Jetting: Part 1

[jonathan180iq]

Honestyl, Bob, I didn't try to get the carb out without pulling the airbox. I have never, on any other bike, been able to pull the carbs without removing the airbox, so I didn't even try.

I'll have the filters in by Wednesday, so you guys can expect more after that.

-Jonathan

[Jaime]

Hi, I'm from Spain and I'm starting a similar project. The GZ250 is called "Marauder 250" here, and we've got a forum in Spain too: www.maraudercustom.com, successor of www.marauderos.org. I think that you got your workshop manual from there.

Related to this topic, I've purchased several main and pilot jets and a new jet needle to try it. I've already removed the air filter box (mixture becomes so lean) and I'll replace it for a "powerfilter" (our carb's mouth is 50mm diameter) and then I'll carb the bike. By the way, there's no need to remove anything to gain access to the carb and the jets.

You can view the carburettor config of my GZ250K6 in the last column of this chart, extracted from the workshop manual.


Also, the product codes of the jets are the following:
Main jet - N102.221
Pilot jet - N224.103 or VM28/486

I'll share with you my experiences as soon as I'll test the stuff.

Sorry about my English. :blush:

[Stretch]

I wish half of my students could write as clearly as you did! I hope you continue to tell us of your experiences with jetting. I am on the fence about it myself. I do have the sixteen tooth sprocket on order though -- this forum sold me on that mod!

Buena suerte!
-Bob

[jonathan180iq]

It's nice to see that we're getting some international attention here. Best of luck to Jaime with his jetting as well. I would ask that you please make a separate post, perhaps called "Jetting: PART 2", so we can have varying options and advice on jetting without confusing the reader.

Also, I appreciate your compliments about writing. It's important to speak and write as clearly as possible so that people don't have to ask a hundred questions in order to understand what it is that one is saying.

The filter that was sent to me was the wrong part number. I ordered the correct number but received a different one.
So, plans are on hold for a bit longer.

We'll get there,
Jonathan

PS: Check the How-To section for a walkthrough of changing the sprocket.

[Stretch]

I did see the guidance on the sprocket change -- in fact it was that excellent "how to" and pictoral that convinced me that even someone with two left thumbs (like me) could do it. I enjoy my daily ride too much to miss it because the poor girl is scattered all over the garage floor while I try to figure out what piece went where.

-Bob

[jonathan180iq]

HAHAHA! Or becuase you were in a hurry and knocked your bike over on the floor... :blush:

[Jaime]

I've installed the filter above, but it's nearly as restrictive as the original one, so I'm going to buy another with bigger filtrating surface. Then I'll try the jets and maybe I'll start the "Jetting: PART 2" section.

[Stretch]

Clumsy is as clumsy does Forrest...

...but it always galls me that when I reassemble something, there are always a couple of "installed spare parts" left over or a freshly bent bracket with half of one of my knuckles smeared all over it.

So my hat is always off to those of you who make it look so easy! :bow:

[Easy Rider]

Originally Posted by Jaime

I've installed the filter above, but it's nearly as restrictive as the original one, so I'm going to buy another with bigger filtrating surface. Then I'll try the jets and maybe I'll start the "Jetting: PART 2" section.

If your bike was sold new in Spain, you may be in an ENTIRELY different situation than those of us in the US and Canada. You probably have bigger jets already.

Well, I just TRIED to look it up in my service manual. Alas, I can't really tell what the carb. specs. are for Spain. It depends partly on what year model it is.

At any rate, the carb mods are only required if you open up the air intake, open up the exhaust a bit and notice a DECREASE in performance (or no change). If you notice a slight INCREASE in performance, then tinkering with the carb. is probably a waste of time.

[Jaime]

Originally Posted by Easy Rider

If your bike was sold new in Spain, you may be in an ENTIRELY different situation than those of us in the US and Canada. You probably have bigger jets already.

Well, I just TRIED to look it up in my service manual. Alas, I can't really tell what the carb. specs. are for Spain. It depends partly on what year model it is.

At any rate, the carb mods are only required if you open up the air intake, open up the exhaust a bit and notice a DECREASE in performance (or no change). If you notice a slight INCREASE in performance, then tinkering with the carb. is probably a waste of time.

I posted my jet sizes in this post's first page. I think they're very similar to yours.
About the need to recarb, replacing the original air filter makes the mixture too lean that you can't accelerate the motorbike above 1/3 throttle. That's because the original filter is as intentionally restrictive as it looks. The inner filtering surface is partially covered with plastic!