily by blipping the throttle almost like loading it up then unloading it. That seems to be the easiest way to cause the ping that you hear in the video above but it does happen just sitting at a light and on a few occasions while riding the bike at different points in the throttle range.

This issue is a really pain to figure out so far!

 

[Buford]

Maybe running too lean?? I don't know what else I can suggest... I believe you're on the right track with the checking the float and/or timing. Hw about the almighty "SeaFoam"

Sorry I can't be much more help.

 

[BillyD66]

If checking for leaks around things you can spray brake cleaner or the like but be warned they are highly flammable. If the idle goes up it means the cleaner is getting into the chamber which it shouldn't. Also make sure it won't get on painted surfaces or if so won't cause them harm.
I'm no expert either but I'm guessing if the rear cylinder wasn't firing you'd really notice that and like you said it would have to be dumping the unburnt fuel somewhere...
What about trying to adjust the carbs with a little throttle first and then checking to see if still balanced/synched at idle?
And just a silly suggestion/question but did you use some carp cleaner as well? Been a looooong time since I had to deal with carbs, chokes, points and the like and I can say I'm not missing any of it. Modern electronics are great of course till you have to replace them. Then they are just expensive and you wish for the good old days.
Go step by step no matter how silly it sounds. Look at both plugs and if not identical see why. Also check the gap and if in doubt replace them since they are cheap.

A float issue could explain the excessive fuel. How old is the bike and how well maintained has it been especially if you are in a winter area like me?
Off the cuff and if the job isn't too entailed I'd look into cleaning and rebuilding the carbs and then synching them assuming the other items like spark plugs look fine.

 

[Adrenaline Revolution]

My guess after thinking on this for a while is a sticky valve that stays open too long and some of the compression (a very small amount) is popping back through the carb sounding like a spit.
Good luck.
There are a lot of good wrenches on this site. It won't be too long before you get it running right again.

 

[gerdawg]

When we first had the bike it was running terrible...anything over 1/2 throttle would cause the motor to bog to the point of it feeling like it was going to blow up. A 1/2 can of seafoam made a world of difference for that issue.

I think the next steps are going to be changing the out the floats at this point and doing a leak down compression test to make sure that the intake valves aren't leaking during the compression stroke. Other than that we'll have to do the timing check (draining the oil, pulling covers off, checking markings, etc.)

So far it seems like no one has really ever heard the type of sound before so it would be interesting to figure out what the **** it is. The bike does run which is a plus but it has these idiosyncrasies that i'd love to identify and squash if at all possible.

 

[gerdawg]

The other thing I think I'm going to try is ohm out the TPS sensor and see what that's reporting. Maybe there some screwed up advance or timing being created by a faulty reading pushed to the computer from the TPS.

As for the leaks, I've tried to do a leak test on that and it seems to come back clear. I had checked plugs and the front cylinder is what you'd expect while the rear cylinder is clearly running rich. I'll see if balancing the carbs at a higher throttle helps as well.

 

[toby]

Ping? Timing chain tensioner? and carb/s diaphragm, wont stated synched when throttle up??
I would completely rebuild the carbs and check timing and tensioner.

 

[WOLFStryke]

Same thing happened to my friends bike, turned out it was the TPS

 

[gerdawg]

Same thing happened to my friends bike, turned out it was the TPS

Wolf did you get a chance to watch the vids and if so did it sound the same? I'd be really curious because everyone we've talked to so far had never heard anything like this. To me it sounds like pre-detonation of some sort or screwed up timing.

I was thinking about testing out the TPS and seeing if the OHM's where were they should be. Did your friend end up replacing the TPS or did he end up rotating it till it was at the correct spec?

P.S. - This is me helping a friend of my own with their bike.

 

[chris]

loose camshaft chain you can try getting one more click out of the camshaft tensioner to verify but from you saying your getting some gas pooling and some backfiring leads me to you need to replace the stretched camshaft chains.

 

[Stryker2012]

loose camshaft chain you can try getting one more click out of the camshaft tensioner to verify but from you saying your getting some gas pooling and some backfiring leads me to you need to replace the stretched camshaft chains.

I don't know...I replaced a few timing chains, and in my experience they tend to make a rattle noise more than a clinking...sounds like backfiring through the carb.

 

[chris]

I don't know...I replaced a few timing chains, and they tend to make a rattle noise more than a clinking...sounds like backfiring through the carb.

Ive done lots and have heard many different sounds they make mainly on atv's but pretty much the same and the symptoms is the one that are pointing me to the chains. Now i'm only going off of the audio from the clip. But I have been wrong before.

 

[toby]

I don't know...I replaced a few timing chains, and they tend to make a rattle noise more than a clinking...sounds like backfiring through the carb.

Worn timing chain tentioner rollers and guide and/or stretched chain would cause back firing from eratick timing from the slop, rpm up and down, intake valve not all the way closed when it fires pushing gas back through the intake manifold/boot and carb out the air intake end of the carb.

 

[Stryker2012]

Sorry, I should have been more specific. I was referring to the sound being made, not necessarily the cause. When was the last time the valve clearance was checked???

 

[gerdawg]

Sorry, I should have been more specific. I was referring to the sound being made, not necessarily the cause. When was the last time the valve clearance was checked???

I'm not sure it ever was. He bought the bike from a guy used and it has 16k on now for an 04.

it won't hurt to check how much tension its on the chain...we'll just have to take apart the side casing first. I'll probably check the tps first though before going that route. Can a chain be really loose at only 16k?

 

[toby]

It's really hard to tell if that noise s a ping, back firer, arc, spit or rattle from the video?? So all any of can do is give you ideas of possibilities from your described symptoms. You should do a series of processes of elimination test to narrowing it down. Good luck.