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bike dying after running for 30 minutes

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Just had my bike rebuilt and now it runs good up to about 30 minutes and then will just totally die on me.

And will not start until it sits for about a half hour.

Also while it is running there is a strong fuel smell coming from the exhaust and it is very black and wet.

The bike guy replaced the choke flap in the carb with a new one without the flap thing hanging off it so could this have made any difference to it??

And after sitting for a half hour it will only run for a few minutes and then will die again, very fustrating.

Any ideas??

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Elaborate more. Did you have the engine rebuilt? What exactly was done? Any carb work besides the choke flap replacement, rejetting and such?

How easy is the bike to start when cold? Will it start without choke?

Are you sure you're not riding it with the choke on? Choke off is with the lever all the way down.

What is your current jetting? Stock exhaust? Any airbox mods, filter?

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I have just had the top end rebuilt again after the previous shop that did it totally stuffing it up, head bolts upside down, one head bolt threaded, piston slapping because of too much clearance and a bad hone on the head!

The guy who just redid it has a really good rep over here and he rehoned the head and put an oversize piston in her, also helicoiled the threaded head bolt.

The bike is easy to start when cold, but will not start without the choke.

It's always been a one or two kick to start bike.

The choke is definately not on because when she started to cough and die i had my hand on the lever making sure it wasn't coming on so i know thats not the problem.

i don't know what the current jetting is because i have never has any problems with the carb before so haven't looked at it.

Apart from the choke flap replacement, he said he didn't make any adjustments to the carb at all, but he did say something about hacing to bend a little tab to get it in.

I thought it may have been the air filter as he replaced it with a new oiled one and as i only ride it on the street i have never oiled mine because i remember trying it a few years ago and it ran very poorly until i put a filter with no oil in it.

I have no mods to the airbox and a stock exhaust, really the only thing i can put it down to is its got something to do with the choke flap he installed.

Maybe the carb needs to be leaned out?

Thanks for your help :-)

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The bike is easy to start when cold, but will not start without the choke.

>>>>>>>Ok, that's good.<<<<<<<<<<

Apart from the choke flap replacement, he said he didn't make any adjustments to the carb at all, but he did say something about having to bend a little tab to get it in.

>>>>>>>>I can't think of any "little tab" he would need to bend in order to install a choke plate. Unless he's talking about the tab on the outside of the carb that the choke lever interacts with when activating it.<<<<<<<<<

>>>>>>>>>

The choke plate has no effect on air/fuel ratio when it is in the off position. Since choke is only used during starting, I doubt it's the problem. <<<<<<<

I thought it may have been the air filter as he replaced it with a new oiled one and as i only ride it on the street i have never oiled mine because i remember trying it a few years ago and it ran very poorly until i put a filter with no oil in it.

>>>>>>>>I would definitely look at the filter and make sure it isn't over-oiled. Take it off and wrap it in an old rag and squeeze out/soak up any excess oil.<<<<<<<<<

Maybe the carb needs to be leaned out?

>>>>>>>>>If the carb was over jetted to make up for poor engine work/ air leaks the last time, then now, after the last job correcting all that, the carb "could" be over jetted. Hard to say without knowing jetting history from then to now? I would remove your jets and find out what they are. I would also check/set the float level.<<<<<<<<<<<

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I know this sounds crazy, but I had a bike do that once and it was the vent stopped up on the fuel tank. What happens is as the fuel leaves the tank air needs to come in to keep it from getting air locked and creating a vacuum holding the gas from the carb. At least thats how it works in the Northern Hemisphere, you guys down south have toilets that swirl the wrong way, winter when its summer, etc.

It takes about 2 seconds to check, just open the cap when it dies and see if it starts back.

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I'll check the vent on the fuel tank when i pick her back up tomorrow morning, thanks for the tip.

The mechanic seem to think it's because its running out of fuel!

How that would explain it starting back up again after sitting and cooling down i have no idea!!

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The mechanic seem to think it's because its running out of fuel!

How that would explain it starting back up again after sitting and cooling down i have no idea!!

If the fuel tank cap doesn't vent, as fuel is drawn out of the tank while you ride, a vacuum is created in the tank. Eventually the vacuum in the tank overcomes the gravity feed to the carb and the bowl runs out of fuel, the bike dies. As it sets for a while and the vacuum in the tank bleeds off, tank equalizes with atmospheric, flow to the carb is restored.

