Off idle hesitation



21 replies to this topic
  • Qwazipsycho

Posted June 14, 2015 - 06:05 PM

#1

Aloha,

 

New Thumpertalk user, seasoned rider and wrench here.  Newly converted smoker to stroker.  07 YZ450F.

 

I recently bought this bike and it ran great.  However, it was blowing water out the radiator overflow.  Discovered a loose headbolt and obviously blown head gasket.  I tore it down and bought a OEM top end gasket kit.  Reassembled and it started on the first kick.  I took it out for a ride and it runs exactly as before and maybe even a little more power.  However,  I get an off idle hesitation that if I just flick the throttle real quick, it sometimes even dies.  

 

Initially I thought maybe it was just still cold. Considering that's it's holding its water now, maybe it takes a bit more to warm up.  Not so.  Then I thought maybe the throttle pump.  Nope, it is squirting nicely when I twist the throttle while the bike is off. So now I'm a bit stumped.  

 

Now I'm wondering - There are 3 marks on the flywheel when timing the engine.  They don't seem to be far enough apart to make any difference in timing.  As long as you're within the range of the 3 and your cams are lined up, all is well.  Is it possible to be one or 2 marks off on the flywheel?  

 

Anybody have any idea why this would start hesitating simply be replacing a head gasket?

 

Thanks in advance 



  • Qwazipsycho

Posted June 15, 2015 - 09:07 AM

#2

Well I found the problem and it doesn't have anything to do with the carb.  

 

It turns out that the rear valve cover bolt extends through the cam cap.  If it goes in too far,  The intake cam lobe with smack it.  I've got a buggered cam lobe tip.  That seems to be the only damage.  The valve cup doesn't show any signs of that lobe chewing it up.  So I'm going to try again and this time I'm going to make sure I use a torque wrench on those valve cover bolts.

 

OK, Now I've done something else really stupid.  While disassembling this time, I dropped one of the half moon clips that goes between the cam bearing and cap.  It appears that it fell down into the timing chain well.  I've tried a long magnetized screw driver but I need something flexible.  I've pulled the head and cylinder again to try and get at it but I still can't see it and the magnet won't pick it up.  Any ideas?

 

Ya, I know.  I feel really stupid having to post moronic problems like this.  I'm usually not this incompetent.  

 

 



  • grayracer513

Posted June 15, 2015 - 09:20 AM

#3

Lean the bike over to the right a little and remove the left side crankcase cover.  That's where the bottom of the chain tunnel ends up.  Your half ring is probably either hung up in the chain, or stuck to the magnets of the flywheel. 

 

You also need to get the correct valve cover bolts, which are shouldered Allen bolts, and can't over-compress the gasket.  The bolt striking your intake cam is not very likely to be the cause of your bog, BTW.



  • Qwazipsycho

Posted June 15, 2015 - 10:34 AM

#4

Lean the bike over to the right a little and remove the left side crankcase cover.  That's where the bottom of the chain tunnel ends up.  Your half ring is probably either hung up in the chain, or stuck to the magnets of the flywheel. 

 

You also need to get the correct valve cover bolts, which are shouldered Allen bolts, and can't over-compress the gasket.  The bolt striking your intake cam is not very likely to be the cause of your bog, BTW.

30 years of turning wrenches and I still benefit from talking to others.  I forgot about magnets on the flywheel.  

 

Thanks!



  • 03yzf450-kuke

Posted June 15, 2015 - 02:50 PM

#5

Aloha,

New Thumpertalk user, seasoned rider and wrench here. Newly converted smoker to stroker. 07 YZ450F.

I recently bought this bike and it ran great. However, it was blowing water out the radiator overflow. Discovered a loose headbolt and obviously blown head gasket. I tore it down and bought a OEM top end gasket kit. Reassembled and it started on the first kick. I took it out for a ride and it runs exactly as before and maybe even a little more power. However, I get an off idle hesitation that if I just flick the throttle real quick, it sometimes even dies.

Initially I thought maybe it was just still cold. Considering that's it's holding its water now, maybe it takes a bit more to warm up. Not so. Then I thought maybe the throttle pump. Nope, it is squirting nicely when I twist the throttle while the bike is off. So now I'm a bit stumped.

Now I'm wondering - There are 3 marks on the flywheel when timing the engine. They don't seem to be far enough apart to make any difference in timing. As long as you're within the range of the 3 and your cams are lined up, all is well. Is it possible to be one or 2 marks off on the flywheel?

Anybody have any idea why this would start hesitating simply be replacing a head gasket?

