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Discussion Starter · #1 ·
Driving to work this morning my VTX 1300 just started doing decal backfiring. Not the super loud 'CRACK!' sound, but just a noticeable amount of soft popping every time I decal. Since I've read enough about this symptom, my first reaction for what to check is a possible leak in the exhaust head connection causing a lean condition.

When I get time this weekend I'll see what I can do to fix this. I invite anyone to comment with their knowledge of this symptom/issue.

Lastly, I read some people saying they did a pair valve mod and it 'fixed' their backfiring, however I don't understand how that would fix a situation where the issue is air being sucked into the exhaust heads due to a loose pipe/seal condition, but maybe in those cases where the pair valve fixed the issue they had other issues than an exhaust leak?

I have the stock acorn nuts on my exhaust connections, so I plan on buying new gaskets and using some washers when I tighten the acorns down to ensure good closure. Those acorns have a reputation of not holding the flanges down as tight as they should.

I'm hoping this is all I need to do because I'll be stumped if it's still backfiring after I make sure the exhaust has no leaks.
 

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Have you ever replaced the slide diaphragm in the carb? Might want to take a look at that. Mine did started acting up while cruising and sure enough there were visible cracks and gaps in it.
 

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diaphragm
intake manifold cracked
cracked vacuum hose(s)
cracked vacuum "T" fitting, if you still have one.
leaking exhaust head pipe seals... ( one or both )
 

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Discussion Starter · #5 ·
Have you ever replaced the slide diaphragm in the carb? Might want to take a look at that. Mine did started acting up while cruising and sure enough there were visible cracks and gaps in it.
I never replaced my slide diaphragm, but I'm familiar with it from when I did the SCAR mod. I'll order one just to have it on hand even if mine turns out in good shape.

Thanks.
 

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HOP.. I had the same issue, the decel pop was due to loose exhaust head pipes. I got tired of trying to keep the acorn nuts tight so I replaced them with these. You can see they have the serration grooves and they stay tight. Home Depot has them in the bolt/nut bins.

188057
 

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Old Goat
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Acorns and stainless washers here.....good luck
 
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Discussion Starter · #8 ·
Acorns and stainless washers here.....good luck
I really like the look of the Acorns and I think if I use split lock washers (like below) that and some Loctite should keep the acorn nuts in place another 10 years. ; )
Value Collection - #6 Screw 18-8 Stainless Steel Split Lock Washer -  87925129 - MSC Industrial Supply
 

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I really like the look of the Acorns and I think if I use split lock washers (like below) that and some Loctite should keep the acorn nuts in place another 10 years. ; )
I used a very very light coating of antiseize (almost nothing) and regular open ended nuts. I did have to retorque to 17 ft lbs 3 times over the next 1k miles. So far it has held up since (2 seasons). I would be afraid of using loctite, those studs are very delicate, and if you have to remove the nuts you may have a problem.
 

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Lastly, I read some people saying they did a pair valve mod and it 'fixed' their backfiring, however I don't understand how that would fix a situation where the issue is air being sucked into the exhaust heads due to a loose pipe/seal condition, but maybe in those cases where the pair valve fixed the issue they had other issues than an exhaust leak?
The pair valve puts fresh air (non-exhaust air) into the exhaust system for the purposes of burning any fuel that may still be in the exhaust gases. Fresh air + hot exhaust with unburnt fuel = bang. The bang is considerably louder on an aftermarket exhaust, since everything about them is louder. So, if it fixed it for them, it is because of this, not because of loose headers. They could have had multiple issues, and the fixed one issue and still have other fresh air getting in.

I do still on occasion have a backfire. Maybe once every 500 - 1000 miles, but my vacuum lines are all new, pair valve is removed, and my diaphragm is brand new.
 

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I used a very very light coating of antiseize (almost nothing) and regular open ended nuts. I did have to retorque to 17 ft lbs 3 times over the next 1k miles. So far it has held up since (2 seasons). I would be afraid of using loctite, those studs are very delicate, and if you have to remove the nuts you may have a problem.
Agreed.

I followed that advice from a Northstar Riders U tube video, before I did mine.(y)
 

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Discussion Starter · #12 ·
Agreed.

I followed that advice from a Northstar Riders U tube video, before I did mine.(y)
Loctite comes in various degrees of hold, and I know better than to use the red/permanent hold, but was thinking of using the blue. I did a quick lookup (see below) and the blue will not likely hold up to the heat range of the headers, so

188093





222 - Purple - Low strength thread locker, designed for precision metal fasteners under

3/4". Protect threads from rust and corrosion. Removable with hand tools. Temp range -

65 to 300 degrees F. Cure Speed 20 min. Full 24 hrs.

242 - Blue - Medium strength thread locker for fasteners up to 3/4". Cures reliably even

on stainless steel. Tolerant of oil and other contamination. Protects threads from rust and

corrosion. Parts can be disassembled with hand tools. Temp range -65 to 300 degrees F.

Cure speed 15 min. Full 24 hrs.

262 - Red - Permanent strength thread locker for fasteners up to 3/4". Designed for

extreme environmental/chemical conditions. Especially useful for holding tight Grade 5

and 8 fasteners. Protects threads from rust and corrosion. Localized heating and hand

tools required for disassembly. Temp range -65 to 300 degrees F. Cure speed 30 min.

