The pursuit for a brown sparkplug
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I do have the entire pice where the snorkel existed cut out. So there that as well.
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@irongamer727 You donkey,
Why dont you try and restrict Air by patching up a section of the Airbox,
By doing so, i’ll bet a Roast dinner that it sorts out your lean condition.
I’ve played around alot with this, you’ll stuggle to fuel this properly with the TM28
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@darty there isn't a good way of doing it, patching the Air box up I mean. In theory, I'll just get a slightly higher fuel consumption than "everyone else". From what I've understood the airbox is quite restrictive.
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@irongamer727 True, there are ways around it with Aluminum plate and bolts,
Basically, deal is, you cant complain if you dont see results without trying this first.
If you are determined, Start larger with a main, 350 - work backwards, its safer.
I personally dont recomend having the Airbox chopped completely.
Yes it's restrictive as standard, but otherwise you’ll see a significant drop in torque under 6k.
And without a larger carburettor, insignifcant Power gains at high RPMs without ignition timing adjustments.
Mostly bark, no bite
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https://imgur.com/gallery/wFEtwC6
Alright so I have now made a basic Air restrictor. As you know my DT is running slightly lean with a 320 main jet. Probably due to the fact that the airbox is cut open. I now installed the restrictor and for the first time ever she was running really rich.
What should I do?
A: Take out that stupid restrictor and upjet with the top cut out. (I know it's running lean)
B: Install the restrictor, maybe drill a couple of more holes, and downjet.
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@calum drill a couple of more holes or keep as it is?
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@irongamer727 What's your jetting. YOu said it was like 320.
So just knock that down a tad.
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@calum yes 320 now. But I don't want to loose power doing this.. some power decrease is acceptable..
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@irongamer727 Yeah, you're not really getting the art of tuning...
Bigger jets don't necessarily mean bigger power.
The pathetic carb you're running is what is letting your engine down. You can only marry up so much oxygen with the fuel. More fuel doesn't mean more air as you simply are not flowing enough air. You need a bigger carb if you want to start chasing that power.
Knocking the jet sizes down won't affect power unless A. You're dangerously lean, or you were already at that sweet spot.
The optimal jetting would be to run the engine as lean as possible without incurring detonation. This would be indicated by the brown tan.
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@calum do you think there will be a big difference in fuel consumption with a 350 jet and let's say 260?
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@irongamer727 not drastic. I would exect significant consumption in incorrect jetting due to poor pwower delivery and optimised combustion losses. Also an increase in carb sizes will result in losses.
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@calum yeah it's mainly for the fuel consumption and the hassle of fitting a new carb that stops me from doing it. I'm essentialy only after a strong, reliable DT. I won't be able to beat my friends gasgas 125 and husaberg etc. Not even with zeel, bigger carb, and a fat exhaust.
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That top pic is lean as looking at the picture it looks melt down lean, does look like its dragging air in somewhere looking at that but also sounds like its overfueling at the topend if it wont pull at the topend which is a contradiction on its own. Strange one though as they usually rev on there own if they are dragging air in somewhere.
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You need to start at the bottom and work through mid to top. If u want to improve the guttless bottom remove the snorkel and dial out the bork with experimenting with pilots and the mixture screw till u get it sweet take no notice of people who say dont, that just because they cant set it up. Then move to the mid with the needle stock seems ok. The main only comes into play at 3 quarter throttle anyway.
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@scrimsmustang she runs mint and lulls hard up to 3/4. That's when nothing really happens.
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The Aprilia RS 125 SP, or Aprilia AF1 125 Sport Pro run a Dellorto PHBH28 RD 28mm carb. This carb together with a Gianelli exhaust, gives more than 2HP extra power over the 34mm carb version! More than 35hp at rear wheel...
The DT 200R makes 33 bhp and uses a Mikuni TM28SS carb so do not always need a bigger carb for more power, but a well set up carb with jetting spot on 100%. -
@2stroketerry The RS's quoted to make 33BHP ran the VHSB carb. They later restricted the bikes to 26 BHP and used the PHBH.
I don't know the models which used the VHSB, but certainly the SP would have.
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Small update, fitted my restrictor and landed on a 270 main. She runs better than ever. Sadly I lost my kickstart nut during testing.
Funeral held tomorrow.
