Deceleration Popping

[miscott]

   Ok, here's what going on. Have my Valk in the shop for a front fender replacement, and since I noticed some deceleration popping before it went into the shop, I've been reading through some of these tech topics and have learned that two of the primary causes of deceleration popping are loose header bolts and pilot screws needing re-adjusting. I'm having the shop do those two things while they've got the Valk.
   In some recent conversations with the previous owner of the bike, he told me that the bike has a K&N Air Filter, a 6 degree Trigger Wheel, and that the "Needles" have been "shimmed" .0020th's
He ran the Cobra 6:6 for quite awhile and I guess this setup worked good. Now running the OEM exhaust with the front and rear baffles drilled out. Other than the popping on deceleration, it seems to be running great.
   I have no idea whether he's talking about the slow jet needles or the other jet needles, or if I've completely misunderstood which "Needles" he's referring to.
   My question is, are the above modifications something I need to tell the shop about before they get to resetting the pilot screws, or is resetting the pilot screws something that is done to achieve an optimum result that is by criteria regardless of/other than the mods listed above. ie; setting the timing & idle speed on your blown big block really has nothing to do with the fact that your big block has a blower on it.
   Thanks before hand for any information!

[Patrick]

I don't know how bad your popping is,, but,, generally its caused by loose band clamps and/or vacuum lines..
Pilot setting should be 2.25-2.5 turns on 35 low jets or 1.5-1.75 turns on 38 low jets..
Some folks change high jets with Cobra's or other after market pipes,, but,, most just change or shim the needles.. It probably would be a good thing to 'un-shim' your needles if you changed back to original exhaust.. Just remove the chrome vacuum chamber and remove the shims.. I think you meant that the shims were .020"..

[Ricky-D]

it will be very hard to rid the exhaust of the popping you report. The cures you consider will have very little effect on the popping.

You have increased the popping by drilling out the baffles in the stock exhaust.

A good carburetor synchronization is the best medicine to stop the popping and can still leave some small noise under the circumstances.

***

[WamegoRob]

I try to only decelerate twice a day... cuts down on that stuff.

[salty1]

+1 on Ricky-D's comments. Have you ever consider doing a desmog?

[Patrick]

Well yes,, I agree.. The more open and louder the exhaust,, the more likely it will be to pop on decell.. It shouldn't pop too much though,, an open factory system should kinda 'burble'..

[Bigwolf]

A lean fuel/air mixture is at the root of decel popping.  What happens is that such lean mixtures do not always fire when zapped with the spark.  Then the unburned mixture is pushed into the exhaust system where it explodes when the next lit and still burning mixture is pushed iinto the exhaust. The first thing to check is all vacuum lines and all 18 intake tube clamps. 
There are two systems on the Valkyrie that deal with decel popping.  The PAIR (smog) system adds air to the exhaust port under normal throttle conditions but stops adding air when the intake vacuum goes above 15.7 inches HG.  That helps the exhaust entering the header to be less prone to popping.  Vacuum tubes linking intakes 3 and 4 go bad and so does the PAIR control valve.  The PAIR reed valves can break which also causes problems.  Many people just remove the PAIR system entirely thereby eliminating these possible problems.
The other, and probably most important, system to stop decel popping is the air cut valve on the side of each of the carbs.  Make sure the vacuum hoses conecting them are good and not split out on the ends.  Also, check these valves for proper operation.  At 25K on my standard Valk, all 6 hoses to these cut valves were bad and 5 of the 6 cut valves were leaking vacuum.  Once I fixed my cut valves and replaced the hoses to those valves my decel popping was gone.

Bigwolf

[texaninsouthfl]

it will be very hard to rid the exhaust of the popping you report. The cures you consider will have very little effect on the popping.

You have increased the popping by drilling out the baffles in the stock exhaust.

A good carburetor synchronization is the best medicine to stop the popping and can still leave some small noise under the circumstances.

