Modified stock pipe saves big $$$

Greg, no need to use a sarcastic smiley , you are going at it from a flow stand point and I am talking about an increase from stock flow versus sound level stand point. If this pipe is modded and used for racing, at least where we race here they do sound checks, removing all the baffles or drilling too many holes will get you thrown out of a race for sound infractions. For flow purposes the pipe #1 in Dodjy's pics is 1452 mm2 #2 is 660 mm2 #3 is 314 mm2 #4 is 227 mm2 and the tail pipe is 314 mm2. Drilling 1/2'' or 13 mm holes(154 mm2) through the baffles increases flow slightly , but also increases sound. So if you are being anal, then all mods should be done using a sound check to verify that you haven't gone out of limits. All I was saying is that I should have only drilled 2 holes to stay with in the sound limits a little better, 3 holes is just over the 96 db limit for our races here, and yes I have fashioned a 43 mm id tail pipe the same as Dodgy did. WR Dave.

OK, so to keep it simple, I think I'll leave the big rivets alone, remove the stinger end cap, drill out the rivets in the tailpipe and remove the inner thingy (this is instead of buying the $50 GYT-R insert, right?). Then I'll drill 2 1/2" holes to the left top (circle section) of the pork chop.

Does that sound about right for an '09 WR250F?

That should work except for the tailpipe section, it is still very small so you may want to leave it out all together and just run with the spark arrestor in place with the two extra holes. If your bike doesn't pass sound check then it may be best to carry the small tailpipe with you so you can quickly put it back in to pass sound. My results are for a WR 450 so the 250 may end up in a different place sound wise. You may have to rejet a bit for a slight increase in exhaust flow. Best to try it out before hand and you should be good to go. WR Dave

.

Dave,

PM sent.

Cheers,

Greg

PS is this one ok? :thumbsup: .... LOL!

That should work except for the tailpipe section, it is still very small so you may want to leave it out all together and just run with the spark arrestor in place with the two extra holes. If your bike doesn't pass sound check then it may be best to carry the small tailpipe with you so you can quickly put it back in to pass sound. My results are for a WR 450 so the 250 may end up in a different place sound wise. You may have to rejet a bit for a slight increase in exhaust flow. Best to try it out before hand and you should be good to go. WR Dave

Thanks,

That was such a nice PM Greg I'm :thumbsup:.

Last one was great by the way. WR Dave

That should work except for the tailpipe section, it is still very small so you may want to leave it out all together and just run with the spark arrestor in place with the two extra holes. If your bike doesn't pass sound check then it may be best to carry the small tailpipe with you so you can quickly put it back in to pass sound. My results are for a WR 450 so the 250 may end up in a different place sound wise. You may have to rejet a bit for a slight increase in exhaust flow. Best to try it out before hand and you should be good to go. WR Dave

Thanks Dave! I drilled two 1/2" holes, left the tailpipe out and reassembled it with the spark arrestor. I haven't had a chance to ride it yet, but it sounds great. Also, I was trying to do a quick sound check. Before I drilled the hole, I bolted the sparky back on and just popped the stinger end cap on (without bolting it up) and started the bike. Then I drilled the holes and restarted the bike. The exhaust flow was so much more dramatic that it popped the stinger right off the muffler:thumbsup:

My only concern now is decibel level. Dave, did you test yours with the two holes, minus the tailpipe? Also, does anyone know where I can test the sound level out prior to the race? I'm afraid that it may not pass even with the tailpipe in.

Thanks,

I'm pretty sure it will pass with the tailpipe in. I didn't test with 2 holes, I tested with 3 and got 96.5 dbs at a race test. They let me go as that was close enough that it could have been an error in testing. Like I said just bring the tailpie and some tools with you and then you should be ready for anything before the race, although yours is a 250 and I don't have alot of experience with how that system will react. Good Luck -- WR Dave

I'm pretty sure it will pass with the tailpipe in. I didn't test with 2 holes, I tested with 3 and got 96.5 dbs at a race test. They let me go as that was close enough that it could have been an error in testing. Like I said just bring the tailpie and some tools with you and then you should be ready for anything before the race, although yours is a 250 and I don't have alot of experience with how that system will react. Good Luck -- WR Dave

Is that with the tailpipe in but that inner thingy removed via drilling the rivets?

