Exactly my point. The people that designed the carb also sell the kit, so there must be a reason they make it. Inherent design flaws?
Anyhow its all hearsay until fitted and tested, we could sit here and chat about it until the cows come home. Real world experience is what is needed.
The Mikuni website begs to differ "Kit may be installed easily on TM and VM series Motorcycle and Snowmobile carburetors."
And I spotted a DT125LC with one fitted recently.
To be clear we are not talking about main or pilot, or any other internal jet on the carb, Its an additonal Jet that bolts into the inlet flange before the butterfly and operates at WOT. Just how the main and pilot overlap this overlaps with the main jet for more top end fueling control.
There around a score so I've ordered one to try anyway, will report back with findings 
I'm aware of the principles, just wondering if anyone has real world use experience good or bad to share. Thanks.
Just wondering of anyone has experience with power jets on the standard carb or otherwise. Did you need to re jet or make any other adjustments?
@Calum What years out of interest had cats?
When you look at it £175 is less than two weeks worth of charges, so it would pay for itself pretty quickly.
There are a few post 2007 strokers available like the KTM's and Huskys, so in theory a two stroke has the possibility of passing.
I'd hate to see cities without the occasional sound of a two stoke reverberating off the buildings and a whiff of two stoke, it would take away some of the character 
Alternatively we could just wait, as I believe Historical vehicles (40+ years) are also exempt. Classic Lambrettas and Vespas should be cool.
So, there is that ULEZ zone around London and pre 2007 bikes must pay a £12.50 charge to enter. It doesn't currently cause me problems commuting but it may well do when the area expands in 2021. Other cities will most likely follow suit down the line, so would be nice if we can work out if a DT could pass the test.
It would be handy to pop into town on the bike if I wanted too of course
There seems to be 3 main ways of conforming to the rules.
First and second is to obtain a certificate of conformity or a homologation certificate from the manufacturer to present, some seem to be now charging for this privilege. So, what do you think the chances are of Yamaha having these for a DT?
Thirdly, is to take your bike for an emissions test on a case by case basis, so just because one DT passes does not mean yours will. Currently only 1 place in the whole of London has been authorised to do this, Riverbank Motorcycles, and they want £175 for each test. What they are looking for are the Nox levels and the magic number is 0.15g/km or lower.
Lots of older bikes seem to be passing, albeit I've yet to see a 2 stroke mentioned in any blurb I've read yet.
What do we think? Is this possible for a DT, anyone got any idea of Nox emisons on our bikes?
Oh yeah, did any year DT's come with a cat in the silencer? 
@Glynn123 In my bookmarks, woo
https://www.thetuningworks.co.uk/store/product_info.php?products_id=1268
I didn't need to read that, damn it :grinning_face_with_smiling_eyes:
Good read.
@Calum So there are other heads apart from them two, cool I didn't now :winking_face:
At least the whole top end can be ruled out now, plus ive got a spare head to play with, so not all bad. Just need to get to the bottom of this issue once and for all.
At this rate I'll have a nice stash of spares :face_with_tears_of_joy:
@NINJA I've been doing plug chops but nothing untoward has been spotted, here is the most recent, was a new plug when the new piston went in
And here is the old head with no casting on top, yet the heads dome defo isnt the restrictive head
And the new fitted
I cant see anything wrong with the plug, but feel free to chime in :winking_face:
It's still basically the same 
Gotta be something else....not much left really, CDI, crankcase seals or clutching at straws for an extremely worn carb?
I've never inspected the reeds and the exhaust is a bit of an unknown, so could both be causing possible issues and shouldn't be overlooked.
Got a second hand CDI winging its way to me to rule that out. I'll do that and go from there....
@Calum It had a few small nicks, but was a whole load better looking than the other. Got it from where I bought the bike, it was the best 3mb he had, got loads of the more restrictive ones though.
Sadly no snaps NINJA, I think maybe it's a slightly older head as it had 3mb and Yamaha embossed on the top of it which the other does not
Agreed :smiling_face_with_sunglasses:
Little update. After running it in a little and opening it up a bit, I wasn't particularly impressed. It felt worse than before up top. So I did mess with the squish too much I think. Luckily managed to get another 3mb head in a more normal condition for £25 and have just fitted it and compression tested it and its up, so hopefully tomorrow's ride will be an improvement.
Now I have the old head here may as well look into getting it sorted properly at some stage and swapping back later down the line.
Could have done with this about a week ago
@Calum I'd adjusted the throttle too much so when I fired it idled around 7k I think was the reason. Took it out for 15 gentle miles yesterday and all seemed well, and took to work this morning, so far so good. Just trying to be gentle and keep the revs relatively low for the meanwhile and get some miles under her belt.
Its back together and running. Not ridden yet, but let it get to temp and adjusted idle. Took about twenty kicks to start first, but now its starting first kick. Took a compression reading before I started the engine with the exhaust off
Pretty busy tomorrow, but If I get a moment Ill take it for a spin and see what is what 
I'll be keeping a close eye on things, regular compression tests and plug chops to see whats going on.
I think I've done what I wanted with the head for now. I'd say I've given it more of a polish than anything
Its far far from perfect, but also a lot better than what it was :smiling_face_with_open_mouth:
one of the marks is still fingernail deep, but I'm reluctant to go much further without taking it somewhere knowledgeable with two stroke machining. I'm happy enough to fit and find out for now :winking_face:
@Calum The way I see it, whatever I'm removing now is needed and more to be corrected. Its already looking better.
@Calum Yes I understand and will most likely get another head down the line to do correctly. For now I'm going to tidy it as best I can while being sympathetic to the compression ratio but at the same time loosing any sharp edges that will be hot spots and prone to kickstarting a det situation. Basically I'm going to do the best I can with what I've currently available to me :winking_face:
