GZ250 fuel issue

[draser]

Pulled the carb and spray cleaned it using a thin wire in jets

When cleaning the carb(s) ensure that the passages in carb's body are clean as well - you'll need to look at the carb and figure out what passages run where then spray cleaner on one end and see if it comes out at the other end (of the passage).

But, if the bike starts easily that means the pilot jet is open, also if bike responds to choke then the choke circuit is open.

The problem seems to be when engine is fully warmed up. Do you see any black smoke coming out the pipes as engine's warming up? Do you smell gas, like engine is running rich? Are the plugs black and soothy?

If the bike starts w-out choke it's possible that mixture is too rich and it kills the engine when warmed up, but you'll see the signs - black smoke, soothy plugs, etc.

 

[bplandis]

Oil in crankcase was overfull. Solved my issue.

 

[Goofie]

Oil in crankcase was overfull. Solved my issue.

Thank you for the follow-up.

I cleaned the carb again. Checked the float needle tube and there was no screen. There was a little gunk so I cleaned it good.

I checked the petcock. It was very clean and in good working order.

Changed the plug. It was a little black, but not bad. I'll check the new plug tomorrow.
(I need to buy a shorty flathead to mess with the air/fuel needle)

Changed the oil. It wasn't bad but did smell a little like gas.

The bike ran really good after the carb clean, new plug, new oil &filter. However, it did the "wanting to die" at idle after it warmed up. I feathered the throttle and it stayed running. I tried the idle adjustment screw. That made it rev real high and then slowly settle down to an idle and then try to die.

I didn't have the gas cap loose today. But if it stays running with throttle, I doubt it's the tank vacuun..

I'll check to see if we over filled the oil.
(I just checked the specs while typing this. We put in just shy of 2 quarts. The info I just saw says 1.5 quarts if changing the filter)
Must be over the high mark.

Hopefully draining some oil will fix the issue.

Thanks for all the info and support on this.

 

[Goofie]

When cleaning the carb(s) ensure that the passages in carb's body are clean as well - you'll need to look at the carb and figure out what passages run where then spray cleaner on one end and see if it comes out at the other end (of the passage).

But, if the bike starts easily that means the pilot jet is open, also if bike responds to choke then the choke circuit is open.

The problem seems to be when engine is fully warmed up. Do you see any black smoke coming out the pipes as engine's warming up? Do you smell gas, like engine is running rich? Are the plugs black and soothy?

If the bike starts w-out choke it's possible that mixture is too rich and it kills the engine when warmed up, but you'll see the signs - black smoke, soothy plugs, etc.

When I remove the jets to clean, I always spray out the passage ways are clean as well. That has but me in the past. An old dirt bike has a blade of grass in the passage way that I missed when trouble shooting the carb. Drove me nuts for an entire day!

Good info and tips, thank you.
No black out the exhaust. The old plug was a little black but previous owner tried to get it running before sale. Ran rich to show me the bike.

Hoping the oil is overfull and draining a little will fix it.

If not, maybe it's electrical?

 

[draser]

I did not see a mention of bowl fuel level, is it adjustable? (and adjusted correctly). The float valve and seat need to be clean and cut off fuel at set level. I normally polish the seat with a q-tip to ensure it's clean.

Do you have a "hanging idle" - revs take a while to come down, that's a sign of rich mixture. Does it improve with adjusting mixture screw or removing air filter?

Hope this helps.

 

[Goofie]

I did not see a mention of bowl fuel level, is it adjustable? (and adjusted correctly). The float valve and seat need to be clean and cut off fuel at set level. I normally polish the seat with a q-tip to ensure it's clean.

Do you have a "hanging idle" - revs take a while to come down, that's a sign of rich mixture. Does it improve with adjusting mixture screw or removing air filter?

Hope this helps.

The floats seemed to be set right. I did not test if it stopped the flow of gas. I did wipe the needle seat smooth.

