2011 YZ450F Hot Start Problems

Miscellaneous Motocross Yamaha YZ450F 2011 United States Arizona Arizona Cycle Park

26 replies to this topic
  • brandonkranich

Posted January 11, 2016 - 04:11 PM

#1

Hello Thumper Talk Community,

 

I am reaching out and in need of some advice and help.

 

Some background on the bike:

2011 YZ450F that I purchased used, I am the second owner. The bike was claimed to have 15 hours on it. It does have strong indications of sand dune use as well as the original owner said he had run it out there. It does have stock chain and sprockets but chain was stretched to max setting when purchased. They have been replaced.

It seems as though poor maintenance has been practiced by the original owner. Air filter was extremely dirty and sandy, some sand found in the fuel injection and even inside cam cover. Everything has been cleaned thoroughly with new air filter and all new fluids.

 

Bike has started well while cool since I purchased it but seems to be troublesome while warm. Otherwise the bike seems to run perfect while motor is running.

The bike jumped timing while at the track recently. It was running fine, had it parked on a stand. When kicking it over to go back out the intake cam jumped about 6 teeth after further investigation. It never ran while missed timed. After inspection of the piston and valves, they seemed to have avoid psychical damage.

 

Took the bike apart and could not find anything that seemed to stand out as a problem. Cam chain did have some slight kinking it, it has been replaced. I believe that is why it jumped timing. I replaced the chain and reset the timing. Valve clearances were inspect but on the tight side of the range after reassembly. Did a compression test. Performed a homemade leak down test.

 

After putting it back together it starts up pretty well while cool, but it a beast to start warm. Hot starting now seems to be worse.

I then re-shimmed the valves to put them at the loose range of the spec. Did not seem to help anything.

 

I am not sure what to do and this is my first fuel injected bike.

Any advice or help would be appreciated!

 



  • grayracer513

Posted January 11, 2016 - 04:24 PM

#2

As odd as it may sound, try hot starting with the cold start knob pulled.  (It's not a choke or an enrichener)



  • brandonkranich

Posted January 11, 2016 - 04:52 PM

#3

Thanks for the response.

I have actually seen you mention that is some other posts. It does seems to help to pull the knob when warm, but is still very difficult.

I do try to ensure a proper technique when kicking, stroke through to top dead center and nice smooth stroke with a little hold at he bottom of the kick, no gas.

I could get my 07 yz450 to start first or second kick hot or cold. Something just isn't right..



  • SAKs YAMAHA

Posted January 11, 2016 - 10:04 PM

#4

I had a honda that did this. The valves hit the piston just enough to tweak them. When I re-timed it, it would start fine when cold. When hot, I could spend all day kicking. After I replaced the valves, it worked great hot or cold. That's just my experience.

I also replaced the piston just to be safe

Edited by SAKs YAMAHA, January 11, 2016 - 10:04 PM.


  • brandonkranich

Posted January 12, 2016 - 06:05 PM

#5

I was concerned about the valves being slightly tweaked but hard to say without pulling the head apart. It interesting to hear about a similar scenario. I am leaning now towards getting the head rebuilt. I was just hoping to find a simpler and cheaper solution.



  • grayracer513

Posted January 12, 2016 - 09:01 PM

#6

A leak down test would show that.



  • czykone

Posted January 13, 2016 - 07:07 PM

#7

I have an 11, I put on a 9 oz flywheel weight which helped with starting and stalling. The bike is a bear to start when hot. There is a routine to follow. Pull in clutch kick 10 times slow with throttle wide open, then leave off throttle and kick one hard time and it will fire almost every time. I have 30 hours on mine and it is getting easier to hot start as it is getting time. My bike is otherwise stock. I think this is a pretty common problem with 10-12 models.

  • SAKs YAMAHA

Posted January 13, 2016 - 09:52 PM

#8

I have an 11, I put on a 9 oz flywheel weight which helped with starting and stalling. The bike is a bear to start when hot. There is a routine to follow. Pull in clutch kick 10 times slow with throttle wide open, then leave off throttle and kick one hard time and it will fire almost every time. I have 30 hours on mine and it is getting easier to hot start as it is getting time. My bike is otherwise stock. I think this is a pretty common problem with 10-12 models.

 

That sounds terrible! It sounds like there is an issue somewhere. I have a '10 and it starts with one kick damn near every time when hot. Cold is two or three. Having to go through your routine every time I killed it on the trail would just about ruin my day.



  • brandonkranich

Posted January 14, 2016 - 06:37 AM

#9

Gotcha. Sounds like it's generally a tougher bike to start but damn. Like stated, something isn't working properly. I'm going have a proper leak down test performed and take it from there.
Also upon pulling the head off it seems as though it's been running really rich. A lot of carbon build up. Is this normal? The plug was dark, more towards black than brown. Have you guys with 10/11 had to lean the bikes out at all? Through mapping is the only way right? Have you guys had problems with leaky injectors? Could that be contributing to starting problems?
Thanks all..

  • UncleLuke

Posted January 14, 2016 - 07:29 AM

#10

Gotcha. Sounds like it's generally a tougher bike to start but damn. Like stated, something isn't working properly. I'm going have a proper leak down test performed and take it from there.
Also upon pulling the head off it seems as though it's been running really rich. A lot of carbon build up. Is this normal? The plug was dark, more towards black than brown. Have you guys with 10/11 had to lean the bikes out at all? Through mapping is the only way right? Have you guys had problems with leaky injectors? Could that be contributing to starting problems?
Thanks all..

