Why do pods "cough"?

[Spyder]

Hmmm, That's starting to sound like a mixture issue... Are you still getting sooty black plugs?

[salty_monk]

My skunk will do it on Choke after it's first started up. (VM's), more so if I haven't ridden it in a couple of weeks or more.

Can't remember my CV's ever doing it on the 1000G or the 750ES.

They both had K&N's on at some point.

[pitbullmccoy]

I have the same issue but I can say I really don't think it is all pods. On my bike now '78 gs1000 it has a few coughs at warm up and maybe a couple at say 1\3 throttle like going up the back road from my house but when i hit the hwy and run 70mph or really give it gas while shifting no prob at all. "BUT" I had the exact same problem with a sporster. And i mean exact. Pope's at warm up and mid throttle. I never got it completely worked out on that bike but after several tries, and its way easier with a single Carb,I got the mixture very close to perfect. I personally wouldn't get overly worried but that's just me. I haven't had my gs very long but rode the absolute **** out of the sportster with it doing the same thing. Other than a being annoying I had no real issues. But that's just my 2 cents. I think it would take a seriously seasoned mechanic way beyond my years to get all 4 working flawlessly.

Just be sure to let us know if you track down the cause and get it worked out. Good luck with it.

[tbirdhd]

hi new to this link but i had that and figured out i had a air leak in the exhaust , ,, changed exhaust backfire gone , just some thing to check ,

[Steve]

One other question. Are all of these "coughing" bike running VM carbs? ...

Not mine.

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[MisterCinders]

Not mine.

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Steve has special bikes. He's not allowed to have a chain.

[Seana23]

With my bikes particular cough is actually a spitback... I have seen it happen. A spray ov vapour blows back out the carb/filter manifold...
usually, its number 1 carb... Less often its number 4... Not noticed it with either 2 or 3.

Xxx

[keman]

This can also be caused by weak valve springs. The weak spring allows the intake valve to hang for a split second. This hang allows gasses to escape back into the intake and 'cough' back through the Carb. IF 'IF' this is the cause, no amount of tuning well make it go away. 30 year old springs get weaker with age, especially on bikes that tend to run hot.

[TheCafeKid]

Not to be contrarian, but in my experience in tuning carbs (and while it's not the decades of experience of some guys on here, I can say I've tuned more than a "couple" sets) popping or backfire through the carb is generally cause by a rich mix. Unburnt fuel vapor hanging around the intake combines with a sudden rush of cooler dense air on the next intake stroke and will pre-ignite. Pay attention to when it happens next. We're you blipping the throttle softly at the light? Sitting and idling for a good while??
Could be your fuel screw needs backed off a hair, air screw needs opened a hair, or float levels are off.
Much the same reason the bikes pop a bit through the carbs on choke when first started. The cylinder is up to temp, fuel condenses on the cylinder wall, or intake rail, and when enough builds up, "cough". On "choke" (actually an enrichener, not a choke) you're dumping nearly straight fuel into the cylinders.

Which, brings up another point of contention for me. Often times you will see people say that opening up your mix screws on the CV carbs will allow the bike to warm up quicker. This seems a bit counter-intuitive to me.
If you're adding more fuel/air mix (which is what the mix screws control on the CVs, the fuel and air are pre-mixed, the screw simply controls how much of that mix goes in) more fuel will keep the cylinder cool. The longer it stays cool, the longer it takes to warm up. Open them up too much and you're just wasting fuel.
I dunno, just things I think about sometimes.

Anyway, with your "cough" I'd look at being rich more than lean. A lean mix would mostly be sounded by poppin through the exhaust, although a rich mix can do that as well...

Plug chops, or a sniffer...
Pods pop. Just the nature of the beast...

[OldVet66]

Mine will do it once in a very blue moon, but I believe it's as TheCafeKid described "blipping the throttle softly at a light".

[MisterCinders]

My cough doesn't happen while blipping at a light. Instead, it seems to trigger when pulling away or accelerating from low speeds.

I'll definitely consider the rich possibilty. I generally have an overall richness issue with this bike -- e.g., poor mileage, sooty plugs, etc. -- though that has improved recently.

My floats are pretty solid at 24mm, no drips or overflowing, good showing with the wet level test right below the bowl gasket, etc.

I also get some exhaust popping on decel.

[pete]

I haven't contributed yet so here's my 2 cents...

I get this quite regularly at the moment, usually while sitting idling at traffic lights or occassionally after starting the bike a very short time (less than a few minutes) after shutting it off. Occassionally it will stumble at idle and a blip of the throttle will do the same at that point.

I know my carb circuits are rich, and particularly at somewhere around 1/8 - 1/4 throttle.

I only ever assumed that the richness was the cause of my "coughing" and that it would get sorted when I finally get some carb tuning done.

I also get popping on deceleration, more so in traffic when I'm not opening the throttle as much and can't get constant flow...

And yes, a wideband tuner is on my agenda to get these issues sorted once and for all but it's been postponed a bit for the moment...

[Seana23]

I actually am just interested in the replies.........sorry.

But could it be from the length of the intake being so much shorter than stock? Maybe causing a hiccup in the intake pulses? Obviously just a guess.

Ok, thats.interesting...
Hmmm. Could be!

Well.done.
Xxx

[Steve]

Steve has special bikes. He's not allowed to have a chain.

