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]

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/R1sAAOSwQ0ZjRb2i/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.

[Demon49]

I'll get one of those tachs asap and check. I've drained the tank with the petcock set to "prime" and it flowed great. It did have a slight kink in the fuel line coming from petcock to fuel filter, I got it out and replaced the line. The fuel filter looks good, but I guess that doesn't really mean much. Do I really need a fuel filter? It didn't come factory with one did it? I'll try draining the carb before I ride and after it cuts off and see if it's the same amount. My choke won't stay in the "on" position by itself, I have to hold it the whole time. Is that a problem? I've tried removing the gas cap and riding and it does nothing, it still dies. I'm gonna go ahead and rebuild the petcock just in case. How long does it take generally for a 02 gz250 to warm up? I'll check the bikes coil before ride and after but I don't know if it's getting to full temp in that short time. Would that matter? Thanks you all very much for your advice!!!

[Vegas Street Rider]

You mentioned you have to hold the choke to "On" the whole time. Are you releasing it once the bike has run for a minute or two? Once it warms up a bit, the choke should be fully off.

I don't know the quality of the fuel you buy, but 87 octane is all you need for fuel. Unless you are buying your fuel from some fly by night place, I would eliminate the fuel filter all together. I have run mine for close to 36K miles without issue. I add Seafoam to the fuel about every 3 to 4 tank fulls and the carb jets stay very clean.

[Demon49]

I don't have to use choke to start it. I was just mentioning it just in case it was a problem. I'm gonna take the fuel filter out I think. I got carb cleaner in it now.

[Axeman88]

How long does it take generally for a 02 gz250 to warm up? I'll check the bikes coil before ride and after but I don't know if it's getting to full temp in that short time. Would that matter? Thanks you all very much for your advice!!!
My '06 GZ250 needs full choke to start in ambient temps below around 50F, and even in the hottest part of the summer, it seems to want 1/2 choke for start up. It warms up in less than 2 miles of traveling, a couple of minutes, but if I take the choke off too soon, it will stall. With the friction in my lever, I can set it to various intermediate choke positions, and I'll ease it off a bit at a time until I've traveled to certain waypoints that I know from experience it should be fully warmed up by. In a warmer environment, less choke might be required.

You might want to investigate the choke lever mechanism to see if there is some sort of friction adjustment.

[Demon49]

Ok, I'll check into that asap. If I can't get it running myself in the next couple weeks I'm gonna take it to a shop to fix or sale it. I'm aggravated with it to the point I'm about done with it. I love riding and have been for awhile. I don't care much for the bike anyways, it's way to small for me but it would be perfect for my gf to ride. She went and took a motorcycle safety class to learn more than I could teach her, she got her license and the bike immediately quit running well.

[Demon49]

Ok so, I been riding it and just tinkering with the idle. It's running better, I can get about 4 to 6 miles now before it sputters and dies. It idles high the whole time and I can't get it to come down now. I'm gonna order that tach today and I ordered a petcock rebuild kit from partsgiant.com. I'm starting to have some hope, but let's see how this kit makes it run then we will go from there. Also I was wondering about the choke, how can I tell if it's stuck open and that's my problem? Thanks

[Axeman88]

I was wondering about the choke, how can I tell if it's stuck open and that's my problem? Thanks

Usually, it's pretty obvious it an enrichment device (choke) on a single cylinder engine is working or not. The engine runs and sounds differently with it engaged and disengaged.

If I wanted to verify operation, I'd carefully disconnect the nipple that attaches the enrichment feature and make sure that the spring loaded slug was retracting and advancing when I worked the lever on the handlebar. It's spring loaded and the spring needs to overcome any friction in the sheathed cable that connects it to the lever. The cable should be lubricated periodically anyway, so I'd certainly do that while I had it disconnected.

The enrichment feature is shown disassembled in this picture and is directly above part #9
http://www.carburetors.com.ua/index.php?route=product/product&product_id=35

This is actually a larger BSR type in the image, our GZs have Mikuni BSR32 installed by the factory.

[Demon49]

Ok, thank you for the info. I've never had to use the choke to start the bike. I been looking at cable lubes and lubers but I haven't figured out which is the best for the choke. I doubt it's ever been done to any of the cables. I'll check the choke and see if its operating right. The only reason I ask is because when I try to use the choke it doesn't make any difference and I have to hold it where I'm trying to use it. I got my petcock rebuild kit and been wanting to do it but it's been raining and I don't have a dry place to work on it. I'll get it done and let everybody know how it's doing. My gf is getting excited that it's running better than before and says thanks for the advice.