There is a hanging idle. I played around with the mixture screw a little. It was out almost 4 turns. Previous owner was trying to get it running without cleaning the carb. Probably messed with the adjustment.
I screwed it in and then out 2 turns. Adjusted it to get a smooth idle. I need a better short screwdriver for that.

I forgot to try it without the air filter. The air filter did smell like gas the other day, but it was not wet.

There was a little too much oil so I corrected that. The bike runs a little better now. But the idle will still slow down and eventually die, unless I feather the throttle. The hanging idle is somewhat better but still there.

My next step is to replace the vacuum lines.
If that does not work, I will remove and inspect the boot. I sprayed carb cleaner on it while running and there was no change.

Has anyone replaced the carb with an upgrade? They look to be $40 and up. I could buy a new carb for the price of rebuild kit and diaphragm kit.
I watched a YouTube where the guy did that and it fixed his issues. He claimed the bike ran better with more power. But he is not very clear on the upgraded carb info.

It looks identical to oem but has a hand choke and an electrical throttle position sensor that is not needed.

 

[nerobro]

Did you ever get the problem solved? I just picked up a 2005 gz250 with 2700 miles. Its for my daughter to learn on.*snip*
My neighbor thinks it might be an electrical component warming up and losing connection. But the bike starts right up in 3 to 5 minutes after dieing.
If it's vapor lock, how is that fixed? I'm at a loss here.

Woof.

Don't add a fuel filter.

Most bikes will run if you address JUST ONE circuit in the carb, the pilot circuit. The only two you really need to address are the pilot screw (it's on the bottom, marked part 26 on parts diagrams) and the pilot jet. I dont' know the setting of the pilot screw, but I expect it will be 1.5 turns or 2.5 turns out. (I'm a GS head, not a GZ head)

3-5 minutes of running can be charging system, or pilot circuit. Vapor lock, is kinda not a thing on bikes. Vapor lock was the fuel boiling in fuel lines and causing havoc under the hood of the car. Starvation can happen, but that's usually limited to long runs at WOT, where there isn't enough vacuum signal to keep the petcock open.

The floats seemed to be set right. I did not test if it stopped the flow of gas. I did wipe the needle seat smooth.

There is a hanging idle. I played around with the mixture screw a little. It was out almost 4 turns. Previous owner was trying to get it running without cleaning the carb. Probably messed with the adjustment.
I screwed it in and then out 2 turns. Adjusted it to get a smooth idle. I need a better short screwdriver for that.

I forgot to try it without the air filter. The air filter did smell like gas the other day, but it was not wet.

There was a little too much oil so I corrected that. The bike runs a little better now. But the idle will still slow down and eventually die, unless I feather the throttle. The hanging idle is somewhat better but still there.

My next step is to replace the vacuum lines.
If that does not work, I will remove and inspect the boot. I sprayed carb cleaner on it while running and there was no change.

Has anyone replaced the carb with an upgrade? They look to be $40 and up. I could buy a new carb for the price of rebuild kit and diaphragm kit.
I watched a YouTube where the guy did that and it fixed his issues. He claimed the bike ran better with more power. But he is not very clear on the upgraded carb info.

It looks identical to oem but has a hand choke and an electrical throttle position sensor that is not needed.

You don't need a perfect seal with the float valve, just good enough that the carb doesn't flood while running. That's why we have vacuum petcocks. Speaking of which, the vacuum levels these bikes work at, as long as it's "there" it's going to be ok.

Your pilot screw setting is probally slightly lean. For the later carbs with the finer pilot screw threads, 2.5-2.75 seems to be the right starting point.

You're got a leaking carb boot. Most probally, it's JUST the o-ring under it, those things have a lifetime that's around 10 years, and they get glass hard in the end. Go to the local hardware store, and get a replacement o-ring, it'll be less than $1. If you want a replacement part that will last forever, you can spend $5-10 on a silicone one.. but I've never bothered.

"Other carbs" is opening a bag of worms you really, really, don't wanna open up.

Keep in mind, this is a CV carb, and it will only perform correctly when it's got the airbox on it, with the air filter in it.