Yamaha MX175
Moderator: Team
Yamaha MX175
Does anyone have any info on modifying this dirt bike? Its a 2-stroke and I'd rather follow something tried and proved rather than experiment since I'm new to 2-strokes.
Its a 82 model I'm fixing for my brother (it was his as a kid) and I would like to make it just a little nicer, I'm open to anything from milling to carb modifying to porting, etc, just give me some direction please!
Its a 82 model I'm fixing for my brother (it was his as a kid) and I would like to make it just a little nicer, I'm open to anything from milling to carb modifying to porting, etc, just give me some direction please!
LOL, according to the post count I'm an "expert." The only thing I'm an expert at is asking questions.
-
- Guru
- Posts: 1912
- Joined: Tue Aug 18, 2009 2:53 pm
- Location:
- Contact:
Re: Yamaha MX175
This one was posted here recently: http://www.bimotion.se/
Please help make Speedtalk a Troll free zone.
Re: Yamaha MX175
Not trying to upset anyone. But that bike and engine combo has very limited potential. It would need a special expantion chamber, highly modifyed ports and reed mods, a much larger carb/free flow air box etc. That bike was ment to be a play/beginner bike when new. Not an MX bike as the name suggest. If all this were done, the suspension would still be inadequate. IMO, just rebuild like stock. Clean-up on the ports is O.K. but don't change the hight or shape. Make sure to clean the silencer at the end of the pipe, as this likes to get clogged, and really restrict the power. All this said, it is still a fun bike to ride, just not a fast one. John
Re: Yamaha MX175
I actually don't want this to be too fast, so that's good, I just want to improve the low end and throttle response, make it more enjoyable to ride.
LOL, according to the post count I'm an "expert." The only thing I'm an expert at is asking questions.
- af2
- Guru
- Posts: 7014
- Joined: Sun Jan 28, 2007 4:42 pm
- Location: Grass Valley, CA :Northern Foothills
Re: Yamaha MX175
The very first thing I would do IF THE ROD IS TIGHT would be to cut the squish down to .025 and be 50% of the bore circumference. You might have to also cut the top of the barrel to get there. I have found on a trail type bike 175lbs is pretty much max compression.ap72 wrote:I actually don't want this to be too fast, so that's good, I just want to improve the low end and throttle response, make it more enjoyable to ride.
Without touching anything else you will be suprized how it acts.
Have fun!
GURU is only a name.
Adam
Adam
Re: Yamaha MX175
That's something I can easily do, thanks for the tip! is .025" too tight though? I get nervous whenever I go past .035".af2 wrote:The very first thing I would do IF THE ROD IS TIGHT would be to cut the squish down to .025 and be 50% of the bore circumference. You might have to also cut the top of the barrel to get there. I have found on a trail type bike 175lbs is pretty much max compression.ap72 wrote:I actually don't want this to be too fast, so that's good, I just want to improve the low end and throttle response, make it more enjoyable to ride.
Without touching anything else you will be suprized how it acts.
Have fun!
LOL, according to the post count I'm an "expert." The only thing I'm an expert at is asking questions.
- af2
- Guru
- Posts: 7014
- Joined: Sun Jan 28, 2007 4:42 pm
- Location: Grass Valley, CA :Northern Foothills
Re: Yamaha MX175
If the rod bearings are good you will be fine. I have not had 1 give any witness marks at .025.
Another thing I do is polish the chamber. It makes it nice to clean down the road on a freshen up.
Another thing I do is polish the chamber. It makes it nice to clean down the road on a freshen up.
GURU is only a name.
Adam
Adam
-
- Expert
- Posts: 793
- Joined: Sat Feb 10, 2007 1:24 pm
- Location:
- Contact:
Re: Yamaha MX175
.025" is way way to tight for a roller/needle bearing crank. I would put it at .050"
Re: Yamaha MX175
JES wrote:Not trying to upset anyone. But that bike and engine combo has very limited potential. It would need a special expantion chamber, highly modifyed ports and reed mods, a much larger carb/free flow air box etc. That bike was ment to be a play/beginner bike when new. Not an MX bike as the name suggest. If all this were done, the suspension would still be inadequate. IMO, just rebuild like stock. Clean-up on the ports is O.K. but don't change the hight or shape. Make sure to clean the silencer at the end of the pipe, as this likes to get clogged, and really restrict the power. All this said, it is still a fun bike to ride, just not a fast one. John
Well said... If your just wanting to play with the little thing for fun then go for it. I've done many of older bikes like this for just the pure fun & enjoyment of it with real seat of the pants improvements
![Very Happy :D](./images/smilies/icon_biggrin.gif)
91 mustang street car..blown sbf hci 5 spd meth inject.... new street motor project.... 408 sbf n/a
- af2
- Guru
- Posts: 7014
- Joined: Sun Jan 28, 2007 4:42 pm
- Location: Grass Valley, CA :Northern Foothills
Re: Yamaha MX175
ap72, Here is a web page you need to read. Chapter 2 explains everything I have posted.
http://issuu.com/jeanlulu/docs/a-graham ... erformance
http://issuu.com/jeanlulu/docs/a-graham ... erformance
GURU is only a name.
Adam
Adam
Re: Yamaha MX175
I owned one of these as a kid.. like was said, if the rod big end is good, bring quench to .025-.030. Put in a set of carbon fiber reeds, or try and find a rage cage for the bike, an fmf silencer tends to help a touch, and port jug only on the leading edges of the chambers, bring them to a razor sharp edge and take any casting out, polish the shortturn radius's as much as possible, and port the exhaust outlet to match the copper crush gasket, bringing it to a gentle taper down in the port, dont open up the csa on the exh port any more than stock. Rejet accordingly, 2 strokes live and die by the tuneup. Do all this and that bike will have you tumbling on your ass when the power hits. It will shred like satan got to it, i promise. Been there, done that with almost every old yamaha 2stroke ever built...
- af2
- Guru
- Posts: 7014
- Joined: Sun Jan 28, 2007 4:42 pm
- Location: Grass Valley, CA :Northern Foothills
Re: Yamaha MX175
Although I totally disagree with the knife edge ( I still have the SF110 to prove it) The jetting WILL have to be UPPED.Dirty Imp wrote: Rejet accordingly, 2 strokes live and die by the tuneup.
They do run the best right before they pop!!!
GURU is only a name.
Adam
Adam
Re: Yamaha MX175
Just posting what worked well for me.... but that was YEARS ago... but my lil 175 wud run with most 250s around my neck of the woods.... in the desert.
-
- Guru
- Posts: 1912
- Joined: Tue Aug 18, 2009 2:53 pm
- Location:
- Contact:
Re: Yamaha MX175
i had an old 77 Honda MR 175 ,,, we did a few things to it ,,, it didn't even have reeds and we picked it up ,,,, first bike i ever bought, ( 1980 ) ,, 150 bux in pieces ,, cosmetics in great shape , just not running ,, got it running in 2 weeks ,,, ahh the days ,,,