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Discussion Starter #1
Hello, I bought a 99 250 quadrunner that smoked like a fright train, I did a top end rebuild and no more smoke. But befor I did the rebuild it wouldn't idle but otherwise ran fine, I chalked it up to plug fouling out from burning oil but that's not the case anymore. You start it up with choke, take choke off after 30 sec or so and it idles beautifully for about 30 seconds then slowly bogs down and dies unless you hit the throttle. I've checked valve clearance, and bypassed the fuel pump by hooking the carb line directly to petcock and running on pri. Same issue. Also no fuel in any vacuum lines. I just went through the carb as well. No change. I'm stumped what else should I check?
 

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Did you clean the carb..? The idle circuit might be clogged or the float may be out of spec.


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I took apart and ran the carb and ran it through an ultrasonic cleaner. I didn't check the float, I just put it back on as it was. I'll check the service manual for the float spec and I'll check that later today. I'm also going to put the fuel system all back as it was to kinda start back from scratch again and I'll get back to you. Thanks!
 

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Ok so I pulled the carb again and checked the float. It was just barely under .5 in, the book says 5.1. It was very close but I adjusted regardless. And I tested it by blowing into it and it seemed to be working fine. Now here's the kicker. I put it all back together, still same problem. So then I took a funnel that fit perfectly on the inlet and by keeping my finger over the fuel line and just keeping fuel in the funnel it ran for a solid 3 min idling even if I revved it once or twice it came back to idle fine. I hook the fuel line back up..... 20 seconds and dead. And I would have to hold the throttle part open to get it to fire again. Could the fuel pump be pushing past the float needle or is there something else I should check first? I really dont want to pull the carb again for the like 4th time but I guess I am getting good at it lol
 

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Is the fuel pump pumping out fuel at all..? It should pulsate out not continuously flow out. And look at it this way. You’ll be so good at pulling and reinstalling the carb, you’ll eventually be able to do it blindfolded, lol. And installing a carb kit may not be a bad idea as well.


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Check the fuel petcocks diaphragm for wear. I ran into almost the same problem. Was a bad petcock.
 

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Discussion Starter #7
Ok so update: I ran the quad all day sunday with a full tank of fuel letting it gravity feed. Ran beautifully never stalled. Hook the vacuum back up to the pump, it dies. So I ordered a carb kit, and took the carb off AGAIN! I'm down to less the 10 min to get it off the bike lol. It actually seemed like the float sealed better so I figured this is it..... nope. I dug into where the fuel pump is and pulled the vac line off there, thinking maybe vac leak but it would idle blocking the vac there too. My next endeavor I guess would be to pull the fuel pump, I might just replace cause it's not big money but I'm running out of ideas. If I have to pull that damn carb off again it's not going back on! But I would like to exhaust all other options befor getting a new carb.
 

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440Tim brings up a good point. Have you checked the fuel petcock to see if that’s your issue..?


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When you pulled the vacuum line off the fuel pump (at fuel pump end) did any fuel come out? If the diaphragm in the fuel pump gets a hole in it it will allow fuel through the line and cause idle problems.
 

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Discussion Starter #10
So I think I have success! I was going to pull the old fuel pump and crack it open a few days ago but I ordered a new one anyway. I have been busy and have not been to the quad so the new one came in anyway. I put the new pump in and huge improvement! It did stall once or twice when I was test riding it but I'm blaming that on I was tweaking the idel adjustment. When it did stall it fired right back up where as befor I would have to give it throttle to start it again. I'll give the quad some good ride time this week and post an update. If I still have the problem I'll replace the carb.... and if I still have the problem after that I'm gonna zip the throttle and knock it in gear at top of a cliff lol
 

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If there’s no damage or cracks in the carb body. Then usually there is no need to buy a replacement. A good carb cleaning and a carb rebuild kit typically does the trick.


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Checking the petcock isn't a bad idea. Even if it's not the issue you could rule it out.

When my petcock went out there was no fuel in the vacuum line. But the diaphragm had a pinhole.

I pulled my carb a dozen times. Checked the timing and did a valve adjustment. Drove me nuts. I couldn't get it running normal.

Finally drained the fuel and checked the petcock. I rebuilt my fuel petcock. While i was at it i replaced fuel line fuel filter and vacuum lines.

New petcockis about $80 rebuild kit is about $25.
 

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Discussion Starter #13
Ok so I may have pre maturely celebrated. I ran the quad for a while s few days ago doing yard work, all seemed well the idle hesitated here and there but never stalled. Till I was going to park it in the shed and it stalled again in the shed. Back to square one, plug the pump vacuum and it would idle, put it on... stall out. Just for the sake of ruling it out I bypassed the fuel pet cock. No change. Tonight I decided to pull the carb and check the float o ring. I noticed a little bit of corrosion where the o ring sits so I tried a fatter o ring. Put all back together..... no luck. But! I discovered a new symptom. I decided to pull the spark plug to see if it was wet with fuel. Not really wet but it was black as night. So I cleaned it all off put it back in and ran it for 3 or 4 min. Took the plug out... black as night again. Is it running to rich? Kinda hard to see in the pic as and it's very light anyway. (The corrosion)
19572
 

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If your plug is black, even if it's not wet, that's a sign of a very rich condition.
The fact that you can plug the vacuum line to the fuel pump supports this. If I do that mine will die.
 

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Discussion Starter #15
I'm going to see if I can get at the air fuel adjustment screw with the carb on so I can adjust it running. Should I try and move the needle that connects to the diaphragm up or down?
 

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I'm also currently trying to get to the fuel screw without removing the carb. I can tell you for sure this DOESN'T work

I have one of these arriving today I'm going to try....
 

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Discussion Starter #20
So ignore my last post lol upon looking at mine in realize they would be to long. Did that second set work? I just pulled there carb off AGAIN and set it at 2 1/4 turns out. Seems better I think but not perfect. I also have not put much test time on it yet. Worse comes to worse does anyone know a decent replacement carb? I only see like 4 and change mikuni carb or cheap $40 ones. I dont want to cheap out but I'm also not spending 4 hundred on a 21 year old atv lol
 
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