New gz250, need help!

lowbeam · 10-27-2017, 09:00 PM

I just picked up a 2004 gz250 for cheap and I am now trying to get the bike running well. When I brought the bike home it was leaking and I saw it was missing the nut holding the head and cylinder together between the exhaust pipes. I put a new nut on and tightened it up, no leak. Checked compression when it was cold and the gauge read 130psi. That number is between the limit of 115psi and normal 150psi according to a service manual I downloaded so I am not sure if that is related to the issue I am having. Also the petcock is dripping slightly in the on and prime positions, as well as the choke cable is seized. I cleaned the carb and air filter/housing out. The Spark plug looks good to me.

The bike starts right up no problem without the choke, and will idle fine but as soon as I give it some gas the engine will race and hang up and the bike will idle fast. I adjusted the idle with the white knob on the carb and it will actually still idle high without the end of the threads even cracking open the throttle. it will hunt for an idle for a long while before stumbling and dying. I am assuming there is air leaking from somewhere. I checked the rubber boot and made sure everything was tight, sprayed it with some carb cleaner and could not find any leaks. My carb only has the vacuum line and fuel line to the petcock. Should there be any other hoses connected to it?

Does anyone have any input before I take the head off and install a new headgasket? When I was cleaning the carb I noticed a small plate on the side near the choke cable but I didnt open it up because I didnt know what was in there, the diagram from the service manual says its a pilot air jet. Anyone want to shed some light on that for me?

Another thing I havent checked is the valves. Could that be part of the problem? I will be doing that tomorrow.

Vegas Street Rider · 10-28-2017, 01:47 AM

Some or all of your idle problem could be your petcock. Mine was leaking through and caused my idle to rev and stay there until I put a load on it. At other times it would stall out. After rebuilding the petcock, everything was back to normal. I would start with that to begin with and see how it runs.

lowbeam · 10-29-2017, 08:39 PM

Ahh thank you for the response. You seem to have had the same problem I am having now. It did not occur to me there could be a leak through the petcock vacuum line but yesterday I clamped the line with some vice grips and it was running much better.

I took the petcock apart, changed the o ring and the rest of the gaskets looked okay but put it back together and it is still leaky. I took the face apart put it back together and its harder to turn after putting it back together. Not sure what happened but I ordered a petcock for an lt80 after some research on the forum rather than a rebuild kit or a new original unit because it was cheaper and on amazon so I should get it sooner. Hopefully it works well.

Also I adjusted the valves to spec but without the choke I could not get the bike to start before the battery died. Sounds like there is good compression and coughed a couple of times but would not fire up. It is unusually cold here in Tampa so I will try again tomorrow. I am looking into getting a new choke because the one I have is split. I might go for a choke button that pulls and stays open on the carb. Anyone know what I am talking about or where I can find one for the carb on the GZ? or where to find an original replacement?

Vegas Street Rider · 10-29-2017, 08:46 PM

Check out Bike Bandit for new choke cable.

lowbeam · 10-31-2017, 05:25 PM

Thanks again the new choke cable is on its way here now. I am still on the lookout for a plunger style choke to clean up the bars a little bit so if anyone knows where to get one let me know!

The new LT80/KFX80 petcock came in today, both the vacuum and fuel lines are smaller diameter than the original petcock so I put a hose clamp on the fuel line and ran a new vacuum line to it. The new petcock nipple is the same diameter as the one on the carb unlike the original where the line flares out. It is not leaking and seems to be getting plenty fuel. The lever will hit the tank so I trimmed it down to clear it. Could have probably just given the tank some massaging with a hammer.

It fired right up today first try without a jump. It is about 80 degrees here now as opposed to the 50 degrees it has been the last few days. Still seemed like it had a vacuum leak albeit it was running much better. The crankcase vent to the airbox seemed loose and was missing a clamp so I shut the bike off and tightened it with a regular hose clamp. After that I cranked the bike over for a couple minutes and it wouldn't fire up and stay running. There was some smoke coming from the front of the engine but it could just be residual or the exhaust could be leaking, I don't see gaskets between the pipes and the head but I cant tell if its leaking there from sound because the bike doesn't have a muffler so it is loud as is. Checked compression while it was warm and had 150+ psi so I will wait until the choke comes in and see if that helps.