Full 24 hrs.

272 - Red - Hi-temp/hi-strength formula. Suited for temperatures up to 450 degrees F.

Fast cure on most surfaces including "as received" fasteners. Recommended for bolts up

to 1 1/2" in diameter. Heat and hand tools required for disassembly. Temp range -65 to

450 degrees F. Cure speed 60 min. Full 24 hrs.

277 - Red - High strength for locking fasteners up to 1 1/2". Prevents fasteners from

loosening due to shock, heat or vibration . Protects threads from rust and corrosion.

Removable with heat and hand tools. Temp range -65 to 300 degrees F. Cure speed 60

min. Full 24 hrs.

290 - Green - Medium strength thread locker for pre-assembled bolts up to 1/2".

Penetrates threads by capillary action: simplifies preventive maintenance. Secures set

screws and other assemblies after settings are completed. Used to seal welds and porous

metal parts. Protects threads from rust and corrosion. Temp range -65 to 300 degrees F.

Cure speed 10 min. Full 24 hrs.

RCGF Aero
 
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Old Goat
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I forgot about the Anti-seize,as mentioned light coat to prevent oxidation,flat stainless and acorns....16 years zero issues...good luck
 
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As mentioned above make sure to re-torque after several hot / cold cycles. I usually re-check mine at the beginning of each riding season. I used the original acorn nuts with a flat and then a lock washer, both stainless. I prefer the look of the acorn nuts.

If you find that the nuts are tight when you check them I would then think since it started all of a sudden it would be a vacuum hose or the diaphragm mentioned above. Maybe just a vacuum hose came off somewhere that did not get put completely back on when you did some work on your bike or just fatigued with age.

That's my .02 for ya
 

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I know when I ride in the mountains at high elevation, I have a lot of popping upon deceleration but when I'm at home near the coast it is non existent. In your case, if it just started out of the blue these guys may be on to something concerning the exhaust.
 

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Discussion Starter · #16 ·
UPDATE:

Ordered new exhaust gaskets and pulled the exhaust off, put in the new gaskets and discovered the pipe now sits too far away from the exhaust bolts in the front to screw on the nut! Tried everything I could only to have to walk away in utter frustration. I think I almost had a heart attack, I was so damn frustrated!

I'm wondering if the mounting bolts are in too far and not sure what the next step is. I can mount them using the old crush gaskets, but that defeats the who point of my trying to rule out an exhaust leak. Maybe if I crush the gasket some. I currently cant get even a few threads to show above the exhaust flange/plate no matter what angel I push the pipes in. What I thought would take maybe an hour took an entire afternoon and my bike is sitting there with the pipe off.

I had to walk away or I'd start throwing tools around the garage!!!

:mad::mad::mad::mad::mad::mad::mad::mad::mad::mad::mad:
 

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Flanges may go in at certain way.
If not good on one fitting, turn it 180 degrees.
Also if the exhaust is out more than normal it may not match.
It may have to go back more toward the engine.
A few towels wrapped around the exhaust puts it out too far.
1" gap = crap, this will never work. It will work, just slow down and try the things mentioned.
 

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Discussion Starter · #18 ·
All my mounting issues are with the front jug exhaust port. I've tried rotating the flange and it makes no difference, I still can't get the pipe aligned with the new gasket in there so I have any threads to start the bolts onto. It makes no sense to me, as it had the old gasket in there, meaning it was mounted successfully before, so why not now? Exhaust lines up and can thread on at the back port, but the front will not mount in/down into the port enough to allow bolt threading. I exhausted myself trying it over and over and over----all lined up, but will not go in enough for threading. (((HEAD SLAM))).

In any event, I have ordered replacement exhaust mounting bolts for front and back, as one of them on the back exhaust port came off when I backed off the acorn nut and the bolt was slightly bent. I'm going to pull off the old front bolts and install the new ensuring they are mounted with enough thread to allow the bolts to grab and pull down the flange into place and crush the gasket. I've also ordered some anti-seize and lock nuts that are going to replace the acorn nuts since I can't use the lock washers and acorn nuts I wanted to.

Once I rule out an exhaust leak, I'll move onto pulling the carb slide out to see if the rubber part is cracked/damaged and letting in air. While I have the tank off I'll look for any hose leaks.
 

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What exhaust do you have??
OEM and front pipe not all the into the muffler??
93k miles - a few slide diaphragms died.
Soft pop--vacuum hoses would be a good choice.
 

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Discussion Starter · #20 ·
What exhaust do you have??
OEM and front pipe not all the into the muffler??
93k miles - a few slide diaphragms died.
Soft pop--vacuum hoses would be a good choice.

My exhaust is a 2-into-1 Roadhouse classic (as shown in my signature).

I'm confused at the question, "OEM and front pipe not all the into the muffler?" The front jug header pipe feeds into the muffler with the rear jug header feeding into it half way down. I've pulled the muffler off the header pipes to reduce the weight and make alignment of the header pipes easier.

I've read about the side diaphragms going bad and will consider checking mine after the other steps in my checklist.

Yes, mostly soft pops on decal so I'll check the vacuum hoses.

Thanks for the advice.


(y)
 
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