Time for another Port Job - YT125 - Pics on page 2

[RubberSalt]

So i pulled my nephews YT125 apart. It was all out of power and finaly just quit running.

Theres a slight lip at the top of the cylinder. The rings are are flush with th episton and can't seal up any more... So i looked and examined and studied.. WOW!! this thing really sucks. I need to fix this for him.

I may make a pipe for this thing also.. Now that i have a better welder(for those of you who remember - works great still!) lol

First things first. Where do i want my power for this little beast. I was thinking maybe mid/top. According ot my software and simulations, this engine should be able to wrap out to around 11k. So maybe it shall peak around 9500 RPM :-p

I'm thinking about maybe... 190 exhaust and 125 transfer on the port timing. I'll shave the head and get something like 125psi comp. I don't want to go to crazy for the kid. Just enough to get him moving.


Shooting for around 24-25hp... about 20hp at the wheels. That should be more than do able...

Or should i go crazy with it and go for the 30hp at the crank.. 25hp at the wheel set up?

[old-yellow]

good luck, keep us informed with your results

[captainweezy]

Is the stock pipe shot or do you just want a pipe that will give you more hp? I have a stock pipe.

[MTS]

I would just start simple...No high end spin,, i picked up a yt125 last year and it had a backwards piston in it, long story short i cleaned up the transfers on the bottom and opened up the exhaust,,about 1mm and widened it out swapped a 175 primary drive and clutch into it...pulls pretty hard for a 125 box in the first 3 gears, need to cut the head down to bump the compression back up,,,but i was pretty impressed with the stock running gear. and if you get 25 at the wheels i wana see!!

[RubberSalt]

I've got lets see... 1..2,3 - 3 spare bottom ends for these things lol.

It's so hard not to make a screamer lol. It's only a hair more work to me when I'm this deep in it lol.

I'll make the port map and get my numberS(like always) before touching a tool. The last toy we sold had a bottom/Mid range pipe on it. stock jug with 1mm bore and our port desi Pulled 32hp at the wheel. Yamaha blaster.
Heres a test vid of the blaster.



** rider in the video is an ATC 250R rider :-D 3 wheels FTW!!

[Swinger]

Thats an impressive little blaster there!

[RubberSalt]

I've got the jug all cleaned up. I'm really impressed how clean it got. I used "Betco oven jell". Talk about some caustic stuff. The thickest nastiest grease that builds up in and around the exhaust... literaly just washed off with almsot no scrubbing.. It was like butter in a microwave. WIN lol

I'm mapping the cylinder as we speak. I can't find my calipers/depth gauge

[RubberSalt]

I've got some numbers to play with now.
I decided to go for max power at 9500RPM. Should net about 18hp at the crank with 100psi. 26 if i can get the compression atleast to 145psi.

Port timing of 186 exhaust, 127 on the transfers.
27.37mm from the top of the jug for exhaust, 39.24mm from top of the jug for the transfers.

Mean transfer area will need to be 4.53cm^2 to 9.29cm^2. The ports are about 81.25mm wide. Raising the transfers to 127 will make them 10.76mm tall. This nets 8.74cm^2 total. Within the range, high end being the limit.

Exhaust. will be 22.63mm tall. This where the fun start happening... Blow down.
I need a total of 8.2CM^2 of exhaust, but 5.74cm^2 needs to be open before the transfers. Unfortunatly, it looks like 5.3cm^ will be open before the transfers. That will be ok, the exhaust will be larger than need be. Timing will be right, blow down will be right.

No triple ports needed for this guy. Ill build it for 145psi, it will operate fine at 100psi. Compression is the biggest factor in power.

[86T3]

I'm really interested in your end result, i love when people do things that really shouldn't be done. haha. You kinda lost me with the technical aspect, but i get the jist of it. Just off the top og my head, 145 seems relitively low. Do these motors have such little compression stock that they're hard to get more out of? No aftermarket higher comp. pistons? Good luck, can't wait to see the ride video.

[RubberSalt]

Yeah, they are 100psi stock >.< 110 for the YT175.

I don't I could push it harder, but the heads suck ballz.

This 1 of them. Beat up head on ebay. They have 4 bolts and an offset squish.

I went and bought a new caliper. Give me a few minutes, ill get accurate port timing.

[RubberSalt]

ewww 159.2 on the exhaust
109.2 on the transfers.

For a comparison. IT175 uses 185 exhaust and 130 transfers. It made like 17hp with no compression and horrible pipe. Flotek's trail port uses 192 exhaust, 124 transfer. The blaster in that video is 196 exhaust, 126 transfer.

I need to raise the exhaust 5.74mm to get 186 and the transfers need to be raised.. 2.92mm to reach 127.


I may need to force blaster reeds into this when I’m done.. lol
Did it to my YT with a reed spacer. Hell, we stuck CR125 reeds in the blaster with a little persuasion lol


So i stuck an old ring in it to measure down and mark the jug... The ring fell through witout resistance. I think it needs new rings and a bore! lol

[RubberSalt]

Ok. I may start cutting the heads lol. I got a drill press yesterday. I've got a precision vice with x and y access movements... and milling bits

[old-yellow]

hey Rubbersalt what do you have to do to get the Namura hi-compression piston to work in the yt175 motor?
Namura Hi-Comp for $69.89 http://www.ebay.com/itm/Namura-Hi-Co...459c67&vxp=mtr

[RubberSalt]

Negative. But I suggest it if your not going OEM.

[RubberSalt]

I decided to go for a 7000 RPM range. 174 exhaust, 122 transfers. Ill toss my old original 175 pipe on it. Ill leave the original carb on it.

raise the exhaust until its 30mm from the top (done!)

Raise the transfers 40mm from the top (next)

Open the transfers on the base, cut the sleeve down, drill boyesens, call it good.


This is for the nephew after all. With the 80-81 bottom end, I better not push it..


Ill build the spare motor hot! :-D