Gibbits YZ490A

[alexbrown64]

Sounds good.. its going to rip when you take her for a blast.
What are you going to do with the tank.  I think you can bleach them, shave them, sand them, full cover decals or tank cover etc..
Also, how did you do the seat cover as i have a mate with an 89 yz250 and he wants virtually the same thing.
Cheers,
Alex

[Gibbit]

Sounds good.. its going to rip when you take her for a blast.
What are you going to do with the tank.  I think you can bleach them, shave them, sand them, full cover decals or tank cover etc..
Also, how did you do the seat cover as i have a mate with an 89 yz250 and he wants virtually the same thing.
Cheers,
Alex

Took her for a gentle run today, just running it in. Seems a bit lean but I'll wait for it to be run in before I play with the tuning.
I got the seat cover from pit replica on eBay then just got my mate who's an upholsterer to sew the gripper seat material over the top of it.

[Gibbit]

I think I will have to buy a new oem tank when I can afford it. Bleaching apparently hardens the plastic and dosent really get them white again. I tried sanding it but the stain is right through. If anyone's done something that's works well, I'm open to suggestions.

[alexbrown64]

Taken from thumpertalk

 "Not wanting to buy a new tank for vanity's sake, I went to my local bike shop to inquire about methods to restore the plastic. I was told by the parts counter that there was no way to remove this staining because it was actually the result of gasoline evaporating through the plastic for years on end, which stains the plastic from the inside out because of the pigments in the gasoline. Thinking this was odd, I went home, grabbed a pocket knife, and scratched the tank with the blade.... pure white just beneath the surface grime! So, I was either handed a line of BS to try to sell me a tank, or the guy just didn't know what he was talking about.

So, long story short is this.... If you get this unlikely story, don't just fork out the cash for a new tank. Try the pocket knife test first. If you get white underneath, it can be cleaned off. Here's how...

To get back to the pretty white shine, I used a combination of two methods... First, I took some sand paper (120 grit) to the tank to scrape off the stained plastic. Then I smoothed it with a finer grit. I also found that Soft Scrub with bleach and a lot of elbow grease took the staining out pretty well, too. The best outcome was achieved with a combination of sanding and Soft Scrub. When the Soft Scrub wouldn't quite do it (staining was too deep), the sanding finished it off nicely. A little disclaimer here... Keep in mind that if you apply sand paper to your tank, you will no longer have that smooth plastic sheen that was orginally there. It'll wind up with more of a matte finish. Of course, if it was stained anyway, who really cares? Anyway, don't say I didn't warn you if you'd be pissed at the matte finish result."  http://www.thumpertalk.com/topic/549226-tip-regarding-stained-fuel-tanks/

DC sells brand new white Clarke tanks for your bike for $230... https://www.dcvmx.com/xcart/product.php?productid=20619&cat=484&page=2

This mob will paint your tank, but its not cheap.. alternatively you can diy.. http://www.mxrestoration.com/tanks.html

This guy had a good go at a white yz tank and it came up pretty good.. http://motorcyclerenew.blogspot.com.au/2014/04/yz80-white-gas-tank-refurbish.html

Cheers,
Alex

[Marc.com]

Took her for a gentle run today, just running it in. Seems a bit lean but I'll wait for it to be run in before I play with the tuning.
[/quote]

YZ490 is notorious bitch of thing to get jetted right, usually you get lots of mid range and no top end or pinging away bottom end ....the Serco head mod lowers compression which is a step in the right direction, IT490 head also works. Judging by the piston and head cracks it was pretty lean to start with, I would jet up a bit before I rode it any more.. They are really sensitive to the needle position, my 490S was like night and day just with one clip position changed.

[Gibbit]

Taken from thumpertalk

 "Not wanting to buy a new tank for vanity's sake, I went to my local bike shop to inquire about methods to restore the plastic. I was told by the parts counter that there was no way to remove this staining because it was actually the result of gasoline evaporating through the plastic for years on end, which stains the plastic from the inside out because of the pigments in the gasoline. Thinking this was odd, I went home, grabbed a pocket knife, and scratched the tank with the blade.... pure white just beneath the surface grime! So, I was either handed a line of BS to try to sell me a tank, or the guy just didn't know what he was talking about.

So, long story short is this.... If you get this unlikely story, don't just fork out the cash for a new tank. Try the pocket knife test first. If you get white underneath, it can be cleaned off. Here's how...

To get back to the pretty white shine, I used a combination of two methods... First, I took some sand paper (120 grit) to the tank to scrape off the stained plastic. Then I smoothed it with a finer grit. I also found that Soft Scrub with bleach and a lot of elbow grease took the staining out pretty well, too. The best outcome was achieved with a combination of sanding and Soft Scrub. When the Soft Scrub wouldn't quite do it (staining was too deep), the sanding finished it off nicely. A little disclaimer here... Keep in mind that if you apply sand paper to your tank, you will no longer have that smooth plastic sheen that was orginally there. It'll wind up with more of a matte finish. Of course, if it was stained anyway, who really cares? Anyway, don't say I didn't warn you if you'd be pissed at the matte finish result."  http://www.thumpertalk.com/topic/549226-tip-regarding-stained-fuel-tanks/

DC sells brand new white Clarke tanks for your bike for $230... https://www.dcvmx.com/xcart/product.php?productid=20619&cat=484&page=2

This mob will paint your tank, but its not cheap.. alternatively you can diy.. http://www.mxrestoration.com/tanks.html

This guy had a good go at a white yz tank and it came up pretty good.. http://motorcyclerenew.blogspot.com.au/2014/04/yz80-white-gas-tank-refurbish.html

Cheers,
Alex

Thanks mate.  I tried the pocket knife test and its not white underneath but it's a bit better (See photo) and will probably make it nicer until I do get a new tank.  The Clarke tanks are long range tanks and look a bit ugly. I will get one of these at some stage for when I race it at Finke, but would like the standard size tank for the majority of riding.

