Running Issue

Yamaha

I have a 05 YFZ 450 that will not start. Ive cleaned the carb completely, changed gas, and new spark plug but I dont know what else to do. the motor turns over just wont spark up. HELP!!!!!

Do you mean it won't "fire" up, or get "spark"?

Did you verify that it's getting gas? Do you have spark?

I've seen a few YFZ's having trouble with the needle jet feeding fuel into the carb bowl. Seems to be the first place to clog up and the easiest overlooked when cleaning the carb.

Its acting like it isnt getting gas. I had my friend pull me to pop start it but when i did that it wiould turnover but when given gas it would making a bogging sound. i cant tell if it isnt getting gas or there isnt a spark. I cleaned through the carb and i did not find any problems at all. It i did find dirt at all anywhere in it.

It takes three things to make an engine run. Spark, the right fuel / air mixture, and compression. This is the easiest way I've found to diagnose what's missing. Pull the air filter and spray a shot of starting fluid or carb cleaner into the intake tract. Crank the engine. If it fires and dies you have a fuel problem. Next pull the plug. Put a finger over the plug hole and crank the engine. The compression should pop your finger off the hole. These engines have a mechanism on the cam that holds a valve slightly open at very low RPM to make the engine crank easier but you should still feel a good pop on compression. If it has compression, put the plug wire on the removed spark plug and hold the threaded end of the plug against the head or any place it can get a good ground and crank the engine. You should see a spark from the center electrode while cranking. If not, you have an electrical problem. Hopefully, this will help get you on the right path to solving the problem!

Thank you! I did all that an there was no starting with the fluid but when I did the spark plug i got nothing also so im sure its electrical. Anyone know what i could do to find what wrong now?

Sounds like no spark to me. Unfortunately, the electrical side is going to be alot more involved as far as diagnosing goes. I can give a bit of advice though, from previous experience. When you take your seat off, and are standing behind the quad.......look down at your airbox. From the negative battery terminal, there is a small gauge wire (around 14-16ga) that is black.....it runs down beside the airbox. That wire was chaffed between my airbox and upper frame rail.....to the point it broke in half. Apparently this is a ground wire for the CDI I believe, so no ground = no spark. I soldered it back together, and was ready to ride. I've heard of several others with the same issue as well.

Hope its something that easy.....let us know what it ends up being though.

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