Backfiring and rough idling

[Antony]

Greetings everybody. I have a 99 Valkyrie Interstate which I bought out of Pennsylvania and had shipped to New Zealand. It turns out it's backfiring under de-acceration specifically from all 3 of the left exhausts. It's a Cobra exhaust system.  Doing my research, I found an informative clip on youtube which talked about the secondary air supply control valve which suppresses backfiring.

See link here, the specific info is at 2:52 into the clip:
https://www.youtube.com/watch?v=eDLTpQCTBsc&t=174s

So I removed the fuel tank and air box thinking I might have a loose or leaky hose, only to find that valve system wasn't even there. Completely absent. Were these fitted to all models or specific to the California only models.

Also, one the bike is warm, the idle is wast to high, it this likely to be directly related?

I have a rally coming up in 2 weeks covering about 800 miles , so really keen to get this sorted.

[gordonv]

Look into this,

https://www.youtube.com/watch?v=YBnA57lEu_0

I suspect that your bike had been desmogged. If it wasn't, could it be a Californian model? I think you can find that on the VIN tag.

I had very slight backfiring on my bike before, but never got around to fixing it. An air leak of some kind is the most likely cause.

Carb intakes, vacuum lines, I think even the exhaust gaskets??

[Ken aka Oil Burner]

How long was it from the last time it was ridden in the US to when it arrived to you in New Zealand? Since it's the left side, and the idle is high, I wonder about the 3 left carbs being partially gummed up, since that's the low side when sitting on the sidestand. If it was de-smogged, the amount of vacuum leak sources is reduced greatly. A spray around the intakes with brake cleaner or starting fluid will locate a leak quickly. Make sure all of the vacuum caps on the inside of the intake manifolds are intact and not split. #6 should have a vacuum hose to the fuel petcock, unless it was swapped for a manual valve such as a Pingel; the others would all be capped if it was indeed de-smogged.

I don't know what's available for fuel system cleaners in your part of the world, but Amsoil PI, Berryman B12 Chemtool, and Redline SI-1 are all good fuel system cleaners. Some swear by Seafoam as well. Running through a couple tanks of well treated fuel may just take care of all of your running issues.

Have fun putting the airbox back in; it can be fun, especially if it's really cold. Make sure all of those tubes seat correctly on the carbs. You can inadvertently fold one in on itself and not realize it. A small inspection mirror and a bright flashlight can help here.

[Psychotic Bovine]

Do this:  in neutral, rev and hold the engine at 3000 rpm.  If the pop is there, turn on the choke slightly and see if it goes away.  If it does, you are running lean.  Slow speed jets are probably the culprit.

Mine sounded like a machine gun on decel and at 3000 rpm with no load.  You could even see the flames from the backfire by looking into the right exhaust. 
My brother and I rebuilt the carbs (every seal using a Redeye kit), but I thought just running a wire through the low speed jets was enough to clean them.  Wrong!  Even after putting the bike back together, problem remained, only it was now on both sides (we didn't put the same jets back into the same carbs).
I ordered a set of low speed jets, installed them, and voila!  Fixed the backfiring.  Bike runs perfect.
We also increased the size of the high speeds a smidgen and changed the needles. (Factory Pro kit, I believe).

[Antony]

I can definitely confirm it has been de-smogged. Now to find the cause of the backfiring and rough idling.

Look into this,

https://www.youtube.com/watch?v=YBnA57lEu_0

I suspect that your bike had been desmogged. If it wasn't, could it be a Californian model? I think you can find that on the VIN tag.

I had very slight backfiring on my bike before, but never got around to fixing it. An air leak of some kind is the most likely cause.

Carb intakes, vacuum lines, I think even the exhaust gaskets??

[Antony]

The shop in Pennsylvania that sold it to me (SRK Cycles) said it had been sitting for a while, but had put $800 work into the carbs and that the bike was now  running beautifully. It was unstarted for a duration of about 3 months from the time of purchase to it's arrival into New Zealand. Iit got fresh petrol immediately and has only done about 150 miles since it's arrival.