[Axeman88]

I been looking at cable lubes and lubers but I haven't figured out which is the best for the choke.

All that is needed is a baggie, a rubber band, and a half teaspoon of light machine oil. Unfasten the lever end of the cable and arrange it so gravity encourages the oil to creep down through the cable overnight, per the linked image. Every cable needs occasional lubrication.
https://www.boatus.com/-/media/images/boatus/article-others/2013/october/control-cables.ashx

Avoid soaking plastic parts in oil.

[Demon49]

Ok I got the petcock rebuilt and it's not leaking. I installed it and rode it for a bit it rode fine for a few minutes then when I stopped and went to go it bogs down some then picks back up. Overall it's running worse now. The idling is getting higher somehow by itself and I had to cut it off cause it was so high I was afraid it would damage the engine. Still haven't got my tach yet, yall know some people on ebay aren't in any hurry. I'm at my wits end, I don't understand how a bike went from running good to barely running with nothing happening to the bike. Any help would be appreciated. Thanks in advance

[Wijohn]

IMO: I am far from an expert, I have only worked on carbs once my whole life. But I am thinking that when you commented that the bike is dying when you come to a stop that maybe you have a pilot jet in the carb that is getting plugged up. If you have the service manual downloaded look for the pilot jet's location. Watch a couple videos on YouTube. Pulling the carb is not too hard to do. The pilot jet has 2 holes in the side of jet and a main hole running through it. All need to be clean. If plugged up, soak it in cleaner for a day or two before trying to clean. The only other thing I can think may be a problem is your choke cable, my bike acts the same, starts with no choke on. I haven't got around to replacing it so I can't comment on that.

[Axeman88]

I don't understand how a bike went from running good to barely running with nothing happening to the bike.
When I came in, at the start of this thread your GZ wasn't running well.

This sounds to me like a fueling issue. CV carbs have a diaphragm on a piston that runs from engine vacuum. We control the butterfly, but the main slide runs from the engine vacuum. I've seen engines with CV carbs run wild when there was an intake manifold leak on the engine side of the carburetor. Extra air coming in anywhere after the jets can have the effect of making the engine runaway. This could be the vacuum line serving the petcock, the carb mount, even the carb itself if air is leaking in somewhere.

Also, engines tend to run faster as they lean out, so fuel starvation would account for both increasing rpms and imminent dying. The prime suspect, that would be consistent with all these behaviors, is what suggested in my first post, the vacuum valve in the petcock, but there are other possibilities as well. Have you tested the petcock for functioning under vacuum? I use a hand vacuum pump for this kind of test. https://www.amazon.com/Performance-Tool-W87030-Automotive-Bleeder/dp/B013VUZ7WG/ref=sr_1_6
If one disconnects the vacuum line from the intake manifold to the petcock, and puts vacuum on it, it should HOLD that vacuum, not bleed off.

At this point, if I was you, I'd probably remove the carb, disassemble and clean it, and note the jet sizes. I'd check and set the float position to spec. I'd inspect the intake manifold for cracks and leaks, and carefully reassemble, but leave the air box and intake conduit off for a few tests. I'd try capping the vacuum nipple for the petcock and running strictly in the petcock's "prime" position, just temporarily, and always being sure to return it to "run" position when the bike is parked. When the bike was running "on the bench", I'd be peeking down the carb throat to see if the CV piston was doing its thing correctly, not hanging up or sticking. I've heard that CV carb operation can be tested by using a shop vac to suck air through them as well.

As I tested, If the engine failed at any point, I'd drain the carb. bowl into a container, and compare the resulting fluid volume to the known correct bowl fuel volume, which I'd establish early on.

A good way to find the source of an issue, is to remove as many elements as possible, then add them back in, one at a time. For example, one thing I'll do during diagnosis/testing is to run from a hanging, gravity fed auxiliary fuel tank, thus bypassing all the fuel system components, including fuel tank, filter, pump, and all the fuel lines. https://www.amazon.com/Auxiliary-Servicing-Accessories-Balancing-Carburetor/dp/B09XQVY6BL/ref=sr_1_5

If components and subsystems can be individually tested, the diagnostic/repair process gets a lot less hit or miss. One is then in a position of building up from known good building blocks, rather than trying this or that change to a complicated complete system. It's not impossible that more than one thing is wrong.