Backfire on deceleration

[Hajya]

I have a 1998 Valkyrie with Cobra Six into Six pipes on it. The carbs were re-jetted by my motorcycle mechanic when the pipes were put on and it ran great for 4-5 years. But this last few months it has been running rough. I have been reading the posts on backfires on deceleration, etc. I am having problems with sputtering and some backfiring out of my number one cylinder on deceleration. It is also starting to have the same problem on the other side out of at least one of the other cylinders. I have run two cans of Berryman's B12 Chemtool through the tank based on my mechanic's recommendation with no improvement and have now bought both Techron and Seafoam to try next. After reading the posts, I tightened the exhaust manifold bolts and the 12 hose clamps above the carbs, many of which were loose in both areas. Today I noticed that if I have the choke on while the engine is at normal operating temperature, all the sputtering and backfiring goes away, although the bike runs a little rough while idling. Anyone have an opinion if the change with the choke would indicate whether the issue is an exhaust leak, vacuum leak or carburator issue? I am trying to avoid removing the tank and getting in over my head, as I have only worked on older carburated engines years ago and have never worked on a motorcycle, other than to change the oil and air filter. Any help would be greatly appreciated. 

[nogrey]

Since it was running well and this just started, it's probably one of the following:
1: Cracked or leaking vacuum line or cap. Check all 6. If you see cracks, replace them. You can get viton- B from redeyerich@ecrater.com, or you can just take one to an auto parts store. I bought some at NAPA once.
2: The choke smoothing things out is a clue, and in my experience is usually related to dirty slow jets. Using the enrichment lever (choke) adds fuel and "makes up" for the dirty/clogged jets. If you can isolate which of the cylinders it is, you can simply remove the downdraft, then the float bowel, and remove the slow jet without having to remove the carb bank. Clean the jet with carb cleaner, and spray it in the slow jet port in the carb as well. You may also just continue using B12 Chemtool and it may, over time, improve things.
3: Leaking vacuum hoses on the air-cutoff valves. These are the little plastic valves on the side of each carb with an "S" shaped vacuum hose running from the valve to the carburetor. Hose is about 4" in length. You can see them if you look just above the chrome rail cover (the chrome metal piece that screws on to the carbs on both sides to cover the choke rails). These lines are often overlooked, and at the age of these bikes are most likely in need of replacement anyway. You can also get these from redeye, but you have to ask for them.
4: It may be a leaky or plugged pilot. These can also be removed without removing tank or carb bank. Remove the chrome downdraft tube and the pilot will be a little "D" shaped screw on the bottom of the carb. To remove these, you either need the tool, or many simply etch a slot in it and remove with a screwdriver. The procedure is to screw them IN first (carefully) until they stop, counting the number of turns, as this is the adjustment. Then back them out all the way. Spray carb cleaner into the hole, and on the pilot screw as well. Clean the pilot screw until there is no visible signs of varnish. Any visible varnish here will cause problems. DO NOT USE STEEL WOOL, OR ANY OTHER TOOL. Pilot screws and slow jets can be damaged pretty easily if scratched or if a metal tool is used to clean them. Just stick with a cloth and carb cleaner. Reinstall, and remember to turn all the way in, then back out the number of turns you counted on removal. Do these one at a time.
4: I've seen the same issues if the carbs are out of sync. Can't think of any reason yours would be since you haven't touched them, but still, this is a symptom of out of sync carbs. Slow return to idle and missing on accel are also symptoms of carb sync issues.

One of my Valks is doing the same thing right now.  I've replaced all the rubber, removed all the smog stuff, re-sync'd and replaced pilot screw O-rings and springs. It runs great when warm but doesn't idle smooth on start-up like my other vales. So it bugs me. I have just ordered #38 Slow Jets and am going to go after it again....as time permits. I've got another valk torn apart right now that needs a little TLC.

Hope this helps.

[Hajya]

Thanks. I'll try your suggestions before taking off the tank or carb bank(s)...

[Hajya]

Now I am also considering a desmog kit just to eliminate the unnecessary opportunities for a vacuum leak...

[cmawest]

i am starting to see a pattern here with the pop on deceleration. I have It on my 99, it has had all the baffles punched, and the pop started shortly after, the piggies cut off, and cobra 4" slash cuts installed, my brother has cobra 6 into 6 and has the pop, his will wake dead people up when it pops., my 03 had straight out of the box stock pipes and never did it until I punched the baffles, now it does , my buddy in calif. left his stock and it has no pop either.

so tell me, how many of you that have not molested your pipes have the pop on deceleration and how many don't ?

[nogrey]

i am starting to see a pattern here with the pop on deceleration. I have It on my 99, it has had all the baffles punched, and the pop started shortly after, the piggies cut off, and cobra 4" slash cuts installed, my brother has cobra 6 into 6 and has the pop, his will wake dead people up when it pops., my 03 had straight out of the box stock pipes and never did it until I punched the baffles, now it does , my buddy in calif. left his stock and it has no pop either.

so tell me, how many of you that have not molested your pipes have the pop on deceleration and how many don't ?

When you modified your pipes, you changed the back pressure enough to effect fuel mixture. Your problem should be easy to resolve. First thing I'd try would be to back out the pilot screws one full turn. That probably won't fix it but it's worth a try. Next step would be to go up a size in slow jets.  Your popping is due to a lean fuel mixture.

[cmawest]

when I bought this bike it was all gummed up. I had to remove the carbs 3 times before I got it running right. I would tear out the exhaust and buy a new set, and adapt it to my trike before I'd tear them ^^%$%$$ carbs out again !!!!!!!!!!!!

