Bike that won't start.

I'm pretty new to the small engine thing. And I've never dealt with carburetors. But I got my hands on a bike that won't start and I'm seeking help to trouble shooting what the issue is from someone who knows more then me.

 

My bike is an 07 YZ450F.

 

I know the motor rotates easily, motor is good, I have spark, I have gas flow, air filter was cleaned, I cleaned the carb, fresh gas and new oil and coolant. New plug today. How would I go about adjusting the carb on a bike that won't start, or how would I diagnose if the carb is being a dink at all?

 

 

Have you checked compression?

Did it run previously or hasn't ran since you got it??

Sometimes an easily rotating motor is a bad sign, should have tons of compression. Is decompression switch stuck open? There are many things to check and compression should be first

Sometimes an easily rotating motor is a bad sign, should have tons of compression. Is decompression switch stuck open? There are many things to check and compression should be first

I had the plug out, I changed the timing chain and when I had the valves all closed I was rotating the flywheel with my hands. I don't have a compression tester for the smaller engines mine only fits a normal sized spark plug but I will get it tested soon, the piston and valves looked brand new, the valve gaps were all spot on aswell. And is the decompression switch the little lever on top of the clutch lever?

 

 

Have you checked compression?

Did it run previously or hasn't ran since you got it??

 

Not yet. I know it has compression from trying to kick it and even rotating in with the plug in. but I don't know the psi's yet so I can't say its good but i believe its probably in range. and Yes I did get the bike running when I first seen it, didn't run awesome but it idled with like 6 year old gas in it. I didn't want to work it too much till i got it looked over well.

Has timing been properly set? Didn't run after the timing chain swap??

Yeah I believe I got it timed right. Had the mark on the flywheel lined up with the mark on the stator cover and the cams were set properly.

Here's a pic

Or maybe not lol. My phone doesn't want to upload a pic.

image.jpeg

Edited by Spilly

Would need to see crank mark to be sure it was set right

And the front gear looks like it's off one tooth to me in pic

Set the fuel screw at 1.5 turns.

Raise the idle / turn the screw in a 1/2 or more turns

Clear the cylinder; 10 kicks with the throttle wide open and the kill button on

Fresh fuel

Set the fuel screw at 1.5 turns.

Raise the idle / turn the screw in a 1/2 or more turns

Clear the cylinder; 10 kicks with the throttle wide open and the kill button on

Fresh fuel

Ok, I'll give it a go. Thank you

Would need to see crank mark to be sure it was set right

And the front gear looks like it's off one tooth to me in pic

I'll add it for you

Flywheel

 

The camera was off to the side a bit, it looks a bit off but it was right on. I had the light in one hand and phone in the other.

image.jpeg

Edited by Spilly

The lever on the clutch perch is not a decompression lever, it is a hot start lever, don't use this when trying to start a cold engine, it won't hurt anything just make it harder to start. There are many videos about starting a yz450 that are very helpful. I have a 07 yz450 my starting procedure is this, cold engine- turn gas on- pull chock out-give two to four full twists of the throttle-move engine to top of compression and kick. has yet to fail me on both 07 450s that I have owned. 

...is the decompression switch the little lever on top of the clutch lever?

 

 

No, it's automatic, internal, and it's not a switch. And it won't "stick open", either. 

Alright did everything everyone said and I can get it to back fire now. Still won't fire up but there is combustion

I'm going to go look over it again, make sure my timing is on and stuff.

Maybe start with pulling the carb and just cleaning it out .

I know a lot of people wouldn't recommend this. But sometimes what I do is hold the throttle open and just spray 1 squeeze of gas in. (make sure it's the mist and not stream). Then close throttle and kick.The engine should start and run for a second or two

Edited by dougla12

Here's a pic

Or maybe not lol. My phone doesn't want to upload a pic.

 

 

Cams are correct. Just be sure you are on the right mark on the flywheel.   Some of the yamahas have the following mark >>    "   I  "      "  I     I  "       " I---I  I "  

 

always use the last mark, or if there is a T.  NOT F

What elevation are you at? What are your mods?

 

Im going to tell you how to check everything. I need to know as much as possible about this bike. 

PM me if youd like

PM me if youd like

Perfect! Bikes a 2007 YZ450F

 

Fuel Screw = 1 1/4 turns

Main = AB165

Pilot = 42? (paper has oil on it and can't complete read the number, looks like 42 but can't see the 4 real good)

Needle = 5 (I moved the needle from 4 to 5 when cleaning via some advice I got on how it was stuttering in the mid range)

 

My elevation is under 500ft, aroung 350-450.

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