pre-gen runs rough under load

[emoyer]

idles fine & seems happy spinning easily, but hit an upgrade or roll on gas without downshifting & it seems to "miss" or "cough". (generally i would downshift in these situations anyway, but it doesnt seem like it should do this.)

the following things have not helped: valve adjustment, new plugs, syncing carbs, new battery.

my son also has a pre-gen & thinks mine has never been as strong in the midrange as his. he thinks it might be running lean, and the old plugs kind of looked that way. (they didnt look rich anyway.)

i dunno. what would you try next?

thanks.

[alex.s]

clean the main jets

[n4mwd]

My bike did the same thing under load. The main jets were partially clogged. Time to rebuild the carbs. Just be careful not to get gas or cleaner on the diaphragms. That allegedly ruins them. You probably wont need to buy a rebuild kit. Both jets in each carb are easy to get to once the carb is off the bike.

[emoyer]

ok, sometime soon i will bite the bullet & try to give the carbs a good cleaning. my thanks to both of you for the info. i have been reading about how to do it.

obviously as part of that i will try to get the idle mixture set right. but im curious -- why is there only screws for the IDLE mixture? why is there no way to adjust the mixture for the rest of the throttle range?

thanks.

[Motofool]

Yes, you can adjust the middle range by modifying the height of the needle.

For this bike, additional washers are needed, since there is no factory adjustment here.

Small flat washers of 2 mm thickness work.

http://www.dansmc.com/carbs2.htm

[choneofakind]

The mid range can be richened by raising the needles. WOT can be adjusted by installing different size jets, and the low end response can be adjusted if needed by changing the float level.

The main jets are simple; they dump fuel into the airstream at WOT, and mix is controlled by how much fuel they dump into that airstream via changing the diameter of the jet. Adding a way to adjust that with a screw like the pilot system would turn something simple into something complicated.
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[alex.s]

Originally Posted by choneofakind

and the low end response can be adjusted if needed by changing the float level.

also pilot jet size, pilot mix screw adjustment

[n4mwd]

Unless its an elevation thing, I'm thinking the only thing he needs to do is clean his main jets. The bike should never cough or miss regardless of the load.

I have the ultimate main jet test. Slow down to 35-40 mph in 6th gear, then WOT. If the engine gives you any grief, you have a main jet clogged.

[choneofakind]

Originally Posted by alex.s

also pilot jet size, pilot mix screw adjustment

yes. Forgot that part.
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[emoyer]

Originally Posted by n4mwd

I have the ultimate main jet test. Slow down to 35-40 mph in 6th gear, then WOT. If the engine gives you any grief, you have a main jet clogged.

oh it will definitely fail that test. it does that in FOURTH gear, and without the throttle being wide open. however, if i keep winding on gas, it will eventually smooth out and get going.

another question: my understanding is that to clean the main jets i have to remove the carbs from the bike & take them apart. if that is correct, shouldnt i clean everything while im at it? im certainly not looking for extra work, so if its a big difference in effort, then no, but im just wondering...

(im completely new at this. i did rebuild the carb on my chain saw, but i really didnt understand anything i was looking at, if you can believe that... )

[choneofakind]

Yes you should clean everything while you're in there. An air compressor and a spray can of carb cleaner make quick work of that.
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[n4mwd]

Before using carb cleaner or even letting the carbs sit on their side, remove the diaphragms on the top and put them in a safe place. They are very easy to damage and very expensive to replace. Reportedly, carb cleaner and gasoline will destroy them.

My experience has been that its more work to get the carbs off the bike than it is to actually clean them. Some people cut the battery box off which greatly simplifies things, but I elected to keep my bike original.

With an unmodified bike, removing the carbs requires that you loosen the front part of the rear fender and push the air box rearward. There is a hidden bolt in front of the rear tire that you need to get out. The rest should be easy to figure out and there are plenty of DIY's if you can't.

As far as the carbs go, its probably a good idea to go through everything. The pilot jet is hidden and needs a properly fitting flat head screw driver to remove. If it doesn't fit exactly right, it will damage it. The main jet is easy and will come off with a socket.

Use spray carb cleaner and 32 gauge wire if you have to. Use copper wire if you want to play it safe, but steel wire is OK too if you are careful. The jets have holes that flow both axially and radially - make sure you don't miss any.

