Noob with Cobras

[RudyF6]

Had my first Valk since new in 2001, a standard with I/S bags and trunk, exhaust is stock with piggies cut to accommodate I/S tips.
Just bought a tourer with Cobra 6x6's with baffles in them. Most of the time it sounds like a V-8 musclecar - love it! However, between 2-3k rpm's with steady or light throttle and load, it sounds like it's missing. It doesn't feel like it, just sounds like it along with a little pop and burble occasionally.
Is that just the way it is with the Cobras or is that an indication that maybe it wasn't re-jetted when the pipes were changed? How can I tell?
I know it's been said that you lose a little power with Cobras, and it doesn't feel as smooth and strong as my stocker, but I do love that sound! (most of the time   )

Note: It ran kinda' crappy when I got it - 3 intakes leaking at the head and all clamps loose - fixed that for a very noticeable improvement. 

[Chrisj CMA]

Id run some techron through it and see if those slight troubles go away.  Also it not desmogged, you may need vacuum lines and caps

[9Ball]

that's the sound/characteristics of running lean...if you have shimmable needles, move the "e" clip down one notch.  If you're sure you chased down all the air leaks then this is your next check before considering pulling the carbs.

Also, pull a plug or two and look at the color...let us know what you find.

[mmurffy03]

maybe a clogged slow jet

[RudyF6]

Thanks guys. Pulled plugs, all are very light tan, not quite grey. All 6 look the same. Don't think slow jets are plugged, it starts, idles and runs great. Is the RPM range about where the carbs transition from slow to main jets? I kinda get CV carbs but haven't worked on them much.
9-ball: if I want to try needle adjustment, I pull the cap and spring, the slide comes out with the diaphragm, right?

[9Ball]

Thanks guys. Pulled plugs, all are very light tan, not quite grey. All 6 look the same. Don't think slow jets are plugged, it starts, idles and runs great. Is the RPM range about where the carbs transition from slow to main jets? I kinda get CV carbs but haven't worked on them much.
9-ball: if I want to try needle adjustment, I pull the cap and spring, the slide comes out with the diaphragm, right?

Yes, once you remove the diaphragm assembly, thread one of the screws you removed from the cover into the needle holder and pull it (with a sharp tug) and the needle holder will come out.  If you have stock needles, then there will be only a shim washer and a plain needle.  If you have aftermarket needles, there will be a washer and an "E" clip-probably in the third notch.

To reinstall, snap the needle holder back into the diaphragm, make the diaphragm look like a mushroom and place it in position and push down to seat it (careful-if it is properly centered there will be no resistance-if it binds then the needle isn't centered properly and could damage the seat)...Also, be really careful to have the diaphragm properly set in the groove so you don't damage (or tear) the rubber when you install the caps.

[HayHauler]

Thanks guys. Pulled plugs, all are very light tan, not quite grey. All 6 look the same. Don't think slow jets are plugged, it starts, idles and runs great. Is the RPM range about where the carbs transition from slow to main jets? I kinda get CV carbs but haven't worked on them much.
9-ball: if I want to try needle adjustment, I pull the cap and spring, the slide comes out with the diaphragm, right?

Yes, once you remove the diaphragm assembly, thread one of the screws you removed from the cover into the needle holder and pull it (with a sharp tug) and the needle holder will come out.  If you have stock needles, then there will be only a shim washer and a plain needle.  If you have aftermarket needles, there will be a washer and an "E" clip-probably in the third notch.

To reinstall, snap the needle holder back into the diaphragm, make the diaphragm look like a mushroom and place it in position and push down to seat it (careful-if it is properly centered there will be no resistance-if it binds then the needle isn't centered properly and could damage the seat)...Also, be really careful to have the diaphragm properly set in the groove so you don't damage (or tear) the rubber when you install the caps.

+1
The diaphragms are EXPENSIVE.
16111-MZ0-A00 PISTON, VACUUM
Around $75 each!

