2003 wr 450 hard to start hot


11 replies to this topic
  • mtahoe

Posted August 05, 2012 - 08:42 PM

#1

Bikes starts up ok cold then when i run it or it stalls ist hell to start again jets are stock at 6000 feet any thoughts??

  • Bandit9

Posted August 05, 2012 - 08:56 PM

#2

You using the Hot Start lever?

  • AKmud

Posted August 05, 2012 - 09:28 PM

#3

You using the Hot Start lever?


+1, it's a must.

  • mtahoe

Posted August 05, 2012 - 09:50 PM

#4

Yes i am that why its so frustrating. Which starter jet makes it easier, its a 65 now..lower

  • MANIAC998

Posted August 06, 2012 - 03:28 AM

#5

Valve clearances? If a bike is hard to start hot, then usually the valve clearances are tight.
Maniac

  • mtahoe

Posted August 06, 2012 - 07:25 AM

#6

i'll check again, but seemed to be in spec.. thx

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • William1

Posted August 06, 2012 - 10:09 AM

#7

The #65 jet you mention only functions when the choke is opened. Hot Start works by adding air. Most common reason for poor hot starting is too rich on the fuel screw/too large a pilot. Not valves. Valves are only a issue on cold start as they have LESS clearence when cold.


Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm, but go by the spec in your manual.

  • MANIAC998

Posted August 06, 2012 - 02:53 PM

#8

The #65 jet you mention only functions when the choke is opened. Hot Start works by adding air. Most common reason for poor hot starting is too rich on the fuel screw/too large a pilot. Not valves. Valves are only a issue on cold start as they have LESS clearence when cold.


Wrong!! Valves don't have less clearance when cold!
Maniac

  • William1

Posted August 06, 2012 - 04:51 PM

#9

Wrong!! Valves don't have less clearance when cold!
Maniac

Here is a reposnse to the PM you sent me for everyone;'s benefit.:

Valves do have less clearances when the engine is cold. for example, A engine with receding valves can have zero clearance when cold, hence them being so hard to start yet when they heat up (the alloy of the head expands more than the alloy of the valve stem) the clearances increase and the engine can be kick hot started.
When checking clearances, all that matters is what numerical value is used. For example, a engine with .010" cold might have .015 hot. Which is easier and more consistent to check? A cold engine. So if the clearance ideally is .015" hot, Yamaha (and more manufacturers) let the engine cool down, then they checked the cold numbers and that is what they have us use. It is only in cases where rocker arms or there are 'odd' valve geometry involved where a hot check is done.
I came up with 'this stuff' work for the factory.
Will



  • MANIAC998

Posted August 06, 2012 - 05:44 PM

#10

Well, I guess I'll have to find out for myself. I need to check my valve clearances anyhow, so I'll check them cold and then check them again after they are good and warmed up. Have no fear, I'll post the results either way.
Maniac

  • mtahoe

Posted August 06, 2012 - 08:38 PM

#11

The #65 jet you mention only functions when the choke is opened. Hot Start works by adding air. Most common reason for poor hot starting is too rich on the fuel screw/too large a pilot. Not valves. Valves are only a issue on cold start as they have LESS clearence when cold.


Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm, but go by the spec in your manual.

This site rocks I've read for days and it was the air/ screw and a new spark plug got It firing right up again first kick, also after a good carb cleaning the the pilot was trashed.. thanks again everyone!!!!!!!!!!!!!!! Guy had wrong spark plug and would not start hot.../..

  • MANIAC998

Posted August 07, 2012 - 04:36 PM

#12

William, This is a public apology to you! You were right, and I was wrong. The valves did exactly as you said when the engine gets hot, and the valve clearance increased! I never would have thought this possible. Anyhow, I apologize for my ignorance! Thank you Sir!!!
Maniac




 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.