[choneofakind]

Compressed air gets everything and there's no worry about damaging the jets by jamming wire into them. You just blow the crap out of them. You're fine to sit the carbs on their sides without worry about the diaphragms; they're supported by the slides and have no sideways movement. Definitely take them out for carb cleaner.
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[alex.s]

Originally Posted by n4mwd

I have the ultimate main jet test. Slow down to 35-40 mph in 6th gear, then WOT. If the engine gives you any grief, you have a main jet clogged.

this is a good test for mid range needle transition.

topping out the vacuum pressure in the engine is what needs to happen to completely open the needle valve (main jet wide open)... so WOT + redline in a higher gear.

[n4mwd]

Laying them on their side wont cause mechanical damage but gas in the bowls could leak out and damage the diaphragms.
it's just best to take them out and put them in a safe place so you don't have to worry about them.
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[choneofakind]

Seeing as there's a hole in the bottom of the slide that allows a mixture of fuel and air to contact the slides every time that you ride, I really don't think gas is going to harm the slides. Maybe don't soak them in gasoline for a week, but a little bit of straight gas touching the diaphragms once is not going to hurt anything.


If he's going to be opening the carbs to clean them, the gas will be drained anyways.
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[emoyer]

thanks for the input everyone. i hope to do the cleaning this week. i will try to be careful of the diaphragms. im glad you mentioned that. i have been doing some reading & its nice to finally start to understand a little how it works.

when i tried to start the bike to go to work this morning, she wouldn't. it cranked fine just wouldnt catch. only did this one time before & then by turning off the choke and feeding a little gas she finally started. but not this time. kind of surprising to me because since the valve adjustment & carb sync she has idled beautifully.

anyway, i was holding off on cleaning the carbs because i was gonna ride with my brother yesterday & wasnt sure if i would get it done in time, but now im just gonna do it. probably start taking it apart tonite after some other stuff is done.

i will let you all know how it goes. thanks again.

[choneofakind]

How are you choking the bike? It will fire more easily if it's cranking while the mixture transitions to rich; apply choke (staring at nothing and ending wherever the bike starts and idles) AS it's cranking. Don't just give it full choke and then start cranking. That will be rich and it won't be as easy to start. I used this methods and had no problem whatsoever starting, no matter what temperature it was outside.
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[n4mwd]

The last time I did my valves I set them wide. The unexpected result was that the bike wouldn't start with the choke at all. I had been accustomed to using the choke every time. By accident, I found that it started right up without the choke and no throttle just fine.

[alex.s]

maybe its out of gas

[emoyer]

no theres gas in it. though maybe the petcock could be clogged or theres a problem with the vacuum thingy.

turning up the choke as its cranking sounds like a good idea.

before doing valves i had to put the choke at more than half & it was maybe 5 minutes before it would idle without it. after the valve adjustment (maybe 700 miles ago) it still seems to want some choke to start, but not as much and not as long. all the valves were 1 or 2 thousandths too tight & we set them at the large end of the spec

thanks.

[emoyer]

monday nite i starting taking the bike apart & last nite i got the carbs off. i might not get a chance to start cleaning them until saturday.

btw, this seems like a ton of work. i cant imagine doing the "try this, then try that" thing i keep reading about concerning carbs.

anyway, my question at this point is: since this is so much work, and since as i understand it most EX250s tend to be a little lean in the midrange anyway, while i am in there should i go ahead and raise the needles a little?

besides reducing gas mileage, is there any other possible downside? i dont wanna accidentally get it too rich & have to take it all apart again.

what would you do? and if you decided to raise them, then how much? 2mm?

thanks.

[choneofakind]

Getting the carbs out of a pregen really isn't bad once you've done it a couple times.

Add 1 washer (or 2, depending on how it feels after 1) that is 3mm ID and about 6mm OD. You want it to be as thin as possible. Usually they're about a half of a mm thick.
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[n4mwd]

Getting the carbs out seemed like the hardest part to me. If you are worried that you might have to do it again, there is a battery box mod that makes it easier.

As far as shimming the needles with washers ... If you don't have a good reason, then don't. Your carb has clogged jets and/or passageways. They are your real problem.

A good reason to mess with the shimming and jet sizes is stuff like a new exhaust or intake. Or you live in a high altitude area. Other than that, the bike runs fine stock.