Actually, ALL of my bikes have "a chain", except the Wing.

This can also be caused by weak valve springs. The weak spring allows the intake valve to hang for a split second.

I could almost buy that theory if I was running at higher revs, but this happens at IDLE.

Which, brings up another point of contention for me. Often times you will see people say that opening up your mix screws on the CV carbs will allow the bike to warm up quicker. This seems a bit counter-intuitive to me.
If you're adding more fuel/air mix (which is what the mix screws control on the CVs, the fuel and air are pre-mixed, the screw simply controls how much of that mix goes in) more fuel will keep the cylinder cool. The longer it stays cool, the longer it takes to warm up. Open them up too much and you're just wasting fuel.
I dunno, just things I think about sometimes.

For start-up, though, you NEED a richer mixture just to get it to run. If the mixture is too lean, it simply won't light as easily as it should. It may be a proper mixture for a warmer engine, but is simply too lean for a cold start. That is the whole purpose of the "choke" in the first place. Yes, the engine might not warm up quite as quickly with a slightly richer mixture, but we are talking about taking an engine from 70 degrees to 250, vs 70 to 275, so it doesn't really matter all that much. What does matter is that the mixture is rich enough to light consistently. Consistent firing will warm up the engine quicker to the point where you can remove the "choke" and get on the "normal" circuits quicker.

That's my opinion, and you are certainly entitled to it.

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[TheCafeKid]

Oh I'm not saying the theory is incorrect Steve just that it seems a bit odd to me. I suppose, if one had a CarbTune or something, you could adjust it till the "blue light" comes on, and that's it. Or simply adjust to highest idle and call it good. But I think that people sometimes assume that mix screws will magically fix issues like decel popping when in fact they can be simply exacerbating the problem by dumping more fuel into the cylinder.

I used to always think decel popping was due to a lean mix. While it most certainly can be an indicator, I tend to think more now that it's more indicative of cold air getting into the exhaust, whether it be via pods or bad exhaust gaskets (of which I think people also tend to overlook, they're pretty much good for one or two "seals" then they've been crushed to the point of not being as effective) or bad gaskets around the junctions on stock systems where the two middle pipes join the outer.

My reasoning for this theory is that certain other manufacturers have used a reed valve set up in the heads of their bikes for many years, even back to the late seventies and early 80s as a way to clean up the exhaust gasses without robbing horsepower from the motor. These are a one way valve that allows cold, clean air to be dumped into the exhaus pipes when the throttle is closed. This is designed to ignite any unburned fuel in the pipes up near the headers where the temps are hot enough to do so. The result of this is a popping sound. On a stock bike wih this set up, the mufflers are usually baffled well enough to cover this up or deaden it to the point of it not being an annoyance.
But remove that pipe, and install an aftermarket exhaust and suddenly there is decel popping that cannot be tuned out with carb adjustments.
I at first thought perhaps my pilot circuit was lean, so I added some mix screw. This in fact made it worse. More fuel unburned to ignite in the pipe.
I did some reading, and found out about this system and how to eliminate it (many modern carbureted bikes use this as well, often referred to as a PAIR valve) On MY bike the two easiest methods are either to remove the hoses from the reed valves and simply plumb them into each other. No air gets in.
Another way is to use aftermarket "block off" plates to eliminate the valves altogether.

Anyway, while popping can be a sign you're lean, it can also be a sign you may be rich, and have an air leak resulting in ignition of this fuel in the pipes themselves.

Those gaskets around the "Y" junctions will let air in, and many times that will cause popping. Exhaust gaskets at the head that are no longer sealing completely may also being sucking air and causing it. You can try to tighten up your header bolts, or replace the gaskets and see if t helps.

Even if your LM1 or whatever you use to check your AFR reads that you're good while on the throttle, I think more telling is what happens when you close the throttle. Does the fuel level or air level spike?
I wonder what can be done, if anything, to cure that? I'd assume if you tried to tune that out, it would probably have a detrimental effect when the throttle is opened. Unless perhaps you could decrease the size of the air corrector jet.

I've also found that the popping can be cured by fine tuning the needle clip rather than adding more turns out onthe mix screws. Listen to where the popping occurs. Is it more in the midrange of the tach on wind down? Maybe the needle can be adjusted a half step with some washers onthe clip to fine tune it.

Just thinking aloud. I'm certainly no carb expert, but I DO like to tinker with them alot. There's nothing quite as satisfying to me as far as working on a bike than having it respond as close to perfect as possible in every circuit. I'm not currently happy with the way my ZRX responds at WOT, but I've come to the conclusion that the design of the needles in the Dynojet kit for this bike are simply not as good as other companies designs. The needles in the last half inch look like hypodermic needles, there's no longer any metering of fuel by the needle at that point. I've tinkered and tinkered with these things.
Eventually I'll try a different kit. But even still, the problem is tiny, simply have to back out of the throttle for a split second when you get up to wide open or it sort of gags a little. Many probably wouldn't even notice it.

But otherwise, that bike carburetes smooth as silk. And that is quite enjoyable to me, especially when you're whipping her like a rented mule in the twisties. You know exactly how she's going to respond under any circumstance. At that installs quite a bit of confidence. Like you and the machine are one, it is simply an extension of your body. Beautiful