Anyone running J & R expansion chambers on their 380?

[JFISHSOLEVIBE]

There is a set locally that I'm going to pick up on Saturday. Was curious if anyone is using them and if so, what I can expect. Plan on running stock airbox (pods if there is gain to be had) and stock carbs. Does anyone have jetting advice? Thanks guys!

[Craig380]

I've got a set of J&Rs (well, I'm pretty certain they're J&R, there's no marking or badge on them) that I fitted back in 2009 and have run ever since.

The rest of the bike is absolutely bone stock (factory airbox, filters, filter cages, standard carbs, standard porting etc). It runs great with the pipes. Below 5,000rpm is just like with the factory exhaust, pulls smoothly and without drama or flat spots. 5,000 to 7,000rpm is fun time, the bike is transformed and makes the most glorious noise while flying

It will stop revving at 7,000rpm like it's hit a brick wall, there really is no point trying to rev beyond this point - just change up a gear. It's the nature of the J&R pipes. The good news is, the pipes make 6th gear fully usable on the road, and not just an overdrive. It will actually pull 6th into headwinds and up grades, and accelerate to overtake in 6th without needing to drop a gear (providing you've got 5,000 on the dial). You really don't feel it's lacking any performance on the road. The set of 3 pipes also weighs about the same as a single factory outer pipe.

After around 10,000 miles on these pipes, I have not needed to rejet, in fact it's maybe a shade rich. I use B8EIX Iridium plugs and removed the airbox intake snorkel. Pilot screws are set 1.25 turns out.

Fit them and enjoy, just check your plug colours to see how your bike takes to them ....

[JFISHSOLEVIBE]

Craig, thats great info! Now Im officially excited. Im also running those plugs (and newtronic ignition), and currently Ive got pods on so Im up a size in both pilot and main jets, so once I return to the stock airbox, perhaps Ill be right where I need to be. As youve said I have heard most often that the huge benefit is the weight loss. Ill be greatly looking forward to that.

Final question - the gent who is selling them advised that there is only one baffle. The baffles from the other two pipes are MIA. Are yours silenced? Does the baffle on an expansion chamber effect performance greatly or is it simple to quiet them down? Can I run them without baffles altogether or should I concern myself with fabricating some replacements?

Thanks again!

[tz375]

J&R pipes for the 750 have an internal stinger to keep noise down, but they also need the baffles to keep it quiet and they are designed to keep pressure right inside the pipe. The term people use is back pressure but that's not really correct term.

Fortunately J&R baffles are fairly simple. A couple of end plates and a length f perforated tube the right size and a bag of wadding.

[JFISHSOLEVIBE]

Awesome! Thats what I thought after looking at one of the baffles. Im pumped! They oughta mount right up to the current mounting points correct?

[Craig380]

They should mount up .... the 380 J/K had the rear exhaust mounts in a slightly different position to the later models so you might possibly need a little adapter plate to link the pipe mounts to the frame location point. You will have to lose the centre stand, if it's still fitted.

Baffle-wise, see what's missing. There are 4 pieces to the 'baffle' assembly:

- a collar with a spring that receives the perforated tube inside the pipe
- the perforated tube which (from memory) is 22mm inside diameter and about 24cm long. One end goes into the sprung collar, the other end butts up against the end cap
- the end cap
- a big circlip which holds it all together

If you've got one complete baffle assembly, then you'll have what you need to fabricate the rest. I wrap the perforated tube in some moto-x wadding, and then wrap all of that with some coarse wire wool to really pack out the 'end can' section.

[JFISHSOLEVIBE]

Got it! Any idea where one can find this perforated tubing?

[Craig380]

I did find an off-road bike accessory store that sells it ready-made. Worth having a search locally to see if you can get it cheaper / less shipping cost:

http://trialstribulations.net/index.php ... ts_id=1358

[JFISHSOLEVIBE]

Craig,

Got my spannies on today and they're BRILLIANT! The sound is perfect and the bike came alive! So refreshing.

One question:

How do you address kick stand clearance? Mine lays on the left pipe and sticks out a bit and I am worried about cornering clearance. Did yours need to be modified or is mine just bent and I don't realize it?


Thanks again for all the help! It's a whole new bike:)

[Craig380]

My kick stand sticks out a little but I've never decked it ... my left-hand chamber has a shallow dent in it where the kick stand tang goes, I guess a previous owner must have made that.

Glad you like the pipes, I found they really do perk up the bike without affecting the easy-going character too much. As mentioned, mine runs a little rich with the chambers (everything else stock, apart from removing the airbox intake snorkel) but check your spark plugs for mixture readings carefully until you're confident.

[JFISHSOLEVIBE]

Gotcha! Will play around with it and see what I get.

Another quick follow up question:

Does your center chamber make contact with the center stand Frame tab at all? Mine does slightly but I think perhaps it's due to the angle that I have the center header pointed. When looking at the motor from the front, does your center pipe header cock slightly to the left or is if centered?

Thanks again!

[Craig380]

Yes, the centre chamber is VERY tight to the main stand mounting tabs. Again, a previous owner of these chambers has put a small dent in the chamber to make the fit better.

If you just slacken the centre chamber at the header and rear mount, you can make some adjustments but between the main stand mountings, the rear brake torque arm etc, it's all pretty tight down there ...