300cc tuning and performance - Page 5

Vegas Street Rider · 04-29-2018, 04:08 PM

Good luck with your R&R.

Water Warrior 2 · 04-29-2018, 09:10 PM

WOW, that could have been a lot worse. We are learning by your experience how far a GZ can be pushed until parts fail or try to live in a slightly different position. Carry on.

kilo0195 · 05-31-2018, 05:34 PM

https://ibb.co/ckMXFy

Back together and running well. New piston, rings, wrist pin, and valve guide.

kilo0195 · 06-04-2018, 05:14 PM

Took it apart after 200 miles to do a good inspection and all is well and no contact. Put the timing back to 0° to be safe. A custom high comp piston would be the best route for proper valve relief and able to achieve 12/1 CR, but that's more money than it's worth. This was supposed to be a cheap build, so I'm done with everything that isn't a lot of $$$$. If anyone is buying a 300cc kit I would definitely have the jug decked .040-.045 before you install it. The one point bump in CR is well worth it and very noticeably improved low end torque around town and back highways. You can get someone to do it for $50 or less. If you go with the cam as well be sure to keep the cam timing at 0° 😁. Keep in mind I'm still running a 2.43 final drive (16t front and 39t rear) and can easily cruise 70-75mph with my wife and I both (320#). Do note if you want to carry that much weight you need to replace the rear shocks. I bought mine off Amazon for $60 the pair and as a pair have a spring rate of 1400#. Plenty of strength and has enough give even riding solo to still have a smooth ride. Definitely helps it handle better as well. With the 2.43 final drive 5th is ultimately an overdrive. 4th is good to reliably get you to 70-75 and then 5th for cruising. 5th gear cuts so much torque though that you're not accelerating very fast at any speed. Ultimately fits my riding style perfect. The bike is also light enough we can through it on the hitch carrier and bring it with us on trips. Anyways... the 300cc kit and deck job should be rather cheap, reliable, and turn the bike from 14.5 whp to 22-23 whp. Which is pretty impressive for such a cheap mod, and definitely helps on a 320# bike.

Water Warrior 2 · 06-06-2018, 09:07 PM

Sounds like you have managed to make a GZ a lot more useable without sacrificing reliability. My only suggestion would be to use a very good oil to help deal with added heat and degradation.

kilo0195 · 07-07-2018, 06:50 PM

Alas my GZ is no longer mine. I traded it for a 07 KLR 650 with 5k miles. Going to turn it into a clean looking scrambler. If anyone has any questions about a 300cc build i will pop on periodically to check though I'm pretty sure its straight forward if you just follow the advice in the thread.

Rowdyrolla · 09-21-2018, 11:00 PM

Kilo0195 - so I have read this post in its entirety. I do have a question for you. Just wanting to make sure I’m clear Bc I don’t want to blow my valves or piston. The 90-95 dr250 cam will fit and work on a stock piston and head?

I have a 2005 GZ250, current mods are as follows. Slant cut the factory exhaust behind the baffle near mounting bracket, removed air filter inlet cover on filter, jetted main and pilot jets by using a jet drill kit moving up one size from bit that would slide thru the factory hole in jet, swapped bars to coupons, adjustable levers and brake master, custom made hard tail struts and rear fender with sissy bar, 130/90 front tire to match rears width, side mount plate and taillight assy, changed front sprocket to 16t from the factory 15t and purchased a 37t sprocket for the rear from the up for a Suzuki rg250 gamma.

Parts now needed due to the way I ride. Going to install a set of Barnett’s Kevlar clutches and springs with steels, also going to perform dr250 cam swap. The biggest and most expensive part of this build is I’m going to install a gt15 turbo and 42mm flatside carb with external oil pump and oil tank.

Like you I have a fascination with the smaller bikes and love to just go balls out when it comes to proving a point when I’m told I can’t do something. Lol

kilo0195 · 12-30-2018, 05:36 PM

Sorry it's been a while... Yes a 90-95 Dr 250 has the same cam profile just make sure it's one for use without a mechanical tach.

