Aggravating 426


19 replies to this topic
  • craigdieselmac

Posted November 27, 2008 - 11:30 AM

#1

Won't start unless I ether it and I don't want to have to do that, I can kick it all day and it doesn't seem to be getting gas to the cylinder, I know that because when I pull the plug it is dry, even after about 12 kicks, 5 twists of the throttle, and the choke out. If I pull the filter and ether it, it fires up first kick, but dies. You have to spray and kick it 4 or 5 times to get it to stay running. Once it starts running, you can shut it off and it kicks over the first kick, even if it sits for 10 min, a couple hours later though she is not starting.. here is what I know...

Plug is good
Good compression
Good Spark
There is gas in the tank
Gas is on and gas is being provided uninhibited to the floats
Floats work properly and bowl is full
jets do not appear to be clogged

Seems I am just not getting gas to the cylinder on start up. Once it is running, it runs as it should.. once it gets cold or sits for a few hours.. its back to not starting... any help would be appreciated
Thanks
Jeff

  • bustersat

Posted November 27, 2008 - 11:59 AM

#2

Check to see if you have a leak on the carb boot or a loose connection. It sounds like you have no vacuum to the cylinder. Other then that clean the carb completely

  • bustersat

Posted November 27, 2008 - 12:01 PM

#3

check your valves as well.

  • locorider

Posted November 27, 2008 - 12:32 PM

#4

check your valves as well.


Also check your valve timing. You may have jumped a tooth on the exhaust valves.

  • craigdieselmac

Posted November 27, 2008 - 01:02 PM

#5

I am pretty sure its the carb, or a combo of carb and valves (because of the starting issue). When it is running, it will not idle correctly, it idles smooth, but it will idle high and when I try to turn it down, it bogs way down and unless I give it gas it dies then it goes back to idling high.. gonna take the carb all the way out and soak it in cleaner. Anybody got any do's and don'ts for this particular carb or is it pretty straight forward. I am pretty good with rebuilding carbs and motors, but this is my first Yamaha thumper...
THanks
Jeff

  • 642MX

Posted November 27, 2008 - 04:09 PM

#6

I am pretty sure its the carb, or a combo of carb and valves (because of the starting issue). When it is running, it will not idle correctly, it idles smooth, but it will idle high and when I try to turn it down, it bogs way down and unless I give it gas it dies then it goes back to idling high.. gonna take the carb all the way out and soak it in cleaner. Anybody got any do's and don'ts for this particular carb or is it pretty straight forward. I am pretty good with rebuilding carbs and motors, but this is my first Yamaha thumper...
THanks
Jeff


Kind of sounds like its idling on the needle. Meaning the pilot jet is restricted so you turn the idle up to compensate for it. I'd check the valves and clean the carb. Be careful of soaking the carb, lots of small o-rings that don't like chem-dip.

  • craigdieselmac

Posted November 27, 2008 - 05:18 PM

#7

Before I rebuild and clean, I'm gonna run a tank or two through it with some carb cleaner and see if that cures it.. I've had success in the past with that on atv's. May not be the right way in some people's eyes, but it is a lot easier, I will keep the site posted.

  • divebobber

Posted November 27, 2008 - 05:34 PM

#8

You mentioned everything except your accelerator pump (AP). If my 2000 426 is cold, it's hard to start if I don't first twist the throttle one time to get a little fuel in there. If your AP is bad, you won't get any fuel when you twist the throttle. When it's started and warm, if you have no bog when you twist the throttle, your AP is probably ok. If you bog, I would look down the throat of the carb to make sure the pump is squirting fuel when you give it a quick twist. If not, your diaphragm may be bad, or the little check valve that lets fuel into the pump housing may be clogged. Mine wasn't getting any fuel. I put an R&D power bowl on and am a very happy thumper rider now. Good luck.

  • craigdieselmac

Posted November 27, 2008 - 06:35 PM

#9

I did take the cover of the AP and there was fuel in there(under the diaphram), and the diaphram looked good, not torn or anything.

  • Family Man

Posted November 27, 2008 - 11:46 PM

#10

dont use ether to start your bike. It explodes instead of burns. Ive have been tol that once you start using it you have to continue using it.

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  • grayracer513

Posted November 28, 2008 - 06:39 AM

#11

dont use ether to start your bike. It explodes instead of burns. Ive have been tol that once you start using it you have to continue using it.

Not true.

However, as long as the bike likes a shot of fuel to get going, why not give it one? Twist the throttle 1-3 times to prime the engine with the accelerator pump.

If it starts and runs for 30 seconds on the choke, then won't idle when the choke is turned off, that may only mean that it's too cold, or the idle's too low. If you get it running, warm it up, then evaluate the idle performance.

  • craigdieselmac

Posted November 28, 2008 - 07:16 AM

#12

I checked the AP to see if it was torn because I don't seem to be getting gas even when I give her a couple 2-3 twists on start up. It doesn't look torn, and when it does get warmed up, it is pretty snappy and doesn't bog at all. I'm gonna take her out today and run some clean gas through her and some carb cleaner and see what happens. I was told that this bike was not run a lot (I just picked it up) and changed hands at least 3 times in the last couple of months due to people being scared of it... Imma go throttle it like I used to do on my old CR and see what happens!:bonk:

  • YZERIK

Posted November 28, 2008 - 07:28 AM

#13

when was the last time your timing chain was replaced??

  • craigdieselmac

Posted November 28, 2008 - 07:31 AM

#14

I Just picked up the bike.. so I don't know.. its not making any noises that are odd.. doesn't seem to be anything mechanical.. I am pretty sure it is the carb. Is the timing chain a scheduled maintenance thing?

  • grayracer513

Posted November 28, 2008 - 10:53 AM

#15

It's a good idea to make it one. Depending on how much riding you do, a year, yea-and-half is good. Thing is that the crank timing sprocket is cut directly on the left crank axle, so wearing it out is expensive.

  • craigdieselmac

Posted November 30, 2008 - 04:57 PM

#16

Who's got 2 thumbs and can start his bike now...... give up?
THIS GUY!! (pointing at myself)

Took a good day of riding for me to get the system down but I think I have it, I can get it most times first kick even when cold. My AP still sucks, the bike bogs with a quick snap of the throttle, and it is still having issues idling. I am going to tear the carb apart completly this week and clean it out. It is having issues in the choke circuit I think since the choke doesn't seem to make a difference on or off. I will tear into it more and see what the deal is. I am just happy I can make it start!:bonk:

  • divebobber

Posted November 30, 2008 - 09:31 PM

#17

I believe the reason my AP didn't work was that the little port with a ball and spring check valve in it wasn't allowing fuel into the AP housing. I replaced the bowl with an R&D power bowl with new AP and it runs quite awesomely (if that's a word ) now. I used to run better with the choke on without a good AP so I put in a richer main and set the needle rich. Now with the good pump, I am actually running rich and am heading things back to where they were before.

  • cmore

Posted December 01, 2008 - 06:30 AM

#18

there was Fit it Mod called the BK mod, this was to fix the bog. Do a search on this I know there is site Here on TT with pictures on how to. I did it on my 426 & took care of the probem.

  • craigdieselmac

Posted December 01, 2008 - 08:05 PM

#19

I found the BK mod... gonna do it maybe this weekend.. maybe next..

  • divebobber

Posted December 01, 2008 - 08:22 PM

#20

I did the "O" ring mod before the R&D Powerbowl mod. It worked some, but didn't get rid of the lack of fuel in the housing. Make sure you're getting a squirt from your AP.





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