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Decel Popping

Engine, Fuel and Exhaust

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Old May 27th, 2009, 01:51 PM     #1
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Decel Popping

I read in one of the threads here that exhaust popping on deceleration is normally caused by exhaust leaks, and not the state of tune (rich/lean). So, I attempted to check the exhaust on my 08 Street Bob with Reinhardt Crossbacks. Well, you can't get to the upper nut on the rear cylinder with the heat shield in place. Guess what, you can't remove the rear heat shield unless you remove the front pipe. A lot of twisting and turning later, I managed to finally get on the upper nut, and it was a little loose. So was the lower nut, and both nuts on the front. Go for a test ride, better, but still popping. Bite the bullet, buy a set of exhaust gaskets, take the pipes off, change the gaskets, reinstall the pipes. Modified the rear heat shield so I would not have to remove it any more just to check the nuts. Popping almost completely gone. BUT, now had a rattle in the heat shields. Unable to tighten them enough to stop the rattles, one hose clamp is stripped. Remove the front pipe, pull the heat shield off the rear pipe. Hose clamps in bad shape. Buy new hose clamps, put everything back together. No rattles, still a little popping, but greatly reduced from original condition. It sure is good to have something that keeps me off the street and out of the bars.
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Old May 27th, 2009, 03:17 PM     #2
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Re: Decel Popping

Isn't owning a Harley wonderful sometimes........
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Old May 27th, 2009, 03:40 PM     #3
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Re: Decel Popping

Hi Hobbit,

I have the ThunderMax. There is complete control of the fuel maps, but a little scary. There is one map for every 256 RPM, from 0 through 7936, for each cylinder. They are based on fuel flow vs. throttle position. Then you have the ability to fine tune using the AFR maps. Also can adjust timing against RPM and throttle position. Not sure how much and where to adjust.
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Old May 27th, 2009, 04:50 PM     #4
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Re: Decel Popping

The exhaust flange is not the only place for leaks; the slip joint between the muffler and the header pipe can leak as well. My experience with Rineharts has been that you can't tighten the muffler to header pipe clamp enough to stop a leak. A little RTV high temp silicone will seal the joint. Not familiar with the Crossback system but have worked with the True Duals. I have had to trim the heat shield on the last two sets I installed to access the exhaust flange nuts.
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Old May 27th, 2009, 05:54 PM     #5
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Re: Decel Popping

looks like i have a couple of things to look at when i get home
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Old May 28th, 2009, 11:17 AM     #6
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Crossbacks do not have a separate muffler, all a single welded unit. Exhaust flange is only joint in system. Thanks for the thought.

When I got the exhaust gaskets from the dealer, the parts man told me that the stock gaskets did not work well with aftermarket pipes, and brought out a square cross-section gasket, less than 1/4" across. These have not sealed that well, but may be due to me.

Is this the correct gasket for these pipes? The end of the pipe is a rounded shoulder, not square like I would expect for a square gasket.
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Last edited by Speed; May 29th, 2009 at 08:36 AM. Reason: merged
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Old May 28th, 2009, 01:53 PM     #7
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Re: Decel Popping

The SS exhaust gaskets like the Cometic type and I believe James or someone else makes a copper set. Those seal well and don't creep over into the port when compressed. I think the MoCo offers a SS exhaust gasket as well.
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Old May 28th, 2009, 02:50 PM     #8
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Re: Decel Popping

Thanks, I'll check into it.
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Old Jun 3rd, 2009, 01:37 PM     #9
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Unhappy Re: Decel Popping

Got a set of Kuryakyn copper gaskets from RealHog. Installed yesterday and took a test ride. Still getting significant cracking and popping on deceleration. After the engine cooled, I retorqued to 115 inch-pounds per the manual. Ran engine for 5 minutes, let it cool down, retorqued again. Test ride after this shows no improvement.

So far, I have gone though the stock type gasket, a stainless steel square section gasket, and a copper square section gasket. None of them seem to seal very well. I have to start believing that my technique is lacking.

Question : Is there a specific procedure or technique to getting the exhaust gaskets to seal? Should they be hot torqued? Retorque when cool? Whatever?

Thanks in advance,
Jake
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Old Jun 3rd, 2009, 03:10 PM     #10
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Re: Decel Popping

Quote: Originally Posted by RetiredJake View Post
Hi Hobbit,

I have the ThunderMax. There is complete control of the fuel maps, but a little scary. There is one map for every 256 RPM, from 0 through 7936, for each cylinder. They are based on fuel flow vs. throttle position. Then you have the ability to fine tune using the AFR maps. Also can adjust timing against RPM and throttle position. Not sure how much and where to adjust.
If you have the thundermax you should be able to get rid of nearly all the popping. Make sure you go into your basic setting and set the value of the decel fuel cut off to 1. 1 is on, and 0 is off. If it's still doing it when it's on pay attention to what rmps it's popping at and adjust the hi and low rpm's for the decel fuel cut off accordingly.
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