wr400 wont idle


70 replies to this topic
  • matt4x4

Posted April 07, 2008 - 10:07 AM

#21

It might not be getting gas properly....
Gurgling after shutting it off means it's filling your bowl - which it shouldn't be.
Remove the fuel hose from your petcock and see how the flow is, if you have good flow with the gas cap on tight, then everything should be good, if your flow is restricted, then your petcock could be plugged up or your standpipe in the tank could be messed up and dirty too.
Try changing to your WR petcock.
Also, if your gas cap vent is blocked it'll restrict flow of gas out of the bottom of the tank. (open gas cap to test if problem persists)

Once you've gotten beyond the tank being the possible problem, check your needle valve in the bowl if you still have the problem - although it shouldn't be an issue, but the gurgling may mean there is.

Also, open your fuel screw to (1 and 5/8) out - I think that's stock on the 99 and even with cam and exhaust changes, it should still run with that.
NOW play with your idle screw, get a good idle, THEN play with the fuel screw, go in til the rpms drop, then out til the rpm change again at the other end, find the mid point and that should be a good setting for the fuel screw.

  • manther

Posted April 07, 2008 - 11:24 AM

#22

It might not be getting gas properly....
Gurgling after shutting it off means it's filling your bowl - which it shouldn't be.
Remove the fuel hose from your petcock and see how the flow is, if you have good flow with the gas cap on tight, then everything should be good, if your flow is restricted, then your petcock could be plugged up or your standpipe in the tank could be messed up and dirty too.
Try changing to your WR petcock.
Also, if your gas cap vent is blocked it'll restrict flow of gas out of the bottom of the tank. (open gas cap to test if problem persists)

Once you've gotten beyond the tank being the possible problem, check your needle valve in the bowl if you still have the problem - although it shouldn't be an issue, but the gurgling may mean there is.

Also, open your fuel screw to (1 and 5/8) out - I think that's stock on the 99 and even with cam and exhaust changes, it should still run with that.
NOW play with your idle screw, get a good idle, THEN play with the fuel screw, go in til the rpms drop, then out til the rpm change again at the other end, find the mid point and that should be a good setting for the fuel screw.


Good news. I put my old wr gas tank back on and it idle's fine with it! So I'm gonna try switching the petcocks on the two tanks. And then I can go through the steps listed above.

  • manther

Posted April 07, 2008 - 06:29 PM

#23

Get this, it's not the petcock, it's the tank... I switched petcocks on the tanks, and still only my old tank will run the bike... The new tank has plenty of gas in it. It's completely full infact. I've tried it in reserve mode and on mode. What can go wrong inside a plastic tank?

  • manther

Posted April 07, 2008 - 06:58 PM

#24

oh and btw I tried it with the cap off the tank.

  • maxtherat

Posted April 07, 2008 - 08:29 PM

#25

Go figure. Who would think that a tank would do that??? Maybe the vent on the tank not letting air in, but with the cap off as well? That was a lot of typing for a lot of ideas that did not solve the problem. Glad to hear that you got it narrowed down. Now, why just that tank???

  • manther

Posted April 07, 2008 - 09:05 PM

#26

Apperantly it's not over yet. I looked in the new tank and there is nothing wrong with it. I'm starting to wonder if it's the angle the the new tank puts the fuel line at.

  • matt4x4

Posted April 08, 2008 - 04:57 AM

#27

Ok, now that's STRANGE!!!
but then again, if I was a WR and someone wanted to YZ me (that's starting to sound dirty), I'd be complaining too!!!
Hmmm, pondering here...The only thing that would stop a tank from draining is a clog or too tight of an air seal.
You've eliminated air being a problem by leaving the cap off which will give you more than enough air....tank is still slow to fill.....how much gas is in it - could you overcome the problem by keeping more gas in the bike?
Your range would suck though if the problem shows it's head at 1/2 a tank....
Are your standpipes off the petcock clean and in good condition?
What if you run it on Reserve setting only? (probably the YZ way anyways)...
Try replacing the fuel line, or make sure there's NO upward curve on it, horizontal and downhill only - might have to cut 1/2" off the line to do that.

