Exessive stall, and wont start when hot


38 replies to this topic
  • ttr250dude

Posted July 27, 2010 - 12:17 AM

#21

Alright. Thanks guys. Turns out im going to our warehouse tommorow to work. Hopefully i'll be able to work on my bike when i finnish and let you guys know how it goes. (we keep all of dirtbikes and whatnot at the warehouse)

  • ttr250dude

Posted August 01, 2010 - 08:38 PM

#22

So heres the story:

On friday i went to the warehouse to do packaging and what not and work on my bike. I got done around 4:40 so i decided that i would stay late after everyone left to work on my bike. Everyone was gone around 5:30. At 6:40 i got a call from a friend saying that we were gonna meet some of the guys for dinner at 7:30. I still had to go home and take a shower so i was rushing to get my bike put back together and test ride it. By this time i was getting kinda sweaty so i took off my socks, shoes, and shirt. Around 7:00 all i had left to do was oil the air filter. I ran outside because i didnt want to get oil all over the shop, oiled the filter, and ran to go back inside. Fu*k... i had accidently locked the door behind me and the front door was locked too, nobody but me was at the building. I was stuck outside with nothing more than boxers, shorts, a belt, a lighter, and a half pack of cigs. I had no phone, no keys, no wallet, everything was locked inside. Around 7:20 a couple pulled up to walk on the bike path and were kind enough to let me use their cellphone. I called my mom's cell and the home phone(the only two numbers i had memorized that were home) but none answered so i left a messege. Dam.. i couldnt get ahold of anyone with a key(dad was out of town) to let me in so my only hope was that they would check the messege and stop by. Around 7:40 my mom pulled in the parking lot with a key. Awesome. Missed most of dinner with my friends but at least i was in. I threw everything together then called my friend to give me a ride to pick up my car( he owed me cus i picked him up a few days before when he was piss face drunk).

So thats the story, it ran perfect after i did the air filter, pump gas, spark plug and fuel screw. Today i had a race and it was a totaly different story. More to come...

  • ttr250dude

Posted August 01, 2010 - 09:33 PM

#23

Today was another enduro race for me and my pops. There were so many people that the first mile or so was literally stop and go traffic - stop for 45 seconds, ride for 15 seconds, stop for 45 seconds, you get the picture. I could smell it was getting hot and when we got back on the mx track it started blowing steam like crazy so I pulled off and let it cool down, after awhile i went back to the pits and topped off the coolant. I brought with a water bottle of coolant and headed out to attempt a full 4 mile lap. About a mile in i could smell the clutch/engine getting way too hot but no steam. I stopped every few hundred to prevent steaming and damage.

Shortly after my pit stop i couldnt let it idle or else it would it would die. Whenever i would pull over for a few minutes to let it cool it would start fairly easily but it kept having the same problem. Eventually i asked an official the fastest way to get to the pits or a road. He showed me a side trail and told me to cut straight through the woods to the pit area. I really didnt want to keep it that hot or start blowing steam again, i'd rather drop out of a race than spend hundreds of dollars and time on rebuilding a top end.

I'm assuming the clutch and engine overheating was because of the slow speeds, high revving, and alot of clutch use. Right? What about the stalling issue again?

  • nwbikerider

Posted August 01, 2010 - 09:59 PM

#24

My 09 yz450 was stalling, overheating, and blowing coolant in the tight woods on Sat. and it wan't even a race. Lots of clutch and slow speeds, revving up hills, without air flowing over the rads. Welcome to the world of woods...

  • grayracer513

Posted August 02, 2010 - 07:21 AM

#25

The first order of business is to ensure that there is no underlying cooling system problem, such as a weak cap, a radiator with a coating of scale in it, head gasket, etc.

If all of that is in good order, and you find you still have trouble with this as a result of the kind of riding being done (very low speeds, etc.), then you can take other steps:
  • Add a fan
  • Increase cooling system pressure
  • Increase the boil over temps

Adding a fan is probably the best choice, because it actually solves the problem by creating air flow where there isn't any, and lack of air flow is the root cause. Small DC fans can be mounted against the radiators and run from a battery. You can include a handlebar switch so as to conserve the battery.

Raising the cooling system pressure raises the boiling point. Do this by using a 1.6 bar (23 psi) cap. Be sure your hoses are healthy and tight. This does not reduce heat, just controls it.

You can also use something like the high temp racing coolants from Zip-Ty or Evans, which don't address the heat problem either, but they don't boil until well over 300 degrees, even under low pressure. Your engine will still be hot, but at least it will have coolant in it.

Stalling and hard restarting when hot is often due to being too rich. The hotter the engine, the leaner the idle wants to be. If you are one of those people who fattened your bike up to get rid of every bit of exhaust backfire, or so that you could yank on the throttle like a 13 year-old two stroke rider, or if it's just adjusted wrong, you might find the cure in just leaning the idle out a bit. Do a mixture trim when it's at full normal temperature and see if that helps.

  • ttr250dude

Posted August 25, 2010 - 08:09 PM

#26

Alright so i was in another race on sunday and it started stalling after 15 - 20 mins so i said " " and went back to the pits, i had already had enough of the stalling thing. This race wasnt all tight woods, part of it was a snowmobile trail/narrow fire road, so it wasnt overheating. In the pits i noticed that i had bent a radiator so im glad i dropped out when i did. Luckily i didnt leak any coolant.

Here's my idea: my valve clearances are too tight so when it gets to full temps and things start expanding the valves arent seating all the way when theyre supposed to be closed. Does this seem like a likely culprit?

