Carb help, bike not getting gas


43 replies to this topic
  • tribalbc

Posted January 06, 2011 - 08:13 AM

#1

07 WR450, just finished rebuilding. Bike has new camchain,HC piston, rings, valves, springs and head was flow ported. Timing is good, quadrupled checked, valve clearances good, and bike has good compression, ring gaps are in spec and orientated correctly.
As far as carb work I raised the needle a clip, didn't touch slide, put in a new needle jet emulsion tube, new richer pilot and main. I also removed the fuel screw, couldn't find theold washer and oring, so added one I had from an old fuel screw. There could possibly be 2 in there......
Floats are good and I can blow unrestricted through all vent tubes and fuel intake with floats open. I'm getting a squirt on the acelerator pump when wicking the throttle.
Problem is I can kick and kick and kick, get the odd backfire but when I check the plug it's bone dry. Spark is good.
It also seems to be some kind of blockage for fuel entering the carb, like it makes a vapour lock. When I tip the bike it seems to take longer and have less flow from the overflow. And then when I disconect the fuel line at the carb it's only less than half full, like it can't get fuel. I've tried 2 different petcocks, and fuel lines. When I turn on the petcock from the tank disconected from the carb it runs freely......
And no, there is not a rag in the intake or exhaust :smirk:

Any ideas out there????

  • jayh300

Posted January 06, 2011 - 08:59 AM

#2

do you still have the vent valve in vent line...i had one of those go bad.. also had a cap go bad, would not vent either...

loosen the gas cap half a turn, maybe.....

  • SXP

Posted January 06, 2011 - 09:04 AM

#3

Just to confirm that the float bowl is filling up, open the drain screw (allen bolt on left side) and make sure fuel comes out the common drain/overflow hose. If it does, at least you've eliminated the float needle valve as being the culprit and you can look elsewhere.

  • tribalbc

Posted January 06, 2011 - 09:22 AM

#4

do you still have the vent valve in vent line...i had one of those go bad.. also had a cap go bad, would not vent either...

loosen the gas cap half a turn, maybe.....


no vent line on cap, but I haven't tried blowing through the cap.
But I did try 2 different tanks....

  • tribalbc

Posted January 06, 2011 - 09:29 AM

#5

Just to confirm that the float bowl is filling up, open the drain screw (allen bolt on left side) and make sure fuel comes out the common drain/overflow hose. If it does, at least you've eliminated the float needle valve as being the culprit and you can look elsewhere.


It was coming out, but not as full of flow as I remember. The big thing was how the intake fuel line from the tank would only be half full when removing it from the carb??? Like it wasn't drawing gas properly....
I just pulled my float needle valve, all looks good. I can see a screen in the tube for the intake of the float needle valve. I heavily brake clean sprayed and blew out with compressed air that screen from the inside out. Hopefully that fixes my problem :smirk:

  • William1

Posted January 06, 2011 - 09:36 AM

#6

Why did you go so rich on the jetting?

Now, to your fueling issue.
  • Fuel line off the carb, fuel line in a jar, petcock open, does fuel flow?
  • Fuel line attached to carb, drain open, petcock open, does fuel flow?
  • Petcock open for 30 seconds, then closed. Drain carb into a glass jar, about 4 ounces?
  • Float bowl off, float and float needle removed,fuel line connected, petcock open, is the flow rate about the same as #1?


  • tribalbc

Posted January 06, 2011 - 09:44 AM

#7

Why did you go so rich on the jetting?

Now, to your fueling issue.

  • Fuel line off the carb, fuel line in a jar, petcock open, does fuel flow?
  • Fuel line attached to carb, drain open, petcock open, does fuel flow?
  • Petcock open for 30 seconds, then closed. Drain carb into a glass jar, about 4 ounces?
  • Float bowl off, float and float needle removed,fuel line connected, petcock open, is the flow rate about the same as #1?


I richened the jetting as it's unridable cold out right now, 20 degrees, and I put a new exhaust system on that recomends richening the jetting from an 08 YZ450 system, which is what I had on the bike before. I'm in a heated shop, but it's probably in the 40's. I only went one step richer on all the circuits....

Thanks, I will go through all these steps and see were I stand :smirk:

  • tribalbc

Posted January 06, 2011 - 10:00 AM

#8

Now, to your fueling issue.

  • Fuel line off the carb, fuel line in a jar, petcock open, does fuel flow?
  • Fuel line attached to carb, drain open, petcock open, does fuel flow?
  • Petcock open for 30 seconds, then closed. Drain carb into a glass jar, about 4 ounces?
  • Float bowl off, float and float needle removed,fuel line connected, petcock open, is the flow rate about the same as #1?


