Interesting 1998 wr400f problem


10 replies to this topic
  • FASK

Posted March 03, 2007 - 07:57 PM

#1

So i have tried to be a good boy and i have searched the forum looking for the answers i need. I haven't found any post that exactly details my situation but i have found some posts that closely resemble it.

First, here is the problem:
First ride on this bike ever, fired it up in the morning (about 0deg. C) and started on second kick. Went out for a snowy trail ride, bike was running great. (temp. went up to about 7deg. C). I stalled the bike being a bonehead, trying to find neutral and failing. :naughty: The bike was very hard to restart after this.. did not want to start with the hot start, did not want to start with the choke, did not want to start normally but finally gave up and fired up. Idle sucked. badly. The revs were going up and down by about 500 either way and the idle got progressively weaker until it would give out if the throttle was not near constantly blipped. :eek: After 1/2 throttle the shottyness was totally alleviated and i took it for some high speed pavement runs.. :ride: This bike is fast!:applause: So... no problems past 1/2 throttle. It was however very hard to start every time after this until finally when i got it home and tried to start it after it cooled off it would not start at all :worthy:

Here are the specifics on the bike:
I JUST bought this bike from its second owner. The guy seemed like he really took care of this thing as he had just replaced all the wheel bearings/swingarm bearings/fork and shock seal. I got a good vibe from this guy. Anyways, he told me that it has a yz450 carb (im guess to get around the throttle slide desintegration issues) and fmf slip-on exhaust. At the time of purchasing it, i did not know of the yz timing/grey wire mod, so i never asked about this.

Here is the deal:
From what i have read on the forum it might be one of the following three things:

wet ignition coil
broken woodruff key
vacuum leak

At first i thought that maybe a piece of dirt got lodged into the idle circuit jetting or somthing which would explain the troublsome starting and poor idle but i don't see how it could have gotten past the petcock filter.

I am going to go work on her tomorrow, starting with all the logical tests that i have read about, but i just wondered if any of you fine gentlemen might be able to give me some specific direction and possible save a fella some time and headaches :lol: I am lost on this one :lol: .. + alittle stressed that my new toy is sick :lol:
Any help would be appreciated

F. A. Spencer King

  • billykidd2000

Posted March 04, 2007 - 12:03 AM

#2

try putting in a new spark plug! same thing happened to mine when I brought it out in the snow. Ran fine for a bit but then bogged down and won't start the next day. Put a new plug in and fired right up!

Good luck!

  • John221ex

Posted March 04, 2007 - 10:34 AM

#3

Not as easy or cheap as a sparkplug, but if that doesn't do it, check your diaphragm on your accelerator pump. On my 400, bought used, it was trashed. It also didn't help that the mixture screw was all the way in (!)
It, too was hard to start. Taking care of those two items and it starts easier than my XR250!

John

  • FASK

Posted March 06, 2007 - 05:55 PM

#4

Guys, thanks for the advice thus far. I decided to do what i thought would be the EASY thing and check the spark... man is that plug tough to get out. Spark is fine. Next i took the carb. off (not as hard as the spark plug!)... Well John, the diaphragm was in BACKWARDS. The hot start plug o-ring looks like it is toast as well. I'm not a huge fan of the hotstart to begin with. So the next two questions are...

1. Where does a fella get a new fcr diaphragm
2. Where doesa fella get a block off plug for an fcr hotstart

Thanks abunch guys

F. A. Spencer King

  • new2blu

Posted March 06, 2007 - 06:34 PM

#5

Guys, thanks for the advice thus far. I decided to do what i thought would be the EASY thing and check the spark... man is that plug tough to get out. Spark is fine. Next i took the carb. off (not as hard as the spark plug!)... Well John, the diaphragm was in BACKWARDS. The hot start plug o-ring looks like it is toast as well. I'm not a huge fan of the hotstart to begin with. So the next two questions are...

1. Where does a fella get a new fcr diaphragm
2. Where doesa fella get a block off plug for an fcr hotstart

Thanks abunch guys

F. A. Spencer King

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  • FASK

Posted March 14, 2007 - 09:20 PM

#6

:goofy: :goofy: :applause: :eek:

So i put some new parts in the carb., new diaphragm, new hot start seal... cleaned her out real good and put her back on...

same problem! :lol: :lol: :lol: :lol: :lol:

Any ideas anyone?

The only thing i can think of doing next is ripping off the case cover and checking the woodruff key

  • Scott krough

Posted March 14, 2007 - 10:28 PM

#7

so i just gotta ask?

Does it have brand new fuel in it....fuel goes bad in 30 days.
Air filter clean and oiled???
How are you starting the bike? Bring the piston to just past tdc with the comp release then no throttle and blast kick it.
I would leave the hot start alone... of course replace any o -rings that may be bad...
New plug....good spark...good fuel....Bike ran fine then just won't go???
check the ignition module???

sorry just trying to cover all bases...

  • bg10459

Posted March 15, 2007 - 06:17 AM

#8

Post your jetting specs.
I'm going to guess that you're way too lean due to the cold weather. I re-jet for every 15-25 degree F change.

The bike won't start at all if your woodruff key is sheared.

  • ncampion

Posted March 15, 2007 - 06:55 AM

#9

Early bikes didn't have a woodruff key problem. The FCR carb can be very touchy. They have lots of very small passages in them that can get obstructed. Water in carb can cause corrosion and screw it up. A thorough carb cleaning might take care of it since it did run right at one time. I finally got rid of my FCR and have been very happy ever since. Good luck.

  • drtbk4ever

Posted March 15, 2007 - 10:56 AM

#10

so i just gotta ask?

Does it have brand new fuel in it....fuel goes bad in 30 days.


I'd be willing to bet one or more of the jets in the carb are clogged up a bit.
Happened to me last year. The pilot jet got clogged up with some of the varnish from the old fuel, even though the old fuel had stabilizer in it.

So pull the carb and spend some time with the carb cleaner and clean those jets. Drain the old fuel out and put in fresh fuel.

Just my 2 cents.

  • Crashly

Posted March 16, 2007 - 02:22 PM

#11

Sounds like a carb problem, remember dirt can still get past the petcock filter and also past those screen filters. Rembember that the carb has three circuits that it runs on depending upon the throttle location. If you only clean the small jet it will not usually solve the problem. The whole idle circuit needs to be cleaned! I have rebuilt more than my share of carbs and the best way that I have found it to ultrasonically clean them then blow them out with carb cleaner with the small hose that comes with it. While you are spraying the cleaner check and make sure that it is comming out of the proper holes, then block those holes and see where else it comes out. After doing that blow all of the circuits clean with compressed air. I found a small, tiny air nozzle kit that will fit into most of the holes in the carb, and it really helps with the final cleanout of the carb. Also dont be cheap, if you went to all of the trouble of getting the spark plug out put a new one in. Even though it is getting spark it can still be to weak to be effective. Also it is a good idea to do a compression test while you are there. That way you can effecively guage when it is time for a top end rebuild. Good luck




 
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