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Thread: Xr70r issues

  1. 12-17-2015, 10:16 PM #1
    e5earley
    e5earley is offline First Time Rider Arm chair racerNew to the board
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    Xr70r issues

    Putting together an xr70r for me son's birthday this Saturday and am having some issues.

    Background on the bike. When I picked it up it was smoking blue smoke. Knew it needed top end work. I have since rebuilt the carb, installed new piston, rings, and cylinder. Fired it up and now it backfires constantly. Will not idle. I'm thinking it is running lean. Had to keep it on full choke for it to run. Plan on checking throttle needle adjustment and valve clearance tomorrow. Bike started and ran fairly decent before teardown, but definitely needed top end work. Anything additional that the experts here think I should look into.

    Thanks in advance.

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  2. 12-18-2015, 12:58 AM #2
    NeverLift's Avatar
    NeverLift
    NeverLift is offline Just Too Addicted Arm chair racerJust too addicted
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    Did you check the cam chain? Double check the timing. I just replaced the cam chain on my 400ex. It was worn and stretched so I couldn't get it timed perfect and it ran just like your describing. I cleaned the carb and adjusted the valves but the cam chain did the trick.
    85 Tri-z Power valve on Inverts
    85 Tri-z Basket Case
    01 gsxr750 engine/Tri-z frame (long long way from complete)
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  3. 12-18-2015, 08:35 PM #3
    e5earley
    e5earley is offline First Time Rider Arm chair racerNew to the board
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    Well, I checked the timing again. Got it to TDC, pulled the cam and made sure the lobes were facing towards the rear. Timed the cam and buttoned it all up. Noticed the intake valve had no play at all. Set the valve clearance and fired it up. Cranked easy and idled good. Would bogg down and backfire when I tried to throttle it up.

    Took a break from it then hit it again this evening. Thought I may have an exhaust leak so I pulled the pipe and cleaned everything up. Got it all back together and cranked it over. SUCCESS!!! No backfiring, good throttle response, and running great.

    Was really beginning to get worried. Birthday party is tomorrow at 1:00. Was almost to the point of hitting Craiglist to find a running bike for my boy.

    Thanks to all that offered suggestions.

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  4. 12-18-2015, 09:58 PM #4
    NeverLift's Avatar
    NeverLift
    NeverLift is offline Just Too Addicted Arm chair racerJust too addicted
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    That's great. Next year for his birthday 88cc big bore kit?
    85 Tri-z Power valve on Inverts
    85 Tri-z Basket Case
    01 gsxr750 engine/Tri-z frame (long long way from complete)
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  5. 12-18-2015, 10:37 PM #5
    e5earley
    e5earley is offline First Time Rider Arm chair racerNew to the board
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    I had actually thought about ordering one of those. Decided to keep it stock. I picked up one of the Niche Industries cylinder kits off of Ebay. $47.00 with free shipping. Time will tell if it was a good deal or not. Machining looked good and ring gap was in spec. It costs me $40 just to have a cylinder bored here locally.

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