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DT125R FORUM

BBK opinions

Scheduled Pinned Locked Moved General Discussion
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  • declanD Offline
    declanD Offline
    declan
    wrote on last edited by declan
    #1

    Right I’ve got a carb set up for a 70cc but the bikes a 50cc another “but” is I want a cheap 90cc big bore kit will the carb be able to meet the demands of the 90 kit with jetting or am I better off going with a 70 kit and has anyone tried a cheap 70 kit and can tell me if there decent on power

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  • CalumC Offline
    CalumC Offline
    Calum
    wrote on last edited by
    #2

    Literally no idea what you're on about, or why you would waste money on such things.

    You've got a DT haven't you? Why mess around with cheap pit bikes when you've got the real deal.

    So the carb is setup for a 70cc, but the engine is 50cc and you want to go to 90cc.

    Common seizure of engines is incorrect fueling.

    When you overfuel, you wash the oil from the bore, known as bore wash, you then get metal on metal contact and the engine seizes.

    When you underfuel, the combustion temperatures rapidly increase, igniting the fuel before ignition, causing the upwards stroking piston to meet the explosive gases, shaking the engine to pieces, known as detonation.

    Either way, both conditions cause the engine to destroy itself.

    Fueling has to be spot on for reliability to sustained.

    Will the bike work setup as a 70 for a 90, probably. To be fair, the cc increase is so small that the jets might not make a difference. But for the sake of a few quid, just buy some more jets and needles. It's not hard once you know what you're looking for.

    Always Originate, Never Pirate!

    declanD 1 Reply Last reply
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  • declanD Offline
    declanD Offline
    declan
    replied to Calum on last edited by
    #3

    @calum it’s not a pitbike it’s just a little project of mine nothing special money wise so I don’t mind it blowing up or setting a light but I’d prefer it not obviously, I was thinking more will the carb supply the right air I’m not looking for a race machine just something to thrash

    CalumC 1 Reply Last reply
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  • CalumC Offline
    CalumC Offline
    Calum
    replied to declan on last edited by
    #4

    @declan Whilst the carb does meter the air, that's not really what they mean when they say "Set up for a 70cc". They're talking about the fueling, since that is the part you can alter. You alter the air, by adjusting the throttle. The air is fixed by the cut away. It can be permantely bored out with a dremel if you so wish.

    So Air wise, yes that should be fine, although potentially limiting the power.

    Fuel wise, I would still jet it accordingly.

    Always Originate, Never Pirate!

    declanD 1 Reply Last reply
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  • declanD Offline
    declanD Offline
    declan
    replied to Calum on last edited by
    #5

    @calum okay I’ll probably be building it soon I’m gonna try get it running on the 50 first need to set needle back to stock

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  • MiniaM Offline
    MiniaM Offline
    Minia
    wrote on last edited by
    #6

    As Calum said, you'll have to Jet it accordingly to try and get the best amount of mixture possible. But in my opinion it really just depends how much time you're willing to perfect it. If it's just something you want to thrash and aren't worried about the results you can probably skip a couple steps... I've certainly done that.

    Owned: Yamaha PW50 - Yamaha PW80 - Yamaha RT100 - Yamaha DT125R Black, 2000
    Own: Yamaha DT125R Blue 2002, GasGas 250 Pampera 2001, XT 125 1982, Benelli BN302 2015, Yamaha WR250 1992

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