  • manther

Posted April 08, 2008 - 07:11 AM

#28

Ok, now that's STRANGE!!!
but then again, if I was a WR and someone wanted to YZ me (that's starting to sound dirty), I'd be complaining too!!!
Hmmm, pondering here...The only thing that would stop a tank from draining is a clog or too tight of an air seal.
You've eliminated air being a problem by leaving the cap off which will give you more than enough air....tank is still slow to fill.....how much gas is in it - could you overcome the problem by keeping more gas in the bike?
Your range would suck though if the problem shows it's head at 1/2 a tank....
Are your standpipes off the petcock clean and in good condition?
What if you run it on Reserve setting only? (probably the YZ way anyways)...
Try replacing the fuel line, or make sure there's NO upward curve on it, horizontal and downhill only - might have to cut 1/2" off the line to do that.



Yeah I'm starting to think it might be an upward curve issue. The YZ tank sits lower and the tube bends ever so slightly upward for just a second before it goes back down. I have a shorter line I will try at lunch today. Sorry WR's I like WR bikes better, but YZ ergo's better. :thumbsup:

  • maxtherat

Posted April 08, 2008 - 08:22 AM

#29

What brand and capacity tank is it? Like Matt said, pull the fuel line from the carb and see how fuel flows with an upward curve versus a continuous downhill angle. With the tank at it's fullest point there is about .5 PSI(.433 PSI per foot of head) at the carb so that may not be enough to push past an air pocket in the line.

  • manther

Posted April 08, 2008 - 08:56 AM

#30

What brand and capacity tank is it? Like Matt said, pull the fuel line from the carb and see how fuel flows with an upward curve versus a continuous downhill angle. With the tank at it's fullest point there is about .5 PSI(.433 PSI per foot of head) at the carb so that may not be enough to push past an air pocket in the line.


Well I just went home and tried a few tests, before I read this. I filled both tanks up to the same level. (not nearly full, but about two inches above both the "on" and "reserve" standpipes ). I have two fuel lines and have tried both. There is no blockage there... I tried both tanks at various angles. Trying to make sure that the fuel lines aren't curved up at all. After several tests it looks like both tanks have the problem. I think I got one or two good run out of the old tank last night and jumped to conclusions that the tank was the culprit.... So I guess that points back to a carburatuion issue. And that really makes the most sense because the bike run's with the choke pulled out. If I was truley having a problem with the fuel not getting to the carb I doubt the choke would help.

Oh, btw it's a stock 2003 YZ450f tank.

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  • maxtherat

Posted April 08, 2008 - 09:08 AM

#31

Is the hot start knob tight or does it stick at all? I'm just taking shots in the dark now.

  • manther

Posted April 08, 2008 - 09:11 AM

#32

Is the hot start knob tight or does it stick at all? I'm just taking shots in the dark now.


I pushed it in as far as it would go. Niether of the hot start lever or the choke lever unscrew to allow constant flow as in old PJ carbs do they? I'm about to make a run back home again. I wanna take a real close look at some before pictures I took. To be sure that I didn't hook the wronig hoses up to the wrong places when I put the octopuss back together.

  • manther

Posted April 08, 2008 - 11:18 AM

#33

Ok I ran a few more tests. I have been distracted from what is probably the real problem (carb adjustments) by the idea of the tank being the problem. So I got back on track with troubleshooting the carb. I made sure the pilot screw was bottomed out, and I turned the idle knob up all the way. The bike runs and will idle, but it is rough. (It kind of surges).

I began adjusting the carb by turning the idle screw down until it stalled. I then turned the idle screw back up a little bit. I restarted the bike. At this point it is idling very slowly and sounds like it's going to stall. So I begin to turn the pilot screw out a little bit at a time until it seems to idle a little smoother. It is now idling smoother but still slow. I begin to think that I am getting somewhere. But just then I see coolant on the ground. (I have the overflow hose disconnected right now). The radiator is spilling a small amount of coolant. I look at the header pipe and it's glowing red. I've always heard that this means you are too lean. Could it just be that the bike was running all the way lean for a minute or two while I was trying to find a good idle speed? Here are my jets:
pilot is #48
main is #170
paj #75
maj #200
I'm seriously thinking of removing the ACV octopuss, but would I need to change my paj, and maj?