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I think the "choke plate with the flap thing hanging off" is just a good description of the stock choke plate... heard lots of stories of this little flap falling off and destroying good engines. And although a tank vacuum could hold fuel back from the carb and cause the bike to die, there will very likely be some sputtering and lurching before it dies outright. And it does not explain the black wet exhaust.

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Well i have just got her back again and she has got a full tank of fuel, and maybe im a sucker for punishment but im going to take her to work again today and see what happens!

I'm pretty sure it's not from the gas tank not venting as when i was there i mentioned it to him and it's not obstructed at all, as in you can blow air through it.

As for the black wet exhaust he said it's from the motor blowing up last time and theres a lot of oil in there still.

Not sure whether i agree with that though, because after i got to work the other day on her the exhaust was pretty dry, and it wasn't until after the bike died on the way home which was only about 5 kilometres up the road and i checked her and then it was very definitely wet and black then!

Maybe i should splurge and get a pumper carb!

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What exhaust are you running? Is it the type that takes a packing and is replaceable?

If so, I agree with the mech. If the packing is soaked, exhaust pressure will force oil out of the packing, and work its way towards the exhaust exit.

You haven't said yet what year and model bike we're talking about.

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Sorry mate, its a 2001 xr400, and she still has the stock exhaust on her but with the baffle removed.

well i will know 100% for sure whether it's a running out of fuel in the tank issue or not as its a 80 kilometer round trip to my work, she has a full tank and i always got around 185 kilometres before i ever had to go onto reserve.

Another thing that makes me think its not due to running low like he thinks is on sunday when i had to get my housemate to bring me some fuel is i put 5 litres into her then i reset the odo and i only got 55 ks until she died, maybe shes running so rich that the fuels not getting burned and is coming out the exhaust.

So i possible may need to adjust the mixture, but not sure how to do that.

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"running out of fuel" and "running out of fuel" can be 2 different things. Huh?

You may have fuel in your tank but not in the carb. Confused yet? What they are trying to explain is that you have effectively 2 fuel tanks....well not actually tanks but your carburetor has a bowl that fills up. Something may be interrupting the flow to the bowl and causing the bike to die. I had several 2 smoke outboards that would die because the tank wasn't vented. This may be your problem. Not as eloquent as Trailryder or Kendunn.

I am still interested in the sparky thingy. What does it look like? Black? White and melty looking or tan? Pretty easy to get a peek at the plug.

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He replaced the plug after the first time it happened and he said that it looked fine, i didn't get a look at it myself.

What i'll do if it starts to die on me again today is to take the fuel cap off straight away and if it still dies then i will have ruled out the venting problem, yes?

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Another thing that you might want to rule out is the ignition coil. Some times when a bike has a bad coil, it will run fine until heat from the engine starts building up and then makes a coil fizzle out. Some things like a crack in the molded part/etc... If the fuel issue just leads to dead ends, start with some ohm readings on some of the ignition components. Could also just be a bad ground or something to that effect.

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Ok thanks for the heads up on that mate, they are not too expensive if i want to replace it.

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Another thing that you might want to rule out is the ignition coil.

I agree.

While we're still ruling out the carb, Are you running an in-line fuel filter between the petcock and carb?

Check the carb vent lines that come off the carb and hang down below the frame. Make sure they're not kinked or clogged.

As for electrical, check wiring connectors and grounds for tightness and coorosion.

Make sure the spark plug boot is secure/not loose on the end of the coil wire.

What spark plug are you running?

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Well after filling her up today and going to work and back again which is about 80 kilometres, it hasn't happened again.

If it really was just running out of fuel i'm gonna feel like such an idiot haha, but in a way it will also be a big relief as well.

In one of my posts i said i put 5 litres in her, better make that i THINK i did, my housemate cant remember how much she actually put in there, bugger :-)

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If the fuel tank cap doesn't vent, as fuel is drawn out of the tank while you ride, a vacuum is created in the tank. Eventually the vacuum in the tank overcomes the gravity feed to the carb and the bowl runs out of fuel, the bike dies. As it sets for a while and the vacuum in the tank bleeds off, tank equalizes with atmospheric, flow to the carb is restored.

What do you think the hose is for on top of the tank cap? Believe me, if it doesn't vent it won't run. I was riding down a connector road one day and the bike seemed to run out of gas. Check to make sure the gas was on, opened the cap and heard this loud sucking sound. Fired right back up and a few minutes later did the same thing. Had a plugged vent hose.

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Ok it's official i'm a dumbass it was just running outta fuel, good thing is after beiung rebuilt by this guy is that he's done it properly and shes sounding really good :-)

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