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Discussion Starter #1
My 05 1300C still backfires even though I've removed the PAIR valve and capped off the reed valves, replaced all 5 (slip ons, crossover and crush) gaskets in my stock exhaust, and replaced the acorn nuts with flange nuts torqued at least twice after riding. Also using stock air filter. I've also adjusted the idle and a/f screw according to the manual. So for some reason I'm still burning fuel in my pipes on the deceleration. Bike has about 65K miles on it and I'm getting pretty good MPG at 40-42mpg.

I'm thinking it may be time to look inside the carburetor to check whether the pilot diaphragm may be torn or any other gaskets may be cracked or rotting. If I do dig into the carburetor, would it be helpful to increase the jetting to run a little more rich while I have it apart??
 

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I did everything to stop mine.. Pair, Intake, torqued exhaust, Jets..
Nothing worked.
Then I drilled my pipes !!
Side effect was the popping stopped 99%....
Must be a back pressure thing or?????
And it sounds much better to.....
Best of luck.......


.
Did you do the "Honest Abe" exhaust fix? (
) I had a friend do that to his boulevard C50 and it stopped popping and made a better rumbling sound and didn't have to drill the chrome. Mind you I am not sure what the ends of stock 1300 pipe looks like so it may not work..
 

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My 05 1300C still backfires even though I've removed the PAIR valve and capped off the reed valves, replaced all 5 (slip ons, crossover and crush) gaskets in my stock exhaust, and replaced the acorn nuts with flange nuts torqued at least twice after riding. Also using stock air filter. I've also adjusted the idle and a/f screw according to the manual. So for some reason I'm still burning fuel in my pipes on the deceleration. Bike has about 65K miles on it and I'm getting pretty good MPG at 40-42mpg.

I'm thinking it may be time to look inside the carburetor to check whether the pilot diaphragm may be torn or any other gaskets may be cracked or rotting. If I do dig into the carburetor, would it be helpful to increase the jetting to run a little more rich while I have it apart??
think about that statement. you are backfiring because you have excess fuel in the exhaust. Do you want to add more fuel to the fire????
 

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Discussion Starter #7
think about that statement. you are backfiring because you have excess fuel in the exhaust. Do you want to add more fuel to the fire????
I'm an old programmer by trade so I probably misunderstood - I was under the impression that since our bikes were set lean off the assembly line, that there wasn't sufficient fuel to enable full combustion in the cylinder causing excess unburnt fuel to escape into the exhaust. So maybe you can help to educate me with what is actually going on between our carburetor and the cylinders that allows excess fuel to escape.
 

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Actually combustion is almost always incomplete, strictly speaking. What happens, specifically when decelerating, is that you transition from a high volume to a low volume charge. In that transition you always end up with a fuel rich charge and that gets discharged into the very hot exhaust. If there is enough O2 in the pipe, it will ignite the fuel, hence a pop. This is far more pronounced and far more likely with the pair valve operational, or with an exhaust leak because some fresh air gets introduced.

There is only one way to stop this, but the methods vary, and that is to create a condition in the exhaust pipe that is unfavorable to ignition.
1) Create a situation where there is not enough O2 present to allow combustion of unburned fuel. That is done by rendering the pair system nonoperational and ensuring you have no exhaust leaks that may allow fresh air into the system to allow combustion
2) Create a situation where there is not enough fuel available to allow for combustion. FI bikes may try a strategy of completely cutting off fuel at anything much above idle when the throttle is closed. Can't really do this with a carbed bike.
3) Create an overly rich condition where there is not enough O2 present to allow combustion. Again, with FI bikes there is a strategy to actually increase fuel at anything much above idle when the throttle is closed. Ever wonder why you can have a fuel pump and wires inside of a fuel tank? The conditions inside of a fuel tank are so rich that even a spark cannot ignite the fuel, There simply is not enough O2 present. Same thing in your exhaust pipe. Raising your AF ratio in your idle circuit can push your high RPM / closed throttle exhaust fuel ratio past what will cause a pop.

I'm not sure if you know any of this, so if you do, you can just skip this. The perfect AF ratio is 14.7:1 (by mass). That is 14.7 parts air, 1 part fuel. This is considered the stoichiometric mixture where there is no O2 and no fuel left. Combustion is complete. An AFR (Air Fuel Ratio) of 8:1 and richer will not ignite (referenced to gasoline). And AFR of 18:1 and leaner will not ignite (referenced to gasoline). The addition of ethanol will shift these numbers richer BTW. Best power is at about 12.6:1 and best economy is at about 15.4:1. That's in the combustion chamber, of course.

So if you can create a condition in your exhaust when you would normally see popping where the AFR in the exhaust is richer than 8:1 then you will effectively eliminate the much hated popping. This is what you would be reaching for by changing jetting. Your bike would rich a bit richer down low, but would be really rich during decel. That's how I first dealt with the problem on my 1800, by using a Cobra FI2000, like an electronic jetting kit.
 

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I did everything to stop mine.. Pair, Intake, torqued exhaust, Jets..
Nothing worked.
Then I drilled my pipes !!
Side effect was the popping stopped 99%....
Must be a back pressure thing or?????
And it sounds much better to.....
Best of luck.......
Same issue with my previous 05' 1300R. I did the PAIR valve removal, carb cleaning, and replaced the exhaust head gaskets.

With stock pipes, I would leave the office, start the bike with choke on, drive a few blocks and "lower" the choke. After an additional 4 blocks I'd slow down coming into downtown traffic and BOOM! The pipes would sound like a shotgun going off. I'd often look down half expecting the pipes to be blown off the bike.

