DR350 running lean problems

[proximity]

Hi all,
I bought a DR350 and rebuilt it as it was cosmetically not great. Now that its finished i'm having trouble with it running lean.

It misfires over about 75% throttle and doesn't like high revs. The airbox has had its snorkle cut out, which according to everything I read on the net suggests it needs a 140 main jet. It currently has a 142.5 main jet and 40 pilot. I have checked that the carb is clean.
It has the mikuni pumper carb.

It runs hot, so hot that last time I went out on it, it melted its side panel, and burnt out the stator. The exiting exhaust gas it also really hot even at idle, it will burn your hand. It pops on decel a lot.

I'm quite confused because it is jetted richer than any other DR350 I have read about on forums, it even has the stock exhaust.

I taped off part of the airbox inlet as a test and it runs much better at the top end, no stumbling, but seems a bit rich down low like this. I have also lowered the carb fuel height as it was quite high (I know this only makes it leaner, but I thought its best to have things as they are supposed to be).

Lowering the float height has introduced a new problem whereby the idle is so low that it often stalls when coming to a halt, BUT it also hangs at about 4000rpm or so, I either get this, or it stalls. I cant win.

Any help would be MUCH appreciated as I'm not sure what to do next, I could up jet but people don't seem to even need 150 mains with a free flowing exhaust let alone the stock one. Also the guy that had it before me ran it like this for 7 years, so I doubt it had this issue for him.

Jason
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2004 Aprilia Tuono

[P.addy]

Pop the spark plug out and see what colour it is..

[Bezzer]

Sorting the fuelling should be from the top. First main jet for high to WOT, then needle for midrange finally mixture screw for idling to low. Only problem is you're using the accepted parameters for what you've got with possibly the exception of the needle and everything seems to be way out. I honestly think it would be well worth the money for a dyno run to find out what exactly is happening mixture wise before you do some expensive damage to the motor.
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I used to be indecisive but now I'm not quite so sure.

[proximity]

I have attached a pic of the plug after I did a chop after holding high revs and throttle for about a minute, just around where it does its thing of pretending to be out of fuel.

I'm not one to be identifying plug colours but to me it doesn't look too bad, though i'm unsure of why it has black speckles on it?

The pic is from a phone and the colours are a bit off, it actually looks more grey and less like a brown colour in real life.

https://i54.tinypic.com/i4fxc8.jpg
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2004 Aprilia Tuono

[----]

Looks pretty lean compared to mine!
Are the jets genuine mikuni ones ? I was told sometimes the cheaper ones were'nt too accurate...

I have a 147.5 main jet(cheap make) and standard pilot and it's still a tiny bit lean...

Carb is easy to remove and jets are only a couple of quid so just try bigger and see how it goes...

[proximity]

Yeah i think i will try some bigger jets, the reason i'm asking is I didn't want to work around the cause rather than find it if you know what I mean, there are loads of threads on thumpertalk about fitting 140s.

I might try a new plug and see if I can find a spare coil as the resistances on that aren't anywhere near spec.
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2004 Aprilia Tuono

[----]

Have a read through the tech pages over at Maximum suzuki
They have covered most issues with these bikes and were helpful when i was asking about jetting...

Coil on ebay for about £10 Clicky

Parts are cheap as fuck for these bike

[proximity]

Cool, thanks for the tips. Do you ride on road only given that you have supermoto wheels? Just noticed that you are local is all.

J
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2004 Aprilia Tuono

[----]

[proximity]

I'm sure there are plenty with the likes of hamsterly forest etc, I just haven't found them
I thought about joining the TRF to get to know some decent lanes, just haven't got round to it yet.
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2004 Aprilia Tuono

[----]

[proximity]

Bit of progress with this today, after fiddling with the needle over and over again without success I decided to drill out a main jet.

Well I took a jet out of some mikuni carbs I had lying around, they were 110 main jets, but then to my surprise after taking out the DR jet, the 110's are much bigger than the 142.5 that is in the DR, so i'm thinking maybe you were right Scrap and the jet I have is chinese crap. The 'fake' jet I have is marked RD.