  • Frostbite

Posted April 08, 2008 - 11:41 AM

#34

Apperantly it's not over yet. I looked in the new tank and there is nothing wrong with it. I'm starting to wonder if it's the angle the the new tank puts the fuel line at.


I'm just jumping in here, and haven't read all the fine points so this may already be covered.

2 things -

1 - I just installed an IMS tank on my 450, and it caused the fuel line to kink at one of the preformed bends and caused problems at full throttle. I rotated the line a bit and now it doesn't kink. Restricted fuel flow would cause more problems at higher RPM, so I don't think that's causing your idle problem.

2 - In one of your first posts you mention valve slap. Are you referring to the slang term for valve clearance, or are you actually describing noisy valves? Did you select the shims by comparing the measured clearance with the table in the manual, and did you get the specified clearances after you installed the shims?

All things considered equal, the most common cause of poor idle after dismantling is an air leak.

  • manther

Posted April 08, 2008 - 11:47 AM

#35

I'm just jumping in here, and haven't read all the fine points so this may already be covered.

2 things -

1 - I just installed an IMS tank on my 450, and it caused the fuel line to kink at one of the preformed bends and caused problems at full throttle. I rotated the line a bit and now it doesn't kink. Restricted fuel flow would cause more problems at higher RPM, so I don't think that's causing your idle problem.

2 - In one of your first posts you mention valve slop. Are you referring to the slang term for valve clearance, or are you actually describing noisy valves? Did you select the shims by comparing the measured clearance with the table in the manual, and did you get the specified clearances after you installed the shims?

All things considered equal, the most common cause of poor idle after dismantling is an air leak.



Yeah when I started talking about valve "slap" I meant at first I over shimmed the valves and the cam lobes were slapping against the valve stem buckets because there was too much space. I did choose my valve shims based on using a guage to determine the gap, then referred to the chart. Problem was none of the dealers had the size shims I really wanted, so I settled for slightly larger shimms then I needed. I have sense remedied this problem by ordering the shim sizes I really wanted through the mail. now my valve slap noise is gone. (Still a loud valve train though). So I'm interested in what are some common air leak areas to watch for? Obviously the carb boots.. Where else. I also re-oiled my air filter. Maybe I put too much or not enough oil on it..

  • Frostbite

Posted April 08, 2008 - 11:50 AM

#36

Dude you totally right! When that spring showed up I had my "removed from this bike" parts box right there. I bet that's the auto decomp spring, and it just fell out of that removed parts box...Now onto the no idle problem... Can tight valves really cause idling problems? I messured the gap and put a certain size shim in. (went to 172, 172, 172 from 178, 179, 178) on the intake side... Got valve slap... Bumped it up to a 175, 175 175Valve slap gone...


This is the post that has me wondering about setting the valve clearances.

You say you installed 172's and got valve slap, and then "bumped it up" to 175's. I hope you're simply talking slang and not going by sound. When you installed the final set of shims, what were the valve clearances? I think a tight valve would scr#w up the idle.

  • manther

Posted April 08, 2008 - 11:56 AM

#37

This is the post that has me wondering about setting the valve clearances.

You say you installed 172's and got valve slap, and then "bumped it up" to 175's. I hope you're simply talking slang and not going by sound. When you installed the final set of shims, what were the valve clearances? I think a tight valve would scr#w up the idle.


Yeah I used a gapper to measure and find out what size shims I wanted. When I say I bumped it up to 175's, 175 was what size I really wanted when I first set out. After I put the 175's in I remeasured the gaps and they were within range. But I don't remember what the numbers are. Here's what I can do though. I can re-measure them when I get home tonight, and report back. Who knows maybe I DO still have a valve clearance problem. I'm not ruling anything out anymore.

  • Frostbite

Posted April 08, 2008 - 12:07 PM

#38

Yeah when I started talking about valve "slap" I meant at first I over shimmed the valves and the cam lobes were slapping against the valve stem buckets because there was too much space. I did choose my valve shims based on using a guage to determine the gap, then referred to the chart. Problem was none of the dealers had the size shims I really wanted, so I settled for slightly larger shimms then I needed. I have sense remedied this problem by ordering the shim sizes I really wanted through the mail. now my valve slap noise is gone. (Still a loud valve train though). So I'm interested in what are some common air leak areas to watch for? Obviously the carb boots.. Where else. I also re-oiled my air filter. Maybe I put too much or not enough oil on it..