Well it passed all these tests. I'll put her on and try again.....

Sorry for the double thread :smirk:

  • tribalbc

Posted January 06, 2011 - 11:03 AM

#9

Well I'm stumped :smirk:
Won't start, still a dry plug.

  • SXP

Posted January 06, 2011 - 11:56 AM

#10

When you had the float needle valve off, did you try blowing through the carb inlet tube with your lips wrapped around it so as to get a feel for any restriction in that passage? I know you said you blew compressed air through the opposite way, but doing it with your mouth in the direction the fuel flows might give you an indication of any restrictions in that passage.

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  • William1

Posted January 06, 2011 - 12:40 PM

#11

Well I'm stumped :smirk:
Won't start, still a dry plug.


We'll talk about the jetting once you get it running.

So you've confirmed the float bowl completey fills. I assume the gas is new and the bike is stored in youe 40 degree shop, right?
When you look in the throat of the carb, is there a little space at the bottom of the slide, ie, can you see through the carb?
Did you have the slide out of the carb?
You positive the cam timing is correct and the cams are not reversed? You do have what feels like 'normal' compression?

  • tribalbc

Posted January 06, 2011 - 12:53 PM

#12

We'll talk about the jetting once you get it running.

So you've confirmed the float bowl completey fills. I assume the gas is new and the bike is stored in youe 40 degree shop, right? Yes new 94 octane gas, carb was completely dry for a couple months, and bike is stored in shop

When you look in the throat of the carb, is there a little space at the bottom of the slide, ie, can you see through the carb? Yes I have idle set so there is a 1/16-1/8 inch space at the bottom of the slide
Did you have the slide out of the carb? No
You positive the cam timing is correct and the cams are not reversed? You do have what feels like 'normal' compression?

I'm revisiting timing and clearances again as I am stumped. But yes when I put eveything together I rolled the motor through and checked timing several times. I did go with a YZ intake and WR exhaust this time rather than both YZ cams.
Good compression



  • tribalbc

Posted January 06, 2011 - 12:55 PM

#13

When you had the float needle valve off, did you try blowing through the carb inlet tube with your lips wrapped around it so as to get a feel for any restriction in that passage? I know you said you blew compressed air through the opposite way, but doing it with your mouth in the direction the fuel flows might give you an indication of any restrictions in that passage.


Yup, clean unobstructed blow with the mouth. The float bowl is definately getting fuel.....

  • SXP

Posted January 06, 2011 - 01:08 PM

#14

Yup, clean unobstructed blow with the mouth. The float bowl is definately getting fuel.....


Hmmmm..did the tangs on the float get bent by any chance resulting in too low of a fuel level in the carb bowl?

  • tribalbc

Posted January 06, 2011 - 01:17 PM

#15

Hmmmm..did the tangs on the float get bent by any chance resulting in too low of a fuel level in the carb bowl?


Tangs looked fine. Didn't actually measure my float level, but it did seem normal observing it while tilting the carb.....

  • William1

Posted January 06, 2011 - 01:25 PM

#16

Put in a new pilot jet yet?
Confirmed the Hot Start is adjust right?
Confirmed the choke circuit is clear of obstructions?

  • jayh300

Posted January 06, 2011 - 01:37 PM

#17

just for grins.... put a hose on the carb with the bowl off and blow thru what would be the fuel inlet as you raise the float level and see where it shuts fuel off....

  • tribalbc

Posted January 06, 2011 - 01:38 PM

#18

Put in a new pilot jet yet? Was a new one I put in, but haven't changed it, but pulled it and it looked clear and fine
Confirmed the Hot Start is adjust right? Yes
Confirmed the choke circuit is clear of obstructions? No.....will check



Thanks for all the help guys, hopefully will figure this out soon.....

  • tribalbc

Posted January 06, 2011 - 01:40 PM

#19

just for grins.... put a hose on the carb with the bowl off and blow thru what would be the fuel inlet as you raise the float level and see where it shuts fuel off....


Done that, you pretty much have to tip the carb right over to shut it off, so float level seems good....

  • jayh300

Posted January 06, 2011 - 01:57 PM

#20

Done that, you pretty much have to tip the carb right over to shut it off, so float level seems good....


its gonna be something stupid.....(atleast if it were mine)

just re read the first post...could the missing fuel screw oring be lodged in the carb ? blocking that circuit ? (no answer for the missing washer tho)




 
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