Jetting: Part 1

[jonathan180iq]

Exactly.

The reason you cannot accelerate above 1/3 throttle is because the mixture is now too lean. There is not enough gas getting into the mixture to produce enough boom to make the bike go faster. You are basically breathing too much.

I've got my filter, jets and some know-how. Now, I just have to find time to go outside and get it done. Hopefully, it will happen before the Franklin, GA meet next weekend.

EDIT:
In response to what Jaime said, even removing that little cover over the filter mouth makes a difference. Image what happens when the resonance of the air box is removed from the system entirely. On top of that, you are increasing the amount of air 10 fold.

Remember, LEAN = TOO MUCH AIR
RICH = TOO MUCH GAS

[jonathan180iq]

I'm glad that someone else here is trying the same thing. Hopefully, between the two of us, forum readers can get a pretty solid idea of what is involved in re-jetting their bike.

From the outset, it can seem intimidating. However, as long as you can follow instructions and have a little mechanical know-how, this isn't all that big of a deal.

Take care,
jonathan

[Easy Rider]

Originally Posted by jonathan180iq

On top of that, you are increasing the amount of air 10 fold.

I have great respect for the effort you are putting into helping your fellow GZ riders get the most from their bikes.

I cannot, however, let the above statement pass without comment.
It just simply isn't true.
The throat of the carb is only SO big. The only way to "increase the amount of air 10 fold" is with a supercharger; even a turbo doesn't provide that kind of boost! :roll:

Keep up the good work.......but let's try to keep it "real".

[jonathan180iq]

Ok.

So let's pull out the phrase "10 fold" and say "by an exaggerated amount" or "by a lot".

I don't know the flow capacity of this carb or I would attempt to give some real stats.

The point is that the removal of the compact air box and the replacement of the restrictive cottom element with a pod filter will significantly increase air flow.


Jonathan

[Easy Rider]

Originally Posted by jonathan180iq

The point is that the removal of the compact air box and the replacement of the restrictive cottom element with a pod filter will significantly increase air flow.

Not sure I completely agree with that .......but don't completely disagree either. :cool:

You've made your case; I'll make mine and then we can move on. Probably won't be able to "prove" it one way or the other with any scientific certainty. :roll:

Air box:
Is HUGE, compared to the carb throat. Can't see how that the box itself would offer any significant restriction. (And I think at one point you said you weren't sure that removal was worth the hassle).

Filter/air inlet:
Some restriction both these places. Some easy (and reversible) changes can be made here.

What I plan to do: (hopefully in the next week or so):

Borrow or buy a moto-tool so that I can remove the center of a stock filter (while leaving the mounting tabs for the diverter). This should remove a lot of restriction, with a much bigger hole and access to more of the filter element. I might then rotate the filter 90 degrees and put the diverter back on facing forward; will try it both ways.
This change can be reversed simply by getting a new stock filter.

Since it seems that nobody has done it (this way), I plan to drill 4 each 1/4 inch holes in the muffler back plate, INSIDE the ring. This change can be reversed by tapping the holes and screwing in 1/4 inch machine bolts (stainless, probably).

If these two changes achieve the desired result, I may then have a LOT MORE interest in your jetting project !!!! If not, nothing lost.

[jonathan180iq]

Sounds good.

I can give two pieces of advice for personal experiments/mistakes.

My first experience, which was not a mistake, was to rotate the air filter housing 90degrees, as you have mentioned. I couldn't detect any noticeable change. Now, granted, I didn't go to lengths that you will in opening the filter mouth.

As for the muffler drill, I would consider this a good idea. It should open up some deep tone without affecting bike function. And, as you said, it's reversible.

I will warn you against drilling or punching the baffle that is down inside the muffler. I, on a curious afternoon filled with stupidity, decided to drive a punch down into my muffler and open up a louder exhaust note. THIS WAS A $600 MISTAKE. It makes the muffler sound like....well it made it sound like it had a hole in it. I was so obnoxious that I shelled out the extra cash for replacement muffler.
Bottom line: If you get a whim of curiosity and decide to try it out.....DON'T.

Let us know how your experiment goes.

-Jonathan

[Jaime]

The air box isn't restrictive, but we must remove it if we want to use an universal filter. You can check this removing just the filter and running a bit; you'll get the same unusable bike than also removing the air box.

So, modifying the original filter is a good option too and requires fewer tweaks, but maybe you'll get better results with the full mod and it'll be more expensive if you want to undo the changes (original filters are quite expensive).

[Easy Rider]

Originally Posted by jonathan180iq

My first experience, which was not a mistake, was to rotate the air filter housing 90degrees, as you have mentioned. I couldn't detect any noticeable change. Now, granted, I didn't go to lengths that you will in opening the filter mouth.

Let us know how your experiment goes.

Yep, will do. Looks like it won't be done as soon as I hoped.
Too hot and humid here to do much of anything right now.

I'm really content with stock performance with the 16T sprocket..........until I hit that wall at the top end. That's all I really want to do is get just a tad bit more on the highway in top gear. I figure that's the only place that rotating the air scoop would make any difference anyway; a ram-air effect. Might not even do that since it's behind a cover.

Thanks for the advise!

[Jaime]

Originally Posted by Easy Rider

I figure that's the only place that rotating the air scoop would make any difference anyway; a ram-air effect. Might not even do that since it's behind a cover.

The "ram-air effect" is achieved at very high speeds throughout a well designed ram-air system.
Let's compare it to the stock ram-air system of a sports bike like Kawasaki Ninja ZX-10R that boosts power from 128.7kW to 135.3kW. It's about a 5% increase. We could get the same 5% in our GZ250s (from 15.1kW to 15.87kW; such tiny increase) at a speed that we'll never reach (around 150 mph) and considering that our design is good.

Conclusion, you'll get an improve only if the original design causes turbulences and rotating the filter eliminates them, but not because of the ram-air thing...

[Easy Rider]

Originally Posted by Jaime

Conclusion, you'll get an improve only if the original design causes turbulences and rotating the filter eliminates them, but not because of the ram-air thing...

Very likely that you are 100% correct.

I think, however, that my chances at a (significant) improvement doing that are just about as good as removing the air box to install a marginally less restrictive filter !!