I have a 99 WR 400 and have had it since new, and have worked on it a lot, so I hope I can help you out here.

A small air leak will affect idle but not affect performance above idle. On older bikes it was common for the rubber intake boot between the carb and head to dry out and crack. They were hard to see but if you bent the boot a bit they would open up. I haven't had that problem on my 400 though.
Did you reconect the hotstart hose from the airbox? Maybe your hotstart button is leaking - allowing air in even when it's in the off position. The choke button on my 400 is worn out, so maybe the seat for your hot start plunger worn and leaking. Try plugging the hose with your finger to see if it helps.

The 400's are notorious for boiling over while sitting still, and for the cherry pipe. The pipe is a thin single wall so it turns color a lot faster than the older dirtbikes, and the 400 does run a bit hot.

When you oil your airfilter, you should wring out as much oil as you can. A simple test to eliminate the oil filter as the problem would be to remove it and see if the idle stabilizes or improves. Running the engine with no air filter for a few minutes in your driveway shouldn't hurt.

One off the wall thing to check is your crankcase breather hose. They are routed down under the engine and the clamp holding mine in place used to get bent up sometimes. it would be easy for the line to be pinched closed.
I never had a problem with this on my 400, but did recently on my 450. The bike was working great and then started idling rough. I kept riding and one of the 1/2 moons in the valve cover blew out and hit me inside the knee. The vent hose on the 450 is routed into the airbox. Riding at below freezing temperatures caused it to plug with ice. This let pressure build in the engine, causing rough idle, and eventually enough to blow out the valve cover gasket.

  • manther

Posted April 08, 2008 - 01:02 PM

#39

I have a 99 WR 400 and have had it since new, and have worked on it a lot, so I hope I can help you out here.

A small air leak will affect idle but not affect performance above idle. On older bikes it was common for the rubber intake boot between the carb and head to dry out and crack. They were hard to see but if you bent the boot a bit they would open up. I haven't had that problem on my 400 though.
Did you reconect the hotstart hose from the airbox? Maybe your hotstart button is leaking - allowing air in even when it's in the off position. The choke button on my 400 is worn out, so maybe the seat for your hot start plunger worn and leaking. Try plugging the hose with your finger to see if it helps.

The 400's are notorious for boiling over while sitting still, and for the cherry pipe. The pipe is a thin single wall so it turns color a lot faster than the older dirtbikes, and the 400 does run a bit hot.

When you oil your airfilter, you should wring out as much oil as you can. A simple test to eliminate the oil filter as the problem would be to remove it and see if the idle stabilizes or improves. Running the engine with no air filter for a few minutes in your driveway shouldn't hurt.

One off the wall thing to check is your crankcase breather hose. They are routed down under the engine and the clamp holding mine in place used to get bent up sometimes. it would be easy for the line to be pinched closed.
I never had a problem with this on my 400, but did recently on my 450. The bike was working great and then started idling rough. I kept riding and one of the 1/2 moons in the valve cover blew out and hit me inside the knee. The vent hose on the 450 is routed into the airbox. Riding at below freezing temperatures caused it to plug with ice. This let pressure build in the engine, causing rough idle, and eventually enough to blow out the valve cover gasket.


Hey this is an awesome amount of information. Here's what I'll do. I'll check the valve clearances first. If the valves are off everything else gets shoved to the side. While I have the carb pulled I'll inspect the carb boots. I did move to the YZ subframe so my intake air boot is angled slightly higher then it used to be. I can make sure the extra stress didn't open up a crack. I seriously would like to remove the acv octopuss though. Problem is I'm not sure if I need to change up my paj, and maj. I guess for now I can hook back up the acv. But I'll put the carb back in and try running with out the air filter for a few. Also I'll eleminat the hotstart by pulling the tube off it and plugging it up.

  • maxtherat

Posted April 08, 2008 - 07:16 PM

#40

Frost, glad to see you have gotten into this one. I'm fresh out of ideas and all that I can think about is riding Jawbone cyn. tomorrow. Good luck manther. I'll check back on sunday to see how you did.




 
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