Hey guys,

I recently took all the packing out of my Yosh slip on to make it a loud as possible.... Now here's the problem, ever since doing so, my bike seems to have lost a TON of power and doesn't start as well as it did before.

Does this sound like a valve issue due to lack of back pressure?
Any help on where to start first would be greatly appreciated!
Thanks, Wheelie King

 

You didn't hurt anything like the valves. But your motor would be better off power wise with some back-pressure. You're essentially running a straight pipe, right now. Re-pack it. Done.

 

Would the lack of back pressure cause the hard starting issue?

 

No, back pressure won't cause a hard start. Back-pressure is what helps volumetric efficiency once your bike is running to maintain a correct a/f ratio. A stock motor sucks a certain amount fuel into the motor. With valve timing overlap, compression, TB, porting, etc - back pressure helps keep any of that "un-used" fuel from escaping out the port

When you unpacked your exhaust, did you do anything else? Did you, literally, just un-bolt the end can and un-pack it, as in you touched nothing else?


It takes thousands of miles to hurt valves in the way you mentioned - and even then, the exhaust needs to be considerably shorter. When there are straight/open exhausts - valves can get hurt 2 ways. A) You run too lean, the valves run much hotter and end up getting warped B) The exhaust is so short that after the engine heats up and you turn the engine off - cold air hits the valve and warps it.

I ran a shortened exhaust (a mid pipe with exhaust tips welded onto it) for over 5,000 miles - a whole spring/summer/fall with no issues whatsoever. That motor is still running strong to this day (I sold it to a friend)

 

I'm so glad someone else understands that the lack of back pressure in itself won't ruin valves.

The loss of power is felt because of a lower amount of back pressure though. While you may feel a little power in the higher end you will drop a little on the lower end.

 

Now if only people would understand that a lack of backpressure doesn't automatically mean over scavenging of the intake charge from the cylinder. Le sigh.

 

Now if only I could understand what you just said.

 

and here i am.. trying to find a place to live which in my price range with a garage is a condo.. which ban motorcycles.. thanks dude.
do me a favor and do burnouts in condo parking lots with your muffler off because they probably dont allow motorcycles on property there too.
i hate to dump but seriously man, being loud does nothing but annoy people. you going to tune your bike to run no resistance and not meet DB requirements at all tracks or what?

 

You're right - it's over-exaggerated by a lot of people as to how much it changes things. It's not the end of the world. Your butt dyno probably won't be able to tell a difference, but you might feel some flat spots here and there.


Yeah.. it's HIS fault you can't find an apartment. Now I've heard everything....

Just a heads up - anywhere that bans bikes probably isn't a place you want to live, think about all of the other BS rules the HOA has. Straight pipes on an F4i isn't anywhere near as loud as the plethora of Harley's that run open pipes that are in WAY more abundance than sport bikes. Hell, I pulled onto the main street during a bike night with my gutted exhaust (probably the same set up as he's running) and I couldn't even HEAR my bike even though I was on it...

If you think it's really his fault - you'd be a perfect fit for an uptight HOA. Remember to keep your phone on you, too, so you can take a picture and complain about someone's grass being a half inch too long and destroying your condo's value.

 

Seeing where he lives, I can kinda sorta see where he's coming from, though, no, not the POs fault directly.

I've never even heard of a HOA banning m/cs, and your right that wouldnt be a place he'd wanna live anyway, it sounds like the same knee-jerk reaction taken against all riders by Florida law makers, but Jesus, can you blame 'em? I'd damn near be ashamed to ride/own a sportbike in Florida.