evening all,
Have been messing about this summer with a little XLR 125 project picked up in a scrap yard. Good fun in the field but needs a bit more power when it gets muddy.
Anyone ever tinkered with these little honda engines, they are pretty bullet proof but lacking in power about 13hp standard.
Any ideas appreciated. Cheers Phil
more power needed
-
benny hedges
- Posts: 6110
- Joined: Sun Oct 18, 2009 5:09 pm
- Location: Warrington
Re: more power needed
have a look at yoshimura website... they do a lot of kit for these and other singles, like cams, copper gaskets, big valve heads, headers etc.
You do not have to say anything. But it may harm your defence if you do not mention when posting something which you later rely on in quote. Anything you do say may be ripped to sh*t.
Re: more power needed
Yep, tuned the hell out of these a few years back.
They're based on the old CB125S engine, it got used in a load of derivatives, all with the same engine tune.
But it can be improved, fit a good air filter (I used a speedway 42mm cone clamped tight onto the carb; worked fine and oiled foam insert so reusable.
Exhaust needs to be a lot freer, too, if your'e planning to keep it as an off-roader then you'll need something upswept, but anything without baffles will do- a reverse cone mega can be made to fit.
Cams are available from a lot of Japanese tuning houses, so get on the net and translate. And a flat slide would be good, but they're expensive. So try getting any generic 24mm or 26mm carb (not CV) and fit that.
Think I used one of a pair of old carbs from (IIRC) a CB175, vintage unknown.
You might have to turn up the tickover a bit to get it to idle ok.
Apart from that, high comp pistons make a difference, see if you can get one of a set made for the old 500/4 Honda; they're the same bore and stroke and pin sizes, so pop right in.
Only known weakness if the CCT (now, there's a surprise) but in this engine it is because under tension the little spring clip can ping off the internal end, go inside the engine and get caught between meshing gears, if you're unlucky.
A simple fix is to remove it and just fit a bolt from the inside, a locknut on an O-ring outside, and a locknut above.
A small saw-cut in the end of the bolt thread helps to stop it turning while adjusting the tension.
Don't over-tension, as it then pulls the cam down into the head, oil flow isn't high and so you will need a new head, possibly cam as well, if tensioned too much.
But cheap and easy to find spares for.
If it's an old one, the points are on the end of the cam, so you can play with timing to get it to run for peak HP. Replace the points retainer cross-head screws with cap heads, to make adjustment easier.
Never did play with big valve conversions, though- might yield another BHP or two.
But why not nitrous or a blower?
They're based on the old CB125S engine, it got used in a load of derivatives, all with the same engine tune.
But it can be improved, fit a good air filter (I used a speedway 42mm cone clamped tight onto the carb; worked fine and oiled foam insert so reusable.
Exhaust needs to be a lot freer, too, if your'e planning to keep it as an off-roader then you'll need something upswept, but anything without baffles will do- a reverse cone mega can be made to fit.
Cams are available from a lot of Japanese tuning houses, so get on the net and translate. And a flat slide would be good, but they're expensive. So try getting any generic 24mm or 26mm carb (not CV) and fit that.
Think I used one of a pair of old carbs from (IIRC) a CB175, vintage unknown.
You might have to turn up the tickover a bit to get it to idle ok.
Apart from that, high comp pistons make a difference, see if you can get one of a set made for the old 500/4 Honda; they're the same bore and stroke and pin sizes, so pop right in.
Only known weakness if the CCT (now, there's a surprise) but in this engine it is because under tension the little spring clip can ping off the internal end, go inside the engine and get caught between meshing gears, if you're unlucky.
A simple fix is to remove it and just fit a bolt from the inside, a locknut on an O-ring outside, and a locknut above.
A small saw-cut in the end of the bolt thread helps to stop it turning while adjusting the tension.
Don't over-tension, as it then pulls the cam down into the head, oil flow isn't high and so you will need a new head, possibly cam as well, if tensioned too much.