 

I have seen black plugs/excess carbon from a bad/old fuel source



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  • NW Briff

Posted March 04, 2016 - 07:33 PM

#11

Sorry to bring this back from the dead but i felt obligated to post since dealing with a similar issue.
To make a long story short my issue was the mapping at idle and low throttle/rpm was too rich. Along with the ignition too far retarded. On your gytr tuner try -2 on bottom left in the FI map. Enter 0 in bottom left of ignition map. This should get you started. Your requirements may differ my bike specs are below. By bumping the ignition 1 point you can actually feel a difference iin the kick starter.
Set your idle to 18 or 1900 rpm whatever sounds comfortable. These bikess idle high.

Symptoms were cold start 3 to 4 kicks which i thought was normal. Once hot near boiling and dumped over would take 10 to 20 kicks to start and felt too easy to kick. Opening throttle slightly seeemed to help.
I can now cold start in 2 to 3 kicks. The knob on the throttle body seems to aid in cold starting now even though there is less fuel and more air overall and idles the bike up crisply like a choke would. Ran the bike got it hot enough till rad can be heard boiling when shut offbut not puking all over. Layed it on the ground for 45 sec. And starts in 1 to 2 kicks. Did this a few times with good results. (Sure the neighbors think im crazy now) Havent ridden it much to see what it feels like yet i have a paddle mounted currently. And just found sand in the oil filter and top of head. Reroute your crankcase breather!
Bike is yz450f 2011 gytr head cams high comp piston heavy flywheel on race gas
Sorry about grammar this was done on a cell phone. Hope it helps!.

Edited by NW Briff, March 04, 2016 - 08:15 PM.


  • brandonkranich

Posted March 04, 2016 - 09:09 PM

#12

Well that is interesting and very convienent timing! I just got done putting the bike back together: I had just got the head back from the machine shop. New valves, new piston, new rings, machined cylinder, new cam chain. Put it all together, started it up cold after being rebuilt, took a few extra kicks but fired up and ran well. Moment of truth came with bike running well, motor nice and warm, I shut her down. Went to start the bike while warm and could get it started! The bike is timed properly, valve clearness are in perfect spec and leak down test proved its tight and valves are sealing. But it won't start hot!
I am now believing it must be a fuel injection/computer problem at this point. And your post helps to re afrim that. I don't have a tuner! Will a shop dump a map in for you? Can you pull diagnostics with the tuner?
Thanks for the help and bringing this back to light.

  • grayracer513

Posted March 05, 2016 - 09:49 AM

#13

If the bike refuses to start hot, try two things.  First, the fuel injection will mimic the behavior of a carb somewhat, except there's no accelerator pump to be concerned with.  Opening the throttle past about 3/4 without the engine running puts the injection in a "clear flood" mode, which turns off fuel delivery altogether, so pen the throttle big and push the engine though a couple of times to wash air through the top end and dry it up a little.

 

Then, in spite of what your first reaction is, pull the cold start knob.  The cold start does not enrich the mixture in any way.  That's all done at the ECU in response to the intake air and coolant sensors telling the unit the engine is cold.  That won't happen wth a hot engine, and the cols start knob itself just opens an air passage that increases the net throttle opening a little.  Lots of guys find it helps restarting same as the hot start on carb models does.  



  • brandonkranich

Posted March 05, 2016 - 10:58 AM

#14

Thanks Grey,
I will try that out.
I am also picking up a tuner this afternoon in hopes I can fine tune this more.

  • Monk

Posted March 05, 2016 - 11:04 AM

#15

You clean the injector?

  • brandonkranich

Posted March 05, 2016 - 02:20 PM

#16

I really should have! I'm gonna take it off and clean it up also. I'm about to get this tuner fired up also.

  • NW Briff

Posted March 05, 2016 - 03:01 PM

#17

Yes, you can check for diagnostic codes and monitor all of your sensors and rpm in real time with the gytr tuner.

  • billygildark5007

Posted March 06, 2016 - 10:54 PM

#18

I have noticed this symptom to on my '11. Cold starts I can cycle 3-4 times then it always starts 1st kick.
If the motor stalls when hot it's a b%*+h to start. At least 10 seconds best case. The cold start knob does seems to cut that time time in half...
Not to steal the thread but has anyone thought or made a lever action (like the old hot start) on the bars?
A older hot start cable might work if the plunger would still seal?

  • billygildark5007

Posted March 06, 2016 - 11:00 PM

#19

Yes, you can check for diagnostic codes and monitor all of your sensors and rpm in real time with the gytr tuner.

Sorry but you can't monitor the sensors with the gytr. It will only give diagnostic codes. Will show rpm though.

  • NW Briff

Posted March 07, 2016 - 01:24 PM

#20

Sorry I must respectfully disagree.. in the monitor page of my gytr it shows 5 things. Engine rpm, two temperature sensors. Inches of vacuum and throttle position.

It is also my opinion that introducing more air into the system to get it to start hot is a bandaid for a larger issue. you either got too much fuel at idle. Or you ignition is too retarded at idle... ive heard people claim the tuner will not adjust for fuel and ignition at idle. I disagree with that too. It may not be as precise as other methods of tuning but I can feel the difference in the kick starter by adjusting ingnition at low rpm/low throttle.
these bikes should not flood even when dumped upside down. Its fuel injection, not a carb.

Edited by NW Briff, March 07, 2016 - 01:46 PM.






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