92 FJ1200 EXHAUST

[wrinkly12]

Hello All.     When I got my Fj in pieces one of the exhaust silencers (the left one) was badly rusted at the end and on the bottom.   I got a good used set from and XJR 1200 and fitted them.  Not having ridden an FJ before I found it a bit unresponsive when going through the gears and did not want to rev it above 4000 as it felt that it was pushing the motor a bit too hard.   I found that the engine seemed to hold back when riding.    I made a temporary fix to the original pipes and put them on.   The engine seems more responsive now.  It seems to rev a lot higher without too much vibration and goes better.   My question is:   How do I get the XJR pipes to operate like the original ones.   Would I have to re jet the carbs?   Or are there aftermarket pipes that will just bolt on ?   I am in Melbourne Australia.   

[threejagsteve]

Not sure if you're being cautious because you're bedding in new rings or something, but if you aren't revving over 4K, you haven't woken the sleeping beast yet! 

[wrinkly12]

Not being cautious.  With the XJR Pipes the engine was roaring but no huge pickup.    With the original pipes on you could feel the power kicking in but the bike did not sound and feel like it was being pushed too hard.  Someone has suggested punching a hole in the inside of the XJR pipes to lessen the back pressure.   Any ideas out there?

[ren-dog]

Hey Wrinkly12,

Exhaust systems are funny things
They have two operating principles; backpressure and gas speed.
Backpressure can roughly be thought of as the amount of force needed to push the exhaust gas out the end of the pipes.
Given that the mufflers are off a bigger mill this is most likely NOT a problem.
Gas speed is exactly what it says, the speed of the exhaust gas. There is a point, around 350 ft/sec where exhaust
systems start to introduce all sorts of harmonics. Ever played a musical instrument really badly? 
Yet someone with expertise can play the same instrument and make it sound, well like music.

I am guessing, repeat guessing, there is a nasty low pressure zone down low in the rev range because your engine
isn't producing the airspeed necessary to induce these special harmonics. To test this theory go and rev way past 4K.
You are attempting to get the exhaust gases moving quicker. If the engine starts to missfire, fart, burp or generally
run rough then the mufflers are rubbish. If, however, the engine still feels sweet up high, it's all good. Try and shorten
the distance between the end of the muffler and the exhaust valve. Either move the muffler closer, or shorten it.
Because all that is really wrong is the holes in your new muffler are TOO big. 
Get original parts if you can or, if you have $$$$, ask at any reputable muffler shop for a 4 into 1 setup.
The other solutions revolve around engine modifications; eg. bigger pistons, lumpy camshafts.
More fuel will NOT fix your problem.

Cheers,
ren-dog

[Harvy]

Wrinkly..... Klavdy had XJR cans on his FJ for a while, but he opened out the ends some how...... hopefully he is OK after his lightening strike experience and let you know what he did.


Harvy

[wrinkly12]

Thanks Guys.  I was hoping for advice on how to open these XJR pipes up.    Unfortunately they are welded closed so I cannot even drill out the rivetts to have a bit of a look inside. 

[Harvy]

Kev, I tried to search for Klavdy's post on the Yahoo group, but the search function is still not working........ nor can I find it in the archives.

Harvy

[rktmanfj]

Try right here...  scroll to bottom row.

http://www.fjrally.com/picgallery/gallery.asp?action=browse&categoryid=15&whichpage=3

Randy T
Indy

[Harvy]

Well done Randy!    .......didn't realise he had posted photos. I seem to recall there was a write-up about it too (but of course, as I am often told by SWMBO, I may be wrong).   

Harvy

[spsmith_fj1200]

This is the section of the Yahoo yahamafj board that has Klavdy's write up and drawings

http://autos.groups.yahoo.com/group/yamahafj/files/EXHAUST%20MOD/

[wrinkly12]

Thanks Guys.   That answers my questions and now I can fabricate one of these mods and get the bike running like it should.    Please have these internet beers on me.

[wrinkly12]

Please consume your internet beers wisely and maybe not play any driving games afterwards.

[rktmanfj]

Well done Randy!    .......didn't realise he had posted photos. I seem to recall there was a write-up about it too (but of course, as I am often told by SWMBO, I may be wrong).   

Harvy

Well, when at work, there are some things I can look at, and some I can't.

Surprisingly, Barracuda hasn't banned this site and fjrally, but has some of yahoo.

Randy T
Indy

[Klavdy]

Use your existing Headers.
Depending on which year model FJ you have, you may have to get  two  short pieces of exhaust tubing from a muffler shop, 100-150 mm long, flared at each end to fit the XJR mufflers to the existing mounting points, you'll see it easy enough.



These are the things you need to de-restrict the XJR Cans, smaler one is the OEM.
Get them made or buy them.













CLICK ON THIS FOR MORE DETAILS

[wrinkly12]

Thanks for the Pictorial.   I will get started on it in the next few days.