Also looking for a new battery as I think mine is completely dead now.

Vegas Street Rider · 10-31-2017, 06:24 PM

The fact that you have no muffler on the bike will affect the way it runs. It changes the pressures and air balances in the whole system. Looks like you have some more work to do. Good luck with your project and keep us up to date.

lowbeam · 10-31-2017, 08:20 PM

Good point. I was not sure how sensitive these little bikes were to mods but apparently they are already lean from the factory and I am sure the straight through exhaust is not helping. I still haven't been able to get the bike hot and idling for more than a couple minutes or for longer than a trip around the neighborhood without it stalling. I am thinking if the choke does not help me out I am going to pull the carb, shim the needle throw in a 130 main jet and turn the idle mixture screw out half a turn and see where that gets me.

Water Warrior 2 · 11-01-2017, 08:00 AM

A plunger type choke cable is likely found at an auto parts store near you.

lowbeam · 11-04-2017, 08:14 PM

Quote:

Originally Posted by Water Warrior 2

A plunger type choke cable is likely found at an auto parts store near you.

https://www.amazon.com/Mikuni-Comple...=choke+plunger

You think this one will work or is the needle on the end of the oem plunger important? I saw some at the auto store but the cables do not have the button on the end to slide into the oem plunger how would I go about getting around that?

lowbeam · 11-04-2017, 08:26 PM

Update on the bike, I am installing a pod filter to get rid of the air box and eliminate some variables. I have a couple questions.

The mixture screw is the tall post that sticks out of the bottom of the carb on the engine side correct? It seems someone else already drilled out the plug but I see another center punched brass plug tucked down between that post and the float bowl. I am assuming there is another adjustment screw there (could be wrong), should I drill that plug out as well or just leave it?

Another thing I noticed on the top of the carb on the air and throttle side there is a hole that goes down to the float bowl (I noticed when fuel was leaking out of it after I turned the carb sideways) Is this supposed to be plugged or open?

10-27-2017, 09:00 PM	#1
lowbeam Junior Member Join Date: Oct 2017 Posts: 10	New gz250, need help! I just picked up a 2004 gz250 for cheap and I am now trying to get the bike running well. When I brought the bike home it was leaking and I saw it was missing the nut holding the head and cylinder together between the exhaust pipes. I put a new nut on and tightened it up, no leak. Checked compression when it was cold and the gauge read 130psi. That number is between the limit of 115psi and normal 150psi according to a service manual I downloaded so I am not sure if that is related to the issue I am having. Also the petcock is dripping slightly in the on and prime positions, as well as the choke cable is seized. I cleaned the carb and air filter/housing out. The Spark plug looks good to me. The bike starts right up no problem without the choke, and will idle fine but as soon as I give it some gas the engine will race and hang up and the bike will idle fast. I adjusted the idle with the white knob on the carb and it will actually still idle high without the end of the threads even cracking open the throttle. it will hunt for an idle for a long while before stumbling and dying. I am assuming there is air leaking from somewhere. I checked the rubber boot and made sure everything was tight, sprayed it with some carb cleaner and could not find any leaks. My carb only has the vacuum line and fuel line to the petcock. Should there be any other hoses connected to it? Does anyone have any input before I take the head off and install a new headgasket? When I was cleaning the carb I noticed a small plate on the side near the choke cable but I didnt open it up because I didnt know what was in there, the diagram from the service manual says its a pilot air jet. Anyone want to shed some light on that for me? Another thing I havent checked is the valves. Could that be part of the problem? I will be doing that tomorrow. Login or Register to Remove Ads Last edited by lowbeam; 10-27-2017 at 09:05 PM.
	0

