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Old 11-10-2012, 10:12 PM   #1 (permalink)
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Default I'm running out of ideas! 1994 EX250 Won't idle right, hard to start, idle hangs up.

Alright, I'm desperate for help at this point, as I'm simply running out of ideas. I'll start from the beginning, and give a TL;DR at the end.

April 2012.
I, after riding dirtbikes for a few months, am passively considering buying a street bike. I buy a 94 EX250 on CL for 900 bucks, was told it needed "some carb work." it started when I was looking at it at the guy's house, but when I brought it home, it did not start. At all. Couldn't figure out the cause, I figured it'd been sitting a while and the carbs were gunked up. I was right.

I ordered rebuild kits and cleaned out the carburetors really well, but that had little effect. It started and ran, but wouldn't idle on its own, and would constantly hang up at anywhere between 2,000 and 4,000rpm. After starting and letting it warm up for a minute or two I'd take it to the end of the neighborhood and it would be almost guaranteed to stall out. I'd then have to crank it for a least 10 seconds while manipulating the throttle to get it to start again. It seemed it wasn't getting any fuel.

At this point you're probably thinking CHOKE YOU IDIOT! Yeah about that, the bike did not like being on the choke and most of the time I'd have to start it on half choke. It seemed like it was missing on the right cylinder (exhaust on that side was significantly cooler than left) when the choke was on. Idle mixture screw adjustment seemed to have no effect and adjusting the idle rpm adjustment screw would just increase the rpm at which it would hang up. This problem did get slightly better as the bike warmed up.

Summer 2012.
I go through the process of getting the bike registered, taking the MSF course, getting gear, getting stuff to get the bike roadworthy (tires, brakes), etc. I replaced the air filter, oil + filter. The bike is rideable at this point but must be constantly babied at idle or it'll die out. In addition it's a major PIA to start in the morning. I was talking about the issue to an old-timer mechanic I work with, he said it sounds like it's not getting enough fuel at idle, and to slightly drill out the pilot jets to see if that makes a difference. (Yes I know a red flag just got thrown up for all you guys, it was just supposed to be a quick diagnostic procedure to see if a lean mixture was the issue)

It made it easier to start and that's about it, so I figured I was on the right track. He also recommended I spray the outside with carb cleaner while it's running to try to find a vacuum leak. I try this but find nothing. I wonder if I've got a hose routed wrong. We also did a compression test. (forget the results, didn't know the specs at the time, I think they were in the 130 range on a cranking compression test, right cylinder was lower than left.) One more thing a friend (who had a 2007 EX250 for a while) noted was the sound of the bike. he says is "sounds like a 4-wheeler." We noticed that it looked like the baffles in the exhaust were missing. Putting hands over the exhaust outlet to try to simulate back pressure didn't change anything, so I'm confident enough to rule that out as an issue.

Fall 2012.
I feel this is as good as it's going to get and accept the issue. I feel it's a nice enough day outside and traffic's gonna be light enough that I can go for a ride into St. Louis for school. All is normal when I get there. I then have to stop and shut the bike down to talk to someone. When I am finished, the bike is abnormally hard to start. I think nothing of this, finally get it started and ride to my parking spot.

After school, I get on my bike, put on my gear, all is normal. I crank the bike. And crank the bike. And crank the bike. It's not starting. Great. I finally get it running and it's got hardly any power and will barely idle on its own (even worse than usual). I'm almost certain that it's the right cylinder again, something must have gotten clogged up. A plug wire's arcing. Something.

I'm in an automotive program so I have a space to work on the bike, instructor said I could keep it there to work on it before class and get it running. I take out the spark plugs and ground them and crank, they are sparking. I spritz the plug wires down with water and look for arcing. Nada. I take out the carbs and blow carb cleaner through the idle circuit, there was some crud in there, weird. I feel now's a good time to see about bigger pilot jets. I buy some #40s and put them in. It seems to idle a little better when cold, but other than that, doesn't behave much differently. It also backfires.

And my pathetic tale currently looks like a frustrated and idea-exhausted me sitting at a computer contemplating whether to take the bike to a shop, just sell it and buy a decent bike (there's this 600 someone at my work's selling but idk if I'm ready for a bigger bike yet, I feel like I am but don't we all after a season of riding under our belt.), or just throw my 250 off the nearest cliff. My bike's sitting disassebled at school and I'm wondering if I'll ever ride it again.

