2004 YZ450 engine problems.


13 replies to this topic
  • antarius

Posted May 18, 2009 - 05:58 PM

#1

Curious if someone can help me here:

Last week I took the bike out, it was about 60F out and low humidity. The bike ran absolutely great. I put a solid 1.5 hours on the engine meter and was really riding the piss out of it.

Took it home, cleaned the air filter, changed the oil and put her away.

Fast forward to this week:
Same buddy and I go riding. We go to the same place, and at 6am, it's the same temperature. The bike kicks over nice and easy as it always does and off I go. I immediately notice it's surging like mad through the mid-range and popping more than normal, etc.

I ride it for about .4 of hour (in total), to get it back to the truck. My buddy puts his hand behind the exhaust and it melts his glove. We shut the bike off, load up and go home.

We first check the plug, hard to tell here -- after hours on the the plug before, a mere half hour in it's shitting-running-mode didn't show much.

Next, check the valves. All five are spot on within spec. Next, clean the carb and check all the jets. No problems with any jets. Put it all back together, start it up, and it does exactly the same thing. You could hold the throttle still (in the garage) and hear it stumbling/surging. It also got hot enough in literally 30-45 seconds of running, that it started pushing coolant out of the overflow.

The bike is not eating coolant, or oil. The air filter is clean (new as I said). The bike has a slip-on, stock header. When I checked the valves, the notches to line up TDC-C were perfectly lined up and the valves were spot-on, so I don't think it's the timing.

Suggestions? I'm obviously thinking jetting, but why would it run great for 2-3 hours of total engine time, and then all of a sudden start sucking ass? I'm trying to eliminate other options before I start screwing with the jetting, because it really did run great before today...

Thanks in advance.

  • MartyMOOSE

Posted May 18, 2009 - 09:38 PM

#2

Seized hot start!

  • grayracer513

Posted May 19, 2009 - 05:11 AM

#3

Seized hot start!

That's a thought, alright. Worth looking at. If it were stuck open, the symptoms would fit.

  • antarius

Posted May 19, 2009 - 07:23 AM

#4

That's a thought, alright. Worth looking at. If it were stuck open, the symptoms would fit.


I checked the hot start and the choke, both are working properly and not sticking.

Other suggestions?

  • grayracer513

Posted May 19, 2009 - 07:40 AM

#5

The info you've posted suggests an electrical problem. Test the stator and coil, and check all of the connector terminals for good, clean contact.

  • antarius

Posted May 19, 2009 - 08:29 AM

#6

Stupid question:

How do I test the stator?

I should note that it's revving past the point where it stumbles, no problem, so I don't think it's the coil - or could I be wrong?

  • grayracer513

Posted May 19, 2009 - 09:33 AM

#7

Look in the manual. Coil test is on page 6-5, the stator tests are on 6-6.

The one carb thing this sounds like is a broken or inverted slide plate. Sometimes they crack a corner off and run like this. The plate is shown in the picture on 4-9 at 8:00 o'clock from the slide, #4.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • cwf340

Posted May 19, 2009 - 09:37 AM

#8

could you have gotten some dirt/trash in the carb when you cleaned the filter? just a thought..

  • antarius

Posted May 19, 2009 - 10:23 AM

#9

could you have gotten some dirt/trash in the carb when you cleaned the filter? just a thought..


A for sure possibility, but I already pulled the bowl and cleaned the hell out of the carb.

I'll do it again today and see what happens.

I've also noticed, the bike right now is jetted at 162/42. I'm going to put it back to stock jetting, (165/42) and clean the carb entirely, put it all back together and then work from there.

I think it's a lean issue -- somehow. When I pull the choke, the bike dies -- it doesn't speed up like it should. When I pull the hot start, it speeds up like it should.

In theory, the choke should raise the idle right? Unless it was already lean (it doesnt require a choke to start, even when dead cold) and the choke is just killing it all together?

The heat, the surging uppermid-range, and the choke issue is all making me think its just a lean issue.

Not sure why it's rearing it's head all of a sudden though.

  • grayracer513

Posted May 19, 2009 - 12:35 PM

#10

When I pull the choke, the bike dies -- it doesn't speed up like it should. When I pull the hot start, it speeds up like it should.

In theory, the choke should raise the idle right? Unless it was already lean (it doesnt require a choke to start, even when dead cold) and the choke is just killing it all together?

Rich, not lean.

The choke creates a rich condition to aid cold starts. This engine does not need enrichment to cold start - Rich

When you add the choke, it kills the engine rather than supporting it - Rich

If it was lean, it would run better with the choke on, and the Hot Start would kill it.

You might want to check that slide plate, and look at the two air ports in the mouth of the carb to see if you have lodged a a blob of filter oil in them.

Consider, too, the possibility that you over oiled the air filter, or failed to adequately remove the excess.

  • Ga426owner

Posted May 19, 2009 - 12:43 PM

#11

I know you said it is not the hot start but it sounds like classic Hot start issue - Did you remove the plunger from the carb to see if it is not sticking? Or just see if the hotstart lever moves?
On the 03-05 the plastic nut that holds it on the carb will start stripping(which they all do) this will allow water in there causing it to seize up. Recommend replacing the plastic nut with alum and adding a dab of grease to the plunger

If it is not this or jetting issue it is electrical

  • antarius

Posted May 19, 2009 - 05:16 PM

#12

I know you said it is not the hot start but it sounds like classic Hot start issue - Did you remove the plunger from the carb to see if it is not sticking? Or just see if the hotstart lever moves?
On the 03-05 the plastic nut that holds it on the carb will start stripping(which they all do) this will allow water in there causing it to seize up. Recommend replacing the plastic nut with alum and adding a dab of grease to the plunger

If it is not this or jetting issue it is electrical


I've removed the hot start -- and yes, the plastic nut is starting to strip. That said, you can still see the plunger move up and down when you pull the lever, so I don't think it's sticking. An aluminum one is definately in order.

Today the carb came back off, cleaned it out again and rechecked everything. I noticed the fuel screw was out like 5+ turns. I moved it back to 2 turns out (stock) and put the stock 165/42 jetting back in.

Then off came the exhaust, and what did I find? The spark arrestor had broken off the tip and dropped deep inside the pipe. Not to the header, but deep in the pipe nonetheless -- with the smaller end of the cone facing the header.

I didn't get a chance to run it after removing the spark arrestor -- but after fixing the fuel screw and putting the jetting back to stock it was better, running cooler, but it was still feeling as though it was floating in the upper mid-range.

Suggestions?

  • rufusz

Posted May 21, 2009 - 03:48 AM

#13

An aluminum one is definately in order.


Where can you buy such a plunger?

  • grayracer513

Posted May 21, 2009 - 06:35 AM

#14

Where can you buy such a plunger?

He is referring to an aluminum cable retaining nut, made by Zip-Ty and others, to replace the plastic one it came with, not the plunger.





Related Content

Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Wiki
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info


Articles
  • 0 replies
Forums
Photo

YZ450F 03 Sparks driving me crazy by SirAttard


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
 
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.