How long was it from the last time it was ridden in the US to when it arrived to you in New Zealand? Since it's the left side, and the idle is high, I wonder about the 3 left carbs being partially gummed up, since that's the low side when sitting on the sidestand. If it was de-smogged, the amount of vacuum leak sources is reduced greatly. A spray around the intakes with brake cleaner or starting fluid will locate a leak quickly. Make sure all of the vacuum caps on the inside of the intake manifolds are intact and not split. #6 should have a vacuum hose to the fuel petcock, unless it was swapped for a manual valve such as a Pingel; the others would all be capped if it was indeed de-smogged.

I don't know what's available for fuel system cleaners in your part of the world, but Amsoil PI, Berryman B12 Chemtool, and Redline SI-1 are all good fuel system cleaners. Some swear by Seafoam as well. Running through a couple tanks of well treated fuel may just take care of all of your running issues.

Have fun putting the airbox back in; it can be fun, especially if it's really cold. Make sure all of those tubes seat correctly on the carbs. You can inadvertently fold one in on itself and not realize it. A small inspection mirror and a bright flashlight can help here.

[Antony]

Thanks, I'll put the old beast back together and give it a go.

Do this:  in neutral, rev and hold the engine at 3000 rpm.  If the pop is there, turn on the choke slightly and see if it goes away.  If it does, you are running lean.  Slow speed jets are probably the culprit.

Mine sounded like a machine gun on decel and at 3000 rpm with no load.  You could even see the flames from the backfire by looking into the right exhaust. 
My brother and I rebuilt the carbs (every seal using a Redeye kit), but I thought just running a wire through the low speed jets was enough to clean them.  Wrong!  Even after putting the bike back together, problem remained, only it was now on both sides (we didn't put the same jets back into the same carbs).
I ordered a set of low speed jets, installed them, and voila!  Fixed the backfiring.  Bike runs perfect.
We also increased the size of the high speeds a smidgen and changed the needles. (Factory Pro kit, I believe).

[gordonv]

Just start driving and enjoying it. What ever you do that makes the backfiring worse, stop doing it. Get a few tanks through the carbs.

Do you have Chevron there, and do there have Techron in it, or buy it as an additive?

I like the Berryman B12. I start the riding year off with 1/2 a can to my first fresh tank of fuel.

[Antony]

The 6 wide tubes that connect the aircleaner to the carbs appear to be glued in place with a brown adhesive that appears to have failed. As a result, the rubber tubes turn freely and are not air tight. Is it safe to assume these are supposed to be air tight and shouldn't turn?
If they're not air tight and drawing in air, could this be the cause of my problems?

[Ken aka Oil Burner]

The 6 tubes on the bottom of the airbox did have some sort of sealant on them from the factory, but it definitely crumbles off when you work the box in or out of the frame. Nothing to worry about there. A minor air leak before the carbs will not affect the air/fuel mix the way a leak after the carbs does. It would likely have an effect if there was a large difference between carbs, like one that was not seated properly because it folded in on itself and blocked 1/3 of the air inlet. Don't worry about that sealant. Read this, and you'll see that it's common.  http://www.valkyrieriders.com/shoptalk/AirBox%20VentHose/AirBox.htm

[gordonv]

Do you have any staining around the air intake tubes to engine block? Like this one of mine.



If so, you need new o-rings.

[Antony]

I'll have a nosey tonight when I'm putting it back together.

Do you have any staining around the air intake tubes to engine block? Like this one of mine.



If so, you need new o-rings.

[nogrey]

I experienced a similar issue with a 2000 valkyrie standard I purchased. It barely ran to begin with because it had been sitting in a storage unit for some time. I went through the carbs and put it back together. All OK except a not so smooth idle and a nasty backfiring on decel. It has 2 brothers pipes but other than that was stock (jets included). Some said it was normal but I’ve had too many valkyries between my legs and know better. Anyway, after having the carbs out 3 times, I finally found a bad air cutoff valve. There is one mounted to the side of each carb. Small, black bugger. One of the six was completely blocked. The purpose of these valves is to enrich fuel during decel....to eliminate popping. I replaced it and problem solved. They are basically a check valve and should move air one direction only.