03 Yz450f won't start-experienced mechanic lost!



26 replies to this topic
  • nstyleh250

Posted March 16, 2014 - 07:03 AM

#1

Hey guys, need some advice. Let me start by saying that I have owned this bike since 05. It has never given me a bit of trouble and I have been religous on maitinance. Last year at this time I bought a new ktm(I know I know) and this bike sat out last riding season. I started it up last fall and noticed that it was missing a bit, like it had junk in the carb. I made a mental note to clean it out this spring. Well, spring is here and I was hoping to get this cleaned up and sold, but I can't get it running right. I have cleaned the carb, jets, everything three times, and then did it again. Gas is fresh. It starts right up with the choke on, throttle response is quick and responsive. As soon as I try to turn the choke off it dies out without me feathering the throttle. I have also noticed that when this happens I can hear air? being blown back into the tank. Sounds like big air bubbles. Anybody got any ideas on what to check? I'm at a loss and may have to resort to taking this to a dealer to get serviced. 



  • grayracer513

Posted March 16, 2014 - 08:46 AM

#2

Classic clogged pilot jet. The jet might look clean, but the symptoms are saying otherwise.

Read the piece in the Common Threads pinned topic about cleaning carb passages. An almost completely invisible film of dried fuel can make the jet effectively 4-5 sizes smaller than it really is.

Also check the condition of the O-ring on the pilot screw. Could be split.

  • lkeffersyz

Posted March 16, 2014 - 10:02 AM

#3

Classic clogged pilot jet. The jet might look clean, but the symptoms are saying otherwise.

Read the piece in the Common Threads pinned topic about cleaning carb passages. An almost completely invisible film of dried fuel can make the jet effectively 4-5 sizes smaller than it really is.

Also check the condition of the O-ring on the pilot screw. Could be split.

yeah the only true way to clean jets is acid bathing. Your better off getting some bigger jets that aren't used! It makes a world of difference


~Yz426F&Crf250R~

  • lkeffersyz

Posted March 16, 2014 - 10:06 AM

#4

Or your breather tubes could be clogged and its putting pressure into the fuel line. When it comes to carburetors it can be a large # of problems. Just takes practice and experience to diagnose problems on carberator or intake.


~Yz426F&Crf250R~

  • f150jokerstyle

Posted March 16, 2014 - 02:30 PM

#5

Make sure the slide cut out is not installed upside down if you had the slide out. Been there done that...



  • grayracer513

Posted March 16, 2014 - 08:53 PM

#6

yeah the only true way to clean jets is acid bathing. Your better off getting some bigger jets that aren't used! It makes a world of difference
 

 

Explain to me why using the correct sized drill won't clean a jet.  Then explain how putting in a bigger jet is a good fix for a plugged one that's the right size.



  • lkeffersyz

Posted March 18, 2014 - 04:12 AM

#7

Because when you drill them some metal rounds off and blocks the jet ports. I've compared a drilled jet to a aftermarket and aftermarket has much better reaction to throttle

  • grayracer513

Posted March 18, 2014 - 07:02 AM

#8

I'm not talking about drilling them larger, I'm talking about using a drill the same size as the jet to clear the dried film from it, something I have done dozens of times with no problem (including at least 3 times to my current pilot jet).

 

Now, why is a bigger jet supposed to cure anything when the original is the right size? 



  • lkeffersyz

Posted March 18, 2014 - 12:36 PM

#9

Well if you meant drill one I meant get a bigger if your drilling to clean that's fine

  • travisn

Posted March 19, 2014 - 12:23 PM

#10

yeah the only true way to clean jets is acid bathing. Your better off getting some bigger jets that aren't used! It makes a world of difference


~Yz426F&Crf250R~

 

No way, just soak in pine sol for a couple days. I do it to every bike I work on/buy. 



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  • lkeffersyz

Posted March 19, 2014 - 02:45 PM

#11

Good idea never tried it. I have my own acid bath so its easier for me haha.

