YZF400 still not starting


7 replies to this topic
  • zach400f

Posted May 27, 2008 - 08:43 PM

#1

I changed my spark plug, And I am still having problems starting my YZF400. With the old spark plug in it was back firing and not staring, The spark plug also looked very fouled out and it had black crust on it. I changed the spark plug and still not starting. Since Ive had the bike its only ran twice. I need help.:thumbsup:

  • zuch95701

Posted May 27, 2008 - 09:11 PM

#2

have you had a valve job done on the bike or has it had one since new. I would say if it hasent it is well over due for a complet top end rebuild. Most of the starting issues are from poor comprestion and tight or loose valves.

  • King_Air

Posted May 28, 2008 - 03:30 AM

#3

Before you jump into a top end, check for the basics. Air, fuel, and spark. All of these must be present to run an internal combustion engine.

  • intensem1rider

Posted May 28, 2008 - 03:35 AM

#4

Yup, check the basics like stated above, you already changed the spark plug, but did you check for spark? I would take the carb off and clean the starter/pilot/and main jets, they tend to clog if sitting for a while, then if it still does not start, take the valve cover off and check the valve gaps, if they are too tight or too loose you will have a horribly hard time starting it.

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  • BASSic

Posted May 28, 2008 - 07:41 AM

#5

You mentioned since you've had the bike it's only run twice. Have you owned a four stroke MX bike before, or is this your first one? Are you twisting the throttle when you start it? If so, that may be your problem.

The FCR carburetor on a four stroke MX bike has an accelerator pump which squirts a jet of fuel when you twist the throttle. If you twist the throttle too many times without the engine running, there's a good chance of flooding it and getting your plug saturated with fuel. In warm weather, I recently learned that one twist of the throttle prior to kicking is enough to flood my 426.

If you know for sure that your plug is dry and you aren't twisting the throttle, and you still can't get it to start, all the suggestions above are worth looking into. Verify you have spark, clean the carb, and then the next step would be to check the valves.

  • rdefonce

Posted May 28, 2008 - 09:02 AM

#6

You mentioned since you've had the bike it's only run twice. Have you owned a four stroke MX bike before, or is this your first one? Are you twisting the throttle when you start it? If so, that may be your problem.

The FCR carburetor on a four stroke MX bike has an accelerator pump which squirts a jet of fuel when you twist the throttle. If you twist the throttle too many times without the engine running, there's a good chance of flooding it and getting your plug saturated with fuel. In warm weather, I recently learned that one twist of the throttle prior to kicking is enough to flood my 426.

If you know for sure that your plug is dry and you aren't twisting the throttle, and you still can't get it to start, all the suggestions above are worth looking into. Verify you have spark, clean the carb, and then the next step would be to check the valves.


I agree with your comments accept that your bike is a 426, not a 400. There are differences between years (such as the '98 400 and '99 400 starting procedure being quite different from each other).

My '99 400f takes at least 5 pumps of the throttle (since new it was like this) to light it when cold.
Sometimes it just pops once or twice, then doesn't start using the prescribed procedure. Then it's probably flooded, so I give it 1/4 throttle or so when kicking it (with no more priming of the throttle), and it ALWAYS starts 1st or 2nd try of that!

Warm, it always starts 1st kick with hot start.

  • zach400f

Posted May 29, 2008 - 05:04 PM

#7

am i goning to pay alot for a top end rebuild if thats the problem?

  • grayracer513

Posted May 29, 2008 - 07:57 PM

#8

Don't blame compression loss without doing a leak down test (see a shop).

Most starting troubles are either carb problems or ignition issues (assuming you are using the correct techniques).





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