Upgrading performance on an SR250?

T

twistekeys

Been Around the Block
Any ideas for performance upgrades? I already got an aftermarket air filter but I'm looking for more power and speed. Any ideas? Would new rings help after 40 years on one engine? Is head milling only a dirt bike thing? What about larger jets? etc.???
 
There might not be enough people who have knowledge of these bikes. Have you looked to see if they make a big bore kit for it? And aftermarket exhaust and airfilter will help, you will also have to rejet.
 
is the sr400 an overbored version of the 250? if so a barrel/piston swap might be the go
or maybe the xt350? could be the whole engine might fit in?
 
I'd recommend first checking Sonreir's How to Make a Functional Cafe Racer thread. Then maybe read some books...this is kind of a broad topic, and I doubt there are a lot of bolt-on performance products sitting on the shelves for the SR250. Don't go bolting on a 34mm Mikuni flatslide or anything yet in search of a simple fix. Everything needs to work in harmony.

You might run into the point where it's far more economical to sell your bike and buy another one if you really want something faster. How much money do you want to throw at this thing?

Making it lighter can be cheap, but it's also easy to go overboard and throw away useful stuff like front fenders to save a few grams that don't really make any discernable difference to performance.

Making it breathe better can be cheap-ish with air filters and exhaust. If your bike has points, an electronic ignition swap can help things move while simplifying maintenance, and is pretty easy to install. Beyond that, stuff starts to really cost in materials and labor, especially if it's one-off work rather than bolt-on products.

Edit to add: Speed is only one upgrade...handling is another. Adding cartridge emulators to the fork and putting on nice rear shocks, such as Hagons which are still pretty cheap, can transform your bike's ride. Good tires, too. They're not sexy like a titanium exhaust, but they can make an amazing amount of difference; they're the only place your bike actually touches the ground to make things happen.


*I've only learned all this over the past year or two, so take me with a grain of salt...
 
Getnjgywitit said:
There might not be enough people who have knowledge of these bikes. Have you looked to see if they make a big bore kit for it? And aftermarket exhaust and airfilter will help, you will also have to rejet.
Click to expand...

Yeeeeeah not much. I'm pretty used to that though after owning only obscure jap bikes.
 
spotty said:
is the sr400 an overbored version of the 250? if so a barrel/piston swap might be the go
or maybe the xt350? could be the whole engine might fit in?
Click to expand...

It might be, never heard of a factory 400. But that's not personally where I wanna go with it. Thanks though!
 
AgentX said:
I'd recommend first checking Sonreir's How to Make a Functional Cafe Racer thread. Then maybe read some books...this is kind of a broad topic, and I doubt there are a lot of bolt-on performance products sitting on the shelves for the SR250. Don't go bolting on a 34mm Mikuni flatslide or anything yet in search of a simple fix. Everything needs to work in harmony.

You might run into the point where it's far more economical to sell your bike and buy another one if you really want something faster. How much money do you want to throw at this thing?

Making it lighter can be cheap, but it's also easy to go overboard and throw away useful stuff like front fenders to save a few grams that don't really make any discernable difference to performance.

Making it breathe better can be cheap-ish with air filters and exhaust. If your bike has points, an electronic ignition swap can help things move while simplifying maintenance, and is pretty easy to install. Beyond that, stuff starts to really cost in materials and labor, especially if it's one-off work rather than bolt-on products.

Edit to add: Speed is only one upgrade...handling is another. Adding cartridge emulators to the fork and putting on nice rear shocks, such as Hagons which are still pretty cheap, can transform your bike's ride. Good tires, too. They're not sexy like a titanium exhaust, but they can make an amazing amount of difference; they're the only place your bike actually touches the ground to make things happen.


*I've only learned all this over the past year or two, so take me with a grain of salt...
Click to expand...

Thanks for the advice, and yes I have read that, great post. I think I'll start with a air filter since I need one anyway for the custom panels, then go one size up on my ....main? Jet since it was downsized when I got it.
 
twistekeys said:
Thanks for the advice, and yes I have read that, great post. I think I'll start with a air filter since I need one anyway for the custom panels, then go one size up on my ....main? Jet since it was downsized when I got it.
Click to expand...

I'd still recommend figuring out what jet is correct for your bike, not just going "bigger." Jet size is part of tuning your bike, so it can help the bike run stronger if the mixture's not well-tuned, but it's not like you can take a properly-running machine and throw a bigger main jet and it'll go faster.

You might look at the needle position before you change any jets at all. Main jet mostly affects your very top end.

I think many bikes have a very lean mix from the factory due to emissions restrictions, so upjetting to the proper size makes sense and you read about people doing this on many models. But it's because the mixture's not optimal as-is, not because a new jet is a performance "upgrade" per se.
 
AgentX said:
I'd still recommend figuring out what jet is correct for your bike, not just going "bigger." Jet size is part of tuning your bike, so it can help the bike run stronger if the mixture's not well-tuned, but it's not like you can take a properly-running machine and throw a bigger main jet and it'll go faster.

You might look at the needle position before you change any jets at all. Main jet mostly affects your very top end.

I think many bikes have a very lean mix from the factory due to emissions restrictions, so upjetting to the proper size makes sense and you read about people doing this on many models. But it's because the mixture's not optimal as-is, not because a new jet is a performance "upgrade" per se.
Click to expand...