Thanks in advance

the third mark is your tdc mark btw thats what you go off when setting your cam timing. The first two marks are for ignition timing. Also i suggest buying a boyesen quik shot 3 with adjustable leak jet or something of the sort to cure that off throttle bog . Your engine is running cooler now so that could be why its happening now after head gasket replacement.

  • grayracer513

Posted June 16, 2015 - 06:15 AM

#6

 i suggest buying a boyesen quik shot 3 with adjustable leak jet or something of the sort to cure that off throttle bog .

 

I don't.  The stumble is correctable without expensive junk. 



  • 03yzf450-kuke

Posted June 16, 2015 - 08:20 AM

#7

Yes it is correctable without it but its so handy having that adjustable leak jet i found it to be money well spent

  • 03yzf450-kuke

Posted June 16, 2015 - 08:27 AM

#8

Then again i live in canada we have drastic weather changes from day to day

  • grayracer513

Posted June 16, 2015 - 09:50 AM

#9

Once the leak jet orifice size has been set, it simply does not need to be fiddled with constantly, or even occasionally, in order for the bike to run well. 

 

Read: http://www.thumperta...f/#entry3596648

 

Then, if you want to follow up on the matter some more, there are these:

 

http://www.thumperta...d/#entry5069010

http://www.thumperta...-2#entry5077305



  • 03yzf450-kuke

Posted June 16, 2015 - 10:36 AM

#10

Interesting. I actually tend to adjust mine often since a 10 degree celsius change in weather makes it bog again instead of responding like i want it to. I like cracking the throttle quick to hop over rocks on the trails

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  • grayracer513

Posted June 16, 2015 - 11:01 AM

#11

So do I.  And I don't change the fixed leak jet in my carb at any time to compensate for the roughly 50 ℉ (10 ℃) seasonal temperature swing I encounter hereabouts, nor for the altitude change from 4000 ft down to 20 below sea level.

 

The first element of good throttle response is the rider.  It is possible to tune a carb so that it will handle an instantaneous opening of the throttle from near idle to WOT, but not to make the bike run crisply and cleanly everywhere else at the same time.  The first thing that you need to learn is the "roll".  Rolling the throttle involves training yourself to open the throttle somewhat slowly for the first few degrees, then progressively faster as the engine responds.  Once learned, you will do this unconsciously, and the engine will sound and react as if it revved virtually instantly.

 

Other things that feed into the response are how well the pilot circuit is tuned, and the diameter of the upper, straight-shafted portion of the needle.  This last item is what handles carburetion in the 1/16 to 1/4 throttle range, and is hugely important to crisp response. 

 

Did you read the posts I put up?



  • 03yzf450-kuke

Posted June 16, 2015 - 12:50 PM

#12

I will have to read them tonite as i got home to a giant tree that fell and crushed my race car :(

  • 03yzf450-kuke

Posted June 16, 2015 - 06:07 PM

#13

Well took a while but read it all i just dont undrrstand what you wanted me to see... i know how the ap works and i also know the leak jet was not intended to tune it. What part exactly were you pointing me to? I didnt seevany where in there why you should not use an adjustable leak jet to tune the ap

  • 03yzf450-kuke

Posted June 16, 2015 - 06:17 PM

#14

I mean great posts and everything but the only reason i got the boyesen quick shot was because if if was much hotter or colder than average it would bog with quick pumps of my throttle. I read about the quik shot having an adj. Leak jet and bought one and honestly love it. If it bogs i slightly turn it in or out depending on temp. I see what you are saying by it being a cure for issues with jetting and not the ap and ya i can definately agree that you are right. But if i can cure this without opening my carb with differences in temperature what exactly is wrong with?

  • grayracer513

Posted June 16, 2015 - 07:04 PM

#15

You don't have to open the carb up to adjust the pilot circuit, which is usually the only temperature adjustment I find necessary.  In the case of an '03 or '04 like yours that was built without one, the QS does offer a simpler and probably less expensive way to add the advantages of a leak circuit AP system than using updated OEM parts.  The OP already has a leak jet, so he doesn't need it.  Maybe once he gets his camshaft problem fixed, he'll be back about that.



  • Qwazipsycho

Posted June 19, 2015 - 09:59 AM

#16

Hey!  I turn my back for a couple of days and my thread gets hijacked!  :)  No worries.  It was good reading.

 

Here's an update on my original problem.  