  • NitrousR1

Posted March 20, 2014 - 02:59 AM

#12

I'm not talking about drilling them larger, I'm talking about using a drill the same size as the jet to clear the dried film from it, something I have done dozens of times with no problem (including at least 3 times to my current pilot jet).

Now, why is a bigger jet supposed to cure anything when the original is the right size?

You can get OEM Keihin pilot and main jets for $1.50. I'd rather replace them instead of trying to drill out a invisible film. Anytime you try to drill a fixed orfice you run the risk of enlarging the jet. Creating a new problem instead of fixing one

  • lkeffersyz

Posted March 20, 2014 - 06:46 AM

#13

You can get OEM Keihin pilot and main jets for $1.50. I'd rather replace them instead of trying to drill out a invisible film. Anytime you try to drill a fixed orfice you run the risk of enlarging the jet. Creating a new problem instead of fixing one

see its bettr to just replace little things. I mean what's 5$ gonna hurt a bottle of pine sol costs more than a jet

  • grayracer513

Posted March 20, 2014 - 06:47 AM

#14

It's never been a problem.  In the first place, I don't "drill" anything with the drill.  I just push it through the orifice.  The size of the jet orifice is right on the jet with Keihins, so there's no mystery beyond converting metric to English.  A number 45 pilot is .45 mm (0.0177").  How much do you think I'll enlarge it by pushing a number 78 (.016") drill through it?  I have in fact, simply pushed a 77 (.018") drill through a #45 jet on more than one occasion; no problem. 

 

The only problem you can run into is if you do actually try to drill your own jets, and it does have anything to do with metal chips balling up somewhere, either.  The way the orifice is "crowned" (the very slight chamfering at the ends of it) can make a 5-10% difference in actual flow under dynamic circumstances, but we aren't doing that here. 

 

New jets are all very well until you need one and you don't happen to live 2 miles form the nearest dealer, or he doesn't have one, or it's 8:00 o'clock at night before a ride, or whatever else. 



  • NitrousR1

Posted March 20, 2014 - 11:25 AM

#15

Preparation or a assortment of jets can solve that. Besides anyone in this industry professionally should have a Keihin master kit anyways.
I just don't see running a drill with a slightly smaller bit to save $1.50.

  • grayracer513

Posted March 20, 2014 - 11:54 AM

#16

So that leaves the 99% who aren't in the trade professionally with what?

 

And who in his right mind would use a drill motor on a jet in the first place? Even if you did want to drill it out larger?  Do you swat flies with a shotgun? Drills that small are supposed to be used in a pin vise or by hand.  Unbelievable. The "Don't fix anything, just replace it" mentality drives me nuts. 



  • f150jokerstyle

Posted March 20, 2014 - 12:22 PM

#17

So that leaves the 99% who aren't in the trade professionally with what?

And who in his right mind would use a drill motor on a jet in the first place? Even if you did want to drill it out larger?  Do you swat flies with a shotgun? Drills that small are supposed to be used in a pin vise or by hand. Unbelievable. The "Don't fix anything, just replace it" mentality drives me nuts.


Regarding the last sentence, that is the only way anyone is taught any more. Pretty sad to say the least. I'm 27 and their are guys twice my age that I work with that truly do not know how to "fix" anything.



  • travisn

Posted March 20, 2014 - 01:08 PM

#18

dunking a carb in pine sol does more than open the jets, it removes tarnish and gunk from all surfaces and passages. cant really get a drill bit around a corner



  • grayracer513

Posted March 20, 2014 - 02:23 PM

#19

There are no corners in a pilot jet, and I've never seen Pine-Sol open a clogged one, ever.  Besides, why would I soak a jet for what, 3-4 hours to do something I can do in less than a minute with a pin vise?



  • travisn

Posted March 20, 2014 - 03:10 PM

#20

I'm talking about the carb as a whole. Jets, yes obviously clean those with a drill bit or torch tip cleaner, but if a bikes been sitting for any amount of time a good day or two soak does wonders. 







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