New bike owner, first post (main jet question)

Ooates · 10-07-2019, 09:31 PM

Hi there, I just bought a 2007 GZ250 about a week ago as my first bike, super excited to get into this hobby.

The couple I bought it from just had the carbs cleaned and rebuilt (they provided the receipt). The bike runs good, only 7k miles on it.

I bought this bike as a learner to get my feet wet and I know they’re not meant to be speed demons by any stretch, but I’m have trouble getting it to 50mph (I’m 6’1 180). And I know that’s too slow. At about 45 to 50mph when I’m at full throttle I’m getting hesitation/bogging. Not crazy amount, but I feel as if it’s something to do with the mixture being too lean.

So with my limited amount of mechanical know how I tore into the bike to try to diagnose the problem. First thing, front caliper was seized up. So I’m replacing those and that should help with some extra mph. The main thing I saw was a new K&N air filter put on by the guy who rebuilt the carb. Called the guy, he said they didn’t rejet the carbs after cleaning so it’s definitely running lean and he suggested I put the factory airbox back on.

From what I’ve read on here, putting those air boxes on can be a pain in the butt, and if I can get some extra power out of rejetting the carbs I feel as though I should buckle down and learn how to do it.

Any suggestions on what path I should take? The airbox was $180 and I bet if I took the bike in it’d only take a guy 2ish hours to rejet it and it’d be the same price. Or should I do it myself?

(I’m also planning on gearing up to give myself some more top end speed)

Vegas Street Rider · 10-09-2019, 04:17 PM

Gearing up is easy. Just go with the 16 tooth front sprocket. If this is a learner bike, I would go back to the original airbox, then trade up to a bigger bike when you are ready. It's your choice though. Good luck.

Donald McPherson · 10-12-2019, 06:48 AM

In the UK the GZ is only 125cc and I can push mine to 60mph on the level. You should be able to find a original airbox on Fleabay somewhere. I would also check the tappets. Don't mess with the sprockets till you get the carb sorted.

Ooates · 10-12-2019, 01:12 PM

So you suggest putting in the original airbox?

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Donald McPherson · 10-15-2019, 04:14 PM

That would be a big YES

Ooates · 10-15-2019, 07:24 PM

Thanks Donald!

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10-07-2019, 09:31 PM	#1
Ooates Junior Member Join Date: Oct 2019 Posts: 3	New bike owner, first post (main jet question) Hi there, I just bought a 2007 GZ250 about a week ago as my first bike, super excited to get into this hobby. The couple I bought it from just had the carbs cleaned and rebuilt (they provided the receipt). The bike runs good, only 7k miles on it. I bought this bike as a learner to get my feet wet and I know they’re not meant to be speed demons by any stretch, but I’m have trouble getting it to 50mph (I’m 6’1 180). And I know that’s too slow. At about 45 to 50mph when I’m at full throttle I’m getting hesitation/bogging. Not crazy amount, but I feel as if it’s something to do with the mixture being too lean. So with my limited amount of mechanical know how I tore into the bike to try to diagnose the problem. First thing, front caliper was seized up. So I’m replacing those and that should help with some extra mph. The main thing I saw was a new K&N air filter put on by the guy who rebuilt the carb. Called the guy, he said they didn’t rejet the carbs after cleaning so it’s definitely running lean and he suggested I put the factory airbox back on. From what I’ve read on here, putting those air boxes on can be a pain in the butt, and if I can get some extra power out of rejetting the carbs I feel as though I should buckle down and learn how to do it. Any suggestions on what path I should take? The airbox was $180 and I bet if I took the bike in it’d only take a guy 2ish hours to rejet it and it’d be the same price. Or should I do it myself? (I’m also planning on gearing up to give myself some more top end speed) Login or Register to Remove Ads
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10-12-2019, 06:48 AM	#3
Donald McPherson Member Join Date: Aug 2018 Location: Aberdeen Scotland Posts: 47	In the UK the GZ is only 125cc and I can push mine to 60mph on the level. You should be able to find a original airbox on Fleabay somewhere. I would also check the tappets. Don't mess with the sprockets till you get the carb sorted. Login or Register to Remove Ads Last edited by Donald McPherson; 10-12-2019 at 06:51 AM.
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10-15-2019, 04:14 PM	#5
Donald McPherson Member Join Date: Aug 2018 Location: Aberdeen Scotland Posts: 47	That would be a big YES Login or Register to Remove Ads
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10-09-2019, 04:17 PM	#2
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,089	Gearing up is easy. Just go with the 16 tooth front sprocket. If this is a learner bike, I would go back to the original airbox, then trade up to a bigger bike when you are ready. It's your choice though. Good luck.
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10-12-2019, 01:12 PM	#4
Ooates Junior Member Join Date: Oct 2019 Posts: 3	So you suggest putting in the original airbox? Sent from my iPhone using Tapatalk
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10-15-2019, 07:24 PM	#6
Ooates Junior Member Join Date: Oct 2019 Posts: 3	Thanks Donald! Sent from my iPhone using Tapatalk
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