 

Gray, you mentioned not having the correct valve cover bolts.  Not true, I am using the correct shouldered allen head bolts.  This may sound weird but it's the only explanation I have:  Somehow, I lost that circlip on the intake cam bearing during my last assembly.  I've torn the bike apart short of splitting the case. I haven't found the clip.  I ran a magnet through the oil in the bottom of the crankcase by sticking it in the whole next to the flywheel.  Nothing.  My garage is now SUPER clean because I tore it apart looking for this clip.  Never found it.  Ordered a new one from Motosport.  So here's the weird part.  All I can assume is that by not having the circlip installed, it allowed the cam cap to go lower than it should allowing the valve cover bolt to protrude through the cap and touch the cam lobe.  It's not completely logical but it's my only explanation.  

 

I'm re-assembling today - very carefully.  I assume I'll still have the off idle problem when I'm done.  I'll let you know.

 

Thanks guys,

 

Aloha



  • grayracer513

Posted June 19, 2015 - 11:37 AM

#17

I think you're half right regarding the missing locator clip being the cause, but you don't have the effect quite right.  The height of the cap can't vary without the clip because it's determined by the milled surface it bolts down on.  However, the missing locator probably allowed you to install the cam too far to the left or right, which then brought the nose of the cam lobe into contact with the bolt that ordinarily would be safely between lobes.

 

One other thing I don't know if you've considered: maybe the clip was lost by the previous owner, which accounts for why you never found it.  If you were the one who dropped it, you should have had no trouble turning it up.  They're sort of too big to do a lot of migrating around in the engine, especially with the chain trying to glom on to them and that big pile of magnets on the end of the crank right there.  There's always a first, but I've never heard of anyone completely losing one inside an engine.



  • Qwazipsycho

Posted June 19, 2015 - 12:56 PM

#18

I think you're half right regarding the missing locator clip being the cause, but you don't have the effect quite right.  The height of the cap can't vary without the clip because it's determined by the milled surface it bolts down on.  However, the missing locator probably allowed you to install the cam too far to the left or right, which then brought the nose of the cam lobe into contact with the bolt that ordinarily would be safely between lobes.

 

One other thing I don't know if you've considered: maybe the clip was lost by the previous owner, which accounts for why you never found it.  If you were the one who dropped it, you should have had no trouble turning it up.  They're sort of too big to do a lot of migrating around in the engine, especially with the chain trying to glom on to them and that big pile of magnets on the end of the crank right there.  There's always a first, but I've never heard of anyone completely losing one inside an engine.

Ya I agree with you about the cap height.  But there's no way the cap could have moved.  There's 2 guide dowels that aren't going to let it move.  At least not that far.  If you look at the cam cap, you'll see that the hole for the valve cover bolt is machined all the way through the cap.  That hole lines up perfectly with the far left intake cam lobe.  Also, there was no other damage.  If the cap was misaligned the cam probably wouldn't turn.  If it did turn then there would be chewed up journals which there are not.  Weird.  In the end, the only damage was a couple scuff marks on the tip of that cam lobe.  That's it.  

 

I know I was the one who lost the clip because I specifically remember putting them both on the first time I reassembled.  Best I can figure is the second time I did it, when I was off one tooth on the exhaust cam, it somehow fell outside the engine like on top of the crankcase or sitting on suspension linkage or something...I don't know.  At that point I went out and rode it so it probably fell of on the road.  I give myself a big 'ol Homer Simpson DOH!! and a slap to the forehead.  

 

Anyway, I'm just about to go out the garage and assemble it one more time.  3rd time's a charm, right?



  • grayracer513

Posted June 20, 2015 - 06:36 AM

#19

I did not suggest that the cap could be misaligned without the locator clip.  The CAM, however, can be moved out of its correct lateral position quite a ways if the clip isn't there, however. 



  • Qwazipsycho

Posted June 20, 2015 - 09:44 AM

#20

So, yup.  The third time was a charm.  Runs perfect and no issues.

 

During assembly I did realize what you were saying about the circlip missing and the CAM moving.  And yes, that's what happened.  

 

When done right, this bike want to take off without me.  You must hold on tight or it will.

 

The only bad news is that I did a valve lash check and found that all 5 valves are at their minimum clearance.  Whenever I would do a valve adjustment on an overhead cam car, I always set the clearance to the minimum because it makes a much quieter valve train and better performance.  However, from what I'm reading on this site, that's the wrong philosophy for these bikes.  Because they run at such extreme's, the valves should be set to the other end of the acceptable range to allow for valve wear.  Can you confirm that Gray?  After that, this thread is done.  And I'm going ridin!







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