IT490 Tech Talk

Discussion in '2 smokers' started by Earthmovin490s, Sep 27, 2013.

  1. Earthmovin490s

    Earthmovin490s Adventurer

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    Hey fellow mega 2 stroke gurus! I want to get a thread started on these still-amazing bikes. I'm looking to do a front disc brake conversion and some cylinder work. I thought about sending the head away to have it ported and polished, but wondered if a YZ 490 would do the trick for less money. Lastly, I was curious if an extra Mikuni flatslide off of my 97 CR 500 would work for crisper throttle response? The boots line up and fit on both sides, throttle cable is good, just stuck on where to even start with the jetting. Thanks everyone for stopping by.
    #1
  2. dhallilama

    dhallilama Long timer

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    while not an IT, I had a YZ490. it was a beast and a pain in the ass to get started. it was also never happy with the jetting.

    then i sent the head & jug to Eric Gorr asking for the "head mod"... transformed the bike. easier starting, way happier with jetting and it may have just been in my head but i swear it vibrated less. it was the best $ spent on that bike, ever.
    #2
  3. Earthmovin490s

    Earthmovin490s Adventurer

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    I am strongly leaning towards having a cylinder sent away for port work, rather than encountering an issue after buying a YZ's. I've heard several people say that they've had issues with 83-85 YZs being on the cantankerous side. Thanks for your input!
    #3
  4. Rot Box

    Rot Box Been here awhile

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    I second the Eric Gorr head mod :evil I'd have him do the porting as well. He is very familiar with those engines and knows how to make them run like they should without the constant pinging and roller coaster jetting.

    The Keihin PWK's are as good as it gets for carbs imo. If you swap out the stock carb that's the one I'd shoot for. They came on a lot of bikes stock so finding a good used one shouldn't be too difficult. Jetting.... Start rich and work your way down.

    Cool bikes. A friend has a WR500 and it is such a hoot to ride :D
    #4
  5. racer

    racer Long timer

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    Indiana
    I had an IT490 that I used to enduro. Sat on the starting line one time for at least five minutes, kicking away, before it finally started. Lots of power, however, I was twice as fast in woods when I bought the little IT200. Wish I still had that bike. Light, easy to start, bullet proof, and simple as a hammer.
    #5
  6. dhallilama

    dhallilama Long timer

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    when i sent my jug/head to Eric Gorr, i asked for the head mod and stated i wanted low-end grunt. hot damn, that mill lugged along at idle with instant throttle response after i got it back.
    i cannot recommend it enough.

    i also sent the rear shock to race tech & got their gold valve cartridge emulators for the forks.

    i used the bike just for trail & desert riding. it was incredibly easy to live with & a monster when i wanted it to be.

    somewhere along the way i had too many bikes and let the 490 go.
    really miss the 490 & intend on replacing it one day.
    #6
  7. Earthmovin490s

    Earthmovin490s Adventurer

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    I gotta give you guys props. I've found out more info from you in one day, than six monthsbof sucky search engines. Never wouldve found Eric Gorr otherwise!
    #7
  8. athomerecords25

    athomerecords25 Banned

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    I already have an few threads here and didn't want to waste bandwith by creating another one.

    My issue is in regards to a 1983 Yamaha YZ90 but it is in the same family as the IT490 so I thought I would post it in this tread. It should also spark this tread along the way.

    I am having an issue with my 1983 Yamaha YZ490 at the moment. New main bearings, new seals, new clutch (I know it has nothing to do with it). Complete cleaning of the Carb.

    First start up and the things starts revving so high I thought that it was going to seize the brand new Top End put in.

    I was told check the Needle Position and Float level of the Carb, Adjusted the Float level per a youtube video that if you go by, then my Float level was incorrect and thus rich.

    I am going to pick up a new hose for the Boost Bottle this week and report back with the results. I hope that if the problem is solved and I place the information up here then it will help the next person if they run into an issue. That is what these boards are all about. Passing on what you have learned.
    #8
  9. athomerecords25

    athomerecords25 Banned

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    Leak at the gasket between the Head and the Cylinder. I am surprised the Top End didn't seize or the Piston and Rings didn't melt.

    Makes me very upset with the local shop that did the cylinder and head work. From now on no more local for "any" bike work. And only Eric Gorr for anything motor/cylinder wise.
    #9
  10. athomerecords25

    athomerecords25 Banned

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    So everyone kept telling me to take the bike to another "local" builder in Concord Ca (I won't say his name because I don't think what happened in the rest of this story has anything to do with him).

    So he opens up my Cylinder, checks my head. Tells me that the other guys did NOT do the head mod to my Cylinder Head and showed me. It was in fact still stock. He also says they barely touched the Cylinder Ports, but did do some grinding to the Cases where the Cylinder meets the Cases.

    Anyway. He gets is all done. Bolts it up tight. I could tell instantly there was way more compression. Things felt much tighter. Starts up. Still idling a little high, but not screaming. I nick it in gear, it BACKFIRES but goes. It seams a little lean, I crack it open to go for it, it BACKFIRES and seizes solid.

    I tried to kick it over it was so stuck that when I tried to kick it, I think the kicker shaft broke as it just went from not moving to going all the way down with no tension. The return spring brings it right back up.

    I am just going to crate up the entire motor when I get the money and send it in to Eric Gorr and get it right. I love the bike when running. I am a huge fan of the 1983 Yamaha YZ490 and Broc Glover, so I am no in any way one of those guys that would just junk it or part it out (I hate seeing bikes getting parted out).
    #10
  11. athomerecords25

    athomerecords25 Banned

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    Even though I am the worlds most broke Vintage Collector (my friends say I have Vintage Bikes because I can't afford a new bike. Yeah some friends). But I wasn't fully happy with the Rebuild on this bike, so this kind of forces me to go back an do it how I planned in the first place.
    #11
  12. Flatlands

    Flatlands Don't member the 70'

    Joined:
    Oct 20, 2013
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    Location:
    Ohio Flat Lands
    I bought a 84 IT490 the other day. It sat in a garage for two years untouched. The PO said he rode it twice and got hurt both times is the reason it sat. I brought it home started at the tank and worked my way down cleaning the varnish out of the entire fuel system. Checked spark with new plug, blue but not real good. Added 24:1 fuel mix and started kicking. It would just pop about every 20 kicks, did this a long time and finely it started. I let it warm up and took it up the road a mile and back. It idled good and had no hesitation when I cracked it. I pulled in the garage had trouble finding neutral and stalled it and it won't start back up warm or cold. Can anyone help me with this starting problem?
    #12
  13. Mr. Carts

    Mr. Carts Been here awhile

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    #13
  14. NortwestRider

    NortwestRider TRIPOD ADVENTURER !!

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    3.7 miles North of Hell...SEATTLE....
    Picking up a running TITLED IT490 next week for $100.My plan is to get it plated .I will have A LOT of questions on the lighting system as time go's.


    I don't ride fast ,I ride far...
    #14
  15. NortwestRider

    NortwestRider TRIPOD ADVENTURER !!

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    Here it is. ..
    [​IMG]
    [​IMG]


    I know a lot about a few things,a little about a lot of things but I don't know everything about anything !!.
    #15
  16. NortwestRider

    NortwestRider TRIPOD ADVENTURER !!

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    Can someone tell me where the VIN plate is on the IT490 ( 1983 ) ??.


    I know a lot about a few things,a little about a lot of things but I don't know everything about anything !!.
    #16