Could use some help with a back fire issue

[ryeknee]

I am having a backfire issue on my 99 standard. About six months ago I noticed some popping on only the right side exhaust during idle when I warmed up the bike. The popping stopped once I would ride away and would run great as always with no subsequent backfiring or additional popping until next time I would warm up the bike and again nothing once I rode away. A couple weeks ago suddenly it started regularly backfiring on deceleration (once a second) but only on the right side and only at low RPM (under 2000 RPM) .... no backfire at all during high RPM deceleration or when on the gas at any RPM. It also seems to get worse as the bike gets hotter. The bike has run great with no issues for 20 years and only has 40k miles. The bike has been garaged kept and very well taken care of with regular standard maintenance. It was desmogged and had the exhaust canisters modified over 10 years ago but has always run great with no issues. The only recent work done was an oil and filter change 2 months ago. So far I have done the following to try and address the backfiring with no improvement:
1) Tightened up all 16 hose/intake clamps
2) Changed plugs
3) Synced the carbs
4) Emptied the fuel tank and then ran through 3 full tanks of gas with Sea Foam added
4) Replaced all 5 nipple plugs with new ones
5) Inspected the vacuum hose on #6 which looks fine
6) Inspected the air box and cleaned the K&N air filter
7) Tightened the bolts on all chrome intakes
I know there are lots of other areas that could be suspect such as the intake orings (but no residue at all around the intakes), spark plug wires, carb cut valves, etc. but was hoping maybe someone that may have experienced a similar situation where the backfire is only on the right side and only at low RPM deceleration and found the culprit. Any experienced suggestions would be greatly appreciated.     
 

[WintrSol]

You might check the torque on the exhaust headers at the head. If the gaskets weren't replaced the last time the rear tire was changed*, one could have started leaking, which can cause after-fire in the pipe.

*Removing the right side exhaust is per the FSM when removing the rear wheel.

[gordonv]

You might check the torque on the exhaust headers at the head. If the gaskets weren't replaced the last time the rear tire was changed*, one could have started leaking, which can cause after-fire in the pipe.

*Removing the right side exhaust is per the FSM when removing the rear wheel.

* but is not required to do it. Just loosen the hanger, and either lift/lower the swing arm.

FYI
If the headers have ever been removed, it's easy to leave behind a copper crushed flat oring seal. They need to be picked out.

[ryeknee]

Thanks for the suggestion on the header gasket and connections guys .... I will check the torque ...... I am pretty sure the pipe has not been removed since the desmog and canister mod was done over 10 years ago ...... assuming the torque settings are still to spec ....... is it possible a header connection could start leaking even if it has not been touched for years? Also, since the backfiring gets worse as the bike heats up, would not the header connections actually tighten up under more heat ....... or do you recommend dropping the pipe and just changing out the gasket to remove it from the suspects list?   

[..]

Thanks for the suggestion on the header gasket and connections guys .... I will check the torque ...... I am pretty sure the pipe has not been removed since the desmog and canister mod was done over 10 years ago ...... assuming the torque settings are still to spec ....... is it possible a header connection could start leaking even if it has not been touched for years? Also, since the backfiring gets worse as the bike heats up, would not the header connections actually tighten up under more heat ....... or do you recommend dropping the pipe and just changing out the gasket to remove it from the suspects list?   

Be gentle with the header bolts. I said GENTLE. OK 

[Jess from VA]

Now that you mention desmog, have you checked all the vacuum caps on the nipples on the inside of your intake runners?

My blew off (or in two), and that caused me tremendous backfires.... but mine were mostly high speed decels, not slow speed. 

[ryeknee]

Yes I actually replaced all the nipple plugs as one of the first things I tried ..... the problem is not them

[WintrSol]

You might check the torque on the exhaust headers at the head. If the gaskets weren't replaced the last time the rear tire was changed*, one could have started leaking, which can cause after-fire in the pipe.

*Removing the right side exhaust is per the FSM when removing the rear wheel.

* but is not required to do it. Just loosen the hanger, and either lift/lower the swing arm.

FYI
If the headers have ever been removed, it's easy to leave behind a copper crushed flat oring seal. They need to be picked out.

If a shop changes the tire, they will probably follow the FSM, but, yeah, there's more than one way to skin that cat.

While I don't think the header gaskets can just go bad, after 10 years you may need a new tire, anyway. If you let the shop do it, make sure the old are really cleaned out before installing the new ones. If you do it yourself, there's a small chance that banging around on the pipe *could* flex that joint; really small. Any odds on a vacuum leak in the petcock, that just happens to be temperature sensitive? Just a WAG, as most potential air leaks seem to have been addressed, except new O-rings on the intakes and coast valves, which the OP already mentioned.

[WintrSol]

Just a thought - have you tried the header temperature trick to adjust the idle mixtures? The one where you start cold, and measure the headers until the fan comes on? A carb set too lean or too rich could behave this way with temperature, and the measurements will show if one is leaner or richer than the rest.

