Header pipe dents....

[scharding]

I have two dents, one in each of the outside header pipes as they curve under the motor and they are about 3 inches long and dented in about 3/8's to a 1/4" deep. My question is, will these dents affect exhaust flow and cause rough exhaust sound. (eg. small backfire "pooping"). This is at idle.

Thanks!

Steve

[FJmonkey]

I have two dents, one in each of the outside header pipes as they curve under the motor and they are about 3 inches long and dented in about 3/8's to a 1/4" deep. My question is, will these dents affect exhaust flow and cause rough exhaust sound. (eg. small backfire "pooping"). This is at idle.

Thanks!

Steve

Of course they will affect the flow, but I think you are asking if it will have any bad effects. I am guessing that dents are not on all the pipes or are not all the same size right? If you just dented them then your carbs will be slightly out of balance with the added back pressure on some pipes and not others. But if your pipes are pooping then make sure the bike stays outside or wears a diaper.  If the pipes are badly dented then you will notice a change in how it runs.

In general you will not likely notice a difference under normal riding conditions. It is not until your engine needs full power that it really needs the full pipe.  I rode my 600CBR for years with two of the pipes dented. No problems.

[Pat Conlon]

Nope, not at all. Popping indicates a lean condition. So it's fuel/air/carb related.
To start with....Read your plugs. Be sure your carbs are clean. Check for intake air leaks. Check your air/idle screw settings. Check your float settings.....

On my '92 with a Kerker, I have repaired exhaust tube dents with JB weld (the putty type) Good prep work is the key. Sand the tube down to bare metal with course paper, clean with lacquer thinner, apply the putty and mold/feather as needed, then sand smooth and repaint.
The heat does not seen to affect the JB putty and so far, it's been holding up well for over 3 years now....

Cheers.

[andyb]

They alter the flow a lot less than you'd expect.  They have to be really horribly smashed before you'd even notice it on a dyno.  Worry them if you want for the esthetics, but it's not a big deal.

[FJmonkey]

On my '92 with a Kerker, I have repaired exhaust tube dents with JB weld (the putty type) Good prep work is the key. Sand the tube down to bare metal with course paper, clean with lacquer thinner, apply the putty and mold/feather as needed, then sand smooth and repaint.
The heat does not seen to affect the JB putty and so far, it's been holding up well for over 3 years now....

Cheers.

I have heard of filling them with water and freezing them, the expanding ice pushes the dents back out. Not perfect but quite functional. Since little dents don't have any noticable effect, Pat's fix will be better on the cosmetics.

[scharding]

Thanks for the input guys! The pipes have been like this since I got the bike last Sept. It had been in heated storage for over 10 years and the carbs were totally rebuilt and synced by a bike mechanic. I noticed the dents when I removed the belly pan to locate a small oil leak. This popping sound is noticeable from cold choke start right up to fully hot engine, so this is why I thought it may be the pipe dents.

The exhaust is a 4 into 1 header with a 12" Supertrapp muffler and about 8 disc's.

Thanks,

Steve

[FJmonkey]

It had been in heated storage for over 10 years and the carbs were totally rebuilt and synced by a bike mechanic.

Thanks,
Steve

Rebuilt before or after storage?

[Arnie]

I'd guess that your sync is off, you're getting air leaking into the header at the exhaust port junction, and your idle mixture is too lean.
Richen the idle mix by 1/4 or 1/2 turn with the screws provided (equal amounts on all carbs) and re-sync the carbs.
Depending on the design of the 4 into 1 header you may not be able to seal it properly to the head.

Arnie

[scharding]

Carbs, clutch slave and calipers were all rebuilt after I got the bike last fall.

Ok, I'll give the idle screws a 1/4 turn and go from there.

Thanks guys!!

[RichBaker]

Nope, not at all. Popping indicates a lean condition. So it's fuel/air/carb related.
Cheers.

Not always..... If they're "Pooping" on decel, it indicates a normal and rich condition... High vacuum in the intake pulls excess fuel thru and the closed throttle doesn't let enough air in to burn said fuel. It goes on thru the exhaust and burns on encountering the much cooler and O2-rich outside atmosphere and you get popping or backfiring when the fuel burns.

[FJmonkey]

Not always..... If they're "Pooping" on decel, it indicates a normal and rich condition... High vacuum in the intake pulls excess fuel thru and the closed throttle doesn't let enough air in to burn said fuel. It goes on thru the exhaust and burns on encountering the much cooler and O2-rich outside atmosphere and you get popping or backfiring when the fuel burns.

Rich... Pick one and stick with it... One needs diapers, the other a carb adjustment....

[Pat Conlon]

".....cause rough exhaust sound. (eg. small backfire "pooping"). This is at idle.

Not always..... If they're "Pooping" on decel, it indicates a normal and rich condition...

I agree Rich, but Steve indiacted this was at idle....not on decel.

[RichBaker]

Sorry.... missed that.   

[scharding]

Actually I do get the same noise, only louder on decel, I assumed it was because of the header and short exhaust.

Sorry.

Now I'm confused.

[Pat Conlon]

As Rich said, popping on decel indicates richness, but popping at idle indicates something different, *like* raw air getting into the mix .

Set your idle to 900-1,000 rpm, then sync your carbs, then reset your idle, now you can play with your air idle screws in 1/4 turn increments, in for lean, out for richer and see if you can get it to go away.

*All your adjustments will be for naught if your carbs are not properly synced first*
If you don't have one, buy a carb sync tool from RPM. It's $$ well invested and a easy procedure to do.

When you get a chance, open the carbs and let us know what size pilot jets (#37.5, 40.0, 42.5) main jets (117.5 to 130) and what clip the needle is set at. The airbox also makes a difference, are you running the stock airbox or K&N or Unipods?.

So in answer to your original question, it's not related to the dents in your header pipes, it's fuel/air related. Hope this helps... Cheers!