Yamaha 1981 YZ465 hard to start

[ALOHA]

I have a 1981 Yamaha YZ465 that is an absolute terror to start cold or hot. I can kick and kick and kick without it even popping. It will give an occasional backfire. Then out of the blue it will start.

I have been through the carb repeatedly to make sure all the passages are clean. replaced the pilot jet, the needle and seat, needle jet and jet needle. Put a new set of rings in with proper end gap. Checked and rechecked the timing several times. Changed to new plugs. Checked spark.

There are times that it will start right up. Most of the time it wears me out kicking. A 465 hurts the bottom of you feet after repeatedly kicking. I also have a new crank seal on the mag side. It does not mean that it is not leaking but it is new.

I noticed last night when I got it started that it had a air sound coming from the carb and it sounded like out the back. I also have a problem with it falling flat on it face at high rpm. Nice and crisp from low idle rpm to about just above 1/2 throttle. Then it falls flat and sounds like it is a 4 stroke.

My carb has a 45 pilot, stock needle and needle jet . The needle jet is on the top clip the leanest setting. I also have a 380 main which is one size smaller than stock. This thing is driving me nuts and I cannot seem to get a handle on it.

Any help or ideas would be appreciated.

Tired old man
Thanks
Jack

 

[sm7482]

sounds like the big bore maico 490 ive had problems starting. the fact of the matter is that a big bore twostroke is just hard to start. i'll list the way i go about starting the maico. 1st. turn fuel on pull off plug cap, turn on choke and give it some good kicks to prime the engine. 2nd. replace plug cap, use kickstart to bring piston to top dead center. 3rd. pull in compression release and give it a good hard kick. i'll usually get a few pops, a kick back, then a fire. same exact problem as your big bore. ive adjusted the ignition a bazillion times but i know its not that. carb is cleaner than it was from factory. next time you get it running spray some wd-40 behind the carb, if it picks up in idle you have a carb leak. that could cause it to be hard to start. also i'd try richening it up some. maybe picking up another jet but ultimatley lowering the clip on the needle. remember that with a bike this big, the kicking technique is everything.

 

[Trailrider92]

Mine is hard to start too and i have the same problem but the the way the old dirtbikes run so mine is a 1982 it465

 

[DEANSFASTWAY]

turn on the gas before you put your gear on walk over to bike lean bike over til handlebar touches ground and gas dribbles out vent tubes then try to start with choke on. its kinda like having a primer bulb on an outboard or weedwacker. if not that then check the reeds and seals and stuff if its an old one.

 

[SMarquez]

Put the bike in 2nd gear and rock the bike through the compression stroke with the gas on, choke on. Make sure you get full extension on the kicker and don't be shy when you kick it. I crack my throttle at the bottom of the stroke just a little bit. You could do a head mod too. Lowers compression a little and make starting easier. It involves a 30 degree cut, 8mm wide at the dome. It gives the squish a 3 angle dimension.

 

[2stroke]

plus one on lowering the compression, but an easier way to do that is add a second head gasket. No machining involved.

I would start moving the clip down slot by slot...that will affect the top end...if you r top end is bogging, its starving for fuel...a lower clip will mean a higher needle position at half throttle, and so more fuel.

that may also help the starting, since it will richen it up throughout the range.

Seriously, put the needle half way and try that, and move further down if no results.