@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

@llldennis How much should the port for the 65mm bore,47mm wide (43 in chordal length).It's 42mm like the stock cylinder.
Worth messing,no and yes,what you after is the right question.

@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!

@Arild said in Best Big Bore Kit DTR:

@RubberSalt youve told me most of this as answers to all my questions, still my mind ends up blown after reading this😂 its alot of good information to take in, or try to atleast
Thanks for putting all that together

Well this is all rather very interesting, very very interesting indeed...
After reading that that I might even scrap my plans of a 200 after reading this and seeing what was once an idea become something of a possibility and with both a 4DL setup and 4FU setup spare it’s not like I haven’t got ammo. I haven’t mentioned this either but I also have a spare 4DL head. More ammo?

Also @RubberSalt I have as much to learn as I believe you have to offer. Very well written, whilst I admit it’s out of my depth (at the moment) it’s still easy enough to follow. I also use my phone so I know it can be a pain sometimes. Me and @Arild met the same way you did and had been chatting for a while now, helping each other out and talking about the unexplored possibilities for the DTR so I just got to say welcome aboard and thanks from me and on behalf of my little Swedish g. I appreciate you helping him out a lot, I could honestly only wish to be able to do what you have 😂
Anyways I do believe this could be quite a most interesting endeavour.

Hi all thanks for all the advice it’s really helpful! Yeah he had to skim a lot off because it looks like someone Had prized off the head before with a screwdriver or something and made a big gouge in it! I’ve ordered the copper gasket (budget reasons 🤣) so I’ll try that and see how she goes but if not I’ll give a new head a go. I’ll post an update soon

@rubberfingers

Some have a diamond shape on the pulley end but they all take the same pulley - worth noting so that when setting up you get it the right way round. Best thing thing to do would be to feel up the port with the exhaust off.

I have both a 3SH TDR125 and a 3XP 200WR if you need any info - both engines are in one piece though so cant comment on the internals right now 😉

@Calum thanks for the reply callum. I have a good source of parts so can get the head no problem👍

Yes I'd like to go down the Mick Abby (sp?) route as well but also get him to build a pipe to match the tune along with a new matching ignition set up.

For me the main aim is always to have s bike that runs right with nice healthy mid range power rather than completely all up in the very top end of the rev range.