Personally, I would start with no tailpipe. but have it ready with no inner baffle . Rivets drilled and inner pipe removed. WR Dave

Personally, I would start with no tailpipe. but have it ready with no inner baffle . Rivets drilled and inner pipe removed. WR Dave

I rode Azusa Canyon after drilling the two 1/2" holes. It didn't seem to have any flat spots and ran well. I couldn't really tell if it was much stronger since it was a combination of really loose sand or gravel and I couldn't get much traction. But either way, do you think it's necessary to rejet with just the combination of gray wire removal, AIS removal, YZ throttle stop, the two holes in the baffle and tailpipe removed plus the snorkle and "lid" of airbox removed?

Thanks,

If it's running good you may be OK. If your jetting was good before then this isn't really a big enough change to make you have to go through the jetting again. Give a try in a better traction situation , so ou can have something to go on. -- WR Dave

if worst comes to worst can't you just rig something up that really deadens the sound and then take it out after the sound check and race with whatever you want? if its close then who would care or complain?

.

In regard to the snorkel, the last opinion I heard/read was that it was best to leave it on.

It helps distribute the dirty air across the whole filter, rather than allowing it to concentrate in one spot.

Too late for my bike, the snorkel was taken off by the dealer I bought it off. I never saw it.

Greg

I think I'm going to not drill the rivets in the tailpipe, just in case I do need to deaden the sound. It ran pretty well with it anyways.

On the snorkel side of things, I have a bit of news. Saturday we went through some really long and deep river crossings. The water was up to the bottom of the seat at times. After about four of five crossings like that we went back to the truck and pulled out the filters to dry the bikes. There was no water at all coming from the snorkel area. There was plenty of water pooling below the filter, but it looked like it all came from the vent in the side plates. The filter was a little wet, but it didn't look like it could have made it past. We did this all day, and only once did the bike have any issues. Right after the crossing, it ran really crappy for about a minute or two. Could it have just been that the filter was soaked or do you think maybe it was water in the muffler?

if it ran crappy for a minute or two it sounds like it might have been sucking up moist air from the filter. Do you oil your filter? I would never cross deep water without oiling my filter. I would never not oil my filter in any case, but the oil makes the water bead right off. My brother and i went riding through a creek one time. My IT 250 was in up to the top of the seat and his xr had just the handlebars sticking out. it was just an in and out creek, but we both had zero trouble, the bikes ran great.

.

Right after the crossing, it ran really crappy for about a minute or two.

My '08 did the same thing on it's first run last year. Did a creek crossing and a minute later it ran crap, popping and misfiring. i thought I'd bought a lemon!

I worked out that little drain hose on the bottom of the air cleaner box was sealed on it's end by Yamaha at the factory. There was water sloshing around in there getting on the filter and being sucked into the motor, it couldn't escape.

I cut the end off that hose to allow the airbox to drain and have never had the problem again. I've done heaps of deep crossings since and it always runs fine now.

This was the case (ie the hose being sealed) on my Aussie release bike. Not sure if the US version is set up this way or not.

Greg

.

My '08 did the same thing on it's first run last year. Did a creek crossing and a minute later it ran crap, popping and misfiring. i thought I'd bought a lemon!

I worked out that little drain hose on the bottom of the air cleaner box was sealed on it's end by Yamaha at the factory. There was water sloshing around in there getting on the filter and being sucked into the motor, it couldn't escape.

I cut the end off that hose to allow the airbox to drain and have never had the problem again. I've done heaps of deep crossings since and it always runs fine now.

This was the case (ie the hose being sealed) on my Aussie release bike. Not sure if the US version is set up this way or not.

Greg

When I opened the side panel, it didn't look like it was draining. I'll check the hose. The filter was oily (maybe from the factory?), but I'll make sure to redo when I wash the filter.

Thanks,

i dunno what brands of oil you guys use. I use bel-ray filter oil and it works great, but i haven't tried other ones. i used to just use regular oil, but now that i've tried this stuff, it's waaay better. stickier and seems to catch dust better too.

Hi do you know if the same mods can be done on a 03 stock exhaust? Thanks

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