Lifan LF250B performance suggestions

[Rogerborg]

Ahoy the forum. I've got an EU spec 2009 Lifan LF250B, a copy of the Yahama Virago, with the 2V49FMM engine.



It's done around 5000km and had been stored outside and neglected slightly, but I have no reason to believe that it's been abused.

It's running smooth, is great low down and pulls strongly to 55mph, but the bike tops out at an (indicated and actual) 65mph / 105kph on the flat. Since the original Virago claimed 85mph / 137kph, I'm hoping to get more like 75mph / 120kph out of mine.

What I've done so far:
Oil change to semi synthetic 10W-40 motorcycle specific oil. Change oil filter.
Clean air filter.
Ran through a couple of tanks with Redex to try and clear any jet blockage.
Adjust tappet clearances (aka valve lash) to the Yahama recommended gaps. It was set up too tight, and now idles faster (with no other adjustment), usually a good sign.
Freed up a slightly binding front brake and checked the rear isn't binding. The wheels both spin freely.
Change the front sprocket from 16 to 18 teeth - I prefer the longer gearing and think it makes the lower gears more usable, but top speed is exactly the same with both gearings.
Clean, lubricate, and correctly tension the chain.
Check and correct the rear axle alignment.

The bike now feels great, but it just runs out of steam at 65mph.

What I haven't tried yet:
Check that the throttle is actually opening fully.
Strip, clean and inspect carb.
Increase the main jet size.
Any modifications to the exhaust. It's a catalysed Euro 3 exhaust, very convoluted, and I suspect it's not doing the engine any favours. The (real) rear pipework and cat box are also rusted to hell after just 18 months and 5000km, so I'll need to get it off and sorted before winter anyway.

If anyone has experiences with these bikes, or the Yahama original (Virago / Dragstar XV and XVS 250) then I'd very much appreciate your suggestions about where to find the hidden performance. I'm not looking for a rocketship, just another 5 or ideally 10mph for motorway use.

[jape]

I don't have this particular bike so cannot help specifically but have been talking to mechanical mates about this on my own machine lately and I think you are doing it all right so far. I am surprised the two tooth sprocket change has not increased the top speed by that elusive 10% though. I do get confused by the ratios and what does exactly what best but increasing the front sprocket size by the equivalent of a six teeth drop at the back should have easily given you the higher top speed. We won't go into engine load, preferable chain size and tension alterations here ...
So I suggest you first try the simpler things like increase the air-filter intake size, replace the filter rather than just clean it unless you are sure it flows really well and then punch out the catalytic restriction which stuffs up air flow especially if it is rusted and clogged.

[Rogerborg]

Thanks for the suggestions. Yup, I'll try a short run with the air filter out completely and see if it helps. It's a weird arrangement, where the air filter is on a pod on the side, feeds through a rubber duct actually into the frame, and then down from the frame through another duct into the carb. It all seems a bit complicated. At a minimum, I'll chop bits off of the pod to allow more air to get to the filter.

There's no tacho, so I don't know what the revs are at 65mph. I was hoping that it was just so low geared that it was power-peaking at 65, but that doesn't seem to be it. I may have gone one tooth too far, but I'd really expect to get another few mph out of it.

The exhaust is definitely on the list of things to deal with - I de-catted my 125 Huoniao with some success, although the cats were so solid that I just cut them out and replaced the pipe rather than trying to remove them piecemeal. I'm hoping that the Lifan will be easier, or that there's a quick bodge to help it breathe. I'm definitely not in the market for a new 'performance' exhaust, as it would easily cost half the value of the bike.

Regarding the chain, the Lifan comes with 530 sprockets and chain, while the Virago is 520. The 18 tooth front sprocket that I've just fitted is a 520, and I'll likely switch to a Virago-spec 520 chain and rear sprocket when I replace them.

Anyway, thanks again for the response.

[euphonius]

rogerborg, i see you quoting distances in km but speeds in mph. you somewhere in the US? UK?

cheers

[Rogerborg]

I'm in the UK, it's a Euro 3 spec bike. I'll try to remember to post speeds in both mph and kph for an international audience.

Incidentally, this is the first vehicle I've ever had with an accurate speedometer. Most speedometers read 5-10% high (or more!) but I've checked the Lifan against several radar speed signs and a GPS unit, and it seems to read correctly at all speeds. So when I say 65mph / 105kph, I mean an actual 65/105.

Oh, I tried a run with their air filter out. It didn't help, but it did lean the mixture right out at full throttle (I did a plug chop to check). Actually, it looks to be running lean even with the stock filter in. I'll try up-jetting, once I've found the stock jet type and size - I believe the stock Virago has a Mikuni 26mm carb with a 110 main jet, but God alone knows what's on the Lifan, and He didn't document it in the manual.

[Luis Carlos]

Vblade 250 no Brasil segue o link do manual de serviço

http://www.vbladers.com/arquivos/vbl...nut+e+serv.pdf

[hugemoth]

I suspect your best performance gain will be from a larger jet. My Hensim 250 was also quite lean from the factory but increasing the jet size and lifting the needle made a big difference. At the same time I removed the catalytic converters and put on free flowing mufflers but the jets made the biggest difference.

Q

[humanbeing]

Vblade 250...

Vblade 250 is made by Zongshen

[Rogerborg]

I suspect your best performance gain will be from a larger jet. My Hensim 250 was also quite lean from the factory but increasing the jet size and lifting the needle made a big difference. At the same time I removed the catalytic converters and put on free flowing mufflers but the jets made the biggest difference.

Thank you, I'll try up jetting then.