[biguglyman]

I have a 99 standard with cobra 6x6 pipes and had decel popping until I did a desmog. Virtually eliminated the popping.

[nogrey]

when I bought this bike it was all gummed up. I had to remove the carbs 3 times before I got it running right. I would tear out the exhaust and buy a new set, and adapt it to my trike before I'd tear them ^^%$%$$ carbs out again !!!!!!!!!!!!

You can change out the slow jets without removing the carb banks.

[Hajya]

I apologize for my ignorance in advance. I have never done a desmog before and had never heard of it until I joined this awesome site. 

I have been looking at two desmog kits:

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

and

http://www.xf6-custom.com/partpages/desmog.html

They look completely different to me. The one from Redeye appears to have more rubber short hoses and I from what I have read on this site, I thought the goal was to eliminate the rubber to prevent vacuum leaks.

So my question is which one is better? I don't mind buying or installing either, but I want one for the long term so I don't have to do it again. Also, I want it to look the best that it can. I have my bike all dressed out.

I appreciate everyone's help... 
Hajya

[Willow]

The one from Redeye includes a little rubber that will remain after the desmog removes a LOT of unneeded hose.  He includes those because they could be a problem if they're aged (and they are).

[cmawest]

when I bought this bike it was all gummed up. I had to remove the carbs 3 times before I got it running right. I would tear out the exhaust and buy a new set, and adapt it to my trike before I'd tear them ^^%$%$$ carbs out again !!!!!!!!!!!!

You can change out the slow jets without removing the carb banks.

how would one do that ?

[nogrey]

when I bought this bike it was all gummed up. I had to remove the carbs 3 times before I got it running right. I would tear out the exhaust and buy a new set, and adapt it to my trike before I'd tear them ^^%$%$$ carbs out again !!!!!!!!!!!!

You can change out the slow jets without removing the carb banks.

how would one do that ?

It's not too bad, really. Remove the downdraft tubes on one side. Remove the carb float bowls (you'll need an offset Phillips screwdriver). The slow jets are now available for removal.

[cmawest]

i fought this same problem for years on several bikes, all converted to cobra pipes. one day a chapter member, an old guy riding a harley, came back from daytona on his 96 dresser, one of our members had just purchased a new dresser. went to daytona and paid 1200.00 in repairs to nurse it home. at the next chapter meeting he cornered the old guy and demanded to know why he had ridden his bike over 80K miles with NO breakdowns. he looked the the young gun and said "don't ask questions you are not going to like the answer to" he went on to tell him that he was like all youngsters who bought a new harley for the first time, you cannot get out of the store with out a set of loud pipes, so you have now changed the dynamics of the motor, you jet it up, down, and sideways till you give up and buy a screaming eagle carb and several other giddy gappers trying to change it for the better. a good mechanic advises you to change everything back, but you need that roar to eat up your hearing, so you try re-camming it, then head out to sturgis riding a hand grenade, and wonder why it breaks down. the moral to the story is this, harley (and honda) spent millions on engineers to come up with the best combination, what makes you think as a 3rd grade reading teacher that you know more than they do? leave them alone they are the best (valkyries) bike ever produced and will give you a lifetime of riding pleasure, if you just leave it the way the engineers at honda sent it to you.

[da prez]

  I used to buy de-smog kits. Nothing wrong with the kits.  All I buy is 14mm freeze plugs , NOT 9/16.  Insert the 14mm freeze plugs with a little sealant in the top engine air tube holes.
 I cut off the air tubes and use JB weld or thread and pipe plug them  The air tubes to the bottom , remove and make cover plates with exhaust proof gaskets or plug the flange with a pipe plug.  Harbor Freight sells ball end long allen sockets that work well. Exhaust removal is not needed. When I remove the pair valves , I put silicone sealer in the threads. I either plug or cut off the air box fitting, If cut off , either plastic weld or ABS plastic glue and a patch.  I have lost track of how many I have done.

                                                        da prez

[Willow]

2014?  Really!?  Does anyone think the persons involved in this nine year old conversation still cares?

[ridingron]

2014?  Really!?  Does anyone think the persons involved in this nine year old conversation still cares?

Probably not even still around. But... If you have a similar problem and do a search, will this 9 year old conversation come up? Maybe the old comments and the new ones will help the searcher solve their problem.

[97BLKVALK]

Now I am also considering a desmog kit just to eliminate the unnecessary opportunities for a vacuum leak...

Another option

https://valkyriecarbsandcustom.com/ols/all?sortOption=descend_by_created_at

[psckam]

i fought this same problem for years on several bikes, all converted to cobra pipes. one day a chapter member, an old guy riding a harley, came back from daytona on his 96 dresser, one of our members had just purchased a new dresser. went to daytona and paid 1200.00 in repairs to nurse it home. at the next chapter meeting he cornered the old guy and demanded to know why he had ridden his bike over 80K miles with NO breakdowns. he looked the the young gun and said "don't ask questions you are not going to like the answer to" he went on to tell him that he was like all youngsters who bought a new harley for the first time, you cannot get out of the store with out a set of loud pipes, so you have now changed the dynamics of the motor, you jet it up, down, and sideways till you give up and buy a screaming eagle carb and several other giddy gappers trying to change it for the better. a good mechanic advises you to change everything back, but you need that roar to eat up your hearing, so you try re-camming it, then head out to sturgis riding a hand grenade, and wonder why it breaks down. the moral to the story is this, harley (and honda) spent millions on engineers to come up with the best combination, what makes you think as a 3rd grade reading teacher that you know more than they do? leave them alone they are the best (valkyries) bike ever produced and will give you a lifetime of riding pleasure, if you just leave it the way the engineers at honda sent it to you.

i concur