When I read about bleach making the plastic go hard I think they where leaving it in bleach for days, so maybe a few hours will be ok.  Ill do some testing with the different methods and report back.

A new OEM tank is worth $580 inc. postage.

[Gibbit]

Took her for a gentle run today, just running it in. Seems a bit lean but I'll wait for it to be run in before I play with the tuning.

YZ490 is notorious bitch of thing to get jetted right, usually you get lots of mid range and no top end or pinging away bottom end ....the Serco head mod lowers compression which is a step in the right direction, IT490 head also works. Judging by the piston and head cracks it was pretty lean to start with, I would jet up a bit before I rode it any more.. They are really sensitive to the needle position, my 490S was like night and day just with one clip position changed.
[/quote]

Thanks mate.  The left hand crank seal was in pretty bad shape so I think it may have contributed to it running lean.  The previous owner was running a 490MJ and standard is only a 470MJ. I have a 480MJ in it at the moment (I can't remember where the needle clip is).  It was pinging a little under load when I rode it yesterday so I took the mixture screw from 2 turns back to 1.5 turns which helped. Its blowing a little smoke so I think it should be ok for another hour or so putting around until I start doing plug chop tests.

[Marc.com]

Thanks mate.  The left hand crank seal was in pretty bad shape so I think it may have contributed to it running lean.  The previous owner was running a 490MJ and standard is only a 470MJ. I have a 480MJ in it at the moment (I can't remember where the needle clip is).  It was pinging a little under load when I rode it yesterday so I took the mixture screw from 2 turns back to 1.5 turns which helped. Its blowing a little smoke so I think it should be ok for another hour or so putting around until I start doing plug chop tests.
[/quote]

Needle is worth about 3 main jet sizes in midrange, so start by going up to top position on clip....480 MJ should be about right. Replacing both crank seals and also make sure the seals around the read block are all new and sealing, any air leak is a major issue.

Pick up the needle one clip at a time and see how it goes. Use premium fuel and Bel Ray synthetic oil.

There is another modification that drills two holes ( about 6mm) from the floor of the intake into crank case space, the idea is you boost  the pressure in the intake  when the piston is descending using the displacement of the piston.... that was the set up I used on my WR500 which improved it .... came from the set up Robbie Twyerold used on his 490 which ran the cleanest I have seen.

I like the 490 T really nice looking bike.

[Gibbit]

Now that its run in I have been fiddling with the tuning with not too much luck yet.

It is still pinging about half throttle a bit so I lifted the needle as a quick fix. It stopped the pinging but after riding it for a while it became impossible to start. Each time I checked the plug it was oiled up.  I have put the needle back to the standard setting again and it starts first kick again.  I think I will go up a size in the main jet and see how that goes. Im going to a vinduro this weekend so I might leave it for now as it will be a bit of slow riding without too much WOT.

[Marc.com]

Now that its run in I have been fiddling with the tuning with not too much luck yet.

It is still pinging about half throttle a bit so I lifted the needle as a quick fix. It stopped the pinging but after riding it for a while it became impossible to start. Each time I checked the plug it was oiled up.  I have put the needle back to the standard setting again and it starts first kick again.  I think I will go up a size in the main jet and see how that goes. Im going to a vinduro this weekend so I might leave it for now as it will be a bit of slow riding without too much WOT.

Yes this is where the fun starts as in theory the needle and main are addressing the mid range to WTO and should not influence starting as this happens in the range of pilot and slide. 480 MJ should be enough but I guess try 490 MJ ..  the difference between hitting and missing can be one clip position. My own feeling about the 490 is the problem is a mix of things.... 500 2 strokes like to ping, too much compression and too little flywheel effect plus the jetting. I am sure that the Serco modification to the combustion chamber is effective in as much as it is about lowering compression as it is about squish shape.

One of my friends swore by using 2 head gaskets in his 490 and another used an IT490 head and said that fixed it. 

Finally I solved my 490 issues by dumping it on a 250..... but I do have a soft spot for the old air hammer as they will take a lot of abuse and the 490 T was a pretty looking bike.

[Gibbit]

Thanks mate. I think the phrase 'close enough it good enough' will come into play here. It's either going to be the 480mj or 490mj. Probably will depend on wether I'm trail riding or MX.

[80-85 husky]

run a high quality synthetic oil at say 70 to 1 and see if that helps...just a suggestion. (motorex)

[evo550]

I have an article somewhere on what Broc Glovers mechanic did to their '85 factory 490.
See if I can find it, from memory had something to do with modifying the standard needle and maybe head mods.

[Marc.com]

I have an article somewhere on what Broc Glovers mechanic did to their '85 factory 490.
See if I can find it, from memory had something to do with modifying the standard needle and maybe head mods.

From what I have read Broc 's mechanic lowered the compression ratio, fitted a flywheel weight and from all accounts Broc hated it and rode it as little as possible.

Sounds like PWK carb can be jetted better and using 2 head gaskets like of my mates did isn't a bad idea.

[kim80y]

Don't get mixed up between fixes for the older models V's the newer ones.

IT490 head has less studs than 85 and up YZ490, as IT is side port engine similar to used in 82-84 YZ490.
85 and 86 490 have different ports to the 87 to 90 as well.

............

Cheers
Kim