DT 125 R '88... New project

[Calum]

@CYBER-NINJA It was supposed to smooth out a double dip in the harmonics. The bottle resonates at this frequency and forces stored air out of the bottle.

[NINJA]

@Calum The mind boggles at how they came up with the idea in the first place???

[Calum]

@CYBER-NINJA Probably physics? And Years of iterations.

[andrewj1680]

Ive tried this however the wr200 inlet comes off at a slightly different angle i manage to get it to all go together nice and tight however the carb runs on a angle everytime to open the throttle wide it empties the carb you have to come back off the throttle so it fills back up again, i gave up on the idea of running that carb on a standard dt engine

[NINJA]

@andrewj1680 Modding is like a jigsaw puzzle, finding the right pieces which fit together takes time and experimentation sadly.

[andrewj1680]

@CYBER-NINJA i know what you mean which is why i have opted to swap everything including the engine and loom to allow me to get the best out of it

[jgr72]

DT have been sitting in my garage for some time... But today, I lift it up and changed the front fork seals that I ordered over 6 months ago... Left side had leaked inside the fork boot allready... I decide to fill it up with 15W fork oil... just to make it a bit stiffer... After that I measured the quantity of oil drained out... there was about 750ml (both sides together)... No wonder why it was a bit soft...

To make sure that there are something to wait for... I just ordered Athena 170cc kit for my DT :smiling_face_with_heart-eyes:

Still need to find new exhaust... Maybe some stainless... Lets see...

[oldman]

I would love to have this bike as it is, seems a shame to not make it original. But thats me I guess, endurance blue a great colour.

[Calum]

I must admit, this is probably one of my favourite colours for these bikes.

[Irongamer727]

@jgr72 nice

[jgr72]

Few days ago, I took the engine in parts... and this is what I found:

Thankfully new parts arrived already:

I tried athena barrel and piston, and it seems that tdc is just as with the earlier barrel & piston.

I will measure both heads and calculate compression ratios just for curiosity...

Still waiting for piston pin bearing to arrive... Old one was just fine, but why not change it to a new one, when it can be done easily...

[Calum]

Doesn't look too bad, barrel should hone nicely, might not need to touch the bottom end.

[jgr72]

Yeah barrel might still be useful... I will store it carefully, so I could return this bike original later if I want...

[jgr72]

@Calum Athena 170cc set fits well into this 3BN engine, there was no problem to install it. Original piston remain about 1-2mm below deck and dome comes just about up to deck hight. Athena piston comes to deck hight and the dome is smaller and comes just over the deck. Athena claims that compression ratio is 13.2 and that is also what I endup by calculating it... combustion chamber is about 13ml and 168cc devided by that is around 13. That's not actually the real CR, since 2T engines start to compress only after the channels in the barrel when piston comes up, damn I didn't measure that part of piston travel...

Next step is to find better solution for TMX30... I ordered from ebay WR200 intake, let's see if it will line the carb better past the rear shock. If not, I may need to build up my own intake... At this point it seems that the DT230 Lanza boot was a waste of money, it does'nt seem to fit in any way... Anyone interested?

I also ordered 170cc version exhaust from Romeu Henriques, let's see how it fits and feels... Silencer will be a gianelli alu silencer...

Anyone have idea, where to start settings of that TMX30? 135 mainjet felt best last autumn... Maybe 140-150 mainjet and needle one step up?

And for all that are oppressing me to keep this as original as possible, that's not happening now... I will store all original parts for later time if I feel to return this original back again...

[Calum]

Sounds like you caught the tuning bug, very serious this is.

I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

[jgr72]

@calum said in DT 125 R '88... New project:

Sounds like you caught the tuning bug, very serious this is.

I've had it since 1987

I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

TMX30 will fit quite well to original joint, but the angle is bad... WR200 should have more horisontal angle to avoid rear shock and that joint is originally made for TMX30 carb.

[Calum]

@jgr72 So I'm running a Dellorto VHSA 32mm on stock inlet manifold with no issues.

[jgr72]

WR200 inlet did the trick I need:

Air filter barely misses the rear shock and frame...

Now need to modify those inlet attachment bolt holes to make it fit into crankcase...

Maybe I will loose some bottom torque due to the missing boost bottle!?

[Calum]

@jgr72 Personally I'd want to keep the boost bottle. Whether it actually does anything though as you say.

They did have boost bottles on some WR models. I think it's more useful on road going bikes.

[jgr72]

Yeah, I'd like to have it too... It have been there for a reason... Okey, maybe I need to try to find such a WR inlet that have boost bottle! This bike will be used 99% on sand or asfalt roads...