ZXR250 - hesitation and stalls when warm

[ducatilover]

Been there and ridden them all mate, and I have ridden an 883 that would lick any 4 stroke 250 I've ever ridden. A standard cammed 883 would be beaten when the revs get up there by nigh on anything, the 883 is lucky to make as much RWHP as a 400 4cyl.

The ZXR400 had a pump, my ZZR400, CB, GPZ haven't got pumps. It'd make a difference, yes, but the pumps are still very low pressure. It's the air venting to the bowls that'll do it. What are your bowl vents like anyway?

I thought you said earlier that you have no float valve and seats in your carbs?

[Ultrasonic2]

I thought you said earlier that you have no float valve and seats in your carbs?

no i never said that

It's the air venting to the bowls that'll do it

Not a 100% on what you mean by that

[Ultrasonic2]

ok well lest talk numbers now
the 1200cc nighster makes 61hp and weights 254kg 0.240
my bike makes 43 and weight 141kg power to weight of 0.304

So in theory i will beat it as i have a greater power to weight ratio. i of course dont need to beet it to gain respect from the 1200cc rider. So when im up against the 883 i have No problems seeing it off. It's important to clarify that im talking about 0 to about -120ks

one of the interesting things about bikes is as the size increases they seem to be geared up more and which is counter productive. even my to 250 was geared up to much. ( i geared it down) these massive 4 can do 300km's but who cares by gearing them to beable to achieve that you've decreased their slower speed acceleration

http://www.motorcycle.com/specs/harl...er/detail.html

http://www.knfilters.com/dynocharts/63-1126_dyno.pdf

[ducatilover]

no i never said that

It's the air venting to the bowls that'll do it

Not a 100% on what you mean by that

Your bowls have air venting. If your bowls are incapable of venting, you'll have problems.

ok well lest talk numbers now
the 1200cc nighster makes 61hp and weights 254kg 0.240
my bike makes 43 and weight 141kg power to weight of 0.304

So in theory i will beat it as i have a greater power to weight ratio. i of course dont need to beet it to gain respect from the 1200cc rider. So when im up against the 883 i have No problems seeing it off. It's important to clarify that im talking about 0 to about -120ks

Torque to weight, you have 24nm.....
I'd say a 1200 Sporty will have a ZXR250 up to 120-130 or so. Or at any speed up a hill....in to a head wind...
I don't care either way, I've ridden Harleys that will dispose of a 250 4cyl. Which, let's be fair, is nothing special. A Harley is not designed to be quick and a ZXR250 is certainly not quick.

one of the interesting things about bikes is as the size increases they seem to be geared up more and which is counter productive. even my to 250 was geared up to much. ( i geared it down) these massive 4 can do 300km's but who cares by gearing them to beable to achieve that you've decreased their slower speed acceleration

http://www.motorcycle.com/specs/harl...er/detail.html

http://www.knfilters.com/dynocharts/63-1126_dyno.pdf

Your ZXR should be ideally geared to a true 200k, that's the realistic max you'll see out of one, 205 if you're very, very lucky (been there, done this)
I think the standard gearing was a theoretical 223 or so, not including wheel slip etc. They'll never manage that.
The bigger bikes can afford to be geared longer, better economy and they have enough torque to push the gearing. My ZZR is geared nicely, sits at 5000 rpm at 100, it'll overtake anyone up a hill at those revs. Sadly a 250 won't.

Will you let us know how the next carb strip down goes?

[Ultrasonic2]

Yeah it better not rain on Friday night so i can take it apart. im gonna adjust the float levels or at least know for sure what they are now. im gonna make a measuring device cos last time i tried with a ruler and that was a bit vague

oh the 250 has a jap 180 limiter

[ducatilover]

Yeah it better not rain on Friday night so i can take it apart. im gonna adjust the float levels or at least know for sure what they are now. im gonna make a measuring device cos last time i tried with a ruler and that was a bit vague

oh the 250 has a jap 180 limiter

Use verniers, it's always worked for me. They're cheap to buy and pay for themselves time and time again.
I'd check your plugs to see how they're burning, and go from there

I've never ridden one with a 180 cut out.

[Ultrasonic2]

right carbs have been off and back on again

manual says the float height should be 13mm +-2mm

They were at 14mm so i put them down to 11 mm

I also went one step down all round to 128-130 again after running the 130's to 132's for a week.

The bike was much worse. im disappointed but at the same time it counts the float height out as being the issue and bringing it back to just simply being to lean. Now most people would say you need to put a washer under the needles and i would tend to agree but when i tried it i couldn't even get down the street as i couldn't get the throttle much past idle. i could and probably should re rest this now but that is a big deal having to take the crabs off twice in a row.

I could increase the Jet sizes which would probably pretty much solve the problem but i would think the bike would be super rich by then. i could possible add more via the pilot. i dont know yet. What i do know is the dip is because it is to lean with out a doubt, so i guess i have achieved something.

