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Honda z50 with 88cc bore kit untunable??

This is a discussion on Honda z50 with 88cc bore kit untunable?? within the Z50, CT70 and JDM Monkeybikes forums, part of the General Talk category; I can't get my 20mm carb that came with my 88cc bore kit and I can't get it to run right. I have a 38 ...

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    Honda z50 with 88cc bore kit untunable??

    I can't get my 20mm carb that came with my 88cc bore kit and I can't get it to run right. I have a 38 pilot jet in the carburetor and it back fires and bogs like crazy when you give it gas. It burns oil too.


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    Check your timing chain/cam marks first. Check valve clearance next. If that is good, it sounds like carb issue.
    DFA GSD

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    Sounds like the crap I went through. This was the 1st full summer breaking in my engine and it took the whole time for it to run better. I settled on the 35 and 92 and ran them all summer. Yes it did burn a little oil at first, until the rings sealed up. I was only doing short trips and it got better with 2 mile jaunts at 2/3 throttle. Throttling just off idle still sucks but beyond that it really takes off. Under normal riding the plug looks good and a 4 mile trip close to full throttle it turns a little white. You do need to run it long enough and fast enough to help clean the plug. A small track or well known trail would be a great place to break it in. Hard acceleration, compression breaking and everything in between. I still have a little backfire decelerating but a hole in my muffler is probably the culprit.
    I was brand new at it and after going through it all I believe the trouble comes from trying to do two things at once. An engine that is changing with every ride and trying to get a carb tuned to it. I dont think the 35 and 92 will hurt it. Play with the needle height and ride the crap out of it.

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    The thing is that it was rebuilt about a month or so ago. I think I'm going to take the 38 pilot jet out and but the 35 back in.

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    Quote Originally Posted by 2stroked View Post
    The thing is that it was rebuilt about a month or so ago. I think I'm going to take the 38 pilot jet out and but the 35 back in.
    Leave the 38 in there. Only reason you should take it out is to clean it. Did you let the bike sit for a few weeks? Could be gummed up. Another thing to check for is the spark plug. Make sure it's not fouled up.

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    Good point Haispeed. The reason I know I dont need the 38; it idles ok when cold and doesnt need the choke with the temp in the 50s. All I have to do is bump the idle screw up a little. I probably went through 6-8 plugs through it all. Always keep a handful around.

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    I put the 35 or whatever back in to the carb and there is absolutely no change what so ever. I want to sell this thing, but I can't sell it with it running like this. Valves are set correctly and so is the cam timing.

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    Quote Originally Posted by 2stroked View Post
    I put the 35 or whatever back in to the carb and there is absolutely no change what so ever. I want to sell this thing, but I can't sell it with it running like this. Valves are set correctly and so is the cam timing.
    I told ya there's no reason to change it. I have a 38 in mines and it runs fine. Only difference is you won't need to use the choke as much and the roll on throttle will be better without the notorious Shengwey bog. Did you check the spark plug like I told you too? Get another new plug in and it in there and see if it changes anything.

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    Tell us what exact setup you have here? What bore kit, what head, what piston, what cam, and what carb.

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    Quote Originally Posted by fatcaaat View Post
    Tell us what exact setup you have here? What bore kit, what head, what piston, what cam, and what carb.
    Engine and Carb quick check list - TBolt USA Tech Database!

    1)Install Intake manifold to head and carb, oil gaskets and tighten bolts lightly at first then torque then down gradually in a cross pattern to provide a good seal and avoid air leaks
    Carb slide MUST hit bottom & you MUST have free play in the throttle cable

    2)Make sure the carb is 100% clean, free of debris and you can see light thru both main and pilot jets

    3)Double check you valve tappet adjustment .003intake and .004exh.

    4)Make sure your exhaust gasket is installed properly.

    5)Make sure all electrical connections are tight and you have a solid ground from the engine to the frame.

    6)Check for good fuel flow and fresh fuel.

    7)See our jetting guide and do a plug read.
    http://www.tboltusa.com/store/tech.php?pid=61




    Quick Tips For Small 4-Strokes

    Please Start tuning with a Clean & Properly oiled air filter in place
    Please test ride the bike , you cant jet / tune a bike sitting on the stand !


    • If it boggs or dies right off from an idle when you turn the throttle, your pilot is too lean.You Need to get the Pilot tuned in so it will come clean off an idle BEFORE moving on to other adjustments.
    • Your main adjustment is your Main Jet. Once you get your plug close with your main jet, fine tune from there.
    • When fine tuning your adjustment screws, turn them all the way in, and back out, 1 and a Half Turns, for your starting point.
    T Bolt USA - Let's go riding!

    All the top Pit Bikes, Engines and Parts for Pit bikes & Minis! Let us know if we can help!

    Online Store - Tech Database - Facebook - TheCRKid@TBoltUSA.com - (704) T-BOLT-US - Skype: TBoltUSA

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    Quote Originally Posted by fatcaaat
    Tell us what exact setup you have here? What bore kit, what head, what piston, what cam, and what carb.
    1979 Honda z50 88cc piston, cylinder, race head, race cam. Can I order a keihin 20mm carburetor for it to use since the shengway is a pos?

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    The 20mm ShengWay carb is relatively easy to tune right out of the box. It comes with the #89 main and a #35 pilot jet, both of which you can buy the extra jets from TrailBikes or any TB sales rep. As a baseline setting, I use the #90 or #92 main jet, the #38 pilot jet, set the jet needle at the 3rd or 4th notch from the top, and the air screw at 1-1/2 to 1-3/4 turns OUT from seated. Make the necessary air screw adjustments IN to richen it a 1/4-turn at a time and see what the bike does. With some of the carbs, I've run it to within a 1/2-turn of being all the way IN to get rid of 98% of the off-idle hesitation. You might have to raise or lower the clip on the needle , depending upon your altitude, I'm at sea level.




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    Alright I using the advice you told me I dropped the needle clip down to the fourth position, put the 38 pilot jet back in and it runs really good.
    Almost all of the off idle hesitation is gone too. The engine is wayyyy more torquey than it used to be also.

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    Glad to hear you were able to dial it in..




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