Recent starting issue on 2001 yz426


9 replies to this topic
  • jcm3

Posted July 09, 2010 - 05:00 PM

#1

I was troubleshooting my pilot circuit on my 2001 yz426 due to a little bit of a hanging idle condition, using alot of the tips on this forum. I could screw my fuel screw all the way in and the bike would not stall, which seemed to indicate that it was too large. My manual was marked up with a previous owners notes, and it indicated that the pilot was one larger than stock, which made sense. So, I decided to buy a stocker since it was less than $4. But, even with the hanging idle, it would start first kick about 19 times out of 20, hot or cold.

I ordered and installed a new stock pilot jet. (turns out the pilot jet 'was' stock, but gummed up as I could barely see through it) I also replaced the throttle cables (since they were frayed) and the exhaust washer, which was missing. I think I have the throttle cable adjusted pretty good, and have a little bit of free play. I followed the manual as best I could, but with the way the throttle cable adjusts it seems like there is alot open to interpretation.

With the stock pilot screw swap, the throttle cables adjusted and the exhaust washer in, I am having a helluva time starting it now. I checked the carb boot to make sure it is on tight, and have just done a basic once over. I have done some searches and know that tight intake valves could also contribute, but it was starting perfectly before the changes above. It is taking a minimum of 6-8 kicks now when it is cold, with the same starting procedure. (2 pumps of the throttle, and the usualy decomp lever process) It seems like it wants to start, and seems to turn over a few times but not stay running.

It also seems to pop a little bit, and doesn't seem to be running any better than before.

Any ideas on what else to check? I am going to try some carb cleaner to see if I have a vacuum leak somewhere and will also check the valves.

  • jcm3

Posted July 09, 2010 - 07:21 PM

#2

A couple of other comments:
- it has a fresh plug in it
- gas is fresh
- air filter is clean
- fuel screw was set at around 1 1/2, but I put it out to about 2 and it
seems to be running a bit crisper
- it has the JD jet kit, set up for CA
- it has full exhaust, and I just repacked the silencer (Big Gun)
- Odd, but it seems when it is cold it will start better with the hot start lever
pulled. Not sure if that might indicate something specific that is
wrong. I did not have to do that before. I cleaned out the hot start part
when I put it back in after pulling the carb to swap to change out the pilot
jet.

I'm not aware of any other mods.

I'd like to do the top end and the Hotcams soon, to help with starting and not have to do 'the drill.' I'll probably check the head then, as I have not had anything apart yet.

  • Wiz636

Posted July 10, 2010 - 06:56 AM

#3

You said that before the work you needed to run the fuel screw all the way in, that means you were too rich on the pilot. Then you replaced the 'gummed up' stock pilot with a new pilot, which would make it even richer.

Now you say it starts better cold by using the hot start, that means you are too rich on the pilot.

So, you have two indicators of a rich pilot circuit. I would drop down a size on your pilot jet.

A little bit of popping is not abnormal.

Edited by Wiz636, July 10, 2010 - 07:12 AM.


  • milk

Posted July 10, 2010 - 01:55 PM

#4

wiz, no he said he could run the screw all the way in without it stalling out... in other words the fuel screw did little to nothing. this is what mine has been doing before i just did work on my bike. i went up a size on my pilot after troubleshooting and hopefully will have my bike back together and running here shortly so i can see if it's running any better which by all rights it should be.

  • grayracer513

Posted July 10, 2010 - 03:23 PM

#5

wiz, no he said he could run the screw all the way in without it stalling out... in other words the fuel screw did little to nothing.

And normally, that means that the pilot is too big, or there's an internal leak.

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  • jcm3

Posted July 10, 2010 - 05:37 PM

#6

And normally, that means that the pilot is too big, or there's an internal leak.

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Yes, that was before I changed it out. That is odd though that the old one (stock size) was gummed up, meaning it should have been smaller than stock. With that pilot, it would not stall when I turned it all the way in.

But, I replaced it with a new stock one since I thought it had a larger pilot jet than stock (which should technically make it richer since it is not gummed up), and I am now able to adjust it properly. When I turn it in with the new one, it will stumble as it gets nearly all the way in. So, I am able to follow the pilot circuit adjustment technique now. It seems like it adjusted to around 1 1/4 turns out, but I just adjusted it out a bit farther after doing some other hard starting research on this forum. It seems like at two turns out that it has more snap off of idle and doesn't stumble.

But, I'm still experiencing the starting issue since I replaced the parts, even though the pilot circuit seems to be responding normally.

  • jcm3

Posted July 10, 2010 - 08:58 PM

#7

...with the same starting procedure. (2 pumps of the throttle, and the usualy decomp lever process) It seems like it wants to start, and seems to turn over a few times but not stay running.


I may have found the problem. As I was searching for 'hard to start' threads (which I previously ignored because I had my starting drill down), I came across alot of them that talked about how differently people did it.

I decided to try no pumps of the throttle, which some people do, and it fired right up on the first kick. (with flip flops on) So, I think that I'll try again tomorrow to make sure it wasn't a fluke, and if it starts right up then I'll change my usual drill.

Still searching for solutions for a little bit of a hanging idle. I may try a 2005 and up carb, which I think I read is a good upgrade. The bike is almost 10 years old now.

  • grayracer513

Posted July 10, 2010 - 09:29 PM

#8

Check your valve clearance. Tight intakes can cause this.

  • jcm3

Posted July 11, 2010 - 07:05 AM

#9

Check your valve clearance. Tight intakes can cause this.


Thanks, will do.

  • jcm3

Posted August 19, 2010 - 07:41 PM

#10

Just to follow up, my starting drill did change with the new jet. My old routine (two pumps of the throttle) floods the bike now. I have had great luck with no twists of the throttle.

I started it today for the first time in about 6 weeks or so, which is longer than I usually go. It started on the second kick with just the choke, and no throttle twists.

Just goes to show that what works for one doesn't necessarily work for the next.





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