Carburetor adjustment Suzuki DF2.5 - flat spot

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mullet

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After lots of worsening issues with blocked jets and ethanol residue I succumbed and bought a new carburetor for my 2014 DF2.5 (the old one had become so brittle that both the jets and the carb body disintegrated under gentle force when I most recently tried to strip it to clean).

I fitted the new one and the engine now starts easily and idles beautifully (which is a new experience with this engine!) BUT there is a flat spot in terms of revs/power between idle and mid-tilt. In neutral, if I give the throttle a big twist the engine will carry on running and will pick up - but if the throttle is increased gradually the engine stalls just above idle. And to get up to revs in gear I need to rev and drop it into gear to keep it running (which obviously won't do the gearing any good).

Any suggestions from the brains trust? Carburetors are not my area of expertise at all... I am hoping this is a fettling/adjustment question rather than a feature of the new carb... To cover off a few things that might come up: new gasket; clean fuel tank and lines; aspen 4 alkylate fuel (not taking chances with petrol containing ethanol!).
 
If this is a genuine Suzuki item, bought from a Suzuki agent, they'd be my 1st port of call.
If it's from an independent supplier, I'd also ask them for advice, which might be that "you'll have to set it up".
If that's the case, then YouTube's your buddy with "DF 2.5 carb set up.".
Of course, this is assuming that the air cleaner, spark and fuel stuff are all OK...
 
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My Suzuki 4HP-converted to 5HP-by the simple expedient of bending the throttle stop to allow more opening-had the same hesitation/flat spot.

I removed the blanking plug over the low speed mixture screw and adjusted it the 'old school' way.

It is now perfect. Perhaps your 2.5 has the mixture screw blanked off?

Suzuki sell a new bracket for the 5HP throttle stop, almost twenty quid with VAT and post. Bending mine carefully, checking the butterfly could not 'flip over' and stick on full throttle made a massive difference.
 
Thanks, @rotrax. Yes, the 2.5 does have the adjustment screw blanked off. I’ve seen conflicting information about whether it might resolve a flat spot (or whether it will just help with idling problems). But I don’t think there is anything to be lost by seeing if it helps.

@jamie N It’s an OEM part but bought from a Dutch motorcycle parts dealer (because €75 instead of £350 in the UK). Suzuki have been no help at all in the past so I’ve not even bothered speaking to them and the dealers I’ve spoken to haven’t been interested unless they are being paid to work on it. Have you ever had a DF2.5? The problems with their carburettors are well-known and widespread - and the only people I’ve met who’ve had any help from them are people who had them dealt with inside warranty.
 
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