2 smoker power band

[SMOKEU]

I rode my mates NSR250 today, which has been off the roads for a few years, and he got it in an unknown mechanical condition. It's the first hot smoker I've ever ridden, so I wasn't really sure what to expect from it.
The speedo seems to work fine, but the tachometer doesn't work properly. At about 50kmh in second gear, if I go full throttle I can feel a sudden surge in power, quite unlike a 4 stroke. When the power valves do kick in, it gives a sudden rush, which quickly dies off although it still has plenty of revs left. The power valves seem to stop working at about 60kmh in second gear, although the bike still pulls until 100kmh in 2nd gear.
Overall the bike does feel quicker than mine, but I thought the power valves should make the bike go hard all the way to the redline. The bike has factory spec sprockets.

[bogan]

sounds like the power valves are stuck closed. Powervalves are designed to extend the surge of power, not initiate it. Just give it a visual cheack in neutral to ensure the valves come in at the right rpm, if they are electronicaly actuated it'll be bloody easy to check.

[Taz]

I had good lsuccess with the red powerbands in these. It sounds to me as if he only has the blue bands installed. What ever you do don't try to install both blue and red at once as you'll make them bind.

[Slyer]

Yes, we've all heard that joke a hundred times Anthrax.

[SMOKEU]

I had good lsuccess with the red powerbands in these. It sounds to me as if he only has the blue bands installed. What ever you do don't try to install both blue and red at once as you'll make them bind.

I might look on Trademe for a replacement powerband.

[sefer]

First thing you really need to do is get the tacho working.

The valves open at a specific rpm and not speed (mine opens at approx 7000rpm, but it will vary a lot depending on the bike), and most importantly, it will be the upper end of you max rpm. With no tacho you're risking running it past redline, which the bike isn't going to like if you do it too often.

[Taz]

Yes, we've all heard that joke a hundred times Anthrax.

What joke?

[SMOKEU]

First thing you really need to do is get the tacho working.

The valves open at a specific rpm and not speed (mine opens at approx 7000rpm, but it will vary a lot depending on the bike), and most importantly, it will be the upper end of you max rpm. With no tacho you're risking running it past redline, which the bike isn't going to like if you do it too often.

The reason why I said speed was because 50kmh in second gear should be about half the redline. I thought they had a rev limiter in them anyway, but the power band seems to be in the middle of the rev range, which seems a bit strange.

[porky]

Second hand powerband off trademe?? Na mate you got to buy a new one!!

As Bogan says, sounds like the valve is pft/ or not opening up for max exhaust porting.

Why is tach not workin proper? Signal comes off spark discharge. Are you sure you are getting a spark each time?

[ola_bitchola1]

does sound like a stuck valve my rg150 gets to its powerband then just revs all the way to the redline

[SMOKEU]

Why is tach not workin proper? Signal comes off spark discharge. Are you sure you are getting a spark each time?

The tacho seems to hugely over read throughout the rev range. At 50kmh in 2nd gear it's bounced off the clock!

[Latte]

restricted NSR will feel tame at the top end. Still has the 8k hit, but levels off real quick. and it's all over by 11k (restricted or not) , no 18k screamer like your 4 pot.

When you 1st turn ignition on you should see the power valve assemblies "cycle" , if not either they are stuck, or the PGM has popped.

[Katman]

Check the state of the reed valves.

[Jr_Mechanic]

I know when my TZR resets the power valves you can hear them a whurring sound. But they do get clogged so cleaning them may be an option. that way you can inspect them for wear. My power band starts at 7500 and keeps going to 13000 2k into the red line. good luck