Attached are photos of the jets. The main jet is most likely the problem, but both probably have at least a little clogging.

[Motofool]

Originally Posted by emoyer

........my question at this point is: since this is so much work, and since as i understand it most EX250s tend to be a little lean in the midrange anyway, while i am in there should i go ahead and raise the needles a little?

Your spark plugs are waiting to respond your question:

http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html

All you need to know about working on your carbs,...........and more:

http://www.ninjette.org/wiki/Category:Intake

http://faq.ninja250.org/wiki/Category:Intake

[choneofakind]

n4mwd, a stock bike needs a little help in the midrange and mix screws. Try adding a washer to your needles. You'll see that it's smoother than the stock bike, especially under partial throttle at high rpms while in and out of turns. Stock jetting is not perfect. Wanting better jetting is reason enough to play with it, regardless of if any modifications have been made. stock jetting is a baseline that needs to be individualized for every bike because each bike is in a different location and elevation. Stop telling people to not ever touch their carbs; you're starting to sound like the schmucks at ninja250.org

However, yes, the OP needs to do a thorough job cleaning the carbs.
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[n4mwd]

No I'm sorry, but I stand behind my recommendation to not modify the carbs. His goal is simply to make the bike run right, not to make it into a perfected race bike. A thorough cleaning is all he needs.

Adding washers will make the bike run richer and cause it to use more gas decreasing the mpg.

As far as the "schmucks at ninja250.org", that is a much kinder word than I would use (referring to the mods), but at the same time, I do respect their collective expertise and knowledge. Technical things they say about the pregen can usually be trusted and some of those guys have been working on pregens for over 20 years.

[davenay67]

Without putting the bike on a dyno and actually measuring and analysing the changes you are making, any changes to mixture or jetting is very subjective and without proof that it's doing any good.

Whilst not perfect (for a start they tune lean for emissions), I'm apt to go along with Kawasaki and the millions spent building these bikes. I for one don't think I know better than Big 'K'.

[emoyer]

sorry for starting an argument but i appreciate everyones input & there are a lot of good points being made.

one thing i have been trying to figure out is whether the bike has really gotten worse since ive owned it or whether ive simply grown as a rider (i was a total beginner when i got it back in november) and am riding it a little harder which makes me notice the problem more.

ive put 5000 miles on it, riding a couple times a week right thru the winter & generally adding a little star-tron each time i put gas in. in contrast, the guy i bought it from owned it for 6 months and "took it down the road and back every couple weeks", and the girl he bought it from, who, if as i suspect was the original owner, rode it less than 3000 miles in 5 years.

so i am thinking that whatever gumming up has happened in the carbs probably happened before i got it, and maybe by just getting it clean it will be, at least in my perception, a whole new bike.

on the other hand, it seems like 1 thin washer might make it just a little stronger without too much of a downside. so im pondering.

but thanks again for all the input.

[choneofakind]

Cleaning the carbs should clear up the issue of whether there has been an actual change vs you improving and noticing that spot as a wall now. My guess is that it's a combination of both.
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[choneofakind]

Originally Posted by davenay67

Without putting the bike on a dyno and actually measuring and analysing the changes you are making, any changes to mixture or jetting is very subjective and without proof that it's doing any good.

Whilst not perfect (for a start they tune lean for emissions), I'm apt to go along with Kawasaki and the millions spent building these bikes. I for one don't think I know better than Big 'K'.

using a dyno and sniffer is only good when you want it PERFECT, which is dumb because as the weather changes, so does your jetting. That's $$$ out the window in my mind. Tuning the carbs on your own gets it 90% of the way at the expense of 3-5 mpg on a completely stock bike (think 60-62 instead of 64-65)and a smoother feeling bike without flat spots or hesitations. That's proof enough to me that it is worth your time to test whether a pair of $0.05 washers feels better because in the end isnt it al about if it feels right anyways? Sure it could be better if a dyno and sniffer are used, but that's not necessary unless you're racing and literally want perfection. Even then, sometimes a bike that looks great on the dyno sheet doesn't feel spot on. I'm not saying I know better than Kawasaki, but sport bikes tuned for economy suck.
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[Motofool]

Originally Posted by emoyer

...........on the other hand, it seems like 1 thin washer might make it just a little stronger without too much of a downside. so im pondering.

but thanks again for all the input.

