Only runs with hotstart


12 replies to this topic
  • YoungNastyMan

Posted December 07, 2008 - 03:53 PM

#1

I'm resurrecting an '04 YZ450 from deep storage. Still has original tires with the little nubbies and paint on em, so it is really in great shape. Probably still needs a break in... I just replaced the coolant, oil+filter, plug, and pulled the carb. There was a lot of gunk in the carb obstructing the jets but I soaked it and blasted it with carbclean. I could only get the bike to start with the hotstart engaged. And once its running, it really wants to die if you release the hotstart. So I rode the bike around with the hotstart pulled and it seemed to run fine. A couple quick yanks on the throttle and it was like setting off controlled explosions around my neighborhood, craazy bike. However, when I release the hotstart the thing drops in idle rpm (i have to twist the throttle or it stalls) and seems very rich, boggy. I'm riding at sealevel and ~45 degrees F in Seattle. Stock jetting in the carb. I didn't have the chance to blow compresed air in the carb, maybe that would help?

  • BC3

Posted December 07, 2008 - 08:12 PM

#2

[COLOR="Blue"]I think your confusing the CHOKE with the HOT START...
450s have the hot start on the handle bar and the choke is on the left side of the carb....You didn't clean the pilot jet and it's running on the choke circuit...Remove the carb again and very carefully remove all the jets and run a piece of wire from a steel brush through them...Even soaking in Lacquer thinner with cut the lacquer build up from the bad gas....
Make sure you get a squirt of fuel out of the A/C nozzle when you wick the throttle...Give that stuff a try and let us know how it works ... [/COLOR]


  • YoungNastyMan

Posted December 07, 2008 - 08:56 PM

#3

[COLOR="Blue"]I think your confusing the CHOKE with the HOT START...
450s have the hot start on the handle bar and the choke is on the left side of the carb....You didn't clean the pilot jet and it's running on the choke circuit...Remove the carb again and very carefully remove all the jets and run a piece of wire from a steel brush through them...Even soaking in Lacquer thinner with cut the lacquer build up from the bad gas....
Make sure you get a squirt of fuel out of the A/C nozzle when you wick the throttle...Give that stuff a try and let us know how it works ... [/COLOR]


Thanks, and I'm sure it is the HOT START that I'm pulling to get the bike to run. (shifting was a little difficult holding the clutch with one finger and the hot start lever with the other) And when I cleaned the carburetor, I removed the pilot, the main, the needle, and gave everything a good cleaning. The pilot jet was in bad shape. Had to attach safety wire to a dremel and ream the crap out of it, literally. And the accel. pump is functioning just fine. Tonight I blew compressed air through every oriface, so I'll see if that did anything. My understanding of the HOT START is that it allows more air into the mixture, making it leaner and easier to start a hot engine. So if I need it engaged just to run the bike, that would indicate that I have to make my mixture leaner by changing the pilot jet to a #40 or turning the fuel screw in a bit. But I'm concerned because i shouldn't have to deviate much from the stock settings if its just a bit cooler outside. Especially just to get the thing to idle on its own. Or should I?

  • minton227

Posted December 10, 2008 - 09:51 AM

#4

"My understanding of the HOT START is that it allows more air into the mixture, making it leaner and easier to start a hot engine." - what you just described is the choke. Since 4-strokes have such high compression engines, the compression builds up with heat. The hot start actually opens up the exhaust valves just a little bit to release the compression from the cylinder so it will turn over easier. The hot start is usually a small "1 finger" lever located above you clutch lever.

  • craigdieselmac

Posted December 10, 2008 - 10:53 AM

#5

What he described is not the choke.. a choke does just that.. choke the motor of air thus providing more fuel in the mixture, the hotstart does just the opposite, provides more air, leaning out the mixture... minton..follow your cable, it is not a compression release, it goes to the carb

Young Nasty--You may have to lean it out more with the screw, or jet down... In my opinion your on the right track... could be wrong

  • William1

Posted December 10, 2008 - 11:03 AM

#6

Because your pilot was so full of crap, you really should of replaced it instead of reaming it out, effectively making it much larger. To compensate for all the fuel it passes now, you needed to lean it out, which is what the hot start is doing. Pony up the five bucks, get a new pilot jet.


BTW, a "choke" on nearly every motorcycle is really not a choke, rather it is an 'Enrichment' device. Instead of reducing air, it adds (enriches) fuel.

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  • William1

Posted December 10, 2008 - 11:05 AM

#7

"My understanding of the HOT START is that it allows more air into the mixture, making it leaner and easier to start a hot engine." - what you just described is the choke. Since 4-strokes have such high compression engines, the compression builds up with heat. The hot start actually opens up the exhaust valves just a little bit to release the compression from the cylinder so it will turn over easier. The hot start is usually a small "1 finger" lever located above you clutch lever.


Sorry to say, but incorrect. The hot start opens a passage way in the carb adding more air, effectively leaning the mixture. The hotter an engine is, typically less fuel is needed especially on start. The device that holds open a valve on a 4S is a decompression lever.

  • gleaves

Posted December 10, 2008 - 11:10 AM

#8

Why the blue text?

  • William1

Posted December 10, 2008 - 11:20 AM

#9

Because it matches his user name text color?:thumbsup:

  • craigdieselmac

Posted December 11, 2008 - 05:36 AM

#10

True that william.. I was wrong about the choke... different means to the same end..

  • YoungNastyMan

Posted December 11, 2008 - 10:28 AM

#11

Because your pilot was so full of crap, you really should of replaced it instead of reaming it out, effectively making it much larger. To compensate for all the fuel it passes now, you needed to lean it out, which is what the hot start is doing. Pony up the five bucks, get a new pilot jet.


Definately possible. It took a good 10min to dislodge the crust that was built up inside there. I'll be picking up a new pilot today and trying it out. Thanks for the help, and I'll update with results.

  • YoungNastyMan

Posted December 11, 2008 - 08:27 PM

#12

Replaced the pilot jet today and the bike ran great. Probably need to fine tune the jetting and fuel screw, but for the most part its great. Thanks for the advice!

  • BC3

Posted December 11, 2008 - 08:55 PM

#13

Why the blue text?



I like BLUE...My 450 is BLUE......This is a YAMAHA forum their BLUE....
And most of all it bothers people and I like that.....:thumbsup:





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