[Savage]

Are you running a stock exhaust?

[rug_burn]

Did you replace all your intake tube-to-head o-rings?   If they're leaking, that could cause the problem you describe.  Best to use American inch based o-rings of sizes -122 or -123, nitrile o-ring material.

[Jersey]

I had this happen right after doing a full carb rebuild and many of the things you listed.  It ended up being the air bypass component on one of the carbs.  It was bad and I hadn't check each of them during the rebuild.  This resulted in backfiring as well.

https://www.cmsnl.com/honda-gl1500cf-valkyrie-interstate-1999-x-usa-california_model1082/acv-assy_16510mal600/

[ryeknee]

Thanks to all for responding!

Jersey ….. a bad carb air bypass valve seems like it could be high on the list ……. This is something I will look into ……. Can they be replaced with just removing the tank for access?   

Savage  …. I am running a stock exhaust that had the canisters modified by Viper Creations when the bike was desmoged over 10 years ago ……. I am not sure exactly what they did (they are no longer in business) but I know they drilled the canister somehow to make it louder ……… do you think it’s possible that this modification because of age could be causing the symptoms somehow? ……. the system appears to be super clean, no rust or any other deterioration visible.

Rug_Burn …..  I did not check or replace the intake orings because I saw in previous posts that people said if they were bad there likely would be some residue around the intake locations ……. Its super clean around them all ….. given this do you think it still may be an oring?

Wintersol …….  If it were a petcock issue, would it not impact both carb banks? ….. my issue is clearly only on the right side. I am not familiar with the header temperature trick to adjust the idle mixtures ……. Can you point me to a procedure definition somewhere?. Also, is there a way to set individual carb idle mixture settings without opening up the carb I am not aware of? Is there external access to adjust the pilot screw?

[WintrSol]

Wintersol …….  If it were a petcock issue, would it not impact both carb banks? ….. my issue is clearly only on the right side. I am not familiar with the header temperature trick to adjust the idle mixtures ……. Can you point me to a procedure definition somewhere?. Also, is there a way to set individual carb idle mixture settings without opening up the carb I am not aware of? Is there external access to adjust the pilot screw?

Um, yeah, my bad; I forgot you said right side only, and a vacuum leak at the petcock would only affect #6.

For the temperature trick, see this thread: http://www.valkyrieforum.com/bbs/index.php/topic,110548.0.html
I tried it, and it helped smooth mine out, though mine were already close enough I didn't have exhaust pops.

The pilot screws are on the bottom of the carbs, and require a D shaped tool to turn them. If you use a mirror, you will see a brass screw with a D shaped head.

[Tundra]

What's the LAST thing you touched on the bike BEFORE this started, you already covered all the bases pretty thoroughly. Anybody touch the airbox? My experience has always been rubber related, vacuum lines, boot clamps tightened, nipple caps dry rotting, intake O-rings etc...
Possible the airbox was not properly seated?
I would double check all these simple things prior to touching any settings, if you do touch setting record the changes made.

[ryeknee]

That's what is odd ..... I have not touched anything other than an oil and filter change 6 weeks ago ...... the popping and backfiring came on suddenly one day (and no issues during a 200 mile ride the day before) ...... this is why I originally hoped it was bad gas but I have completely drained the tank and have run thru several tanks with Sea Foam treatment. After some additional testing I have noticed that I can get it also to pop with very slowly increasing RPM from idle but only when stationary and only up to around 3k RPM  ..... above 3k and increasing under load at any RPM runs smooth as silk. It really appears like one of the carbs on the right side is just not delivery fuel properly at low RPM ....... I have ordered a motion pro carb tool just to at least play with the pilot adjustments and see if I can at least tune it out some .......... I am really at a loss at what would cause this as suddenly as it did .......... next step I guess would be checking to see if a pair valve has gone bad but I don't think this would cause the popping when slowing increasing the RPMs as noted above no?

Thanks to all for the suggestions ...... if I can't get this resolved soon with my own skill set I will need to try an find an experienced Valk mechanic somewhere in the North East ....... but I think this is a hard find so if anyone knows someone or has a suggestion please let me know         

[WintrSol]

That's what is odd ..... I have not touched anything other than an oil and filter change 6 weeks ago ...... the popping and backfiring came on suddenly one day (and no issues during a 200 mile ride the day before) ...... this is why I originally hoped it was bad gas but I have completely drained the tank and have run thru several tanks with Sea Foam treatment. After some additional testing I have noticed that I can get it also to pop with very slowly increasing RPM from idle but only when stationary and only up to around 3k RPM  ..... above 3k and increasing under load at any RPM runs smooth as silk. It really appears like one of the carbs on the right side is just not delivery fuel properly at low RPM ....... I have ordered a motion pro carb tool just to at least play with the pilot adjustments and see if I can at least tune it out some .......... I am really at a loss at what would cause this as suddenly as it did .......... next step I guess would be checking to see if a pair valve has gone bad but I don't think this would cause the popping when slowing increasing the RPMs as noted above no?