But cheap and easy to find spares for.
If it's an old one, the points are on the end of the cam, so you can play with timing to get it to run for peak HP. Replace the points retainer cross-head screws with cap heads, to make adjustment easier.
Never did play with big valve conversions, though- might yield another BHP or two.
But why not nitrous or a blower?
It's not falling off, it's an upgrade opportunity.
more power needed
So what kind of bhp increase did you get with all that work? It sounds like you need to chat;). Always great to have experience like this.
Thanks for sharing
Thanks for sharing
No bike (yet).
Re: more power needed
Actually, thinking about it, the easiest route would be to drop in an XL185 engine; they'll fit straight in.
IIRC, the carb on those is bigger, too.
It still needs to breathe better, though.
The engine work as described in the thread above would give you more power, sure nuff, but in that chassis it may not give you more usable power.
PM'd with moby number.
IIRC, the carb on those is bigger, too.
It still needs to breathe better, though.
The engine work as described in the thread above would give you more power, sure nuff, but in that chassis it may not give you more usable power.
PM'd with moby number.
It's not falling off, it's an upgrade opportunity.
more power needed
Hi Tony. I was just interested inthis thread developing. I haven't a 125 but if I did, I'd be calling you;)
No bike (yet).
Re: more power needed
Never bothered dynoing it, but had six of these series engines in various states of tune while I was waiting to rebuild my credibility with insurance companies after a DD ban when I was young and foolish.
I was working building spoked wheels for Hagon at the time, had the smallest but loudest bike in the car park....but they used to seize or blow holes in pistons pretty regularly.
Quicker to slap another spare engine in than mess about, as I was using it for commuting.
Soon as it started smoking, in with a spare.
Used to run them on Castrol R oil sometimes, didn't mind them smoking so much then, as it smelled lovely.
I was working building spoked wheels for Hagon at the time, had the smallest but loudest bike in the car park....but they used to seize or blow holes in pistons pretty regularly.
Quicker to slap another spare engine in than mess about, as I was using it for commuting.
Soon as it started smoking, in with a spare.
Used to run them on Castrol R oil sometimes, didn't mind them smoking so much then, as it smelled lovely.
It's not falling off, it's an upgrade opportunity.
Re: more power needed
OK Tony thanks for all the info,
Will start working my way through suggestions and let you know how it goes, have started with simple stuff like weight reduction, it is now down to bare bones ie all lights accesories etc all gone and just rewired for basic start stop only.
In your list you mention points? this engine has pulse generator and a cdi unit I have seen on an xlr forum about cutting one wire to increase power have you come across this? the engine is a 2002 unit.
Cheers Phil
Will start working my way through suggestions and let you know how it goes, have started with simple stuff like weight reduction, it is now down to bare bones ie all lights accesories etc all gone and just rewired for basic start stop only.
In your list you mention points? this engine has pulse generator and a cdi unit I have seen on an xlr forum about cutting one wire to increase power have you come across this? the engine is a 2002 unit.
Cheers Phil
Re: more power needed
Mine were older series engines with the points plate mounted on the end of the camshaft, which meant that if you left the mounting screws loose-ish you could reach down and turn it while riding, thus setting it for best top speed.
Didn't have money for dynos back then
Pulse generator would still be able to be adapted to fire earlier, but would be harder to adjust. You might be able to find an ignition advancer, though, but too much and it'll burn a hole in the piston, I'd suggest a -2 degree one rather than a -4.
The usual trade-off is swapping torque for top end, though.
Definitely intake and exhaust will show the biggest gains for the least money.
Didn't have money for dynos back then
Pulse generator would still be able to be adapted to fire earlier, but would be harder to adjust. You might be able to find an ignition advancer, though, but too much and it'll burn a hole in the piston, I'd suggest a -2 degree one rather than a -4.
The usual trade-off is swapping torque for top end, though.
Definitely intake and exhaust will show the biggest gains for the least money.
It's not falling off, it's an upgrade opportunity.