10-29-2017, 08:39 PM	#3
lowbeam Junior Member Join Date: Oct 2017 Posts: 10	Ahh thank you for the response. You seem to have had the same problem I am having now. It did not occur to me there could be a leak through the petcock vacuum line but yesterday I clamped the line with some vice grips and it was running much better. I took the petcock apart, changed the o ring and the rest of the gaskets looked okay but put it back together and it is still leaky. I took the face apart put it back together and its harder to turn after putting it back together. Not sure what happened but I ordered a petcock for an lt80 after some research on the forum rather than a rebuild kit or a new original unit because it was cheaper and on amazon so I should get it sooner. Hopefully it works well. Also I adjusted the valves to spec but without the choke I could not get the bike to start before the battery died. Sounds like there is good compression and coughed a couple of times but would not fire up. It is unusually cold here in Tampa so I will try again tomorrow. I am looking into getting a new choke because the one I have is split. I might go for a choke button that pulls and stays open on the carb. Anyone know what I am talking about or where I can find one for the carb on the GZ? or where to find an original replacement? Login or Register to Remove Ads
	0

10-31-2017, 05:25 PM	#5
lowbeam Junior Member Join Date: Oct 2017 Posts: 10	Thanks again the new choke cable is on its way here now. I am still on the lookout for a plunger style choke to clean up the bars a little bit so if anyone knows where to get one let me know! The new LT80/KFX80 petcock came in today, both the vacuum and fuel lines are smaller diameter than the original petcock so I put a hose clamp on the fuel line and ran a new vacuum line to it. The new petcock nipple is the same diameter as the one on the carb unlike the original where the line flares out. It is not leaking and seems to be getting plenty fuel. The lever will hit the tank so I trimmed it down to clear it. Could have probably just given the tank some massaging with a hammer. It fired right up today first try without a jump. It is about 80 degrees here now as opposed to the 50 degrees it has been the last few days. Still seemed like it had a vacuum leak albeit it was running much better. The crankcase vent to the airbox seemed loose and was missing a clamp so I shut the bike off and tightened it with a regular hose clamp. After that I cranked the bike over for a couple minutes and it wouldn't fire up and stay running. There was some smoke coming from the front of the engine but it could just be residual or the exhaust could be leaking, I don't see gaskets between the pipes and the head but I cant tell if its leaking there from sound because the bike doesn't have a muffler so it is loud as is. Checked compression while it was warm and had 150+ psi so I will wait until the choke comes in and see if that helps. Also looking for a new battery as I think mine is completely dead now. Login or Register to Remove Ads
	0

11-04-2017, 08:26 PM	#10
lowbeam Junior Member Join Date: Oct 2017 Posts: 10	Update on the bike, I am installing a pod filter to get rid of the air box and eliminate some variables. I have a couple questions. The mixture screw is the tall post that sticks out of the bottom of the carb on the engine side correct? It seems someone else already drilled out the plug but I see another center punched brass plug tucked down between that post and the float bowl. I am assuming there is another adjustment screw there (could be wrong), should I drill that plug out as well or just leave it? Another thing I noticed on the top of the carb on the air and throttle side there is a hole that goes down to the float bowl (I noticed when fuel was leaking out of it after I turned the carb sideways) Is this supposed to be plugged or open? Last edited by lowbeam; 11-04-2017 at 08:59 PM.
	0

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10-28-2017, 01:47 AM	#2
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,108	Some or all of your idle problem could be your petcock. Mine was leaking through and caused my idle to rev and stay there until I put a load on it. At other times it would stall out. After rebuilding the petcock, everything was back to normal. I would start with that to begin with and see how it runs.
	0

10-29-2017, 08:46 PM	#4
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,108	Check out Bike Bandit for new choke cable.
	0

10-31-2017, 06:24 PM	#6
Vegas Street Rider Senior Member Join Date: May 2015 Location: Henderson, NV Posts: 1,108	The fact that you have no muffler on the bike will affect the way it runs. It changes the pressures and air balances in the whole system. Looks like you have some more work to do. Good luck with your project and keep us up to date.
	1

10-31-2017, 08:20 PM	#7
lowbeam Junior Member Join Date: Oct 2017 Posts: 10	Good point. I was not sure how sensitive these little bikes were to mods but apparently they are already lean from the factory and I am sure the straight through exhaust is not helping. I still haven't been able to get the bike hot and idling for more than a couple minutes or for longer than a trip around the neighborhood without it stalling. I am thinking if the choke does not help me out I am going to pull the carb, shim the needle throw in a 130 main jet and turn the idle mixture screw out half a turn and see where that gets me.
	0

11-01-2017, 08:00 AM	#8
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	A plunger type choke cable is likely found at an auto parts store near you.
	0