Pilot jet/idling issues



4 replies to this topic
  • RedTravis88

Posted April 03, 2015 - 04:27 PM

#1

Hey guys, my first post on this forum. I just acquired a 1999 WR400 a few weeks ago, and am in the process of catching up on some maintenance, road registration, etc. I currently own a 1981 CB900f in addition to the WR, and I used to own a 1979 XR250. Yes, the XR was MUCH less finicky about jetting. I never had to mess with it.

 

My biggest issue right now is the fact that I can't get it to idle. I have read all the pinned posts on jetting, and have also searched for the answer. But the odd part is that any change I make doesn't seem to help.

 

I have gone through the carb twice now to make sure it's clean. As best I can tell there aren't any vacuum leaks, either. All jetting is stock, but the p/o removed the airbox cover and decorked the exhaust (I'm not sure if it's an XR baffle or what, but it's pretty loud).

 

The issue: it will not idle smoothly, the revs hang a little bit, and the pipe glows red after I take it for a ride up the road.

 

What I've done: cleaned the carb thoroughly, installed leaner pilot jet (42 from the OEM 45), new air filter, new spark plug, disconnected TPS (no difference, just less precise throttle response). I have also disconnected the accelerator pump simply to rule it out (to me the worst is that it doesn't idle smoothly, and off idle response, 1/8th turn throttle, seemed rich. However, disconnecting the pump didn't help).

 

Before I changed the pilot jet it didn't need the choke to start when cold. Since I leaned the pilot jet it now needs the choke when cold. So maybe I'm on the right track. However, I don't think it has helped my idling issue. If it did make any difference, it was very slight.

 

It will idle if I turn the idle speed up. But then as the pinned post in this section says, you have to deal with the rev hang. I have attempted to adjust the pilot screw, but it has made no noticeable difference. It makes the problem a little worse if I close it all the way, but anything from 1/2 - 2 1/2 turns out makes no difference.

 

Anything I'm missing? I appreciate in advance any help or direction

 

-Seth


Edited by RedTravis88, April 03, 2015 - 04:31 PM.


  • Wounded Lobster

Posted April 03, 2015 - 04:42 PM

#2

How does the bike run on the throttle?

A pipe glowing red would suggest the bike is running lean.

Can't hurt to try a richer pilot jet and observe what happens.

Also double check all the bits on the fuel screw are there and OK.

 

Just some ideas :)



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  • Krannie McKranface

Posted April 03, 2015 - 04:47 PM

#3

45 pilot, not 42

 

You MUST clear the passage above the pilot jet with spray cleaner and fishing line. It could take ten tries to get it clear.

 

You also must service the slide plate seal (replace), the hot start plunger if you have one (pull, polish everything, and lube) and use a BRAND NEW pilot jet.

 

Next you must make sure there is no debris inside the ACV (if you have one, remove cover and look) or the Main or Pilot air jet (the intake bell has these)



  • RedTravis88

Posted April 04, 2015 - 11:56 AM

#4

45 pilot, not 42

 

You MUST clear the passage above the pilot jet with spray cleaner and fishing line. It could take ten tries to get it clear.

 

You also must service the slide plate seal (replace), the hot start plunger if you have one (pull, polish everything, and lube) and use a BRAND NEW pilot jet.

 

Next you must make sure there is no debris inside the ACV (if you have one, remove cover and look) or the Main or Pilot air jet (the intake bell has these)

 

I think I have the pilot jet size right because on the stock jet it didn't need the choke to start when cold (too rich). Now that I have the 42 in there it does need the choke to start cold.

 

I'll check the passage above the pilot jet again.

 

I don't have the ACV

 

How does the bike run on the throttle?

A pipe glowing red would suggest the bike is running lean.

Can't hurt to try a richer pilot jet and observe what happens.

Also double check all the bits on the fuel screw are there and OK.

 

Just some ideas :)

 

The bike runs pretty good on throttle. I'm not sure it's perfect (there might be a couple minor flat spots, but that's me being picky), but it runs clean all the way to full throttle.

 

That's what I thought about the pipe, but it's also what's confusing me.

 

The fuel screw bits are all there.

 

 

 

However i decided to check the valve clearance today while it was cool, and here are my measurements:

 

Exhaust: .203 and .203

Intake: less than .152, less than .152, and right at .152

 

I can't find out how much thinner they are than .152 because that's the smallest feeler I have.

 

All that to say I would consider that part of my problem. Now I'll need to look into some new shims.


Edited by RedTravis88, April 04, 2015 - 11:58 AM.


  • Krannie McKranface

Posted April 04, 2015 - 02:18 PM

#5

Your theory of starting with/without the choke is erroneous.

You don't need choke at all until you are below ambient temps of 50 degrees, and even then, a few extra pumps with the accelerator pump will negate this.

The pilot does not even work until the motor is running! It needs motor vacuum to work.

 

Pilot size is specifically determined by fuel screw turns out from soft bottoml, to get max idle.

 

1 or less means pilot is too big

2 or mor means its too small

 

Yes, your valves are waaaay out of spec....making starting a changing affair as the motor temp changes.


Edited by Kah Ran Nee, April 04, 2015 - 02:19 PM.





 
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