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Old 18th April 2013, 20:34   #1
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Question Exhaust pop on deceleration, occasional stalling

Apologies for recently flooding this section with threads. My TVS Victor (2004) is aging and for the last 3000 odd km the motorcycle has been experiencing exhaust pop on deceleration (not every decel) and sometimes stalls in traffic not while idling but when throttle is given after idle.

I cleaned out the air filter, changed the spark plug and also cleaned the carb. However, the issue persists.

Took it to a couple of mechanics, one says "need to de-carb and/or check valves". He asked me to leave the bike with him for a day so he could take the engine block apart from the bike and check (I refused).

Another one says "common with aging TVS Victors. I've had several report the same thing. Issue with fuel pump (?), best ignored."

I'm thinking this could be an issue with the timing chain (is it called the cam chain?) becoming loose and in process throwing the spark timing out of whack, leading to unburnt fuel left in the exhaust that burns with a pop in the next combustion cycle. I could be totally on the wrong track, though.

Anyone have any guesses? If it is timing, though, how would one go about getting it fixed? Is the cam/timing chain easy to adjust/replace?

Appreciate your response!
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Old 19th April 2013, 02:11   #2
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Default Re: Exhaust pop on deceleration, occasional stalling

Hi,

The symptoms you face can be caused by a leak in the intake manifold. Check all gaskets in the intake system, and also check for cracks or leaks.

When the engine is running, it tries to suck in air and creates a vaccum in the intake manifold. you control how much air it gets via the throttle and the carb mixes fuel in it. if there is a leak, the engine would suck extra air from it and the mixture would become lean, causing backfiring and erratic idling.

Check the spark plug tip. i guess it would be white in color. ideally it should be brownish if the mixture is correct.

If this is not the case, the problem may also be caused by improper ignition timing. check the CDI and associated parts.

Cheers.

Last edited by dhawcash : 19th April 2013 at 02:16.
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Old 19th April 2013, 08:37   #3
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Default Re: Exhaust pop on deceleration, occasional stalling

If I am correct, there is a part in the carb which handles vacuum (I may be wrong on what it does!), its is a black piece of thin plastic approx 1 inch square. If this has warped or has developed a leak or has just become dirty this may occur. Also, may still be some dirt in the carb/ fuel.
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Old 19th April 2013, 08:39   #4
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Default Re: Exhaust pop on deceleration, occasional stalling

Quote:
Originally Posted by hellmet View Post
the motorcycle has been experiencing exhaust pop on deceleration (not every decel) and sometimes stalls in traffic not while idling but when throttle is given after idle.
The symptomes are typically of "lean" mixture. Before you start further investigations, please try to get the carburettor tuned by a good mechanic, a bit towards richer side.
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Old 19th April 2013, 10:18   #5
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by latentpotential View Post
If I am correct, there is a part in the carb which handles vacuum (I may be wrong on what it does!), its is a black piece of thin plastic approx 1 inch square. If this has warped or has developed a leak or has just become dirty this may occur. Also, may still be some dirt in the carb/ fuel.
If I'm correct that is what is governed by throttle and will not create a vacuum. That is the same thing you adjust when you twist the idle speed screw.

Quote:
Originally Posted by Ravindra M View Post
The symptomes are typically of "lean" mixture. Before you start further investigations, please try to get the carburettor tuned by a good mechanic, a bit towards richer side.
Forget a mechanic, it would be great if you can point me to a good tutorial on how to do it myself and I'll do it properly. Anyway, for the last 30K km, nobody has touched or cleaned the carb but me. After putting the carb back I adjust the idle mixture myself (and I'm not talking about idle speed).

Quote:
Originally Posted by dhawcash View Post
Hi,

The symptoms you face can be caused by a leak in the intake manifold.
Check the spark plug tip. i guess it would be white in color. ideally it should be brownish if the mixture is correct.

If this is not the case, the problem may also be caused by improper ignition timing. check the CDI and associated parts.

Cheers.
Thank you. Will check the line between the carb and the engine head for leaks and will also give the plug a check. Is CDI the only component responsible for timing?
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Old 19th April 2013, 10:54   #6
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by hellmet View Post
Forget a mechanic, it would be great if you can point me to a good tutorial on how to do it myself and I'll do it properly. Anyway, for the last 30K km, nobody has touched or cleaned the carb but me. After putting the carb back I adjust the idle mixture myself (and I'm not talking about idle speed).
Check this video to tune the fuel nut for rich/lean mixture.

