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Discussion Starter #1 (Edited)
Hello all,

My name is Raul, I'm from Europe.

I posted a while back about this problem, but now I have some more details, maybe someone has a clue here.

The bike is a 1996 1500 Vulcan Classic single carb.
Problem is that the bike is popping in the exhaust on deceleration, only in one cylinder/exhaust, the rear one.
After that at idle I noticed that the front cylinder has a sound like bop-bop-bop-bop, and the rear sounds
like bop-bop-pff-bop-bop-pff. So it sounds like popping is present also at idle but almost not noticeable.
Also the spark plugs are different.Front are white/gray indicating a lean condition, while the rear ones are sooth black, no oil but most likely carbon. I replaced them with new ones, but no improvement.Air intake is stock air filter, only exhaust is custom one.Front exhaust pipe is longer than rear one, it is a bagger style. Carb is re jetted(I bought it like that, and it had a 155 main jet).I played around and went down until 120, but not an improvement.I checked compression with a mechanic and I do not know the value but he said it was fine.I also put high flow air intake for testing, but popping was still there.
I am totally lost here.Could it be and ignition problem?Coil?or something else?

Problem short:
-popping on deceleration only on rear cylinder
-almost unnoticeable popping on rear cylinder at idle
-black sooth plugs on rear cylinder, and white/gray on front

Trials short:
-changed the plugs, no improvement
-re jetted carb from 160 to 120 main, no improvement
-tested with stock and high flow air intake, no improvement
-compression check , ok
-valves are hydraulic, as far as I know they auto adjust
-marbled reed valve hose, no improvement

I added some plug pictures.This is how front and rear look like.
And also a bike picture.
I am loosing it guys, please help.
 

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the 120 main jet is much too small. DO NOT run the engine with it.
Popping on deceleration is almost always an air leak on the exhaust pipe.
check around the pipe connections with your had to feel for air leaks. (DONT BURN yourself!)
 

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Any logic in thinking of an intake leak on the front cylinder? My thought is the front is sucking in air through the leak and not grabbing enough fuel and resulting in it running lean. That might also explain why the rear is running rich, because it's getting all the fuel and it's plugs are black.
 

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I second checking hard for leaks in the intake and exhaust area. Use some smoke to check every area. If you find no leaks i would try a different exhaust. One of those pipes is twice as long as the other and this is a single carburetor two cylinder bike. Those pipes might not work without a crossover.
 

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I googled true duals and backfiring and a lot of Harley guys can't get bikes FI mapped correctly after installing this type of exhaust. Something about poor scavenging in the head pipe.
 

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Discussion Starter #7 (Edited)
Thank you all for the replies.

@sunnybob, I will definitely change the 120 main.It ran fine with the 155 main, I just wanted to check if popping gets worse or better, but no change.I just rode it 3-4 miles or so.

@Kawi Rick, a lot of logic in what you say.But where could the front cylinder sucking air?The intake on one side i believe, maybe reed valves or some gasket?

@matt21080 , I will try to check for leaks, by smoke you mean using a cigarette around the exhaust?I also thought of changing the exhaust with a 2 into 1 exhaust, and using one of the actual mufflers for that.
Regarding the spokes, I did not paint them, they are not shinny anymore, and now they have some gray color.

I'll come back with news, If I have any.
Thank you guys.
 

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air leaks on the intake cause whats known as "carb farts", a flat or flapping sound, very different sound to an exhaust popping.

The most likely place to look is the exhaust pipe to the head joint. Is there a gasket in there? Many folk use 2 gaskets to make sure the seal is tight. if you have fitted a coaster in place of the reed valve box, is it sealed properly?

Different length pipes are very common, and don't cause a problem unless you are tuning for maximum horse power.

Cure the leak and I think the plug will cure itself. Its not so far out, and trying to "solve" two problems at the same time is never a good idea.
 

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I'd check the rubber intake between the carb and the two heads as well. That's a "Y" shaped part that slips over the back side of the carb and on to the two heads. It's possible you don't have a good seal between it and the front head. Probably hard to see without taking off some stuff.
 

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Are you sure that you are not getting a rear cylinder miss fire which would also cause the funny exhaust note and black plug you mention?
 

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Discussion Starter #12
@sunnybob , I for sure do not want to tune for maximum HP, and for sure it is no carb fart.I will order next week some new exhaust seals to be sure.
@matt21080, very interesting movie, I did not know that
@KawiRick, i will check the Y again, to be sure
@sfair, I am absolutely not sure.What can cause missfires? coils?ignition?How can I check this?

Thank you all guys!
 

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If you are ordering exhaust seals get Harley Davidson exhaust gasket part # 17048-98. Kawasaki ones aren't seals, just hard washers
 

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If you are ordering exhaust seals get Harley Davidson exhaust gasket part # 17048-98. Kawasaki ones aren't seals, just hard washers
Matt, do the HD gaskets fit most 1500 exhaust ports? And why do you think they are better than OEM?
 

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Thank ya Matt. My 1500 pops a lot too, even while just shifting gears.
 

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Discussion Starter #17
Sorry for the late reply, but was a little bit short on time.
So I did meantime:

-changed exhaust gaskets, and put two of the inside, I did not get the HD gasket.Result: still popping

-mounted new coasters and new reed valve gaskets, so I bocked entirely the reed valves.Result: still popping

-changed spark plugs again.Result:still popping

-changed spark plug wires.Result:still popping

-swapped ignition coils.Result:still popping

- just to be sure, I swapped the exhausts just for testing, I mounted them in a funny position, they were going almost vertical, put popping was still there even with the long pipe on the rear cylinder.Result:still popping.

What I noticed meanwhile is that feeling with the hand the exhausts, the pressure in the front cylinder exhaust is slightly bigger than the rear cylinder one.But maybe my mind is playing with me.
And also at hight RPM, when the popping occurs on deceleration, a little bit of white smoke is coming out.

I am totally lost here now.In the manual at causes for popping appears also the IC igniter and the needle and membrane of the carb.Could that be it?

Regards.
 

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Discussion Starter #18
I forgot to mention, but back cylinder exhaust is a lot hotter than the front one.For sure it is also because of the length but who knows.
And I saw yesterday that condensation is present on both pipe ends after I started the engine.
 

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You have been changing the wrong jet in the Carb. Leave the secondary at 160 and start working with the primary. I recommend
installing a 48 ~ 52. Make sure idle is around 1k rpm.
 

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Discussion Starter #20
Update

Hello all,

Sorry for the really big delay, but I'm really short on time right now.

Bandit you suggested 48 ~ 52 pilot jet, so I bought a 50 one. The old one in the carb was a 45.Right now I am running a 155 main jet, a 50 pilot, stock air filter, and no baffle exhaust.Finally no popping at all, with the adjustment screw 2,75 turns out.
Popping gone completely.
In the next days I shall make a longer test ride, and I'll post back results, and plug colors.

Thank you all for the support here.
 
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