[PhilJ]

For 10 of the 12 months I've had my AVL I've had an 60's BSA muffler on my bike. I t makes a nice sound but... always the what if syndrome... maybe could be just a little bit louder, only a little.

So, all I did was remove the PAV system and install the muffler. I did plug chops and the plug did not change one iota. Now I'm thinking of removing the restricter in the header pipe. Hopefully giving me the "just a little" more sound.

I'd like to know if anyone has done any similar mods to their AVLs and what if any changes were done to the jetting. If any jetting changes were done, what change did you note in fuel economy?

With just the BSA muffler I immediately noted more torque and no change if fuel consumption. I'm really torn between the nicer sound and fuel economy. In other words, I want it all. 

[PaulF]

Phil, I went with the Dunstall silencer, which is, I'm pretty sure, a hollow tube, (installed by the dealer so I haven't had it off to examine it). It must be. Let off the throttle and it will fart and pop enough to get the attention of everyone around it. No restrictions here.

As far as fuel economy, I don't track that. This machine exists for part-time pleasure only.

Jetting was one-up on the primary, (I forget the size), and main went from 110 to 130.

[ace.cafe]

Changing the header pipe to one without the "restrictor" will make it a bit louder, and help to gain the power from the free-flowing muffler.
What's happening is that the restrictor in the header pipe is blocking up the works, prior to the exhaust getting into the muffler, and that's why you are seeing no need for jetting changes. Or at least, that's probably why.

[Cabo Cruz]

Br. Paulie, that's a sweet looking RE, man!!! 

And, Br. Ace is correct in saying: "Changing the header pipe to one without the "restrictor" will make it a bit louder, and help to gain the power from the free-flowing muffler.  What's happening is that the restrictor in the header pipe is blocking up the works, prior to the exhaust getting into the muffler, and that's why you are seeing no need for jetting changes. Or at least, that's probably why."

P.S. I went with the unrestricted header pipe when, in my case, I went with the Goldstar style -- free flowing -- muffler, the K&N filter and a 34mm carburetor.  I had the dealer make these changes immediately after I bought my bike.  These modifications added up to a BIG difference in power and performance.   

[UncleErnie]

Could you post a bigger picture so I can see some detail?  From what I can see, that bike is WAY too clean.

[PhilJ]

Thanks guys. The BSA muffler isn't as free flowing as those that have been mentioned. So I guess I'll just try it and let the chips dribble.

I'll report what happens.

Phil

PS  Yes UncleErnie that bike is way to clean. At the current polishing rate it should disappear in 10 to 12 years.  

[UncleErnie]

I'm developing a custom kit that includes real vintage oil and a special atomizer to spray strategic areas to add a look of authenticity.  My copy writer is working with the engineer to work out the exact instructions.  Should come in around "Three easy payment of only $29.95!"   Let me know if you're interested.  You'll sleep better at night.

[PhilJ]

Well this morning I got all fired up and took the header off. With handy dremel in hand and cut-off wheel made short term of the four welds.

Buttoned it up and took off on a 50 mile ride. The torque seemed to increase some but not as much as it did when the BSA muffler was installed. It did seem to have a little more punch from just under 2 K rpm to 3 K rpm.

Before leaving I put a new plug in and took two readings. But the plug didn't show much. I don't know if having run just around 20 miles had anything to do with the reading. But there was little change in appearance.

Tomorrow, is another day. Wow, heavy, 

[PaulF]

Could you post a bigger picture so I can see some detail?  From what I can see, that bike is WAY too clean.

LOL. Ernie, yup. I should havge bought a military. All that chrome obligates me to keep it that clean.

If you click on the pic, it should get way large if I posted it right.

[LJRead]

While we are on the muffler subject, I understand that if you add a new muffler to the header pipe, it should be at least 46 inches long.  I have a nice twelve to fourteen inch muffler and wondering if I would then need to extend it out to meet the 46 inch requirement.  Don't know where I would get a piece of extension piping though.

Ace, you might know something about this.

[ace.cafe]

While we are on the muffler subject, I understand that if you add a new muffler to the header pipe, it should be at least 46 inches long.  I have a nice twelve to fourteen inch muffler and wondering if I would then need to extend it out to meet the 46 inch requirement.  Don't know where I would get a piece of extension piping though.

Ace, you might know something about this.

Yes, I now a bit about it.
It's not as important when there is a muffler in the equation, because the baffles and the large expansion volume at the entry to the muffler, affect a large portion of what ever wave tuning is happening in the exhaust. Pretty much to the point of not making alot of difference how long the muffler is.

If the pipe was open, with no muffler and about 46" long, it would be wave tuned at a particular frequency and rpm, and could be used to assist power around those rpms, in a narrow range. For street use, it is probably more beneficial to break those waves and not center on a particular rpm point for wave tuning, because it's too narrow and too high in rpm to be of much use to us.

For a racing application, fine.

As far as "sound" goes, the longer the exhaust and muffler, the quieter it will be and the deeper in tone it will be.

[LJRead]

Thanks Ace, I'm going to try the little muffler, maybe this weekend - I had it on briefly, but the fit wasn't quite right and needed a bit of shimming.  It was very loud - and that may be good to let the livestock and people here know I'm coming!

It reaches back to just a bit beyond the rear foot peg.

[PhilJ]

After riding several days since I took baffle out of the header I've decided it has the sound I was looking for only loud when you've cranked it on, and a deep sound saying I'm a thumper when riding normally. Wish I new how to post an audio file.

The best aspect for me is, since the AVL evidently comes a little rich, is I haven't had to change the stock jetting. Since opening up the exhaust the plug readings are actually closer to ideal, as in the pictures shown for properly jetted carbs.

The best of both worlds, at least my world.   For me it's been a total success.

[Retroman]

Hi Phil,
 I have a  2008 AVL and also change the exhaust pipe but not the header. 
 I find out I did not need to jet the bike aether since the new plug I put did not show any changes for almost 100miles follow up checks.
This avl engines seam to be more flexible to changes than other engines I had deal with, but I end up re jetting it when I install a Acorn type air filter just to be in the safe side. I have retain the PVA because I kind of enjoy the sound it produces. also I install a 19T sprocket that did not increase my top end but really easy the engine at top and cruise speeds of "65 and 80" MPH. with minimum of vibrations.

Now I want to remove the header baffle to have higher sound and probably increase power a little bit more,  thanks for posting since I thought that was impossible and I love the curve of the original header.

[PaulF]

Phil, I went with the Dunstall silencer, which is, I'm pretty sure, a hollow tube, (installed by the dealer so I haven't had it off to examine it). It must be. Let off the throttle and it will fart and pop enough to get the attention of everyone around it. No restrictions here.

Jetting was one-up on the primary, (I forget the size), and main went from 110 to 130.

Phil, a little update. Since I was bored and since the stock airbox went bye bye, I can't get this motor to run rich enough to foul a plug, I swapped out the 17.5 pilot jet this weekend with a 20 from CMW, (15 is the stock pilot jet size in the CV). I expected a little more low-end throttle response, which I got. What I didn't expect, is that the fart and pop-back I mentioned dissapeared. I would have thought that a little richer would mean a little more snap, crackle, fart & pop on de-cel. Didn't happen.