JBaptista · 05-28-2020, 10:27 AM

So I know this thread is 3 years old and I’m about to do this myself. So hopefully I don’t run into any issues. But thank you for your informative information because this has given me a lot to think about for my build

GZ300 · 06-17-2021, 10:18 PM

With all due respect there's really not much instruction here on how to do this. Anyone can say "I built a 300 and it's faster now". No shit man. If anything this thread is a warning of what not to do because the objective is not to blow the motor up and have to do it twice. Your jetting approach is haphazard at best and there's NO WAY it's putting out max HP with anything near a 150 main jet. You must be running a CV carb with no airbox or something which is a sure way to lose power.

04-29-2018, 04:08 PM	#41
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,107	Good luck with your R&R. Login or Register to Remove Ads
	0

05-31-2018, 05:34 PM	#43
kilo0195 Member Join Date: Jul 2017 Location: Illinois Posts: 52	https://ibb.co/ckMXFy Back together and running well. New piston, rings, wrist pin, and valve guide. Login or Register to Remove Ads
	0

06-06-2018, 09:07 PM	#45
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	Sounds like you have managed to make a GZ a lot more useable without sacrificing reliability. My only suggestion would be to use a very good oil to help deal with added heat and degradation. Login or Register to Remove Ads
	0

05-28-2020, 10:27 AM	#49
JBaptista Junior Member Join Date: Apr 2020 Posts: 1	300cc kit install So I know this thread is 3 years old and I’m about to do this myself. So hopefully I don’t run into any issues. But thank you for your informative information because this has given me a lot to think about for my build
	0

04-29-2018, 09:10 PM	#42
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	WOW, that could have been a lot worse. We are learning by your experience how far a GZ can be pushed until parts fail or try to live in a slightly different position. Carry on.
	2

06-04-2018, 05:14 PM	#44
kilo0195 Member Join Date: Jul 2017 Location: Illinois Posts: 52	Took it apart after 200 miles to do a good inspection and all is well and no contact. Put the timing back to 0° to be safe. A custom high comp piston would be the best route for proper valve relief and able to achieve 12/1 CR, but that's more money than it's worth. This was supposed to be a cheap build, so I'm done with everything that isn't a lot of $$$$. If anyone is buying a 300cc kit I would definitely have the jug decked .040-.045 before you install it. The one point bump in CR is well worth it and very noticeably improved low end torque around town and back highways. You can get someone to do it for $50 or less. If you go with the cam as well be sure to keep the cam timing at 0° 😁. Keep in mind I'm still running a 2.43 final drive (16t front and 39t rear) and can easily cruise 70-75mph with my wife and I both (320#). Do note if you want to carry that much weight you need to replace the rear shocks. I bought mine off Amazon for $60 the pair and as a pair have a spring rate of 1400#. Plenty of strength and has enough give even riding solo to still have a smooth ride. Definitely helps it handle better as well. With the 2.43 final drive 5th is ultimately an overdrive. 4th is good to reliably get you to 70-75 and then 5th for cruising. 5th gear cuts so much torque though that you're not accelerating very fast at any speed. Ultimately fits my riding style perfect. The bike is also light enough we can through it on the hitch carrier and bring it with us on trips. Anyways... the 300cc kit and deck job should be rather cheap, reliable, and turn the bike from 14.5 whp to 22-23 whp. Which is pretty impressive for such a cheap mod, and definitely helps on a 320# bike.
	1

07-07-2018, 06:50 PM	#46
kilo0195 Member Join Date: Jul 2017 Location: Illinois Posts: 52	Alas my GZ is no longer mine. I traded it for a 07 KLR 650 with 5k miles. Going to turn it into a clean looking scrambler. If anyone has any questions about a 300cc build i will pop on periodically to check though I'm pretty sure its straight forward if you just follow the advice in the thread.
	0

12-30-2018, 05:36 PM	#48
kilo0195 Member Join Date: Jul 2017 Location: Illinois Posts: 52	Sorry it's been a while... Yes a 90-95 Dr 250 has the same cam profile just make sure it's one for use without a mechanical tach.
	0

06-17-2021, 10:18 PM	#50
GZ300 Junior Member Join Date: Jun 2021 Posts: 25	With all due respect there's really not much instruction here on how to do this. Anyone can say "I built a 300 and it's faster now". No shit man. If anything this thread is a warning of what not to do because the objective is not to blow the motor up and have to do it twice. Your jetting approach is haphazard at best and there's NO WAY it's putting out max HP with anything near a 150 main jet. You must be running a CV carb with no airbox or something which is a sure way to lose power.
	0