I have the Dellorto VHSA 32mm Carburettor as found on the Rotax series of engines. I originally source a 4DL carburettor and saw another VHSA on eBay. I made a very good one from both of them, thinking at the time they were the same. They were not and therefore jetting on my DTR is WAAAAYYY different to that of the 4DL VHSA.

All I will say is, jet to suit, what works for my setup (bearing in mind how unique my setup is) may not be good for you.

But in essence, it's like a 140 main jet with a U13 needle (IIRC) But I bought the whole range. I don't run oil pump and have advanced the ignition + ported barrel with VForce4 Reeds and airbox delete with an underslung pipe. All of those will have factors on jetting so kinda take my setup with a pinch of salt.

The spacer I used was just a 1,5mm thick alu sheet that I cut to the shape of a base gasket. Remember the head has to be 'moved down' too, to keep the squish nice and tight. Can be done by machining the top of the cylinder down, or machining the head.
IMHO the head volume is too low from factory, and combustion chamber needs to be enlarged to have a safe CR if squish is below 1mm as I want it (0,8mm now). The 125 and 170 inserts seem to be the same from Athena..

No porting done on mine. I think widening the upper part of the exhaust could add some power at higher revs and keep the low band pretty much the same. Pretty easy to do a portmap on paper, but I did not do it before I installed the cylinder. Just measured the port height and calculated the port timings to get a rough idea what height I should try. Raising it the full 3mm to get the 'full opening' of the transfers gives pretty wild port timings, but it would probably work with custom ignition curve and pipe to make it a screamer (power at high revs). Not what I'm after though. Pretty happy with it as it is now.

Thank you! Then the newer snorkel will not fit the Keihin..

I have the 170kit but the factory head volume was 12.5ml,I went up to 13ml.
0.8-0.7 squish is way too low for the cc of the kit,on high rpm that may become 0.6-0.5.In my tune to be on the safe side the squish is 1.2mm
A good design gasket is that of the DT200R for the kit.

@SpookDog
Loose the mirrors hand guards rear foot pegs change or loose the indicators for a smaller LED style loose the nobly tires for more road orientated and a recon you’d get an extra 2-3mph and on set of DT clocks that’s easily 5mph ! Lol 😂

@SamDrizzy Wheeling bikes has little to do with performance, all about technique.

2001 DTRs are the worst for restrictions mind you. If you want more performance, you'll want to ditch that CDI and get yourself an aftermarket one. Easily best bang for buck. That and a good exhaust and you'll be laughing.

@old-boy-racer
I’ve pretty much had the same symptoms with my sons 2002 DT. Cleaned the carb put everything back to standard and worked forward from then on. I had the luxury of a dodgy oil pump to start off with then wrong main jet caused it to splutter and cut out high up in the rev range. New oil pump and standard 240 main jet sorted that. It’s very surprising how little you need change the carb if not at all by running a different exhaust. Good luck I’m sure you’ll get it sorted !

@Calum ill post up the build photos when its all done and ill take some for ya 😉
just doing my second one as my last one got wrote off by a crash but bored the barrel to 57mm so first time trying Athena but didnt wanna go 170 so ill let you know the outcome bud.

The piston works it was a piston for pre 89 dt125rs from yam bits, the bike has a lot of felt compression now seems way more than it had when it originally had a rebore and piston making me wonder if the rings were defective from new on the original piston, i did tighten the squish up just a tad with a slightly thinner gasket but I highly doubt that's the reason for the increase in compression before the kickstarter had litteraly no fight back on your foot or hand and it was like that the whole time I rode it.

@madgyver said in Carb warming hose delete:

@declan I have done exactly what you say.No problem so far in the summer,for the winter probably will be the same status.

Blanked off this in every two stroke Yamaha I've ever owned and never had any problems, but have had a BWS carb ice and that made for an interesting ride 😉

Think its just a 4dl TZR125R head

@calum said in Athena 170 porting:

@lllDennis I read that the port timings were off by 3mm because apparently the barrel was based off a dtr200. How true that is...

Would love to see before and after dyno pulls though. See how the stock Athena compares to a modified one.

I have compared Athena 170 kit vs 3MB P (and 2RH) cylinders, the only 2 things that's off the athena kit is the piston taller than the stock,the ports are exact copy off the 3MB just a bit wider and the c port is little lower and matches more a 2RH cylinder

The 170 is a mix between the 200cc casing (for the cooling canals and ypvs location) and 125 portmap internally.I searched for a piston that has the dimensions of the 56mm and with bore of 65mm but there is not,only some aftermarket forged that are max 61mm have the right piston height (pin to top).

For reference I’m running about 1mm squish on my engine with programmable ignition, I was melting the tip of the standard range spark plug after a top gear hoon but I think I was a fair bit further advanced than standard on the top end, I’d maybe stick to 1.2-1.3mm, I’m sure that’s the standard figure but my Frankenstein engine with different barrel and head measured something crazy like 1.8mm as it was! So it’s worth checking..
also to note for the future, you don’t want to go any less than about 0.8mm squish on these engines as the Conrod stretch at high rpm will smack the head.

@Calum You absolute legend! Why did i not think to look on fowlers 🤣. Thankyou so much!!, been pulling my hair out all day trying to find them somewhere to no avail. Cheers 👍

@SpookDog yeah thats what i was planning on doing to be honest running it nice and gentle at least for the first 500 miles or so and just gradually increase it. I cant imagine the change of reeds doing a noticeable difference with the mixtures so i'll just as you say keep an eye on the plug after a couple rides or so and take it from there. Looking forward to finally getting it back on road! 🤣. Its been left in the corner of the garage as i got another bike

@Arild You can make crazy numbers like that on road going engines....on Avgas.

But then run the KTM engine on that stuff and you'll see high 40's and 50s.

Fueling makes a big difference in power as you can ignite the fuel a lot closer to TDC without risk of detonation.

On Turbo Cars it's a different thing altogether. Means you can increase the boost marginally without risk of detonation. More oxygen + fuel = bigger bang.

So, I'm sure someone somewhere ran a Rotax 122 engine with mid-high 30 BHP. They are competition engines after all. But likely it'll be on higher octane fuels and a serious setup!