Thanks to all for the suggestions ...... if I can't get this resolved soon with my own skill set I will need to try an find an experienced Valk mechanic somewhere in the North East ....... but I think this is a hard find so if anyone knows someone or has a suggestion please let me know         

This sounds, now, like something floating around in the gas got stuck in a pilot jet, or the vacuum diaphragm of an air valve just let go. The first would make that carb lean from idle up to about 3K as the throttle is lightly advanced, and the second just would lean it out when the vacuum is higher, as in the idle to 3K region, or on engine braking. Have you looked at the spark plugs to see if one of the three shows a different carbon pattern?

[rug_burn]

   Well, Nitrile o-rings according to the Parker o-ring handbook (available free online) have a 20 year service life, at which point they will have slowly hardened to a rock-like state.  So in general, they should be replaced.   All the o-rings exposed to fuel or oil will usually be Nitrile material.   
    But in your case in particular, they may not be leaking yet, as you say. 
    This backfire on decel was an issue on my bike when the vacuum tubes going to the #3 and #4 cylinders developed these slit-like holes from gas that went bad or carb cleaners I had tried and the holes  would only leak, it seemed, when pulling high vacuum on high rpm decel... And yeah, they were real loud backfires. 
   I fixed one side first, and then later had the same problem on the other, and the sound was obviously coming from these sides.   

[Jersey]

Thanks to all for responding!

Jersey ….. a bad carb air bypass valve seems like it could be high on the list ……. This is something I will look into ……. Can they be replaced with just removing the tank for access?   

Unfortunately not.  You have to pull the carb pack and break it down. test each one and replace.

[Ricky-D]

Before doing more complicated work I suggest to try some Techron or Berrymans B-12 for a few tanks of gasoline. And not baby doses but a very strong addition of the additive.

Seafoam is not a very good additive for problems like you are encountering.

Trust me on this.

Many on this forum will say the same thing.

For clogged up carburetors you need strong stuff.

[WintrSol]

Wondering 'out loud' here - do you think you could connect an external vacuum source to the air cut valves without breaking the carbs apart? It is hard to tell looking at them on the bike, but #5 looks possible. The linkage may be in the way for the other two. If it can be done, and if your source can be set to about 10 inches and hold it, you could do a leak test on them.

If it is a small bit of something sucked into a jet, Techron or Berryman's would be my preferred cleaner over Seafoam, too. Seafoam is more for water in the fuel and that paint-like stuff that builds up; it was invented for use in boats. You never know - making high vacuum after a tank of cleaner just may suck it through, and the problem just as suddenly end, like closing the throttle at 6000 rpm in second gear.

[ryeknee]

Thanks all ! ...... I will try all the suggestions made that I can handle with my skill set and keep you posted ....... one thing I did notice as I continue to try things, ride and test the bike is that previously I thought the popping symptom was only on low RPM deceleration (which it still is and has not improved) ....... but I have now noticed that when in neutral it will start popping rapidly as I slowing increase the RPMs (still on right side only) ..... so it seems it is not just on deceleration even though when riding it does not pop on acceleration....... I also noticed that it seems to get worse when I put the choke on (including while riding which I tested to see if making things richer would make a difference) ....... so I assume this could mean the problem may be a too rich condition and not a too lean condition........ and if true would unlikely be a result of an air leak ....... does this logic make sense?   

[Ricky-D]

No, it doesn't make sense.

As you open the throttle, there's a lot more happening than what you are considering.

The explanation that the mixture is enrichening is an assumption  wrongly based.

What's happening in the venturi is more complex, the butterfly valve is turning open

and the slide is rising. The jets are changing roles and the air velocity is modulating.

***

[ryeknee]

Thanks Ricky-D ...... does the popping being worse when the choke is on give you any indication of where the problem may likely be compared to others? ...... Or because under increase in RPM acceleration when riding under a load (i.e, like up a hill) it does not pop at all  ...... but when stationary in neutral under the same rate of increase in RPM it starts popping.

Thanks for any incites 

[Ricky-D]

Sure, you've got a lean condition problem, clogged jets or low speed galleries.

Massive doses of Techron or Berrymans B-12 is what you need.

More that just one tankful I would think.

The choke is simply speeding up the engine causing the pop, it's definitely not a backfire.

Same thing just off idle.

[ryeknee]

Thanks Ricky-D ...... what do you consider "massive dose" ....... how much Berrymans B-12 do you recommend putting in a full tank of gas?

[Ricky-D]

Thanks Ricky-D ...... what do you consider "massive dose" ....... how much Berrymans B-12 do you recommend putting in a full tank of gas?

I think 2 ounces (min) per gallon fuel.