XL250K3 - performance? (lack of....)

[New Haven Neil]

As you may have seen in the 'show us yours' I have an old K3, which occasionally sneaks out onto the road. (Not Manx registered yet - well, we've only been here 9 years...oops).

Anyway, I am busy giving her a big tidy up for the Manx test (once only job for registration - no MOT here) and she really, really is slow. Yeah yeah, I know...but are they really that slow? Anything over 60 needs a good downhill run and a following wind (15t gearbox sprocket). I was wondering if they are all like that, or is the rough exhaust is causing hassles and losing me what power there is?

Mrs NHN has a couple of tidy CL250SC's and they are miles 'faster' - ahem - although boasting the same quoted power. So, is my K3 ill, or are they all like that, and my expectations and memory flawed? It has plenty compression, had new rings about 2000 miles ago, doesn't burn oil etc.

I've got a 250SB to do after this one too....

[Chad]

whats the pick up like , is it slow as in topend slow ie previous owner put on different sprockets for trails riding ?

its a pretty little thing though

[New Haven Neil]

Hi Chad

No it's not gearing, I have owned it for donkeys years - I had geared it right down for off roading, but have now put it back to standard and put the original mudguards etc back on. It pulls like a train low down, very torquey for what it is, but is reluctant to rev out, no top end power. I'm going to strip the carb and get it ultrasonically cleaned, I've bought a new air filter foam, and have made a better exhaust with a micron silencer off my XL250SB - we'll see if it's any better then!

Cheers

Neil

[Chad]

Hi Chad

No it's not gearing, I have owned it for donkeys years - I had geared it right down for off roading, but have now put it back to standard and put the original mudguards etc back on. It pulls like a train low down, very torquey for what it is, but is reluctant to rev out, no top end power. I'm going to strip the carb and get it ultrasonically cleaned, I've bought a new air filter foam, and have made a better exhaust with a micron silencer off my XL250SB - we'll see if it's any better then!

Cheers

Neil

then my moneys on the carb first then once thats back on if no change try the zorst

[416cc]

That downturned end piece to the silencer looks like it's straight though without much baffling. If that's the case then you'd need to rejet the mainjet as there would be insufficient back pressure. Try going up a notch on the needle & up a size or two on the mainjet.

Is the fuel flow sufficient?

Is the airfilter clean?

Is the spark plug a good'un?

Is the points gap correct?

These are all items that can affect top-end power. My brother had one & with a few modifications it was good all through the rev range.

[hwm]

I own the North American version of the 1976 XL250K3 with 9600 miles and a factory stock engine that has never been apart. It has 175 LBS of compression.

With standard gearing, and an aftermarket silencer comparable to the (rusted out) original, it will pull 8000 RPM / 70 MPH in 5th on level paved road with my 210 pounds of bulk sitting bolt upright. If I laid down on the tank and let it rev into the red zone it would probably go faster. It will also pull 8000RPM / 60 MPH (redline) in 4th up any long hill I have tried on local paved highways.

It has good power for a 36 year old 4-stroke 250cc single with a very quiet exhaust system.

After reading through the previous posts in this thread, I would add only that the centrifugal advance mechanism on the end of the camshaft, under the points mounting plate, should be checked. Since your engine lacks power mainly at high RPMs, this may be stuck at idle-full retarded position.

Also, in my experience, and as others have pointed out, a less restrictive exhaust on a Honda may give lower power unless you re-jet the carb richer. This is most noticeable at larger throttle openings where main jet and needle position determine the mixture.

[tattie]

Hi NHn,
I had a K3 back in the eighties and it would manage 67mph flat out chin on the bars and feet on the rear pegs but no matter how long the straight it would not rev out (to the red).

I have a 1977 k3 at the moment in bits, that was going to be a future project 15 years ago !!


Cheers

A.M.

[New Haven Neil]

Thanks AM - that sounds about right!

The latest story, well after riding it a bit during TT (mingling in with the visitors as still not 'Manxed' and therefore not taxed!) with a quiet exhaust made from micron bits off my 250SB, it was exactly no faster at all. I need to check the advancer as suggested, good call, but after a couple of hundred miles TT week the tank sprung a leak so it's back in the garage in disgrace. Anyone got a decent K3 tank????

Also I'm crocked myself with a hip problem that requires nasty surgery, so it may be a while before I'm fit enough to ride again.

In the meantime I'm cheered up by a replica stanless silencer Alldens Exhausts made for Mrs NHN's CL250, looks great & sounds superb (remember that no MOT thing! requested not too much baffling..... ) She's bombing around on it and I'm stuck in the car.....

[xr600shinbruise]

morning my friend,personally i would look towards the exhaust not being stock,in my experience and ive had a fair few xl,s,changing exhausts,or fannying about with the the airbox always reduces top end power.my first xl,an 1980 xl 500s had a sammy miller silencer fitted and wouldnt pull more than 65mph untill i borrowed a stock jobby and removed k&n filter for stock and it gave me an extra 17mph ,although a stock exhaust for yours might be a bit rare now,are you running the original airbox?mark.

[New Haven Neil]

Morning Mark

Yes, it has a standard airbox, recently with a new filter foam. Made no appreciable difference, just quieter! New stock exhausts for these are rocking horse doings, no chance at all of finding one. I've had the bike for years and years, never seen one! The micron pipe is pretty much OK on the XL250SB, but the engines are quite different I suppose.

As it's off the road now becasue of the tank I'll be giving the carb a complete overhaul soon, but it'll all have wait until i recover from my forthcoming operation, not exactly looking forward to that.

laters!

Neil