shut off at high speeds
 

I am having a issue and I would love to call on yalls wisdom.

my gz250 is stalling at high speeds(70mph ish) engine cuts off as i roll off the throttle then the bike dies . After a few minutes it starts right back up again . I bought the bike two weeks ago and I have cleaned the needles in the carburetor , changed the oil and filter.

one issue that might be related , is that when i am accelerating ill be in the power band and then loose it , then get it again .

the bike came with what I guess might be a ebay pipe that back fires and might not have a baffle.

Re: shut off at high speeds
 

ok so electronics are still working when it stalls .

and when I looked under the search someone suggested draining the air box it did have a little oily fluid but not much. and its still stalling after i let off the the gas around 70mph . also im running the bike hard when im testing it which is revealing for problems in the power-band .

Re: shut off at high speeds
 

Will it run if you don't go that fast??

Re: shut off at high speeds
 

If it has an Ebay pipe that is already backfiring, then your mixture is bad and chugging and choking at high speed could also be a symptom of that.

You may beef to up the gas flow a little with a rejet. It's really not hard at all and you can do most of the adjustments without pulling the carb or the gas tank.

Simply drilling holes in the back of your stock muffler will lean the bike out and something as simple as an unplugged breather hose can make it almost unrideable. It's a delicate balance that has to be kept and the PO slapping a universal muffler on there is most likely the cause of the problem.

EDIT: Since this only happens at high speed, close to WOT, it means your main jet is where you need to focus. I'll bank that the PO adjusted the idle mixture screw and the needle, which would take care of low speed and midrange but he probably didn't adjust the main jet.

Re: shut off at high speeds
 

thanks guys .I dont think the previous owner adjusted anything and i have problems all over the power band but mostly when im running at wide open.
i am looking into a hi-flo air filter and shimming the carb . would these be benefit or is the main jet my best bet.

JWR the bike ill run all day lond as long as i dont run at top speed WOT

Re: shut off at high speeds
 

When jetting on your own, you really need to set the main jet first. The main is what gives you the best outcome at full throttle but also has a little effect everywhere else. So, first thing to do is set the main and then adjust idle and midrange after that.

There are several posts you should look at before diving in head first.

http://faq.ninja250.org/wiki/Can_I_impr ... jet_kit%3F
(Use this resource... it's awesome. But be sure to check back here for part compatability.) The Ninja and the GZ are very different beasts.

viewtopic.php?f=8&t=15&hilit=rejetting

viewtopic.php?f=9&t=1058&hilit=jetting

viewtopic.php?f=9&t=513&hilit=jetting

viewtopic.php?f=8&t=617

Re: shut off at high speeds
 

If it acts like it is running out of gas, it could be the float bowl level??
You had the carb off...

Just a wag????

The reason I say that...after it sits a while it will go again...time for the bowl to refill???
Usually with jets or air wrong, it will run, but like crap.

Re: shut off at high speeds
 

ya i think your on to something with the running out of gas . the tank has some redneck engineering on the hoses from the tank to the carb ill take some pics

Re: shut off at high speeds
 

Pics always help.

And it's important to mention all the crazy weird stuff that POs do before asking for help. Shortens response time and lets us zero in on possible source.

http://blog.makezine.com/wood_bike.jpg

Re: shut off at high speeds
 

The hose from the tank to the carb must be straight with no bends or kinks as it is gravity fed.Any abnormal kinks or bends will cause the condition you describe.I know from having a fuel line that was too long with a bend in it.Also if you have a after market muffler you are running really lean.As stated you need to rejet.I ended up using a 132, after intake and exhaust mods.
:cool: :roll:

Re: shut off at high speeds
 

ok so I was fooling with the bike and there is a hose that run out of the front top of the bike that has a bolt in it to plug it up . i dont see where it might have gone to.

when i was looking at the fuel petcock i noticed there is no reserve , you can only turn it to off or on and the off does not work it flows at about half . so it thought maybe i had had the switch on off so i turned it to on and went for a ride , same problem died waited 10 sec and started again . it died again and this time wouldn't start i just pushed it home.

Re: shut off at high speeds
 

Pri
On
Res

These are the only markings on the petcock.

In the on position there should be no fuel coming with the motor off.

Pri lets the gas out to drain or fill the carb with gas, the floats would stop the gas from flooding or overrunning.

Res is the shorter two screen pick-up in the tank.

Does the petcock work as it should??

Re: shut off at high speeds
 

the petcock says off(left) on(bottom) and fuel(right) . it will only turn to off and on and both have flow without the engine on im going to call the PO but i think he'll be clueless

Re: shut off at high speeds
 

Your petcock should have two hoses running from it.your fuel hose,and a smaller one on the back side for vacuum that lets fuel flow when the bike is running.If this vacuum hose is not connected ,the only way you would get fuel is if the petcock is on prime.This vacuum hose must be connected and operating for the petcock to work properly.
:2tup: :)

Re: shut off at high speeds
 

thanks guys .my petcock does look like the one on bikebandit's picture but i only have one hose coming off it the main fuel hose and like i said it says off on fuel

weird sauce.

is my petcock not stock? and where does the vacuum tube go ?

