08 yz450 lean and stalling coming down from 5th.


18 replies to this topic
  • BigAndDusty

Posted November 08, 2015 - 04:22 PM

#1

Hi there. So a few weeks ago I picked up a stock 08 yz450f. When It was stock it ran pretty lean and popped on decel so after some searching here I thought I found the fix. Jetting.

Welp I figured if I'm going to jet I might as well ditch the ugly shorty muffler and got a full Yoshimura rs-2 exhaust.

So I rejet to a 165 main. 48 pilot. And moved the clip to the 4th position. I'm at 1500-2500 elev. and 60-100 degrees. Desert.

The bike still has a nasty lean sounding pop on decel but rips when I get it on! Now here's the kicker that's throwing me off. Not only is it lean, when I hit 5th gear Wide open for a second and then try to slow down and shift down it feels like it's dying. As if I'm holding the kill switch until I come to a stop and stall. Then it will kick first kick and run like a champ again?!

Is there something in the carb that could be getting stuck open at Full throttle and also causing a nasty backfire?

Checked for exhaust leaks with nothing there. Also had my pops check the valves when I got the bike and he said they're in spec.

Did some searching but didn't find much.

  • Krannie McKranface

Posted November 08, 2015 - 06:56 PM

#2

If you are in a high rpm when you shut off the throttle, you should expect some deceleration popping. It is normal

 

A 48 pilot is not normal.

 

You need to add an R&D fuel screw so you can properly adjust the stock 45 pilot. That will crispen up the throttle response off idle, and reduce the decel popping.

Adjust it for highest idle speed, then lower the idle with the idle screw.

 

You should also check your float height, cause if it's a bit too low, it can stall on hard deceleration.



  • BigAndDusty

Posted November 08, 2015 - 07:25 PM

#3

If you are in a high rpm when you shut off the throttle, you should expect some deceleration popping. It is normal

A 48 pilot is not normal.

You need to add an R&D fuel screw so you can properly adjust the stock 45 pilot. That will crispen up the throttle response off idle, and reduce the decel popping.
Adjust it for highest idle speed, then lower the idle with the idle screw.

You should also check your float height, cause if it's a bit too low, it can stall on hard deceleration.


Thanks for the reply. Some popping wouldn't bother me. But this seems like a lot of popping especially compared to my riding buddies 06 yz. It just seems like too much to be right.

You think the 48 pilot is too rich? It seems to pick up and go great from idle. But I'm not very good with jetting stuff yet. I picked up a easier to adjust fuel screw today from the local shop. I plan to get it on this week and play with that some more.

I will have to pull the carb back out to check the float height. It's kind of strange it only wants to bog out and stall coming down from 5th. As if something is getting stuck open and flooding it.

  • Krannie McKranface

Posted November 09, 2015 - 06:51 AM

#4

Don't use an aluminum allow fuel screw, because they are not tapered correctly, making asdjustments a pain, and the tip can actually break off inside the carb



  • grayracer513

Posted November 09, 2015 - 07:53 AM

#5

There is nowhere in Nevada where a YZ450 would be running lean with a #48 pilot.  Your decel popping is more likely either an exhaust leak (mid pipe most likely, the joint at the head the next most), or you have actually managed to get it so fat that it's popping due to being rich.  A 42-45 should be more correct. 

 

Aluminum extended fuel screws are fine, at least the reputable brands are.  I use Zip-Ty screws and have no problems with them (use the stock spring, though).

 

When an engine stalls on rapid deceleration, it's almost always due to a rich idle, which makes the engine idle down so rapidly that it drops beow idle and stalls.  Low idle speed can be a factor, too though. 



  • BigAndDusty

Posted November 09, 2015 - 08:59 AM

#6

There is nowhere in Nevada where a YZ450 would be running lean with a #48 pilot. Your decel popping is more likely either an exhaust leak (mid pipe most likely, the joint at the head the next most), or you have actually managed to get it so fat that it's popping due to being rich. A 42-45 should be more correct.

Aluminum extended fuel screws are fine, at least the reputable brands are. I use Zip-Ty screws and have no problems with them (use the stock spring, though).

When an engine stalls on rapid deceleration, it's almost always due to a rich idle, which makes the engine idle down so rapidly that it drops beow idle and stalls. Low idle speed can be a factor, too though.


So I should go back to a stock 45 pilot? It seemed common on the jetting database. Also it had a bad pop on decel before I went up on pilot so I doubt it's from being too fat.

The idle seems ok. A little high if anything. Like I said it almost seems like something is getting stuck open and flooding it after being full throttle. It's not a sudden stall, it's more like a choking on fuel until I come to a stop. The bike sat for a long time before I got it.

Is there something that could be bad in the carb causing this or is it just idle like you said?

  • grayracer513

Posted November 09, 2015 - 09:36 AM

#7

Read this first:

 

http://www.thumperta...o/#entry6879695

 

If you get an indication that the #45 pilot is lean when using this procedure at 2000feet elevation or higher, it's probably a partly obstructed passageway above the pilot. 

 

If, after you have the correct pilot jetting, you still have an excessive decel pop ("some" is normal), then you need to check the exhaust for leaks.

 

A too rich pilot will cause the engine to idle down very quickly, especially right after a quick shot of throttle followed by a chop.  A too lean engine will have an idle that tends to "hang", or fall back very slowly to idle.



  • BigAndDusty

Posted November 09, 2015 - 12:09 PM

#8

Read this first:

http://www.thumperta...o/#entry6879695

If you get an indication that the #45 pilot is lean when using this procedure at 2000feet elevation or higher, it's probably a partly obstructed passageway above the pilot.