Well now I just need to sort out either the correct drill, or a real 140 size jet. I went for a ride with the 110 in and it rode pretty good actually.

The other bit of confusion I have is that my needle only has 2 clip positions, everything I read suggests it should have 5. Is it possible I also have a fake needle? The thing is though it has the mikuni symbol and correct code on it...
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2004 Aprilia Tuono

[waffles]

I typed in mikuni fake into google and it comes up with quite a few threads about fake carbs being sold, have you checked to make sure your carb is a genuine one? Or maybe fake parts have been mixed into a genuine carb by a previous owner?
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Theory test - 19/8/09, CBT - 11/10/09, MOD 1 - 16/8/10, MOD 2 - 27/10/10
Past rides Yamaha XT125X, Triumph TT600, Honda XR250
Current rides Suzuki GSXR 600, Honda MSX125

[proximity]

I'm pretty certain the carb itself is genuine. I've got a few mikuni carbs and its too good to be a fake.

The previous owner has done the 'airbox mod' to the bike and then I imagine tried to up jet to suit. Thing is the needle doesnt need changing for this mod, so i'm wondering if maybe some of the early models just came with a 2 notch needle. I have only ever seen 5 notch or fixed position needles from mikuni though.

I might be able to measure the needle to see if it is the correct shape, there is a document about needle sizes but I couldnt figure out from it what measurements to do.
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2004 Aprilia Tuono

[proximity]

Found this little chart, I think my jet marked RD could be one of those Precision engineering jets.

https://faq.ninja250.org/wiki/Dynojet_-_Mikuni_-_Keihin_jet_sizes_conversion

Unfortunately the chart doesn't go big enough to find out the drill sizes I need to make it right

Edit: that can't be true as it would mean the jet is 1.425mm, which it isn't, its more like 0.95mm
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2004 Aprilia Tuono

[----]

Get to a local dealers and buy (even in the cheap make) a few different jet sizes.
142.5, 145, 147.5 should do ya

I have no idea about the needle but you said yourself, you put in another jet and it ran better...
Carb jet's are literally about £1 each so it's no real expense

edit: Actually i still have a few sizes here. I think i have 137.5 standard, a 140, 142.5 and i think a 147.5.(maybe 145 not sure which i used now.
You can have them if you come and get them, but it'll probably cost you less to go to a dealers (petrol to get here)

[proximity]

Right well i'm about at breaking point with this now, it's one thing after another.

I ordered a new 5 position needle and range of jets to suit. Fitted them, went for a ride. Piece of shit.

Seems to be down on power quite a bit, no lean bog at the top end but instead a sort of stutter like it is misfiring every second or so.

That's not the biggy because I can rectify that by playing with the jets some more, what is the main problem is the bike will not run below what I am guessing is about 1500 - 2000rpm (I have no tacho).

It will idle, but any amount of throttle about about 10% will cause it to stall, it makes it almost impossible to ride, it stalls in a way that if I let off the throttle when it is stalling it will pick back up again.
If I am riding up a hill for example, as the revs slowly drop, 2000rpm its pullling fine, revs drop slightly and then BAM hit a brick wall like I have hit the kill switch, let off the throttle and it comes back.
Same with going down a hill, open the throttle, nothing, bike is coasting like the key is off, rolling down the hill picking up speed, I hit 2000rpm and shazam shes away again.

It confuses me that it is RPM related. I suspected ignition because it just seems like it gets no spark under load at low RPM, but I have checked the spark as I suspected this, but by adding a second gap to the lead to see a spark, I could see that the plug is still firing when it does this 'issue'. I rewound the stator while waiting for the jets to come, but didn't touch the hall sensor or CDI coil.

Lifting the needle didn't help. I seriously don't know what to do with it.

I would really really appreciate some help. I like the bike a lot, but I have had it in bits so many times it's at the point where I just want to sell it and move on. No I lied, I want to burn it.

Jason
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2004 Aprilia Tuono