I am getting low on ideas. My knowledge of bikes is severely limited, all my knowledge lies with modern automobiles. My current areas of suspect I haven't really checked are airway restriction (I've been in the airbox replacing the air filter but didn't really check for blockage beyond the filter) Replacement spark plugs, valve timing (just wondering if that could be a cause). Valve adjustment (I'm sure the valves are out of adjustment but I'm certain they wouldn't cause THIS bad of an issue. Then again I don't know that much. I'm trying to fight the urge to fork out the money and take it to a shop. A friend of a classmate of mine runs a shop, and is very knowledgable, I'm certain he'd be able to find and fix the problem but chances are it'll cost more than the bike's worth... I just need some advice or suggestions, anything's apprecated! I tried my hardest to list everything that's relevant but I might have missed something if you have a question please ask, thanks!
TL;DR
Symptoms:
  • Doesn't want to idle on its own.
  • Hard to start
  • RPMs hang up
  • backfiring (after I put in bigger pilot jets to see if it was a lean mixture issue at idle)
  • seems lacking power and fuel economy but for a bike as old as me with 22k I'm not complaining.

Areas of suspect:
  • Valve lash
  • Exhaust baffles- one of the previous owners removed them, assumably to make the bike louder, wondering if that jacked the back pressure up
  • Vacuum leak- I did the trick of spraying carb cleaner all around the outside and I didn't get any real confirmation that there was a leak, but I should probably try it again.
  • Burned valve- I don't feel a sucking from the exhaust pipe but I'm still wondering
  • Bad rings -right (bad) cylinder is making slightly less compression than left
  • Weak spark
  • Carburetor issue that I haven't seen yet.

Thanks again and, really, ANY advice from more experienced riders or anybody who's had an issue like this would be great!
Also also also!!! I can't seem to get the airbox boots to seal over the carburetors! I doubt this has anything to do with my issue but all the messing with it in the world, pliers, screwdrivers, nothing seems to be able to get those things on!

Last edited by StickSh1ft; 11-10-2012 at 10:21 PM.
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Old 11-10-2012, 10:42 PM   #2 (permalink)
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-Take a heat gun or hair dryer to the boots on the carbs. It will make a world of difference. They NEED to be mounted correctly.

-depending on how long its been sitting, it could have fouled a plug. My old 99 250 fouled plugs when I left her sit over the winter. It will cost no more than 5 bucks to change them yourself.

-im ASSuming you put fresh gas through the tank?

-id check to make sure the petcock from your gas tank isn't clogged or gummed up.

-how old is the battery? And what voltage is it putting out while you crank the bike over?
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Old 11-11-2012, 12:35 AM   #3 (permalink)
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Quote:
Originally Posted by ZX6R>CBR View Post
-Take a heat gun or hair dryer to the boots on the carbs. It will make a world of difference. They NEED to be mounted correctly.

-depending on how long its been sitting, it could have fouled a plug. My old 99 250 fouled plugs when I left her sit over the winter. It will cost no more than 5 bucks to change them yourself.

-im ASSuming you put fresh gas through the tank?

-id check to make sure the petcock from your gas tank isn't clogged or gummed up.

-how old is the battery? And what voltage is it putting out while you crank the bike over?
Ehm... the boots from the airbox to the carburetors? That leak is before the carbs, wouldn't think it'd create an issue.

Changing the gas was the first thing I did after rebuilding the carbs

Battery was new when I bought the bike.
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Old 11-16-2012, 08:08 AM   #4 (permalink)
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Did you remove the petcock and clean the screen? OK, so lets assume the baffles have been removed and it is running a bit less back pressure, if the filter is stock and the airbox is stock then the stock jetting is fine. Maybe a little popping on decel but fine. So, I was a car guy for a long time and let me tell you you need to be so much more careful rebuilding a bike carb over a car one. Get a torch tip cleaner and dissasemble the carb and remove the jets and poke through ALL the very small orfices. It may be a good idea to find a replacement carb because something that old could just be worn inside. Did you ever sync the carbs?
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