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Hi all, Im recently the proud owner of a 2005 450r. It wont start, which is how i bought it. Valve clearance is within spec. I had my local honda dealer inspect piston and cylinder tolerance and everything was within spec. They told me to put new rings in since i had it apart, so i did. still won't start. Compression is 70 psi cold. I'm at my wits end here folks can anyone help me?

Check to see if it has spark by taking plug out and putting it against the head to ground it and kick it over a couple of times to see if it sparks bright blue. If it does check to make sure carb is clean.

Good spark tried a table spoon of gas in the spark plug hole still nothing. I was going to do a leakdown test on it but cannot keep the engine at TDC.

Update, I've got about 10% leakdown and 65 PSI of compression. I've tried ether and verified acell pump is working. I've tried dumping fuel down the hole as well, still not even an hiccup. I can hear a bubbling noise from the crankcase. Mind you this is new rings and a cylinder and piston that was checked out by a reputable source. Valves are set perfectly lots of spark. Time to part out I guess and go back to two strokes.

Do you have any prior history on the bike ?? , did the prior owner explain the circumstances of its non running condition ??

Have you verified the timing is correct at all 3 locations ?? , which are , and ALL need to be aligned at the same time , ignition cover small round hole/slash mark on flywheel , clutch side case large round hole/dot on gear aligned with mark on case , and slash marks on opposing sides of the cam sprocket/need to be level with head while the cam is in the 2 O'clock position *cam lobes facing rear of engine*

The only thing the prior owner said was it needed a new lower end rod bearing. He said it had a new top end which was not true. The crank speced out fine. He won't return my calls so that option is gone. Yes all 3 marks were verified. Timing is between the two marks on the mag side. The only thing i can see wrong is my static compression is below spec at 65 psi. The manual says 78. Im at a complete loss, ut sure appreciate all the help

Tablespoon of gas is basically flooding th motor. The carb only lets a mist of fuel get into the combustion chamber. Verify that all jets are clean and all of the passages are clear. Also make sure the backfire plate on slide is not upside down. If it is. It will not let enough air through because it blocks the passage. Angle side of the plate should be pointing up. If I remember correctly.

backfire plate was upside down. What is the proper procedure to verify correct float height?

Make the float tang level with the rest of the float body. rarely does the float need to be changed. It was stamped in the position that it runs best at.

Ok will do. Can a failing tps sensor and/or the plate being upside down cause a no start?

Well here we are again.... brand new head new piston new cylinder carb gone thru p.o.s still wont start. Timing is perfect lots of spark. Help please

Well here we are again.... brand new head new piston new cylinder carb gone thru p.o.s still wont start. Timing is perfect lots of spark. Help please

Did you ever get this figured out? I'm having similar issues with a 2005 CRF150f. Bought not starting to fix up, similar compression issues. Replaced the piston, rings, cylinder, and carb and still nothing.