02 250 starts and then sputters out

[Demon49]

I got a 02 gz in November. It had a rare miss to it but I didn't think anything about it. I rode it for about 65 miles and it sit for about a week in the cold. I rode it a few more times until it ran out of gas. I didn't know that your supposed to use 91 so I only put in 87. I ran it for a few days and it started dying on me after about a mile. I let it sit for about 6 to 8 weeks during the cold. I got it back out when it got warm enough. Now on first start I can ride about a mile then it sputters and dies and won't start back again for several hours. I've changed the spark plug and drained the gas and put fresh 91 in it with carb cleaner. It still doesn't run after warming up. What could be the problem?

[alantf]

These bikes are designed to run on the cheapest petrol in the remotest asian countries, so you were ok with the fuel.The carb is the achilles heel of the gz, so add a little carb cleaner or fuel additive every fill up.

[Axeman88]

I found the most likely malfunction on my GZ to be the vacuum valve built into the petcock.

I'd inspect the vacuum line, including fittings at both ends. Until the engine is warmed up and running reliably, it may not be producing sufficient vacuum to hold the internal valve open. I replaced the petcock on my '06 because it was unreliable.

[Demon49]

Ok, I was thinking it was running out of fuel cause the bowl wasn't filling up fast enough. That's what a bad vacuum would do right? I checked around and wasn't able to find a oem petcock. I found what ebay has and they don't look the same. My question is where to get a reasonably priced replacement? Thank you

[Demon49]

Would this be the oem?

[Vegas Street Rider]

Partzilla shows a part number of 44300-12F00. The one you show would probably work too.

Have you considered just getting the repair kit for the petcock? It would save you some coin and they are pretty easy to replace.

Also, be sure to check the vacuum hose on the back of the petcock that goes to the carb. If it is cracked or loose, you would get the same result.

Good luck.

[Axeman88]

Originally Posted by Demon49

Ok, I was thinking it was running out of fuel cause the bowl wasn't filling up fast enough. That's what a bad vacuum would do right? I checked around and wasn't able to find a oem petcock. I found what ebay has and they don't look the same. My question is where to get a reasonably priced replacement? Thank you

A malfunctioning vacuum petcock will block the flow of gas. My GZ has a "bypass" or "prime" position on the petcock that allows gas to flow, vacuum or no vacuum. This will allow the engine to run, but it will also fail to prevent gas leaking past a carb. float valve that might be sticking open, which could potentially flood the engine with gasoline, which isn't a good thing.

I installed a cheap, Ebay replacement on my machine. https://www.ebay.com/itm/353210593178

It wasn't identical, but it works, better than the malfunctioning OEM petcock. The nipples are at different locations than OEM, which meant I had to replace both hoses. Replacing fuel and vacuum hoses once a decade, as part of a maintenance schedule is actually a very GOOD idea and heads off them failing while you are riding.

You may not need a petcock. Another thing that can cause vacuum issues that can cause petcock issues, that can cause the engine to stall, is simply having idle set too low. GZs are supposed to be set to 1300 +/- 100 rpms. What is yours set at?

[Demon49]

It does the same thing in prime. Does that mean it's ok? I took carb spray and sprayed it all around where there's vacuum around the petcock and carb boots. It didn't do anything. I don't know what the rpms are. I'm looking for a tach I can get just to temporarily use. It idles pretty high until it warms up. Sometimes when I Rev it, it hangs and very slowly comes back down and dies. I talked to a local shop and he said it sounds like the carb needs cleaned. I've done it before on gs450 carbs but this one seems more complicated. I've got carb cleaner in the tank and fresh gas. I've took out the air cleaner and sprayed carb cleaner a few times. When I first started it, it runs better than it did when I first got it. It's just the idling. When you use the choke is it supposed to stay in the lower position or do you have to hold it down? Thanks for all your advice.

[Axeman88]

If your bike is having the same problem, dying after a mile, with the Petcock set on the "prime" position, I wouldn't think the vacuum diaphragm is the problem.

You might still have an issue with fuel supply though. Test by disconnecting the fuel line from the carburetor and let fuel run into a pickle jar with the petcock set to "prime". I don't know the design rate, but I'd expect something like a half glassful after a minute, minimum.

If the flow is restricted, it could be a few things.
- clogged fuel filter
- obstruction / kink in the fuel lines
- clogging at the screen above the petcock. Remove the petcock to access this.
- clog inside the petcock

When the engine stops, there's two tests to do.
- Open the fuel tank, listen for it "taking a breath". If the tank sucks in air, and the issue is fixed, that suggests the tank vent line is blocked. If the vent line is blocked, the issue occurs faster with a FULL tank than with one almost empty.
- If the tank doesn't suck air, open the bowl drain screw at the bottom of the carburetor and see how much fuel drains out through the drain nipple into a small container. Compare that amount with how much drained out when you did the same test while the engine was running fine. https://i.ebayimg.com/images/g/R1sAA...i/s-l1600.webp

My GZ250 does the same thing you describe with the carb being slow to react, especially when the engine is hot. I'm not sure if this is a characteristic of the Mikuni BSR32 on this engine, but I think it is typical of a CV carb on a lean running engine. My machine is running quite lean with the factory jets and equipment. I like the fuel economy, so I haven't changed it. Another thing that would cause or exacerbate this behavior is an air leak in the intake boot, or the vacuum system.

My choke lever will hold the "On" position itself.

I use one of these inexpensive inductive sensing tachometers for setting idle and general testing. With four or five wraps around a spark plug wire, these attach easily and are accurate at lower rpms. https://www.ebay.com/itm/162383022438
I don't generally ride around with it. The battery has lasted for several years, mainly just sitting around. The battery isn't supposed to be replaceable, but when it dies, I'll crack the case open and replace it anyways.

[Vegas Street Rider]

You might consider one more thing. The fuel cap is not venting and after running for a bit, a vacuum is created in the fuel tank and won't allow free flow of fuel. Just another thing to check.