Operation "Cheap Thrills" - SR250

Wabba

Don't smoke shisha and ride
Hi all,

So Operation Cheap Thrills takes off. The victim is a -95 78tkm Yamaha SR250 Special. I got the bike last summer and basically just rode it for 14tkm worth. Now when the sun is finally coming out, it's time to get to work. As the name says, it's going to be cheap, which doesn't mean it can't be stylish.

I am not quite sure yet what it's going to look like when done, most decisions will be on "when we get there basis".

The first thing I did was to get it running properly, it used to cut out if given stick. That was cured with a new CDI from the local bike scrapyard, 20€. From the same place I got a motocross handlebar (6€), taken from a XT of course :) and a rear sprocket (7€) to replace the totally worn out one.

The bike is running now +1 front sprocket, but in my opinion is still geared too short, specially for highway use. Will do something about it. Another big question is how to boost that 17hp up a bit, can't cope with scooters out accelerating it.

One challenge this build faces is that the bike is a daily rider and does regularly a weekly 390km trip. This means I can't just dismatle everything and begin to paint and polish, have to do it in bits.

Anyway, some photos attached, I hope you enjoy the build. Any feedback is always welcome, specially if anybody knows what are the bottlenecks of this engine to boost the power up.

Original bike

Mx bar before polishing and painting.

Dropped front suspension and test mounted bars

New painted inverted MX bar in place

Considerably nicer stance. The bike is actually even lower that one would think because of the soft front it really drops down due to the increased weight in front. After some 500km on this setup, the posture is great but now the pegs need to move back... The more forward leaning posture really help riding this 17hp bike in headwind also.

For the time being rear; moved the fender in as much as I could, made a difference to how it looks.

The next step is to begin to figure out the shape of the rear end. The plan is not to alter any structural elements and if possible, make the new rear end/seat to be attached just as the original seat, so that they would be interchangable, a bit like mono seat / hit the beach with my girl setup.. More to follow... Please comment and tell me what you think of it.
 
Right,

Design:

after some very hi tech card board bending and taping, and after 15min of Fireworks magic, we have an idea visualised. I like the rear end to be low, which in this case would mean that the seat section would be lower than the frame.

Colorwise, polished rims, except the middle hump where the wires attach to, that would be red. Wires would be black, as would the hubs also. The exhaust would be wrapped wih sand colored exhaust tape. The construction will hopefully begin soon, at the moment it would be an Urethane mold and carbon fiber for the finished product. I'm still between maintaining the frame black or painting it red.

design1.jpg


design2.jpg


design3.jpg

Power section:

I came across this photo in a TW (Trailway) forum:

pipe.jpg


So it is true, inside the exhaust there is a smaller one, which exlains why it feels so strangled. The left side pipe is SR250 and the right is TW. Apparently the reasoning for this idea is that the smaller inner pipe prevents the chrome from darkening. Well, didn't work in my bike... So, a new pipe would be a good idea, we'll see.

After reading some comments regarding waking up Yamaha Warrior quads, also a 2 valve thumper, I came across info that the bike doesn't breath. So, today I run the bike without the airfilter box lid, as advised ifor Warrior, adjusted the carb and the difference is really noticeable. Now the bike revs easier and I noticed 10km/h increase just with that. Also uphills where before I needed to shift down to second, it climbs now on third. However, it made the bike a lot noisier, I'll construct a new lid with holes or scoop on it to make sure the poor bugger gets air.

Let me know what you think.
 
Yeah, that 2 exhaust pipe thing - Gay...

Diggin your envisioned designs btw! That tail could fit a few niceties inside... I noticed you dropped the front. Just a thought, you could drop it more to balance out the rear section. Up to you though.
 
Back
Top Bottom