Hay 
Jimmyt

[Chrisj CMA]

Main cause of popping is vacuum leaks.  When was the last vacuum line change? and those OEM caps on the unused nipples leak bad after a few years too

[IamGCW]

Just suffered through the same thing.  Diaphragm on the petcock was leaking air.  Another rider here in FL had similar issues and it was the vacuum line to the petcock.  I would start there.  Remove the hose, pull a vacuum on it and see if it holds.   I had the rebuild kit handy since my plan was to rebuild the petcock in a few weeks. 

Gil

[cma1]

what he is describing sounds like every set of cobras I've ever heard, including mine, and mine is running 150%. they pop, crackle, make loud nasty biker sounds and generally make your neighbors wish you owned a Harley, or better yet wish you were dead.

if you decide you want to mellow it out (and eventually you will) take the baffles out and wrap them with some fiberglass matting you can buy at most any bike shop, and put them back in, they sound way better that way and still make your neighbors want to kill you.

[RudyF6]

Thanks again guys, I'll probably be doing vac lines, maybe desmog, who knows what else.....
Petcock works, shut it off and it runs out and quits - turn it on and start right up. Shouldn't be leaking vacuum, right?

[hairyteeth]

I'm riding an 03 standard with cobras. I live an hour south of you if you would like to ride mine to compare let me know.
HT

[Mtn Valk]

I have 6 into 6 TBR's and they have the very same symptoms that you are describing. Mine pops and fluffs mildly between 1500-2500 rpm's. I've tried replacing vacuum lines, header gaskets, and intake seals. The symptoms started when I replaced my OEM pipes with the TBR's.

From listening to the forum here, I believe it's just the inherent nature of the aftermarket pipes, especially Cobra's and TBR's. I will continue to follow this thread though to see if a solution is found.

[IamGCW]

Thanks again guys, I'll probably be doing vac lines, maybe desmog, who knows what else.....
Petcock works, shut it off and it runs out and quits - turn it on and start right up. Shouldn't be leaking vacuum, right?

Mine worked fine as far as On - Off.  But the vacuum test failed.  The valve is separated into two sides separated by a vented chamber.  If the fuel side leaks gas drips out, if the vacuum side leaks air is sucked into the vent chamber.  It did seem I would hit reserve earlier than before.  Next long ride I will know if that has changed.

Gil

[9Ball]

I have 6 into 6 TBR's and they have the very same symptoms that you are describing. Mine pops and fluffs mildly between 1500-2500 rpm's. I've tried replacing vacuum lines, header gaskets, and intake seals. The symptoms started when I replaced my OEM pipes with the TBR's.

From listening to the forum here, I believe it's just the inherent nature of the aftermarket pipes, especially Cobra's and TBR's. I will continue to follow this thread though to see if a solution is found.

Having had both Cobra 6x6 and TBR 6x6, I can say that re-jetting will fix or greatly reduce most of the symptoms you describe.

[RudyF6]

If my needles are not adjustable, can I shim them up with thin washers? Seems like I've heard of that before. How about I/S springs? Aren't they lighter to open sooner?

[9Ball]

If my needles are not adjustable, can I shim them up with thin washers? Seems like I've heard of that before. How about I/S springs? Aren't they lighter to open sooner?

I/S springs only help with throttle response, not jetting-type issues.

Yes, you can try adding washers to shim the needles.  You should try to match them for all 6 carbs.  You might put out a request and see if anyone has aftermarket needles they want to sell otherwise it's about $110 for a needle kit.

[Len]

I have Cobras and they would pop on deceleration after vacuum lines were replaced and adjustable needles were installed.  The fix for me with my second bike was to contact Cobra and order a set of baffles; They only have one size of baffles and they are long...I did not mind the milder tone because I had ridden this bike with the stock exhaust.  The baffled tone is still pleasing and growls when she's twisted....eliminating the popping was just a plus.  Baffles may or may not have eliminated popping for others, but it worked for me.

My pipes are cut down approximately 12-14 inches.

[CajunRider]

Yes, you can try adding washers to shim the needles.  You should try to match them for all 6 carbs.  You might put out a request and see if anyone has aftermarket needles they want to sell otherwise it's about $110 for a needle kit.

I'll make it easy on you... less than $10 with shipping... and you'll have a few spares...

http://www.jetsrus.com/individual_parts/009_396_su.html