GZ250 intake & exhaust questions

[Cliff]

First post in the mechanical section

Anyway...

'05 GZ250

1) Will there be negative effects if I replace the stock muffler with a straight pipe (open, no baffles) just past where the 2 pipes from the exhaust join?

2) Can I replace the air box & filter with something less restrictive such as a cone filter (for example)?

If both can be done, what adjustments to the carb will need to be done in order to make the bike run properly?
I know that when I removed the filter and ran the bike with no intake restriction (other than the plastic box) it spluttered and had no power with anything more than 1/2 throttle; it topped out at 40mph. Yes, I know it's not a good idea to run with no filter; it was just an experiment.

Any ideas or suggestions would be highly appreciated.

Thanks!
Cliff

[Cliff]

Just bought a turned out side exhaust. 19" long which is very slightly shorter than the stock muffler that is on the bike. I has steel baffles which have less back pressure, so I should (hopefully) see a little difference. When it arrives, I will install it and post before and after pics.

The only thing that bothers me (just a little) about the bike right now is if I get up to 65 - 70mph in 4th gear then shift into 5th gear, with the throttle wide open, the bike slows down to about 59. It is not often I need to go that fast, as I usually cruise at 60, but it is nice to have just a little extra just in case it is needed.

[Clint]

I'm surprised to hear fifth gear can't hold speed. Makes me wonder if it's tuned properly as it is.

You might be able to replace the stock element with a K&N. That would let it breath without the expense of a pod kit, which aint' cheap.

[DrBob]

You'll have to drill off the caps and adjust the mixture if you open the exhaust and change the intake filter, as the bike will run way to lean. You might have to change the main jet, as there might not be enough adjustment possible. Either way expect a noticable drop in fuel ecconomy.

As a general rule these types of mods would pick up about a 5% increase in horse power. As the GZ250 makes 20HP stock, and the factory exhaust is a pretty good one, you will see about a 1 HP increase. A more cost-effective change might be to swap chain sprockets to change the RPM at 60 MPH, so the motor is more in the power band at highway speed.

[Cliff]

I cut off the stock muffler and installed the new muffler today.



All I can say is WOW!! The gain is amazing.
It actually sounds like a motorcycle now; deep, low and loud.
Now the bike doesn't slow down, but can accellerate from 60 onward in 5th.
I no longer have to downshift to go up slight hills and no longer have to hold the throttle wide open in 5th just to maintain.
This has given new life to the bike and made it much more enjoyable.

I checked and the outlet hole in the end of the stock muffler is the same size as the outlet hole in the muffler of my father's 49cc scooter. LOL

[DrBob]

Looks great! Sounds like something was adjusted wrong originally, as it should have been able to hold speed in 5th. But it sounds like it is running good now!

[wookie]

I have a stock GZ250 and this thing just won't accelerate much beyond 60 mph (not unless I want to blow my engine again) unless I am doing a downhill run, race-tuck, drafting behind a car, etc.

[2005GZ250]

Originally Posted by wookie

I have a stock GZ250 and this thing just won't accelerate much beyond 60 mph (not unless I want to blow my engine again) unless I am doing a downhill run, race-tuck, drafting behind a car, etc.

When I ride the backroads it is hard to keep my GZ at 60mph with hills but when I get on the highway it will do 65mph with no broblem and still have some throttle to spare. How did you blow your engine?

[jonathan180iq]

I've been studying up on the intake options for the GZ250. The air filter for the GS500 is nearly identical to the filter on the GZ. The top mounting plate is exactly the same and the diameter of the filter is as well. This is good news because K&N makes a stock replacement filter for the GS500. (part # SU-5589)

As far as exhaust, the EMGO turn-out muffler seems to be the only good looking option. I'd love to hear a sound clip, before I purchase it for myself.

Cheers,
Jonathan

[jonathan180iq]

I've been studying up on the intake options for the GZ250. The air filter for the GS500 is nearly identical to the filter on the GZ. The top mounting plate is exactly the same and the diameter of the filter is as well. This is good news because K&N makes a stock replacement filter for the GS500. (part # SU-5589)

As far as exhaust, the EMGO turn-out muffler seems to be the only good looking option. I'd love to hear a sound clip, before I purchase it for myself.

Cheers,
Jonathan

PS: As far as rejetting the carb goes, the new exhaust would basically only be a slip-on. Since we're not changing the headers, a re-jet most likely won't be needed. The K&N may flow alittle more than the stock filter which will probably require a couple of washers shimmed under the needles. I would doubt a larger main jet would be necessary.