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Old 19th April 2013, 11:57   #7
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Default Re: Exhaust pop on deceleration, occasional stalling

Quote:
Is CDI the only component responsible for timing?
The ignition system comprises of a CDI, which gives output to an Ignition coil . The CDI gets its input from a hall effect sensor located near the alternator of the bike. it basically tells the CDI the position of the crankshaft and the timing is dependent on it. if this sensor goes bad, timing would be erratic.

CDI in itself advances and retards the ignition timing electronically. if there is a defect, it will not do so correctly and cause erratic running.

the ignition coil converts signal from CDI into High voltage pulse which fires the spark plugs. if deffective, it wont fire the plugs properly and cause erratic running.

There is also the wiring.

but check for leaks first, before you get into the evils of troubleshooting the ignition system.
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Old 19th April 2013, 13:10   #8
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by dhawcash View Post
but check for leaks first, before you get into the evils of troubleshooting the ignition system.
I notice the rubber intake line between the carb and the engine with cracks in it. Whether the cracks are deep enough to cause a leak is something I'll check after going home. I also see other pipes going in and out of the intake - not sure what purpose they serve. I will post pictures of these as soon as I can get hold of a camera.

Just wondering, wouldn't vacuum leaks cause intake side popping noises(instead of at the exhaust)?
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Old 19th April 2013, 13:40   #9
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by hellmet View Post
I notice the rubber intake line between the carb and the engine with cracks in it. Whether the cracks are deep enough to cause a leak is something I'll check after going home. I also see other pipes going in and out of the intake - not sure what purpose they serve. I will post pictures of these as soon as I can get hold of a camera.

Just wondering, wouldn't vacuum leaks cause intake side popping noises(instead of at the exhaust)?
cracks mean replacement. im sure that will fix it.

You are right about the popping in the intake. if the leaks are severe, it will cause backfiring (which causes the popping noise). used to happen in my pulsar 180 classic. sometimes the backfires were severe enough to blow the carb off its mounting. that was with a huge tear in the intake adapter. the part was of local build, hence used to fail often. Originals for P180 were hard to source as not many 180s were on the road at that time.
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Old 20th April 2013, 16:14   #10
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Default Re: Exhaust pop on deceleration, occasional stalling

This is a picture of the intake rubber manifold on my vehicle. Notice the cracks on it. Do you think I can just go out to TVS, buy the new manifold and put it in, or do I have to buy some sealant to seal the piece of rubber to the carburetor (as suggested by some other websites). I'll also be replacing the air filter manifold since that has cracks too (although that wouldn't be contributing to the current problem).

Name:  IMG_3612.JPG
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A couple of tubes I have no idea what purpose they serve. Notice the crack on the tube in the last picture.
Exhaust pop on deceleration, occasional stalling-img_3607.jpg
Exhaust pop on deceleration, occasional stalling-img_3608.jpg
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Old 20th April 2013, 23:34   #11
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by hellmet View Post
A couple of tubes I have no idea what purpose they serve. Notice the crack on the tube in the last picture.
Get a new manifold as it will be a peace of mind later on.

Regarding the last picture the pipe seems to be the Crankcase breather tube.

Anurag.
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Old 20th April 2013, 23:46   #12
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Default Re: Exhaust pop on deceleration, occasional stalling

Decel popping is a symptom of a lean mixture in the idle/pilot circuit.
Lean mixtures are usually caused by 2 conditions.
1.> Air Leak between carb and engine (Replace the cracked manifold)
2.> Clogged pilot jet or incorrectly adjusted fuel screw.

The tube in your second picture is a vacuum line that operates the secondary air injection valve. This can cause the symptoms if cracked or unplugged, check the other end of this tube.

The tube in the 3rd pic is the crank case vent. This has no effect on your Air Fuel Ratio.

