[Karleemrose]

OK first post long story but I’ll keep it short, here goes 05YFZ 450 just got it replaced the head gaskets because there was oil in coolant and coolant in oil. Has a 480 big bore kit and hot cams. Also replaced The following: time chain, battery, spark plug, oil and filter change, coolant flush, carb cleaned, Stater was inspected and is working as far as I can tell and hearing a clicking in the relay, stator was replace before I got it, At the voltage of 12.46 the bike just cranks and it won’t start, it’s irritating as hell! Spark plug is getting spark gas in carb. Charge the battery to 13.96 and then occasionally it’ll randomly fire but sometimes not and after running the bike it will fire immediately after turning off. Checked the valve clearance and timing is fine. Also for some reason I have to pull the clutch in to try and start the bike even when I’m in neutral, not sure if that’s standard or not. When the bike does run it runs and idles great

 

[QuadManiac]

So you say it won't start and run, yet you say 'when the bike runs it runs and idles great.'

So it DOES start and run... under what conditions? Is it only under the higher battery voltage? What do you do that makes it run? What is different that causes it to be able to start and ruin? Temperature? Recent battery charge? Alignment of the planets?

A lot more info is necessary to make any kind of analysis here. Have you tried starting fluid when it won't start? You're sure that it DOES have continuous strong spark when it won't start?

Tell us more - be detailed - a long story will help here!

BTW what matters is battery voltage WHILE the starter is cranking... It can be 13v all the time while sitting, but if it drops to, for instance, 8v while starting you can have issues. Jumper it to a fully charged auto battery and see if it will start regularly.

 

[QuadManiac]

So....?

 

[Sazjun]

QuadManiac - I would like to pick up here Karleemrose started and left off.
I am having a similar issue with son's YFZ450 (I ride a 700
3 years ago we did a full engine rebuild, nothing left undone and everything done to the max, it was a $2500 engine rebuild by the time we were done with everything. Cause you know, while the engine is out, it's a perfect time to powdercoat the frame....you know how it goes,, anyhow. It ran like a raped aped for the first few times out and then on the last trip that year we could not get it to fire to a run, just sputters, or if we pull started it it would sputter out. SO we parked it, and then my son move out and now 3 years later we have time on our hands to go riding again. "thanks covid", So I've been fixing it up.... How is that for a long story so far?
This week I went thru the wiring and found the red and blue wires off the battery/relay block were worn thru from rubbing between the plastics and the frame. so I spliced them back together and wrapped them. Then I drained the fuel and oil, cleaned the air filter and replaced the battery.
It slowly fires to an idle if I spray it with starter fluid (no air cleaner on)
After several attempts it idled long enough for me to get it revving really good with the throttle and then it idled okay after too.
But it still required a spray to get it started again right away.
Next day I pulled it out, cant get it to fire up to an idle.
Starting fluid only gets it to fire a few times before it sputters out.
It has a half tank of new gas.

Is it as simple as tearing down the carb for a cleanout since it sat that long, or is it more complex?
Help o' master of the electron, I need your wisdom and guidance.

 

[morphrider]

Do you have free flowing fuel from the tank to the carb with the fuel hose removed from the carb? Does it have any kind of filter in the petcock within the tank?

 

[Motorman455]

And have you checked the valve lash? When it gets to tight, 4 strokes become very difficult to start.

 

[Sazjun]

I did check the petcock and flow today - the hose to the carb flows well.
I will check the Valve lash next. That would make sense being a fairly new build with break in time.

 

[Sazjun]

It was a gummed a carb, had to replace the pilot needle, did all the gaskets and seals along the way.
She's running great again. Thanks everyone for input.

 

[chris_pritts]

OK first post long story but I’ll keep it short, here goes 05YFZ 450 just got it replaced the head gaskets because there was oil in coolant and coolant in oil. Has a 480 big bore kit and hot cams. Also replaced The following: time chain, battery, spark plug, oil and filter change, coolant flush, carb cleaned, Stater was inspected and is working as far as I can tell and hearing a clicking in the relay, stator was replace before I got it, At the voltage of 12.46 the bike just cranks and it won’t start, it’s irritating as hell! Spark plug is getting spark gas in carb. Charge the battery to 13.96 and then occasionally it’ll randomly fire but sometimes not and after running the bike it will fire immediately after turning off. Checked the valve clearance and timing is fine. Also for some reason I have to pull the clutch in to try and start the bike even when I’m in neutral, not sure if that’s standard or not. When the bike does run it runs and idles great

OK first post long story but I’ll keep it short, here goes 05YFZ 450 just got it replaced the head gaskets because there was oil in coolant and coolant in oil. Has a 480 big bore kit and hot cams. Also replaced The following: time chain, battery, spark plug, oil and filter change, coolant flush, carb cleaned, Stater was inspected and is working as far as I can tell and hearing a clicking in the relay, stator was replace before I got it, At the voltage of 12.46 the bike just cranks and it won’t start, it’s irritating as hell! Spark plug is getting spark gas in carb. Charge the battery to 13.96 and then occasionally it’ll randomly fire but sometimes not and after running the bike it will fire immediately after turning off. Checked the valve clearance and timing is fine. Also for some reason I have to pull the clutch in to try and start the bike even when I’m in neutral, not sure if that’s standard or not. When the bike does run it runs and idles great

i have been having this EXACT same issue with my yfz450r after getting top end rebuilt. have you found the problem yet?