If, after you have the correct pilot jetting, you still have an excessive decel pop ("some" is normal), then you need to check the exhaust for leaks.

A too rich pilot will cause the engine to idle down very quickly, especially right after a quick shot of throttle followed by a chop. A too lean engine will have an idle that tends to "hang", or fall back very slowly to idle.


I appreciate all the help. Looks like I have to break down this carb again. The whole bog down and stalling thing happened to me with the stock jetting as well. And it backfired with the stock pipe. I don't think it's an exhaust leak but I will be sure to double check.

I think I may need a deeper cleaning and tuning.

Also I forgot to mention when I went to adjust the fuel screw after the rejet it was screwed all the way in. Tight. I screwed it out 2 1/2 turns and saw little to no difference? Before I bought the bike the guy I bought it from took it to a shop for a carb cleaning but I don't think they did anything right.

  • Krannie McKranface

Posted November 11, 2015 - 08:17 PM

#9

The passage above your pilot jet is probably partially clogged.

It happens, there is a 90 bend up there

 

Use fishing line, and spray cleaner to clear it all the way out.



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  • BigAndDusty

Posted November 21, 2015 - 02:39 PM

#10

Ok. A little update. Fixed the decel pop!

It ended up being an exhaust leak to my surprise. There was a lot of crap built up around the copper gasket that I didn't see the first time that needed to be cleaned up and a new gasket installed.

Now the bike absolutely rips with no pop. The only problem is the stalling.

I have gotten it to stall for me a bunch now that I'm out here at the dunes. It seems to be running out of gas when held at higher rpms for a while. Is it possible my new desert tank had some particles in it that are clogging the petcock?

I had a buddy take apart the whole carb with me and we cleaned everything with compressed air and carb cleaner. Checked accelerator pump and all. The carb should be totally clear and clean.

If the bike sat for a long time with gas in it can the petcock be the issue?

  • BigAndDusty

Posted November 21, 2015 - 02:40 PM

#11

I have a few GoPro videos of it stalling on hill climbs but it basically looks and sounds like I'm running out of gas.

  • Krannie McKranface

Posted November 21, 2015 - 03:08 PM

#12

Ok. A little update. Fixed the decel pop!

It ended up being an exhaust leak to my surprise. There was a lot of crap built up around the copper gasket that I didn't see the first time that needed to be cleaned up and a new gasket installed.

Now the bike absolutely rips with no pop. The only problem is the stalling.

I have gotten it to stall for me a bunch now that I'm out here at the dunes. It seems to be running out of gas when held at higher rpms for a while. Is it possible my new desert tank had some particles in it that are clogging the petcock?

I had a buddy take apart the whole carb with me and we cleaned everything with compressed air and carb cleaner. Checked accelerator pump and all. The carb should be totally clear and clean.

If the bike sat for a long time with gas in it can the petcock be the issue?

 

Why don't you use a flashlight and look ?



  • jimbopitts

Posted November 22, 2015 - 09:03 PM

#13

In my 06 i had a 170 main, stock needle and 55 pilot with the r&d powerbowl, leak jet adjusted to 20, and the flex jet fuel screw at 1 1/2 turns out. Ran perfect in southern California, Milestone and glen helen. No decel pop and awesome acceleration

  • BigAndDusty

Posted December 06, 2015 - 12:58 PM

#14

Ok my petcock was pretty clogged up. Got a whole new one in. I went back to a 45 pilot. And she still wants to stall at high rpms.

Here's a video of it in action. Any suggestions?

http://youtu.be/oBV39MfMzjs

  • BigAndDusty

Posted December 06, 2015 - 01:00 PM

#15

Oh and the popping in the video only occurs when it's stalling like that. Other than that it doesn't backfire and has plenty of power

  • Snider

Posted December 06, 2015 - 04:14 PM

#16

I had a problem similar to yours with a keihin PWK 38 carb and it ended up being the float bowl nut under the main jet.. It was tightened by the previous owner so tight , that it colapsed/bent and ended up being too close to the main jet.. after wide open riding the fuel supply had to catch up cause the main jet was so close to that bowl nut it restricted flow.. took me forever to figure it out.. i'm not sure if your carb is like that but i figured it's worth a look



  • Krannie McKranface

Posted December 06, 2015 - 05:08 PM

#17

Ok my petcock was pretty clogged up. Got a whole new one in. I went back to a 45 pilot. And she still wants to stall at high rpms.

Here's a video of it in action. Any suggestions?

 

Does is start right back up

Does you tank vent ok



  • BigAndDusty

Posted December 06, 2015 - 05:11 PM

#18

Does is start right back up
Does you tank vent ok


Yup. It's starts right back up and runs great again. I imagine the tank is venting ok. It's the stock cap and vent hose. I did a 5 hour ride yesterday and the problem didn't happen. Today it happened within 30 minutes. It's so hard to catch.

  • BigAndDusty

Posted December 06, 2015 - 05:16 PM

#19

I had a problem similar to yours with a keihin PWK 38 carb and it ended up being the float bowl nut under the main jet.. It was tightened by the previous owner so tight , that it colapsed/bent and ended up being too close to the main jet.. after wide open riding the fuel supply had to catch up cause the main jet was so close to that bowl nut it restricted flow.. took me forever to figure it out.. i'm not sure if your carb is like that but i figured it's worth a look


That sounds really similar to my issue. Hmm. I'll have to look into that. Thanks.





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