my friend drilled 1/4 in holes in his baffle on his sporty i heard bad things not rejetting and back pressureissues he swears upand down it doesn't affect backpressure or mixture . but i beg to differ.If it is okay might do this mod but i'm kinda reluctant, i mean no rejetting at all???good backpressure, sounds like bs right???

my thoughts exactly jus wanted to hear it from you  guys . apperciate that

It's all about balance,..  matching the in, to the out...
Better breathing can increase HP's,.. but only by allowing more fuel burn, which requires mores fuel (rejet)... without rejet, you're just getting more air, making you lean,... you have to match that extra air with extra fuel...
...but,... you pay for more HP peak by having a narrower torque/power band...  and torque is what gives you that sweet kick in the pants launch...
... a Stock Harley Sportster muffler is a popular swap on our bikes,... Yes, rejet,...
... and you get nice sound, and better breathing, while keeping a wide power band...

really...its likely you should rejet whether you change mufflers or not. These bikes come from the factory lean. But hell...if you gotta do one anyway you might aswell do the other.

As to your buddies sportster...its possible that drilling a few holes in the baffle worked without leaning it TOO much. He's most definately leaner than before and he most likely has reduced backpressure but he might still be okay without having to rejet. If you're on the knifes edge of lean/okay (savage) any change from stock will require a rejet. His sportster might be jetted on the rich end of okay from the factory. Or if its newer it might be FI. IDK know anything about FI. I geuss theoretically, FI sensing and compensating for the increased airflow (as if running slightly higher revs) it may auto adjust negating the need to rejet...or jetting in general. But again...I know nothing about FI.

Routy wrote on 06/23/10 at 05:50:44:

Routy you did the white spacer mod that richens it,I drilled my stock muffler up in side with long bit and a 1/2 drill,And I went 1 jet size up on low speed and 2 sizes on high speed and it really runs good.And left the spacer stock.

bill67 wrote on 06/23/10 at 06:30:42:

Bill,
I did the metering needle adjust (spacer mod) because it had a lean ragged running low end,....before ever drilling the exhaust.
After drilling the exhaust, I didn't notice any change, or any evidence of running lean, therefore no jet change.

Doing the spacer mod takes the place of adjusting the slotted needle that was done away w/ years ago,....or so I was told here, and according to the pros is the proper way to enrich the low-intermediate fuel delivery. If you corrected any lean conditions by changing jets, thats good, but if you changed jets w/o any evidence of needing it, that was the sole purpose of my post.

by the way his sporty is carb it's 99 not 07

texsam wrote on 06/23/10 at 17:34:45:





no...