I wasn't aware of that with the mixture. Thanks bud. But the reason I say up size is because the mech that was working on my bike when I got it asked me if I wanted to cruise or nail it more often, I said cruise for fuel efficiency and I sure can tell when I nail it lol.
 
I've got an SR250. It's got a much more open exhaust and a pod filter, and a much bigger jet -- wouldn't run with stock jet it was so lean (and the stock airbox was so restrictive). You can switch out sprockets to improve quickness off the line or lower revs at higher speeds. Despite rejetting, exhaust and filters, mine's still not that quick -- I just don't think these bikes were.
 
carnivorous chicken said:
I've got an SR250. It's got a much more open exhaust and a pod filter, and a much bigger jet -- wouldn't run with stock jet it was so lean (and the stock airbox was so restrictive). You can switch out sprockets to improve quickness off the line or lower revs at higher speeds. Despite rejetting, exhaust and filters, mine's still not that quick -- I just don't think these bikes were.
Click to expand...

Yeah, makes you wonder how modern 250s will cruise at 100 all day and get there way faster than us...
 
twistekeys said:
Any ideas for performance upgrades? I already got an aftermarket air filter but I'm looking for more power and speed. Any ideas? Would new rings help after 40 years on one engine? Is head milling only a dirt bike thing? What about larger jets? etc.???
Click to expand...
How much do you want to spend?
 
twistekeys said:
It might be, never heard of a factory 400. But that's not personally where I wanna go with it. Thanks though!
Click to expand...

What does that mean?
Want an upgrade but don't want a bigger engine?

Why do you think a pod filter is a performance upgrade?
Most bikes I have worked with it is not. Less so if using a cheap emgo on a small CC bike.

Did you get the bike running 100% factory so you have a base line to know if the "improvements"are working?
 
surffly said:
What does that mean?
Want an upgrade but don't want a bigger engine?

Why do you think a pod filter is a performance upgrade?
Most bikes I have worked with it is not. Less so if using a cheap emgo on a small CC bike.

Did you get the bike running 100% factory so you have a base line to know if the "improvements"are working?
Click to expand...

Yes I did?? Sorry I know it's the internet and feelings are invisible, but I sense a slight bit of hostility from you... Just chill dude, it's not like I'm asking for advice on a multi million dollar company...

As far as my quote goes, I don't want to engine swap, or bore it. That costs too much for me and it's not along the lines of my criteria I need to meet for this project. Besides those mods, I think an aftermarket intake (the stock one is ridiculously restrictive) and a little jetting tweak will work fine, after all I'll never be able to do the ton. But I got the half ton down. 8)
 
Hostility?
Delicate flower are we?

Still stand behind the advice to make it run 100% stock first.
Most older bikes are in more need of service items then pods.
Maybe the SR are a lot different, been my experience that the stock air boxes are not the weak link nor are they that restrictive. Mostly they are swapped out to get that open triangle look everyone wants.

Best bet is to spend what is in the tight budget on gas to get out and ride.
Worry less about British plates, pods and checkerboard and more about enjoying the road and bikes.
By riding you might be surprised by the type of riding you like (ie pretend racing, adventure, touring, endro, flat track, ect) and then when the budget allows build the sr up, or find a bike that is better suited for your next experience
 
surffly said:
Hostility?
Delicate flower are we?

Still stand behind the advice to make it run 100% stock first.
Most older bikes are in more need of service items then pods.
Maybe the SR are a lot different, been my experience that the stock air boxes are not the weak link nor are they that restrictive. Mostly they are swapped out to get that open triangle look everyone wants.

Best bet is to spend what is in the tight budget on gas to get out and ride.
Worry less about British plates, pods and checkerboard and more about enjoying the road and bikes.
By riding you might be surprised by the type of riding you like (ie pretend racing, adventure, touring, endro, flat track, ect) and then when the budget allows build the sr up, or find a bike that is better suited for your next experience
Click to expand...

Thanks for the advice... I honestly will work for 5 hours before I go riding for 1. I personally enjoy "motorcycles" more than riding. I refer to myself as a motorcycle enthusiast, as opposed to a motorcycle rider. I love admiring the engineering, materials, the design, the aerodynamics, etc. That they thought of at the time. It's beautiful. Riding it is a perk. This may come from being from a poor family and only ever getting to see motorcycles on the internet, so I've come to love looking at them as much if not more than riding them, but it's who I am. And I'm not causing anyone harm by doing so so don't think this is a negative view.
 
Hope I don't get my hand smacked for linking to another forum...

http://advrider.com/forums/showthread.php?t=542521&highlight=sr250

Read up...in a nutshell. Use an off the shelf YFM350 (Warrior) Wiseco piston with a custom sleeve for 312cc. Can use YFM350 valves once you enlarge the seats...port head, bigger carb, etc. Shouldn't be terribly expensive, but you will still only have 312cc. Should still be a blast, but you could certainly go faster by getting a different bike. But that's not what it is all about, now is it?
 
regal7point5 said:
Hope I don't get my hand smacked for linking to another forum...

http://advrider.com/forums/showthread.php?t=542521&highlight=sr250

Read up...in a nutshell. Use an off the shelf YFM350 (Warrior) Wiseco piston with a custom sleeve for 312cc. Can use YFM350 valves once you enlarge the seats...port head, bigger carb, etc. Shouldn't be terribly expensive, but you will still only have 312cc. Should still be a blast, but you could certainly go faster by getting a different bike. But that's not what it is all about, now is it?
Click to expand...

Thanks for the link. :) Hopefully its not against the rules
 
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