Ready to give up!

I consider myself a good mechanic. Do all the work on my bikes myself. This one has got me stumped. I thought I had a carb promblem. Bought an Edelbrock. Anyways - when I try to start my bike it starts for about a second or two then dies. Did a top end not to long ago, compression is good. Timing is correct, checked about 5 times. New plug. And this all started all of a sudden, my bike was running great. Washed my bike, started it then killed it took it out the next weekend and it would not start. I have torn down my top end twice so far to see if there are any problems. Could this be electrical? I did diconnect my kill switch still did not start. Do CDI units go bad? I also performed the blue wire mod. Please help. I want to go riding so bad. My wife is just about to kick my ass out the door because I am spending so much time tring to get my bike running. If anyone has any ideas! Edelbrock have no choke has anyone had cold starting problems?

Yes CDI's can go bad. Take plug out and rest it on engine kick bike over to check spark should be consistent and strong. If CDI is dead you will have no spark. But if CDI is just #######d then spark will occur but may be faint or timing all over the place. check and respond.

The Edelbrock does have a choke it is on the right side. I have never need to use mine and if I do use it, it wont start. If you need me to I can take a picture of it to show it to you. I had a similar thing happen when I install my Edelbrock one of the vaccum caps (the one for the old hot start on the cylinder head) came off and caused a huge vaccum leak. Also there is a vaccum port on the front of the carb that works great for a ZipTy hot start system it can come off also. Just the back preassure from the engine can blow those caps off I ended up using some small grip wire to hold the caps on. As for your CDI I have never had one go bad so I dont know what to tell you about that. I have had only the best of luck with my Edelbrock I hope the same for you. Let me know if you need any info about the Edelbrock I will tell you what I know or have run into.

When I read the manual that came with the Edelbrock I saw that the one in the diagrams had what was called an enricher(choke). Mine does no have that. And I also think my Edelbrock has only one thing capped off. If you have some pics, I could compare, Thanks! The wierd thing is that it wants to start, seems like it is using the gas from the AP when I open the throttle a couple of times before starting. After it starts it dies rightaway. I did check the spark about a week ago and it was blue I do not now about how consistant the spark was with timing but it looked ok. Maybe I should just take it to a hill and bump it to see what happens. This seriously started after washing my bike and starting it right after I washed it. First time I performed that proceedure. I never started my bike after a wash before. Any ideas?

I always start my bike after washing it so that I can burn all the water off the motor (parts I can't or don't feel like drying). Is it possible you sprayed water around the intake? Other things to look at, maybe the fuel valve (petcock) coincidentally got clogged.....not sure...

when your bike starts does it have any throtle response does it rev at all or does it just go to idle and die. if so try tapping on the side of the carb with the gas on some times the float will stick closed and the bowl goes dry if this is the problem tapping it should loosen the floats. the only other thing i can think of is your cdi is bad sometimes when they go bad you get fire at the begining and then the spark dies of quickly i have had it happpen to me once. more than likely it is a carb problem either an air leak or fuel loss. best of luck.

Took my carb bowl off and there was plenty of gas in the bowl. I have clear gas hose with a gas filter so gas is flowing. My bike stays started for about 2 second at the most and then dies. I think everything is tight. I have new top end gaskets and my intake manifold looks good. I am thinking it is my CDI unit. Has anyone tested a unit if it is bad. Whats the best way to test it. I Do not want to blow the money if it is still good. Thanks!

Swap one with another bike.

I would of swapped it out a long time ago but most of my buddies in Cali are riding two smokers and the guy I could of swapped with lives in AZ.

Did you get the pictures I sent you and if so did they help??

Yes, thanks for the pictures and sorry I am getting back so late to you. I was in Germany for two weeks. My carb is different. I do not has the lever for the so called choke and on my bike I do not have the that brass nipple by the intake that needs to be sealed, 2000 YZ426F? I do not know if I have a new generation carb? Anyways I am probably going to have to take it to a dealer to check the electrical. I have never had a bike at the dealer the be repaired, but I do not no what to do. I have not tried to bump start it yet maybe I will try that first to see if it will stay fired after a couple of revolutions. I still think for some reason it is an electrical problem. Does anyone know if there is a difference in the CDI unit from 1998 to 2001. There are a couple on ebay for a '98 YZ 400? If you want to pics of my carb let me know. It looks exactly the same except for the lever.

I ment fou you to look at the vaccum port on top of the carb. I was just showing you the port that caused the same problem for me. Good luck

hey stan,

I sometimes have problems starting my YZ 450 I kick and kick until i'm blue in the face(almost). I remove the plug clean it then put the plug into the coil and re-connect the coil connector then lay the plug on some part of the bike that is grounded and check for a good blue spark. Occasionally with the dirty plug no blue spark and it fires up inside the plug(short circuiting). Or I can put a brand new plug in and it fires up on first or second kick. I will be doing more research on this and will let you know what I find.


Is your air filter dry? Is it over oiled? Try totally cleaning it and oiling it back up lightly.

I'm curious why you replaced the carb with an edelbrock. Did the problem start after installing it? I once had my idle turned down too far on my yz450 and it would not start. If it has never run on the edelbrock I would try putting the stock carb back on. Also have you tried starting it with the throttle wide open? Just twist it open once and hold it open while kicking to prevent the accelerator pump from squirting each time and flooding the crap out of it. Have you checked the manual to see if there is a test procedure for the cdi or any other components in question? Most can be done with a decent multi meter.

I am going to check the electrical today. You can check everything but the cdi unit. I have always had carb problems. Had to make a new AP nozzle out of brass and when I took that part of the carb apart I saw that a gasket was installed wrong from the factory, pinched and out of groove. Yamaha - keihin does not support that part of the carb, they said I had to buy a new carb - $900.00! I am going to check the electrical and let you know what I find.

If it sparks good enough to start......I would find it hard to believe that the unit is BAD

usually bad means NO SPARK.........The old MX400B would back fire and kick back when the CDI box failed ........did you dry everthing out with a hair drier or heat gun? might try that if you think there is a moisture problem......(lower unit )


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