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Discussion Starter · #1 ·
need advice guys, On my 1500 classic Carbed, with Straightshots
I don't really like the sounds on deceleration, Its really crappy, not really a backfire,
but a plop-sputter-plop- sound, After reading Gadgets site and his article on the marble trick, I am wondering if this will eliminate the sounds I get.

Thanks
Dave
 

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I haven't done this myself, but what I've heard some of the guys here has done it and it really does work. Just wait and see for someone who's done it.
 

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Go to this site (makers of TFI) http://www.dobeckperformance.com and go to the Take the Test section and actually take the test. You will find a lot of useful technical information. Answers to you question is actually on question 5: This is the response I got on Question #5:

” Q5. I have a popping out of my exhaust when I let off the gas. Is it?
Your answer - Exhaust flange gasket leaking is wrong.The correct answer is - Could be all the above
Yes, all the above. We take a fare amount of tech calls related to popping. However, to have an explosion in your pipe you need to have 3 things: fuel, spark, and air. Most of the time your pipe has a supply of fuel. It also, has a spark source. The one thing it does not have is much air. On metric cruiser or sport bikes the air gets in, from the air by pass systems. Many think of it as a bad thing and remove them. The most common problem of popping on these bikes is because the air by pass hoses are not pluged in properly. Harleys have a little different problem. The air needed for the explosion usually gets in from the exhausts. You will find that holding a Kleenex next to the baffle in back, during idle, causes the Kleenex to be drawn into the pipe. This is the main source of the air needed for popping. This is even more common with baggers, which have a dummy pipe on the right side. Fuel of course helps, but it is better to find ways to cut down on the air.”

I removed the reed valves on my Mean Streak and put coasters on it and don’t have any poping noise. However, I didn’t have poping issue before – I was told that the stock exhaust does a good job of silencing the poping noise.
 

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Well, I'd like to hear the comments as well. I have "marbled" the hoses leading to the air injection system and I have a power commander that uses a modified map to optimize the fuel injection system. I have no backfire but have the wheezie sound you describe. I used new crush gaskets on my straight shots and was careful installing the pipes to be sure no leak would occur at the head...still have the sound...accel sound is great though! AND higher rpm decel is good.

T-man
 

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Hi dhdaniel

I installed the Cobra Slash Cuts on my Nomad FI and never got any backfiring. What ever back pressure exhaust sounds that I get are minimal. When I had the bike Dynoed and custom mapped by the Power Commander Tuning Center the rubber hose to the reed valve was clamped off so as to insure proper air/fuel mixture readings.
I did the marblizing as per per the Gadjet Instructions after the Dyno and I've noticed no real difference or change. Zooming off the Cobras sound great when that throttle is cracked .

DfgPilot
 

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Discussion Starter · #6 ·
T Man

wheezie! thats a darn good word for this sound that it makes on decel.

I thought for hours looking for the right word to describe it!!!!

Dave
 

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I have more of a flatulence sound when I back off my throttle and am planning to marble the reed valves. From what I understand that sound will be cured with the marbles.
 

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Discussion Starter · #8 ·
flatulence?? yep that sounds like it too. a good ole fart!

I am going to do this marble stuff this weekend, and I will report the findings

thanks guys!

Dave
 

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I have an 02 mean streak with hard krome pipes and I have done the marble job and now the bike sounds alot better and the sound was alot quieter without the popping sound. Go for the mod if it doesn't work just take the marble out and your haven't spent that much money for a test!!!
 

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I did the marbel trick to my meanie and it stopped the popping on de-accel. Easy thing I have ever done to any vehicle. :lol:
 

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Did anybody ever have a problem with the marbles being sucked down to the engine?
 

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Nope, no problem if you use the right size marble.

BUT, there are two separate subjects being discussed here.

1. Popping during decel
2. Plop, wheeze, "flatulence" in the exhaust sound during decel

THESE TWO SYMPTOMS ARE DIFFERENT!

Item #1 is the presence of excess air coming in from somewhere - either from the air injection system (cured by coasters or marbling the existing hoses to each jug) AND no leaks in the exhaust flange (using new crush gaskets during header installation) AND making sure the air/fuel ratio is not too lean allowing excess oxygen be present in the pipe. If any of these is not satisfied, explosion in the exhaust can occur...popping, backfire,etc.

Item #2 is different. The sound is not a pop but as described in the first post in this topic. My theory is that it is not caused by excess air but is due to exhaust size, exhaust volume, and cam shape. With the free flowing exhaust of straight pipes in lieu of the restrictive factory catalytic converter and baffled mufflers, the natural sounds of flow reversals become more evident. Valve overlap cause some flow reversals that must contribute to sound quality. I don't know of a cure for this. At low flow rates that occur during slow engine RPM decel, this sound occurs. At higher flow rates during decel, this sound is not present because more air is flowing into the exhaust pipe.

Glad to discuss other theories.

T-man
 

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answers

ok, this is why i come here for mechanical advice, i scored a 31.5% on that test. glad i have a resource like this forum to come to. planning on gutting and marbelizing the nomad over the winter. i don't get a ton of decel pop now that my baffles are back in, but there still is some. thanks guys.

david
 

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"Item #2 is different... At low flow rates that occur during slow engine RPM decel, this sound occurs. At higher flow rates during decel, this sound is not present because more air is flowing into the exhaust pipe." - If low exhaust flow is the problem, I wonder if increasing the exhaust flow rate by wrapping the exhaust header/pipe will solve the problem.

"i scored a 31.5% on that test" - I didn't do any better. It's a tough test but I learned a lot from taking the test.
 

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Symptom #2???

If this is the sound on decel that sounds like a trucks Jake Brake...I think that it is perfectly normal...Matter of fact I love the sound...It's the sound of power in my opinion!

T-man said:
Nope, no problem if you use the right size marble.

BUT, there are two separate subjects being discussed here.

1. Popping during decel
2. Plop, wheeze, "flatulence" in the exhaust sound during decel

THESE TWO SYMPTOMS ARE DIFFERENT!

Item #1 is the presence of excess air coming in from somewhere - either from the air injection system (cured by coasters or marbling the existing hoses to each jug) AND no leaks in the exhaust flange (using new crush gaskets during header installation) AND making sure the air/fuel ratio is not too lean allowing excess oxygen be present in the pipe. If any of these is not satisfied, explosion in the exhaust can occur...popping, backfire,etc.

Item #2 is different. The sound is not a pop but as described in the first post in this topic. My theory is that it is not caused by excess air but is due to exhaust size, exhaust volume, and cam shape. With the free flowing exhaust of straight pipes in lieu of the restrictive factory catalytic converter and baffled mufflers, the natural sounds of flow reversals become more evident. Valve overlap cause some flow reversals that must contribute to sound quality. I don't know of a cure for this. At low flow rates that occur during slow engine RPM decel, this sound occurs. At higher flow rates during decel, this sound is not present because more air is flowing into the exhaust pipe.

Glad to discuss other theories.

T-man
 

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BT:

Unfortunately, the sound is not like a Jake brake, more like Jake's grandmother with a bad cold! Actually, it's not that bad, just not the nicer sound of the stock pipe during decel. But the accel sound is worth far more in trade!

PPark wrote about "wrapping the exhaust pipe." I don't know exactly what he means but to go in and internally reduce the diameter would be a task. I tried putting an adjustable restrictor in the form of a butterfly at the end of the pipes, but to no avail. This leads me to believe the cam shape results in exhaust overlap for high rpm scavenging and at lower revs this causes reversal in exhaust flow making the sounds we hear. This also may be due to the two exhaust valve set up.

T-man
 
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