***

I have to differ with you here.... as others have mentioned, my experience is that BAD popping and back firing is caused by lean fuel air mixture which is often caused by bad vacuum lines associated with all the smog crap that came on the bike.  My bike got so bad it sounded like a cursed machine gun when I'd get off the throttle at highway speeds.

The "best medicine" in my opinion (and experience) is to get rid of all the smog crap. I purchased the Shiny De-Smog kit from Redline. Everything fit perfectly and voila', no more popping. At most, now I get a slight burble upon low speed decel. 

http://redeye.ecrater.com/p/8464393/shiny-desmog-kit-chrome-honda

[Thunderbolt]

The small vac lines on the side of each carb to the cut valves will probably have small splits around each end.  Plus all of the other suggestions.  The needles that were shimmed are the ones under the 6 chrome covers.  You will need to remove the covers and the vacuum assembly on each carb and take a screw from the cover and screw it into the body to dissamble.  Pull the plastic body out and you will most likely find that there are two small washers underneath the needle.  Remove one, I think the OEM is the smaller thickness, leave it in and reassemble.  This was a stop gap method to richen up the mixture if I remember correctly.  I did this to my Tourer when it had Cobra's.

[signart]

If a symptom of the popping and/or burbling is an indication of a lean mixture, isn't that the reason for shimming the needles, I mean since the baffles have been drilled front and rear? The reason I say this, my needles are stock, I am experiencing burbling and a slight flat spot just off idle on take off and rolling on throttle out of turns. (Also have drilled front & rear baffles.) Thought maybe slow jets clogging or maybe I need to shim needles.

[Ricky-D]

If a symptom of the popping and/or burbling is an indication of a lean mixture, isn't that the reason for shimming the needles, I mean since the baffles have been drilled front and rear? The reason I say this, my needles are stock, I am experiencing burbling and a slight flat spot just off idle on take off and rolling on throttle out of turns. (Also have drilled front & rear baffles.) Thought maybe slow jets clogging or maybe I need to shim needles.

Your problem, which is only slightly related (burbling) to the original poster's complaint, should be a subject for a new thread rather than hijacking this thread. And yes, you have a problem.

***

[signart]

Not trying to hi-jack, but also related in that baffles are drilled in similar manor and burbling condition. As one poster said drilled baffles  are related to burbling/popping, I don't know. Not asking for help with my problem (yet), just curious if miscotts' problem is related to drilled baffles, shimmed needles or no shimmed needles, which might be related to mine. But if poster's chime in here and say 90 out 100 baffles modified result in popping, I'd say wer'e on to something. Forget I mentioned flat spot, may or may not be related.

[whitestroke]

Is there any one with any kind of modified pipes that can go down a steep hill in 1st gear (no brakes) and not hear popping or burbling?????

[texaninsouthfl]

Is there any one with any kind of modified pipes that can go down a steep hill in 1st gear (no brakes) and not hear popping or burbling?????

I wouldn't know... we don't have any steep hills in down here in Florida. 

[judd]

Ok just thowing this in the mix, You mention the P/O going fron OEM exhaust to Cobra 6 into 6 and back again, is it possible that he may not have changed them little copper exhaust gaskets out during this exchange.................they may now be deformed and could well be a contributing factor to the decel popping....................could be, I don't know for certain but, a cheap and easy piece 'o' mind kind of thing to look into  !!!  

[9Ball]

Ok just thowing this in the mix, You mention the P/O going fron OEM exhaust to Cobra 6 into 6 and back again, is it possible that he may not have changed them little copper exhaust gaskets out during this exchange.................they may now be deformed and could well be a contributing factor to the decel popping....................could be, I don't know for certain but, a cheap and easy piece 'o' mind kind of thing to look into  !!!  

that's a very good point....nice thinking.

 

[RUDE DOG - Steelers]

Good to check the copper gaskets.  When I got my I/S and removed the exhaust, there were 3 copper gaskets stuffed and crushed on the one side of the exhaust and 4 on the other.