Here's what you can do to diagnose what it causing this.
1.> Remove the clamps from the manifold and tape it with insulation tape and put the clamps back on. This will cover the leaks if any and the symptoms should disappear if this was the cause. But do replace the manifold eventually.
2.> Turn the fuel screw in 1/4 turn at a time and check if the symptoms disappear. You might have to re-adjust the idle when you turn the fuel screw. Do this when the engine is hot.
3.> Remove the carb , take out the pilot jet and clean is properly, you should be able to see through it if you hold it against light. Gumming/varnish often plugs up the pilot jet over time. You can use a thin wire to clean the pilot, don't be too aggressive or you might end up enlarging the pilot jet orifice.

Best of luck.

Last edited by Rash : 20th April 2013 at 23:50.
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Old 21st April 2013, 17:39   #13
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Default Re: Exhaust pop on deceleration, occasional stalling

Yesterday evening, I went ahead and purchased the air intake manifold and carb-engine manifold from genuine TVS parts. Today, I spent a while replacing both these rubber parts and discovered that the air intake manifold had developed severe cracks and was letting road dust get into the carburetor - not too much - but I'm sure enough to make the carb go crazy. Replacement involved removing seat and fuel tank to get to the clamp.

Exhaust pop on deceleration, occasional stalling-img_3640.jpg
Exhaust pop on deceleration, occasional stalling-img_3637.jpg

When time came to replace the carb-engine manifold, I was shocked to see that TVS had given me a wrong part. The part I was given was about 1/2cm shorter than the original and totally missed all the grooves the original had. However, to my relief, I found the original's inside to be perfectly crack free so I have put it back for now.

Have to go back to TVS to give them a piece of my mind for wasting my time.

Exhaust pop on deceleration, occasional stalling-img_3617.jpg
Exhaust pop on deceleration, occasional stalling-img_3633.jpg

This makes me believe the issue is something else.
@Rash, I didn't check the other end of the secondary air injection tube, I just read your post now. Will check when I replace the carb-engine part.

Also, the engine tune seems to have changed, don't know since when, but it feels like it's knocking. Are these symptoms all related?
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Old 21st April 2013, 21:10   #14
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Default Re: Exhaust pop on deceleration, occasional stalling

Quote:
Originally Posted by hellmet View Post
This makes me believe the issue is something else.
@Rash, I didn't check the other end of the secondary air injection tube, I just read your post now. Will check when I replace the carb-engine part.

Also, the engine tune seems to have changed, don't know since when, but it feels like it's knocking. Are these symptoms all related?

The engine and carb have probably ingested some dust/dirt. This can cause a ton of things to go bad based on ho long you were driving around with the torn carb boot.

But for now just focus on cleaning the carb and the jets and making sure there are no leaks. Then adjust the carb properly.

You can start with the air screw backed out only 1 turn (Seat it in fully and rotate out 1 turn, don't tighten it when you seat it in, just seat it in turning the screwdriver with your index finger and thumb )

Adjust the idle, and move the screw 1/4th turn in or out till the decel popping goes away.

You should find the sweet spot between 1 1/4 to 1 3/4 turns if everything else is ok.
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Old 23rd April 2013, 12:11   #15
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Default Re: Exhaust pop on deceleration, occasional stalling

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Originally Posted by Rash View Post
The engine and carb have probably ingested some dust/dirt. This can cause a ton of things to go bad based on ho long you were driving around with the torn carb boot.
Yes, that would be my next weekend's project. Meanwhile I'm running the vehicle with some Iftex carb cleaner. I've noticed that after replacing the torn boot the exhaust popping has significantly reduced. During my commute yesterday (of 42km) I heard it only twice against the usual 5-7 earlier. I guess the reduced intake of dust is helping.

I emailed TVS with the carb-engine boot and they say I was sold a genuine part and the impressions are caused by the 'tight fit' with the carb. Hmm. I guess I'll then proceed with replacing this boot when I clean the carb this weekend.

I was highly disappointed by TVS's response for my service manual request:

Quote:
We don't provide service manual to customers. We provide the Owner's manual to customers but Victor Gl is an old model we don't have Owner's manual in our stock. We apologize for the in-convenience.
But why? If there is something the customer can replace himself then why not let him know how, instead of burdening their service centers? In fact, the attention that a customer would give to his vehicle would be a thousand times better than a mechanic's.

By the way, would someone know why an engine would change 'note' or 'beat'? Not the exhaust note, the note at the engine itself. My engine's note is a lot different than I remember it from 3-4 years ago. Just normal aging?

Last edited by hellmet : 23rd April 2013 at 12:16.
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