If the washers worsen the situation, you can remove them without needing to remove the carbs a second time:

http://www.ninjette.org/forums/showthread.php?t=108496

You are welcome !

[emoyer]

thats a good idea about removing the washers, thanks.

started taking the carbs apart today. i dont have a good screwdriver but i was following the advice of my son who has already worked on his some, he said to use vice grips. so i was breaking the screws loose that way and that was working pretty good. but the 2 bowl screws that also hold on the idle adjuster bracket i cant get to with the vice grips so i guess i will have to buy a JIS screwdriver. the screws have the little dot on them.

anyway i bought socket head cap screws to put in when im done so this wont be a problem in the future.

i just wanna be riding again.

[n4mwd]

STOP!

Don't mutilate your carbs with vice grips. You can go to Harbor Freight with a coupon and get a free screwdriver set that will work. For $10 you can get a really good set. Once you get inside, the only way to get the pilot jet out is with a good screwdriver. The main jet needs an open ended wrench.

If you keep hacking at it with vice grips, you are going to ruin it.

[choneofakind]

1) op said that he was only breaking the outside screws loose with the code grips so they didn't strip from a bad screw driver.

2) op said he bought hex head screws so he wouldn't have to use vice grips again

3) op said he was going to get a JIS bit to get the screws that the vice grips can't reach so he doesn't damage the carbs

4) a flat blade screw driver works great on the main jet as well, just make sure it has a wide, non-damaged blade. Using a wrench is just an invite to apply too much torque.

5) you're weird about carbs. Chill.
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[n4mwd]

use the right tools for the job and you won't have to worry about it.
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[emoyer]

i looked at the harbor freight screwdrivers & they do seem good for the price, maybe i will try to get them.

in the meantime i put a little kroil on the problem screws this morning (the diaphragms are already out) & i hope i can get them out tonite. my daughter has a screwdriver i think might be JIS.

btw my son took pity on me this morning & let me take his pre-gen to work. i hope my bike runs as good as his when i am done with all this. he has the throttle mod too so its partly perception but there is definitely more power there. i could use 5th gear just for cruising, where on my bike i could never use 5th below about 60-70 mph or it would just seem like i was killing it.

QUESTION: if i do the battery box mod to make this whole thing a little easier in the future, then what holds the air box in? the only 2 bolts i remember taking out were in the bottom of the battery box, and then that would not help hold the airbox.

[n4mwd]

Screwdrivers: You can use a standard #1 or #2 phillips screwdriver (depending on which fits best) to get the diaphragms and bowls off. You'll also need a metric allen wrench to drain the bowls if you haven't done that already. Both of these tools can be found in the bikes tool bag.

The pilot jet needs a good sharp flat head screwdriver to get it out. Don't skimp there or else you could bugger it up. The main jet comes out with a box end wrench or socket. But be careful reinstalling it that you don't overtorque it.

Airbox mod: The modified airbox is held in place with the rubber strap that goes over the battery. There are different ways to make this mod, I suggest you research them a little bit before cutting anything. Like I said before, I have not done this mod because I wanted to keep my bike OEM. But if you totally mess it up, you can get a new airbox on ebay pretty cheap.

[choneofakind]

The battery box is still there behind the airbox, and the airbox is still attached to the carbs, so it's not coming off the backside anytime soon. It also definitely won't go off either side either. You'll see what I mean when you try and get it out of the frame

There also should be a strap from the back fender to the knob on the airbox. Not that it's really necessary, but it definitely won't allow the airbox and battery box to separate. But even if you don't have that strap those boxes won't go anywhere. I rode around with my airbox and battery box separated for a while without issue.
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[emoyer]

i just had a few minutes before supper & i finally got those screws out and the bowls off. it looks like my jets are already a little buggered up by someone else. i keep finding stuff like that on this bike, even though i bought it with only 2700 miles on it. there was a frame bolt missing, the oil drain plug was way too tight, as were the tappet nuts when we did the valves. i will know more when i actually get the jets out & look closer but i am wondering if i will ending up just buying new jets. they dont seem too expensive on powersportsplus. but the bowls & stuff also look dirty so new jets or not i am glad i am doing the cleaning. more later.........