Sign in to follow this  
Followers 0
-Biggins-

03 450 wants to start but dosent..

12 posts in this topic

Hey guys, I'm new to the racing four stroke world. (Had some XR's in the day) I picked up a 2003 yz450f the other day for the right price. I added some seafoam to the gas, and now it won't start. I took it all apart, checked the valves, (both a little tight, adjusted intake and exhaust to spec, checked for properly seated shims) timed it according to the "I" mark on the flywheel and sticking an Allen wrench in the spark plug hole. Has good spark, good compression, almost perfect timing, cleaned out the carb. Didn't try replacing the gas. Before it would start first kick every time. After I added seafoam, it smoked a little bit when I started it up, but then soon went away about after 2 seconds of running time. So my question is, what am I doing wrong?

Share this post


Link to post
Share on other sites

Start by replacing the gas, including draining the carb of whatever is in there.  If that doesn't clear up the matter, you may have a blocked or partly blocked main or pilot circuit.

Share this post


Link to post
Share on other sites

Got new fuel, it wants to start but dosent. I took the silencer off to pull the subframe back, and I noticed there's unburnt fuel coming out of the header. It has a good vibrant spark. WTF?

Share this post


Link to post
Share on other sites

try a new spark plug

it's LITERALLY brand new. Still won't start. New gas, new plug, valve clearances PERFECT, timed properly at TDC, has great spark, great compression, cleaned carb a week ago, unburnt gas. When I clear it out, (hold kill switch, and throttle wide open, kick it about 20 times) it does want to start. Like it will turn over a couple times, and the kickstarter will make the ratcheting noise.

Share this post


Link to post
Share on other sites

Thanks guys. I'll try that next. I need to currently get a new o ring for the slide assembly as i used carb cleaner and it ruined the gasket.

Share this post


Link to post
Share on other sites

It's not an O-ring, but try letting it dry out for an hour before you decide it's no good.

here's where I'm at now. Re cleaned the carb, new cam chain, re-checked the valve clearances, timed at TDC,(perfectly) got it to start for a breif second with the hot start on. I noticed it had lots of Unburnt fuel in head pipe. But, it will start every time with the hot start on for a brief moment. I got it to run as I revved it, (sounded like sh*t) and it was puffing whiteish/blueish smoke. Didn't smell like coolant. Dosent burn oil I don't think. The smoke stayed around like it was burning oil. I know I need to clean the carb again because it dosent need to be leaner as it ran fine. No popping on decel or nothing. So my question is, what could be the cause of smoke?

Share this post


Link to post
Share on other sites

A leaking head gasket could get coolant into the chanlmber and cause smoke. Are you giving it a lot of gas to start it? Four strokes are not like two strokes, you shiuld not need to give any throttle to start a four stroke. If you do, it floods it and then it will start wfo, but that is not ideal.

Share this post


Link to post
Share on other sites

A leaking head gasket could get coolant into the chanlmber and cause smoke. Are you giving it a lot of gas to start it? Four strokes are not like two strokes, you shiuld not need to give any throttle to start a four stroke. If you do, it floods it and then it will start wfo, but that is not ideal.

it dosent have that maple syrup smell. Smells like the excess fuel is burning off, or oil. No I don't give it gas to start. I've kicked it over about 500 times. That's why. But, the coolant smoke would go away quick, wouldn't it? Has good compression. It didn't smoke before. All I've done to it is shim the valves, install a cam chain, clean carb. Runs for a brief moment like I said with the hot start on. So I need to clean out the pilot circuit better, but I need to know WTF where's this smokes coming from

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0