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Author Topic: MXU 250 wont idle  (Read 6991 times)

Miket

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MXU 250 wont idle
« on: December 01, 2009, 02:11:16 AM »
This is a really great site! I cant believe I just found it.  I have a 250 mxu that wont idle unless the choke is fully on.  It starts backfiring through the
the intake when the choke is turned off.  I know it is running lean, but I don't know why.  I have replaced the spark plug, fuel filter, cleaned tank filter
and cleaned the jets in the carb.  I adjusted the valves to .004 (they were at .005).  The only thing I need to do is a compression check and I don't have
the correct size.  Hopefully I am just a dumby and am overlooking the obvious.  Thanks for anything you may come up with.
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Shaka

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Re: MXU 250 wont idle
« Reply #1 on: December 01, 2009, 02:28:41 AM »
I'm not familiar with your particular engine, but it sounds like you have a good start at troubleshooting.  If it running lean you may have an air leak somewhere between the carb and engine.  Are you running it with the air filter on?  That will make a huge difference!  Have you tried adjusting the air/fuel mix screw on the carb?
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Miket

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Re: MXU 250 wont idle
« Reply #2 on: December 01, 2009, 04:10:38 AM »
I do have the air filter on, but not the lid to the box- I will try that.  The intake is only about 3 inches long and I dont see any leaks.  I can try some propane
enrichment or carb clean to see if anything changes.  Thanks for helping.
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Shaka

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Re: MXU 250 wont idle
« Reply #3 on: December 01, 2009, 04:33:01 AM »
Good deal on the leak testing, that's where I would start.  Put the lid on the air box and good luck!  Post back with results.
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zombie

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Re: MXU 250 wont idle
« Reply #4 on: December 01, 2009, 06:02:49 AM »
You may also have to clean the "ports" for the idle jet. since it is backfireing it is lean. There may be a grain of sand that will not just dislodge in the port. Taking the carb completely appart, and soaking in Chem Dip for 48 hrs will help with organic build up, and a sewing needle will help get into the port. Good luck!
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Miket

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Re: MXU 250 wont idle
« Reply #5 on: December 01, 2009, 12:54:05 PM »
I will try these things and I will post back.  I hate note getting feedback from people when I try to help them.  It helps me when I know what fixed their
problems. Thanks
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axy

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Re: MXU 250 wont idle
« Reply #6 on: December 01, 2009, 01:34:04 PM »
Quote from: Miket on December 01, 2009, 02:11:16 AM
This is a really great site! I cant believe I just found it.  I have a 250 mxu that wont idle unless the choke is fully on.  It starts backfiring through the
the intake when the choke is turned off.  I know it is running lean, but I don't know why.  I have replaced the spark plug, fuel filter, cleaned tank filter
and cleaned the jets in the carb.  I adjusted the valves to .004 (they were at .005).  The only thing I need to do is a compression check and I don't have
the correct size.  Hopefully I am just a dumby and am overlooking the obvious.  Thanks for anything you may come up with.

Mr. Obvious here - did you check the idling screw? I had to adjust it once on my Beverly. It is interesting that the scoot idled just fine above 6 C, but when the temperature reached 4 C and below, it wanted to die on me. One turn to the right and everything was back to normal.
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Miket

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Re: MXU 250 wont idle
« Reply #7 on: December 04, 2009, 04:49:36 AM »
I haven't had a chance to try these things yet.  I will let you guys know
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Miket

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Re: MXU 250 wont idle
« Reply #8 on: December 14, 2009, 12:54:04 AM »
I finally had time to work on it and it appears it was a couple of clogged jets.  I had cleaned them one time and it did not help.  This time I used a
sewing needle and cleaned with carb clean.  A couple of them where a little tight around the needle before I started.  The thing runs like a champ
and I thank you all.  I am going to replace the throttle cable because the boot at the slide valve is broken.
Again, thank you very much.
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zombie

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Re: MXU 250 wont idle
« Reply #9 on: December 14, 2009, 04:03:21 AM »
Good to here! MOST people don't see the buildup that causes the problem. I have had to re-clean several carbs that I swore were clean. Ps. I use 3-M 5200 black to repair both sleeves and boots. Just don't get it on ANYTHING else. It will NEVER come off.
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axy

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Re: MXU 250 wont idle
« Reply #10 on: December 14, 2009, 10:53:09 AM »
Quote from: zombie on December 14, 2009, 04:03:21 AM
Good to here! MOST people don't see the buildup that causes the problem. I have had to re-clean several carbs that I swore were clean. Ps. I use 3-M 5200 black to repair both sleeves and boots. Just don't get it on ANYTHING else. It will NEVER come off.

Zombie, I swear you have a "liquid solution" for every potential internal combustion engine problem! :)

I have a full shelf of "liquid problem solvers" that I used maybe once, and then the canister has to be stored somewhere... ditto for paints in spray...
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zombie

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Re: MXU 250 wont idle
« Reply #11 on: December 14, 2009, 06:36:55 PM »
I am a very frugal mechanic. The name Zombie comes from the fact I have always taken a pile of "dead parts, and with as little $'s as possible bring something to life out of it. Maybe should have been Frankenstien? You should see the back room of my shop! bottles, jars, tubes... I also work with fiberglass, and epoxy resins, so if you need a body panel or a custom dash for your car, or a scratch built airplane, I'm your guy.
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"They have nothing in their whole imperial arsenal that can break the spirit of one Irishman who doesn't want to be broken."   Bobby Sands...

axy

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Re: MXU 250 wont idle
« Reply #12 on: December 15, 2009, 11:06:14 AM »
Quote from: zombie on December 14, 2009, 06:36:55 PM
I am a very frugal mechanic. The name Zombie comes from the fact I have always taken a pile of "dead parts, and with as little $'s as possible bring something to life out of it. Maybe should have been Frankenstien? You should see the back room of my shop! bottles, jars, tubes... I also work with fiberglass, and epoxy resins, so if you need a body panel or a custom dash for your car, or a scratch built airplane, I'm your guy.

:) That`s great, I always wanted to have a space for my projects too, unfortunately, I live in a small apartment so I cannot afford it right now...
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wordslinger

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Re: MXU 250 wont idle
« Reply #13 on: December 30, 2009, 02:39:31 AM »
Quote from: zombie on December 14, 2009, 06:36:55 PM
I am a very frugal mechanic. The name Zombie comes from the fact I have always taken a pile of "dead parts, and with as little $'s as possible bring something to life out of it. Maybe should have been Frankenstien? You should see the back room of my shop! bottles, jars, tubes... I also work with fiberglass, and epoxy resins, so if you need a body panel or a custom dash for your car, or a scratch built airplane, I'm your guy.

...dang...pegged you wrong...thot you were a hard core Rob Zombie fan....dang...lol...
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zombie

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Re: MXU 250 wont idle
« Reply #14 on: December 30, 2009, 03:29:41 AM »
More into The Cure, Sade', Al Green, Sonic Youth... Rob Zombie can sit in the back seat.
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"They have nothing in their whole imperial arsenal that can break the spirit of one Irishman who doesn't want to be broken."   Bobby Sands...

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