Thoughts opinions anyone

[Ultrasonic2]

Right went back to 2.5 turns out with 0.75mm washers under the needles. jets are 128-130
epic fail, will die when you open the throttle

Went to 3.5 turns out and 130-132 jets with no washers
Fail was to rich

Now im gonna try 2.5 turns out and 130 -132 last week i had it at 3 turn out which my have been sightly to rich down low and im wounding since the float height change maybe 2.5 turns out will be fine

[Ultrasonic2]

Right performed the above and it's still rubbish. At this stage i just need it going again so will probably change the float height' it's all a bit disappointing it's possible changing the float fixed the issue at 9k but it's created a whole bunch more that are worse. i kinda want to change the float height to 15mm now. but probably shouldn't my wife would explode if i had to take it apart again. if changing the height did make the issue at 9k worse or better im not sure what i can really do about it anyway.

humm myabe i't try 15mm

What i think would be very interesting would be to put the stock jets back in and leave the float height as i have it now 11mm but im kinda over it again for a while

[Ultrasonic2]

right so i put it back to how it was last week but unfortunately it's still poked and im not sure why ? ill have to take it apart tomorrow again to see if i've picked up a blockage some how or some thing. what this does mean is everything i've said since and including changing the float level is probably not true .. orr

what a epic waste of time

[ducatilover]

right carbs have been off and back on again

manual says the float height should be 13mm +-2mm

They were at 14mm so i put them down to 11 mm

I also went one step down all round to 128-130 again after running the 130's to 132's for a week.

The bike was much worse. im disappointed but at the same time it counts the float height out as being the issue and bringing it back to just simply being to lean. Now most people would say you need to put a washer under the needles and i would tend to agree but when i tried it i couldn't even get down the street as i couldn't get the throttle much past idle. i could and probably should re rest this now but that is a big deal having to take the crabs off twice in a row.

I could increase the Jet sizes which would probably pretty much solve the problem but i would think the bike would be super rich by then. i could possible add more via the pilot. i dont know yet. What i do know is the dip is because it is to lean with out a doubt, so i guess i have achieved something.

Thoughts opinions anyone

11mm on your floats will make it richer. The higher the number, the leaner it becomes.
I recommend going back to exact factory settings, then twiddle from there.

Right went back to 2.5 turns out with 0.75mm washers under the needles. jets are 128-130
epic fail, will die when you open the throttle

Went to 3.5 turns out and 130-132 jets with no washers
Fail was to rich

Now im gonna try 2.5 turns out and 130 -132 last week i had it at 3 turn out which my have been sightly to rich down low and im wounding since the float height change maybe 2.5 turns out will be fine

Right performed the above and it's still rubbish. At this stage i just need it going again so will probably change the float height' it's all a bit disappointing it's possible changing the float fixed the issue at 9k but it's created a whole bunch more that are worse. i kinda want to change the float height to 15mm now. but probably shouldn't my wife would explode if i had to take it apart again. if changing the height did make the issue at 9k worse or better im not sure what i can really do about it anyway.

humm myabe i't try 15mm

What i think would be very interesting would be to put the stock jets back in and leave the float height as i have it now 11mm but im kinda over it again for a while

right so i put it back to how it was last week but unfortunately it's still poked and im not sure why ? ill have to take it apart tomorrow again to see if i've picked up a blockage some how or some thing. what this does mean is everything i've said since and including changing the float level is probably not true .. orr

what a epic waste of time

What you want to do, is set floats, jets, needles to factory. Put the airfilter in.
Get the top end correct, find a jet that pulls well right up top, do not worry about the lower end.
If it pulls good, time to do the needles.
If it bogs down or feels wet at 8000-10,000rpm, lower the needles, if it has a big flat spot, raise them .5mm at a time.
Once that's sorted, get your midrange done, 4000rpm and up is where your floats come in to play, so too rich means you want to lower the float height (bigger measurement) Do it in 1mm increments, I know it takes ages to get right, but that's life.
Once that's done, you can set the idle, you may have problems down low using the factory pilot jet, but I doubt it.
If you need bigger pilots, I might have some here.


This is how I've always done my carbs, it's how Factorypro and Dynojet and all the carb nuts tell you how to do it.

One very important thing Only change one thing at a time.

That's all just off the top of my head, my carb book has gone A.W.O.L

[Ultrasonic2]

Right fixed my issue

im not sure when it happend or why but it's fixed now and thats all that matters and im oddly happy that the bike is just like it was last week

The issue i had was i had petrol in the overflow . now i know you'll all be saying thats the point of the over flow but not on this bike as mentioned before the overflow goes uphill to a valve that then has 4 pipes connected to it .im not going to go into the workings of this except to say it has a huge affect on the fuel of this bike. now no matter what happens at this valve if there is fuel in this line it has to go up hill even after the valve. Any way there was alot of fuel in this line that was completely stuffing up the fuelling of the carbs the bike made the most odd sound when this issue existed now i dont know if the fuel got in there because or the float height adjustment of because of the way i took the carbs off at one stage. i actually believe it was because of the way i removed the carbs that one time. anyway once i tipped the fuel out the problem went a way after a few minutes of riding.


As for the issue im trying to fix i should stop pissing around and actually fix it by jacking up the needle height. The only problem is where do i find 3mm .2 shims from ?

and for the main jets i probably should just do what the others have run which is all 130's( not that i like that thought) i know 125-128's is to lean and i believe 130-132 is to rich. I guess really i need a dyno to answer the question truthfully :-)


anyone know where i can get shims from ?

[ducatilover]

That's quite interesting, good to hear you have it sorted!

Ring around engineering shops, I've always used washers that are .5mm thick.



I'd really like to see pics of your carbs, I've never seen an overflow running up into a valve, is the overflow running higher than the float height?

[Ultrasonic2]

Here's a pic for you. form when i spent ages investigating this valve

http://www.tecpeltier.com/download/f...=138&mode=view


i only have .75 shims and these carbs are pretty sensitive so that's why i'd like to get. 0.2mm shims. i still can't make up my mind on what jets to run


oh and here's a pic of my bike

http://www.tecpeltier.com/download/f...=215&mode=view

[ducatilover]

Doesn't make sense to me lol

Very nice looking ZXR!



Try doing the steps I posted up before.