My "fix" was to replace the rusted stock pipes with clayton moded stock pipes AND all five gaskets, torqued the nuts to the heads correctly...AND still got the "One-Shot" backfire... But now it was a muffled PHUMF sound I could live with. It would only do it once, on decel, after warming up and using the choke OR after constant highway speeds for more than a 1/2 hour or so.

My final fix was to get an 1800.
 

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think about that statement. you are backfiring because you have excess fuel in the exhaust. Do you want to add more fuel to the fire????
That is actually a valid strategy, yes.
 

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OKAY Harkon! (As I throw down the gauntlet of challenge) lol

I'm pretty sure I didn't have and exhaust leak after changing pipes and gaskets. And again to be clear, I didn't have a decel pop-pop-pop issue. It was one pronounced BOOM or PHUMF, depending on the pipes. What do think would cause this?

I also adjusted the A/F mixture and added a "small washer to the jet" (don't remember the mod name) with no change to the pop.
 

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Discussion Starter #12
So if you can create a condition in your exhaust when you would normally see popping where the AFR in the exhaust is richer than 8:1 then you will effectively eliminate the much hated popping.
Thank you for your very thorough explanation. I did not know this, and I'm going to bookmark your reply for future reference.

So given I need to decrease the air volume Harkon, which way should I turn the A/F screw to accomplish this? Clockwise (in) or counterclockwise (out) ?
 

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OKAY Harkon! (As I throw down the gauntlet of challenge) lol

I'm pretty sure I didn't have and exhaust leak after changing pipes and gaskets. And again to be clear, I didn't have a decel pop-pop-pop issue. It was one pronounced BOOM or PHUMF, depending on the pipes. What do think would cause this?

I also adjusted the A/F mixture and added a "small washer to the jet" (don't remember the mod name) with no change to the pop.
I had the same issue with my 1800. It had V&H pipes on it, and I blocked off the pair system, changed the exhaust gaskets, did all of the ground fixes and so forth. The bike ran a lot better, but man, when those V&H pipes had an explosion, it sounded like someone was getting 12 gauged. I added the FI2000 and the decel popping disappeared entirely. I could manage it without buy keeping the throttle slightly cracked as I decelerated.

On a carbed bike, adding a washer under the needle speeds the transition from the idle circuit to the power circuit. It will run richer as the throttle progresses but at closed throttle the needle is relatively ineffective. You may have seen better results by bumping the pilot jet a number or 2. I don't know for sure as I never had a 1300, all I can say is that creating a rich condition to eliminate decel popping is an effective strategy and is done all of the time. For sure any point of fresh air ingress needs to be blocked though. Sounds like you did that.
 

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Discussion Starter #15
SOLUTION: Two years later, I finally had some extra time to work on my VTX. Combination of two things, although I think it was principally #2. I do still detect an occassional low, rumbing backfire, similar to what I can hear on my 2017 Indian Roadmaster.

#1, I pulled out the carb just enough to not require disconnecting the water hoses. Dropped the float chamber, opened and cleaned the fuel pump and vacuum diaphragms, both the main and idle jets. Blew out all the fuel pathways with compressed air. Cleaned out all varnish.

#2, I also found that the petcock diaphram had ruptured, resulting in drawing fuel into the vacuum line. I replaced the entire petcock assembly for about $112. In my uneducated, layperson opinion, This is what most likely was causing extra fuel getting into my system and going KAPOW in my pipes almost every time I decelerated.
 

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How timely - I was literally going to post the same question. I have tried just about everything on my 1300c.

Background - I recently took off stock pipes, replaced with V&H. New crush gaskets (twice removed since they're cheap and new ones placed) - did the washers under the acorn too. No change at all. I've tried monster baffles and then replaced with quiet baffles. Literally no change - so pressure made no difference. I've monkeyed back and forth with the AF mix - I can make it pop more... but not less.

Just did the pair valve removal. But STILL no luck. Still backfires on decelerations. Also - I am experiencing what is uneven acceleration when first twisting the throttle - a little hesitation. Had you experienced the same?

The petcock assembly replacement is interesting - and look pretty easy. Where did you get yours?
 

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Check the Air Cutoff valve diaphragm.

Expensive little sucker.. Cover, spring and diaphragm/valve
Fill it with RTV??? Rubber tire tube to make a new diaphragm??

14 VALVE SET, AIR CUT 16048-MZ8-H00 In Stock $84.02 $65.02

Look up MR VTX Carb 101 for carb teardown pix.
 

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Just ordered - will give it a go - thank you!

Update: replaced the ACO and still same exact symptoms. Hesitates on initial throttle roll on. Backfires on decel. Like a firecracker

To date:

1. Desmog - no change
2. Replaced all vacuum hoses - no change
3. Reseated exhaust - no change
4. All new plugs - no change. And the ones I took out looked great
5. Sea foam - no change
6. Replaced ACO - no change



Does it matter that I’m at altitude in Denver?
 

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Discussion Starter #20
Check the Air Cutoff valve diaphragm.

Expensive little sucker.. Cover, spring and diaphragm/valve
Fill it with RTV??? Rubber tire tube to make a new diaphragm??

14 VALVE SET, AIR CUT 16048-MZ8-H00 In Stock $84.02 $65.02

Look up MR VTX Carb 101 for carb teardown pix.
Hello Hans! It has been a long time. I decided to purchase the entire petcock, because for a little bit more it would also include a new filter screen, and also since the front of the valve is riveted, I couldn't check the condition of the plastic diverter and so didn't want to chance that it was damaged.
 
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