Re: shut off at high speeds
 

The vacuum hose runs from the back of the petcock to vacuum port on carb.If there is not a nipple on the back of the petcock for vacuum hose,than somebody has hooked up a different petcock.Take the hose that you said is blocked off with a bolt,and unplug it with the bike running and see if it has vacuum.I'm betting that it's the hose for the back of the petcock.
:??: O_o

Re: shut off at high speeds
 

yep its sucking in air and I still cant find any place on the petcock to hook it onto

Re: shut off at high speeds
 

I guess i should buy a petcock on ebay?

Re: shut off at high speeds
 

Put GZ 250 petcock in google. it will show you one on this site.

Re: shut off at high speeds
 

ya they dont look like mine and like you said prim on res and mine is off on fuel

Re: shut off at high speeds
 

It's supposed to be on the back side of the petcock.I have a sneaky suspicion that somebody changed to a older style petcock and thats why the vacuum line is blocked off.
:cool: :)

Re: shut off at high speeds
 

thanks guys this is my petcock

http://sphotos.ak.fbcdn.net/hphotos-..._1260873_n.jpg

http://sphotos.ak.fbcdn.net/hphotos-..._2438211_n.jpg

Re: shut off at high speeds
 

If it was working right it would not make any difference. Same as running on Pri.

This the way all older bikes worked. Always turn off when stopped. to keep the floats from having to hold back the gas.

Re: shut off at high speeds
 

Well, there's your problem...

For detailed parts diagrams, and to see how stuff is supposed to go together, check out ronayers.com

http://www.ronayers.com/Fiche/TypeID/26 ... odel/GZ250

Re: shut off at high speeds
 

ouch 76 bucks and i think bike bandit was 79 ill hunt on ebay . do you guys know if there are different petcock that are interchangeable with ours

thanks JWR , Jonathan and Blane , you guys are quick

Re: shut off at high speeds
 

I don't know, but I would get the right one and remove that source of guessing.

Re: shut off at high speeds
 

I agree with JWR, find a used one in good condition if the new price scares you away. But to avoid simply recreating the same problem, use a GZ250 petcock.

Petcock's rarely go bad. Someone must have broken it or damaged a tube while taking it off and thought they needed to replace it with a universal one.

You're almost there. Keep it up.

Re: shut off at high speeds
 

hey guys i bought a petcock on ebay should be here in a week or so . I did the shim mod last night and drilled that plug i brought the screw to 2 turns counter clock wise from lock and the bike is running stronger with less flat spots . but i think reached the point where more turns to counter clock didnt seem to help and im still getting a back fire and running hot and dying .

I am going to pick up some jets . my set up is cheap loud pipe the PO put on no air box mods and now the shim and mixer screw mod. what sizes would you guys recommend i try im not looking max power just soming to stop me from running lean

Re: shut off at high speeds
 

I used a 132 main jet with after market exaust,and a Hiflo-Filtro air filter.When adjusting the idle mixture,you need to adjust to where the bike idles best,turning screw out is richer,in is lean.
:cool: :2tup:

Re: shut off at high speeds
 

thanks blane should i get a couple jets around that?

Re: shut off at high speeds
 

I would get a few from 126 to 132 to try.I probaly could have got away with a 130, as I was running a tad rich.But I would rather run a little rich than lean.
:2tup: :)

Re: shut off at high speeds
 

Running a little rich would also help cool the engine. Sounds like the 132 as suggested might be a good idea.

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so i stick in the jets and adjust the mixture screw?

Re: shut off at high speeds
 

Yes.I would start with smallest jet and work from there.As your air box and filter are stock you probably only need to go up a couple of numbers from stock.Take your time and keep notes of what jets you have changed.That way you can always look at your notes to go back one step if need be.
:2tup: :cool:

Re: shut off at high speeds
 

i got a 127.5 and the bike didnt change to much still runs well but then dies . my mech friend told me that my lack of the vacuum tube on my petcock should be a big deal but when i told him about how it was dying with the 120 and 127.5 he told me to check the flow from my petcock and he was right it flowed well for a 20 seconds and just drip drip dripped . i guess ill wait for my new petcock to arrive

Re: shut off at high speeds
 

You need your new petcock to hook up your vacuum so you can get fuel flow back to normal.The 127.5 main jet should be large enough to keep your bike from running lean.Good luck.Keep us posted with the results.
:cool: :2tup:

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Damit - this was one of the treads i might have been able to contribute to and it's already solved.
Well i'm glad you found the problem but i haven't heard of any interchangeable gz petcocks but on the other hand, i never went looking for one. If there is i'd say the dimensions would be the only issue. Also i don't know this but they might be interchangeable with the GN models which are far more common over here - just a thought - the others will be able to confirm/negate this.

vii

Re: shut off at high speeds
 

Dang - posted the reply before clicking on page 2 - please ignore previous post

Re: shut off at high speeds
 

just got the not so new petcock put it on my bike but i dropped a washer in the tank i sent like 20 min with a magnet trying to get it out , it didnt come out . but the good news is that the bike runs good I haven't adjusted the air/fuel mixture yet but it seems close as it is.

thanks to everyone who helped me

p.s. which parts do i need to order when replacing my fork seals

Re: shut off at high speeds
 

Just the fork seals & dust seals. :2tup: