Engine doesn't like full tit launches!

[Blackshear]

So it was all rainy this evening, so out I pottle for a bit of shenanigans.
Was at the lights with noone else around, when it turned greed. I felt like giving the tail a bit of a wiggle, so up I go to about 11k and somewhat forcibly I let out the clutch.

When I get scared and back off. It was as if the engine wasn't getting enough fuel, or sommat, started burbling and didn't have any oomph. So off I sped in gear, wringing her all the way out. Didn't miss a single beat.

I tried getting the back end loose at the next set... Same goddamn deal.

It's just a 250 I know, but it was wet. The old tyres (Some dryballs Kendas it had on when I got it) would spin the moment I even thought of letting out the clutch, but these new ones stick like shit to a blanket.

Can anyone enlighten me as to why my bike will burble and lose power like it did, when I can redline fine if I'm just 'hooning'?

I'd ask Daddy, but he's asleep.


TL;DR

Bike cuts out when doing a full-tit launch, but will hum along to 16,500 without a single moan of complaint.

[CookMySock]

Try a half-tit launch then.

Naw sounds like you have some good rubber on it.

Steve

[Blackshear]

Try a half-tit launch then.

Naw sounds like you have some good rubber on it.

Steve

Well yeah I can do THAT! Is this wot 'appens to little bikes with carbies?
I can do a full tit launch, just not as much clutch, but the moment I try to make it launch it just turns around and says 'Don't, Chris. Just piss off or something.'

[CookMySock]

Is this wot 'appens to little bikes with carbies?

Pretty much you don't have the torque to wheelspin at low rpm, so the engine revs bog down, which lowers the torque even more.. so its kind of a negative avalanche thing. It's not really 'carb' related.

Steve

[sinfull]

Be in yr carbs ! Larger jets might let enough fuel in to give it a fistfull while its unloaded !
Practice makes perfect ! Try a short jab and grab a handfull of front brake, without locking the front up, (looking silly, lying on the middle of the road), which unloads the back wheel and let the clutch out a bit more (while backs unloaded and fronts still down with a bit of front brake on) and the back should start spinnin, once the revvs are up, the momentum keeps the wheel spinnin while ya let go of the front brake and burnout away from the lights !
(then the plod arrive, take yr bike and ticket you for loss of traction, new boy racer law)

[driftn]

Your going about it all wrong,

take off slowly get her moving put your weight over the front, pull the clutch in give it heaps of throttle(to roughly where it makes peak power) and dump the clutch. It will do one of 2 things.

1: torch the rear tyre (My SRAD was good for this in second then would grip and lift the front (some times even in the dry)

Or if the road is still in good nick and has some grip it will try stand on its back wheel.

Hope this helps now go try it and have some fun, pratice makes perfect.

[Blackshear]

Pretty much you don't have the torque to wheelspin at low rpm, so the engine revs bog down, which lowers the torque even more.. so its kind of a negative avalanche thing. It's not really 'carb' related.

Steve

Yeah, the little toofiddies don't have that much I guess.
Which is a good thing! In the rain.

Be in yr carbs ! Larger jets might let enough fuel in to give it a fistfull while its unloaded !
Practice makes perfect ! Try a short jab and grab a handfull of front brake, without locking the front up, (looking silly, lying on the middle of the road), which unloads the back wheel and let the clutch out a bit more (while backs unloaded and fronts still down with a bit of front brake on) and the back should start spinnin, once the revvs are up, the momentum keeps the wheel spinnin while ya let go of the front brake and burnout away from the lights !
(then the plod arrive, take yr bike and ticket you for loss of traction, new boy racer law)

It's only 3 seconds sustained loss of traction
But yeah who's counting
Just went out and tried it out of traffics way. Just a touch of front brake does the trick, then it becomes your lifeline ha ha.

Your going about it all wrong,

take off slowly get her moving put your weight over the front, pull the clutch in give it heaps of throttle(to roughly where it makes peak power) and dump the clutch. It will do one of 2 things.

1: torch the rear tyre (My SRAD was good for this in second then would grip and lift the front (some times even in the dry)

Or if the road is still in good nick and has some grip it will try stand on its back wheel.

Hope this helps now go try it and have some fun, pratice makes perfect.

You're right about the front lifting, didn't think my fat little Bobbie had that much ooomph in her, 'specially in the wet! Jumped up at about 20k's.


It's just that yesterday, as soon as I let out the clutch she'd bog right down, and sound like she was missing a cylinder. She didn't do that today, which makes me confused. Oh wells!

What kind of gains would I be looking at with bigger jets dialed in on my bike?
I know it's not really worth it with 250's, 2-strokes less so, but yeah. Pretty sure they're just teetering on the edge of the reliabilityower ratio as it is.

[driftn]

What kind of gains would I be looking at with bigger jets dialed in on my bike?
I know it's not really worth it with 250's, 2-strokes less so, but yeah. Pretty sure they're just teetering on the edge of the reliabilityower ratio as it is.[/QUOTE]

Dont bother pissing round with the jets, maybe throw a set of plugs and new air filter up it,

Or save your pennys and get a 600 or bigger if your licence permitts it.

[eelracing]

If all you want is better launches then just change the front or rear sprockets (cheapest performance gain goin)Think of it like a 10 speed pushbike with derailures on both front and rear sprockets.
So if all you want is extra grunt put a smaller sprocket on the front or larger one on the rear

Keep in mind that you will have a slower top speed and at 100kmh your bike will be revving higher.But you will be getting there a lot faster.

A rough guide for motorbike gearing is one tooth extra/less on the front sprocket is equal to 2 and a half less/extra on the rear.

[Blackshear]

Dont bother pissing round with the jets, maybe throw a set of plugs and new air filter up it,

Or save your pennys and get a 600 or bigger if your licence permitts it.

I'll get a zippy 600 when I have my full. Currently on a learners, but can take my restricted whenever I want. Prolly stick some new plugs and filter in it anyway, about due for that.

If all you want is better launches then just change the front or rear sprockets (cheapest performance gain goin)Think of it like a 10 speed pushbike with derailures on both front and rear sprockets.
So if all you want is extra grunt put a smaller sprocket on the front or larger one on the rear

Keep in mind that you will have a slower top speed and at 100kmh your bike will be revving higher.But you will be getting there a lot faster.

A rough guide for motorbike gearing is one tooth extra/less on the front sprocket is equal to 2 and a half less/extra on the rear.

Naw, I'll keep the gearing as she is. Hums along at 10,500rpm @ 100k's as it is.
Just a little frustrated that I couldn't get the back out

If anything, I'd rather take off a tooth or two on the back. She gets up to 60k's in 1st easy enough, but it almost feels bad letting her sit at 11-12k/rpm for an hour to wherever I'm traveling EDIT: (on the motorway).

Cheers for the input guys

[Harvd]

yeah ive been playn around in my street in the wet under trees too and its funn hehehe

urs revs at 10.5k at 100km/h? mines at under 9 and will be at 10.5 at over 120km/h. what year is yours and whats the rev limit?

[The Pastor]

Meh play with the carbs, its fun!

[Blackshear]

yeah ive been playn around in my street in the wet under trees too and its funn hehehe

urs revs at 10.5k at 100km/h? mines at under 9 and will be at 10.5 at over 120km/h. what year is yours and whats the rev limit?

Ha ha, be careful of the moss and dead leaves, works wonders for front traction as well

EDIT: Rev limit around 16,500, 1990 45HP model.

Meh play with the carbs, its fun!

I really don't wanna go poking around with those, honestly.
It would take a good mechanic hours to fix what took me 2 minutes to fuck up.
I can fit an air horn, change chain/oil+filter/replace a headlight etc.

But things that are adjustable don't bode well with my history
It goes at the moment, I'm not touchin in

But maybe when I have some spare time and someone to teach me all this crap.

[The Pastor]

mate theres not too much that can go wrong, just get a can of carb clean and get too it!

[Blackshear]

mate theres not too much that can go wrong, just get a can of carb clean and get too it!

But what if I let them run too lean, or or or!!!