My current jetting is 165 main, 48 pilot, fuel screw 1 7/8 turns out, and im pretty sure the leak jet and needle/position are stock. Should i try 162 main, 45 pilot, fuel screw 1 3/4 turns out?


Thanks for all your help guys!!

Edited by ttr250dude, August 25, 2010 - 10:15 PM.


  • grayracer513

Posted August 25, 2010 - 08:16 PM

#27

Here's my idea: my valve clearances are too tight so when it gets to full temps the valves arent seating all the way when theyre supposed to be closed. Does this seem like a likely culprit?

Did you check the clearance?

  • Wiz636

Posted August 25, 2010 - 09:23 PM

#28

My current jetting is 165 main, 48 pilot, fuel screw 1 7/8 turns out, and im pretty sure the leak jet and needle/position are stock. Should i try 162 main, 45 pilot, fuel screw 1 3/4 turns out?


You are way too rich on the pilot jet. My wife's family is from WI and they have said that it has been very hot and humid lately, and I'm assuming that your elevation is not too high either, plus it is hard to start whe hot so that 48 is too fat. Drop down to the 45 and start with your fuel screw around 1.25 turns out.

  • ttr250dude

Posted August 25, 2010 - 10:29 PM

#29

Did you check the clearance?


Not yet. I'm going to lean out the jetting first and hope that that will solve the problem. I'm really not a fan of working on 4t engines lol

You are way too rich on the pilot jet. My wife's family is from WI and they have said that it has been very hot and humid lately, and I'm assuming that your elevation is not too high either, plus it is hard to start whe hot so that 48 is too fat. Drop down to the 45 and start with your fuel screw around 1.25 turns out.


Thank you. I'll try the 45 pilot and I'll start with the fuel screw at 1 3/4 turns out and go from there. I just picked up my Zip Ty fuel screw so now i can tune on the fly :bonk:

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  • mdkcrf250r

Posted August 26, 2010 - 12:25 AM

#30

Sounds like tight valves to me..

  • ttr250dude

Posted August 26, 2010 - 12:41 AM

#31

Sounds like tight valves to me..


Do i have to take off the head to shim the valves or can i just take off the head cover? What all does shimming the valves require?

  • grayracer513

Posted August 26, 2010 - 06:48 AM

#32

Sounds like tight valves to me..

Not to me. Because the head is aluminum, it expands more than the valves do, moving the cams farther from the valve seats, and actually increasing clearance as the engine heats. This is why you can sometimes see an engine with worn valves that will be "OK" when hot, but have so little cold compression that it's hard to start.

As I said in post 2 and 25, and as Wiz just said, the pilot is too big, and it's probably fouling the plug in the bargain.

Read:
http://www.thumperta...ad.php?t=327405

Heat related problems can also stem from faulty coils like the stator and spark coils. Test them when hot.

Do i have to take off the head to shim the valves or can i just take off the head cover? What all does shimming the valves require?

Just the cover

http://motoman393.th...ech/valves.html

http://www.yamaha-mo...uals/index.aspx

  • ttr250dude

Posted August 26, 2010 - 10:57 PM

#33

Thanks for the links

  • mdkcrf250r

Posted September 09, 2010 - 06:47 PM

#34

Not to me. Because the head is aluminum, it expands more than the valves do, moving the cams farther from the valve seats, and actually increasing clearance as the engine heats. This is why you can sometimes see an engine with worn valves that will be "OK" when hot, but have so little cold compression that it's hard to start.

As I said in post 2 and 25, and as Wiz just said, the pilot is too big, and it's probably fouling the plug in the bargain.

Read:
http://www.thumperta...ad.php?t=327405

Heat related problems can also stem from faulty coils like the stator and spark coils. Test them when hot.

Just the cover

http://motoman393.th...ech/valves.html

http://www.yamaha-mo...uals/index.aspx


I disagree. Yes aluminum expands faster than the steel/titanium valves but the aluminum head has a lot more mass than the valves. An engine with worn valves will start and run fine when hot because the valves expanded not the head which caused the sealing against the seats that were otherwise leaking.

  • grayracer513

Posted September 09, 2010 - 08:28 PM

#35

This is not a theory. Aluminum not only expands faster, it expands more than titanium. Check the valve clearance of a warmed up YZF one time and compare the findings to the same engine cooled off.

As for the valve expanding, there is no method by which the head of a poppet valve with a 45º face can seat better by expanding. The expansion won't make it fit tighter. This is especially true when you consider that the valve and seat expand at roughly the same rates. Furthermore as the valve expands, the stem grows longer. In the absence of any other dimensional change in the cylinder head, the engine would lose clearance by this fact, not seal better.

But, feel free to disagree if you like.

  • arnego2

Posted September 10, 2010 - 05:21 AM

#36

Hello there
When my idle is under 1500 or so my bike tends to stall when braking and I run the bike with a 42 pilot. I think that my clutch tends to grab sometimes, enhancing that stalling when braking issue. I hope after putting in a new clutch it will stop it. :ride:

Good luck
Arnego2

  • ttr250dude

Posted September 10, 2010 - 06:44 PM

#37

During my last ride I set my fuel screw at 2 2/3 turns out and it helped somewhat. Doesnt that sound too far out?

  • arnego2

Posted September 12, 2010 - 07:41 AM

#38

Hello there
not for me, and I think that it would not be the reason for the stalling.

Regards
Arnego2

  • ttr250dude

Posted January 13, 2011 - 12:46 PM

#39

Figured it out awhile ago. I was running leaded 110, switched to straight pump gas and it almost never stalls now.





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