need yfz450 experts

[Snopczynski]

Are you 100% positive the timing chain is set right, and the valve timing is right?

[Ben350]

so does it get a consistent spark now?

 

i would triple check your valve timing, and make sure your valve clearances are OK. A tight valve or the timing being off will lower your compression, making it hard starting and a bad idle

[locogato11283]

Are you 100% positive the timing chain is set right, and the valve timing is right?

im 99% sure. im gonna recheck. i was on the phone with BBIII when i set it. valve timing? i just set the flywheel to TDC and set the cams.

 

so does it get a consistent spark now?

 

i would triple check your valve timing, and make sure your valve clearances are OK. A tight valve or the timing being off will lower your compression, making it hard starting and a bad idle

i dont know. when i pull the spark plug and try to ground it and turn it over, i dont get any spark. it must be getting spark inside the head though because itll fire and run as long as im on the gas.

 

the valves were just checked in october. one was out, but was fixed. this bike ranperfectly fine 5 days ago before i did the rebuild. it wont idle at all. it will only start and run if im on the throttle.

[locogato11283]

spark plug is brand new. did the same thing with the old one.

[2strokespirit]

Thought I combined my post to one, you allready answered, just curious on another note, have you done a cam mod, changing the valve timing to the YZF450s? Try it man... really

[locogato11283]

Thought I combined my post to one, you allready answered, just curious on another note, have you done a cam mod, changing the valve timing to the YZF450s? Try it man... really

yep. did it the day i bought it.

[Ben350]

You really should be getting a spark, i had a problem with mine not starting a while ago due to being frozen and i remember laying the plug/coil onto the top motor mount i think to check spark, and would get a consistent spark. So if you put yours there, it should spark. Do you have a DVOM meter? try checking the resistance between the head and negative cable of the battery. Double checking nothing bad happened when the flywheel was removed/installed was a good idea too

 

Your cam timing (some people call it valve timing) still seems the most likely culprit. Its not as straightforward as it should, lining up the marks, especially with the cam mod done too. Easily could be off. You referring to a manual for how to do it?

 

I think a compression test might be in order too, quick enough to do

 

I have seen a lot of the intake boots tear too, usually tears inside the boot where it wraps around the carb, could have happened when you put the carb on or took it off

[SonOfSand]

I had my head upside down once while looking at it, one of the buckets fell off and I put it back on. I didn't notice the shim had fallen out, I all most put the motor back together like that. Could you have lost a shim while looking for the clip? Could that cause the problem you are describing?

[speed-racer]

You really should be getting a spark, i had a problem with mine not starting a while ago due to being frozen and i remember laying the plug/coil onto the top motor mount i think to check spark, and would get a consistent spark. So if you put yours there, it should spark. Do you have a DVOM meter? try checking the resistance between the head and negative cable of the battery. Double checking nothing bad happened when the flywheel was removed/installed was a good idea too

 

Your cam timing (some people call it valve timing) still seems the most likely culprit. Its not as straightforward as it should, lining up the marks, especially with the cam mod done too. Easily could be off. You referring to a manual for how to do it?

 

I think a compression test might be in order too, quick enough to do

 

I have seen a lot of the intake boots tear too, usually tears inside the boot where it wraps around the carb, could have happened when you put the carb on or took it off

 

^^^^^Good info.

[locogato11283]

You really should be getting a spark, i had a problem with mine not starting a while ago due to being frozen and i remember laying the plug/coil onto the top motor mount i think to check spark, and would get a consistent spark. So if you put yours there, it should spark. Do you have a DVOM meter? try checking the resistance between the head and negative cable of the battery. Double checking nothing bad happened when the flywheel was removed/installed was a good idea too

 

Your cam timing (some people call it valve timing) still seems the most likely culprit. Its not as straightforward as it should, lining up the marks, especially with the cam mod done too. Easily could be off. You referring to a manual for how to do it?

 

I think a compression test might be in order too, quick enough to do

 

I have seen a lot of the intake boots tear too, usually tears inside the boot where it wraps around the carb, could have happened when you put the carb on or took it off

it will fire and run.. so its got spark. it just wont stay running. timing is correct. i was on the phone with BBIII when i set it. i know its right.

 

intake boots are fine. no tears. this bike ran 5 days ago, with no issues of the sort.

 

I had my head upside down once while looking at it, one of the buckets fell off and I put it back on. I didn't notice the shim had fallen out, I all most put the motor back together like that. Could you have lost a shim while looking for the clip? Could that cause the problem you are describing?

they are all there. couple buckets fell out and i had to get them back in place. i checked the rest while i was at it.

[kawiking]

it wont even start without feathering the throttle, even with the choke on.

 

boot is on tight. no leak there. i cant imagine that would make it not start though, even if it was..

 

pics of your girl will make me feel better! :biggrin:

i had her put this shirt on for u tyler...

 

 

i was just saying that , i had the intake boot come off my kfx400 one time... a bitch to try and start . id have to hold it 1/4 throttle to get it to start. if i let off the throttle it would die. just my luck , it was gettin dark and it back fired acouple times.. i saw the flame out the tail pipe and realized it had to be lean ..

yep .. intake was loose.

 

 

i bought a pol pred this summer, it had trouble starting. fresh rebuild, but it would run and start after u pull started it.

i believe it was a exhaust valve stuck open .

 

what does bobby think it could be ?

[locogato11283]

well, i finally figured it out.. my air filter wasnt on. i guess it was getting too much air. its weird though, because i know ive run it before with no filter on it..

 

i knew it was something stupid.. i rechecked the cams and they were right on.. i had planned to clean the filter so i didnt bother putting it back on.. decided to give it a shot. sure as fuck it fired right up. fuckin 4 strokes are some finicky bastards.

 

thanks for all the help and suggestions guys..

 

bobby, thanks for taking all my calls on this. you def helped reassure me my cams were set right and gave me other ideas as well.

[Snopczynski]

Shit, sorry Tyler. I had that happen to me once, and I didn't remember it until you just said it.

[kawiking]

good ,glad it was something simple , bro

[arfountain]

That is some crazy shit right there.