My yz490

[jackdim]

Hi all,

I'm Jack, 22 from Bristol in England. Just bought this 490 yesterday and wanted some help in trying to identify what year it is? The owner claimed it is a 1981 and was first registered for road use in 1992.

Also need some help with stock jetting settings and a stronger right leg would be nice please .

Thanks in advance,
Jack

[merlyn1965]

Definetly an 82 with the mono-X rear suspension and the exhaust on the left hand side. In 81 on this side of the pond, we had the YZ465

[D tom]

Wow! looks nice. I wish I could register my 80ish yz 490 on the road.You can beat any one between stoplights. Cheers. Do yourself a favor put a front disc on her.Its not that hard just find an Aluminum welder to put two mathing caliper threaded lugs on one fork and find a wheel with a rotor. Best of luck.

[jackdim]

Originally Posted by D tom

Wow! looks nice.(...). Do yourself a favor put a front disc on her.

I've not ridden her yet, is the drum brake really that bad? I'll probably see if I can source any newer yz's front end and slot that in. If that fails then I'll look into modding my current one.

I can't wait to ride this 4speed beast, probably after work today I'll give her a quick blast

[D tom]

Like to hear how the ride went.You dont HAVE to fix front brake but from my experience it would be a safer on road experience(depending on the type of riding) . The disc just has a quicker responce time and a bit better stopping power.

[Dan151]

that frame is spotless! clean bike man

[jackdim]

Originally Posted by D tom

Like to hear how the ride went.

Didn't get to ride her, too late and the mix the previous owner had put in was far too rich on the 2t so I didn't bother.

Originally Posted by Dan151

that frame is spotless! clean bike man

Was powder coated before being mothballed for about 7yrs, looks lush eh?

[jackdim]

Had a ride and she's incredibly rough, spark is strong so I guess it's either jetting or possibly timing.

My jetting is:

Main Jet: 400
Pilot: 50
Needle: Middle clip

What's stock settings?

Anyone got a manual pdf I could d/l?

Thanks,
Jack

[jackdim]

About as much help as a chocolate teapot here



My jetting aint far off stock then?? Reeds are good, little play in the throttle slide but not enough to cause this severity of issue. So..........I reckon it's ignition timing, will have to buy myself a strobe and test it.

Also my kicker is totally the wrong one so will have to source myself another, mine looks to be from a rd350.

Ta,
Jack

[D tom]

Not 100% sure its your timing. Can you be more specific about the symptoms? You know it is almost always something stupid and easy.
Spark plug,plugged main jet,leaking intake etc.But if you are sure its timing let me know and we can get you set back close to stock without buying a strobe . Ckeck the hose between intake manifold and box under tank (Looks like it was covered) small hole is all it takes. Did you add a light coil for street riding?If it is an ignition problem you might start there. Ill try and dig up those stock jettings asuming sea level with Mikuni 44mmcarb best of luck.

[jackdim]

Originally Posted by D tom

Not 100% sure its your timing. Can you be more specific about the symptoms? You know it is almost always something stupid and easy.
Spark plug,plugged main jet,leaking intake etc.But if you are sure its timing let me know and we can get you set back close to stock without buying a strobe . Ckeck the hose between intake manifold and box under tank (Looks like it was covered) small hole is all it takes. Did you add a light coil for street riding?If it is an ignition problem you might start there. Ill try and dig up those stock jettings asuming sea level with Mikuni 44mmcarb best of luck.

Well, I completely stripped the carb i.e. emulsifier out, needle out etc and sprayed through all the jets with compressed air and carb cleaner. Every jet is per manual except the main which is a 400 and not a 440.

Spark Plug is brand new, I took the cap off and held the ht lead ~20mm away from the pot and when kicked over got a nice blue spark. Also a nice spark when spark plug in and earth to pot.

The reeds are fine, no damage and close and open properly. The intake manifold looks good with no cracks and a decent gasket.

I've yet to check the ?YEIS? bottle and pipe for leaks so will do that today. It also needs a new air filter as mines got a hole in it.

It's got brand new 95ron fuel with Shell Racing X oil mixed at 40:1.

So, apart from timing I can't think of anything else it may be??? Maybe it was retarded to reduce pinking???

SYMPTONS:

Won't idle by itself, need to open throttle a touch at all times. Won't rev out at all, even with clutch in or in neutral. Juddering when ridden no matter what gear she's in.

[D tom]

Keep in mind that bike will probably never be (smooth) untill you do the head modification ,carb cutout,oversize engine bolts etc. But it should rev better than what you are saying.I'm no expert on setting timing on that year,and I cant find any info. If you want to play with it a bit I think there is only slight adjustments that can be made by removing the flywheel cover and moving the magneto slightly forward or backward.Check to make sure the flywheel is set properly on shaft and has not started working loose or sheared a key .(cant remember if its a key or spline)Hopefully someone who knows will jump in soon.I mix my 490 32:1 and use an NGK B8ES plug and it purrs nicely but i have done all the mods and I had to replace the cylinder base gasket.I did a compression test and got over 150psi (11bar?)

[jackdim]

Thanks again for your help Dtom, I've ridden other singles and know they're not "smooth" as such but this is different. Although it doesn't have a tacho I'd guess it won't rev over 2k rpm no matter what I do or whatever gear it is in. I might take the wheel off today and have look to see what's up.

One she's running as should then I'll look into getting the motor modded .

I can't wait to ride her

[mkpack77]

I've got a manual, let me know the engine and frame serial numbers then I can tell you exactly which bike you have and whatever other info you need.

[merlyn1965]

I do not have the spec for an 82. My book goes 84-90. Now I ain't no expert but just for trying something very quick, take your exhaust off and start it just to prove that it wouldn't be your exhaust almost clogged. I never seen it happen but it would be a cause for the symptoms you're having right now and honestly, it is very easy to check compare to everything else. And your mix is quite lean, it is an air cooled bike so I'd suggest 32:1 at the most. There's no power valve on these so no chance of gumming them up as other engines do.

[OlSchoolFool393]

It could very well be a clogged pipe
On My Maico after rebuild would start and run but would not rev found small rats nest inside Ha Had to wash out backwards
OSF

[D tom]

Thats a good thought.I once had a nest in my yami 485 phaser sled but it had a restrictive silencer and it sounded muffled,Till I rapped it out a few times, Then mice were shooting out .I kinda wonder if the previous owner tryed to quiet the thing with a restrictive silencer?

[jackdim]

I know the spannie isn't clogged as I chucked a nut in there and rattled it about. However, I haven't checked the silencer but will try and start it without it today. My neighbours are going to love me..............

Ta again,
Jack

[jackdim]

Silencer was clogged right up, both the inlet and outlet of silencer was completely blocked! Removed all of the wadding and she ran spot on, revved up etc, but because I needlessly messed with timing I'll have to set it properly again.

I knew it was something simple! thanks to all for your help. once i've done forks seals and got motor back in I'll post some videos .

[merlyn1965]

You're welcome bro. Now watch yourself and enjoy it. Looking forward to watch the videos.