Is this normal? Dies when given throttle during startup, but fine once warm

[Cra1g]

So I've heard of many stories where Ninjette owners say their bikes just outright die when they give it throttle, but not sure if my situation is unique.

Could just be a cold engine, but for the first minute or two of starting her up, if I give it just a tad of throttle, it bogs. And when I give it more throttle it completely dies.

However, once the bike is at least somewhat warmed up, I can give it a little bit of gas without issue, and then once the bike is fully warmed up, it performs like a champ. Basically, once the bike is warmed up, it idles and runs perfectly fine without a hiccup.

When I took it out of winter storage today, it acted extra fussy and I had to give it more choke than usual to get it started at all, but I was able to back it down fairly quickly. Granted it was a bit colder outside than usual (low 50s compared to at least 70s during the spring and summer). I had to let it run for a couple minutes without it completely dying with throttle, but I was able to take the choke off completely after a few minutes of riding. Once I was on the road after those first few minutes, the bike sings like a bird!

And yes, I put Stabil in the gas and ran it through the fuel system before storing the bike.

So is this just a symptom of a really cold engine that just needs warmed up? Or does it have issues that need addressed?

[csmith12]

Something seems off, couple of questions for ya...

What are the idle rps in the following conditions;?

1. Cold idle w/ choke on
2. Fully warmed idle w/ choke off

[Cra1g]

Originally Posted by csmith12

What are the idle rps in the following conditions;?

1. Cold idle w/ choke on
2. Fully warmed idle w/ choke off

1. Depends what my choke is set to, but I always set it to the point where I need just enough of it to keep the bike from not dying, which leaves the RPMs around 1,600-1,700rpms. It does jump around, though, by 100-200rpms when the bike is cold and choke is on. EDIT: I should mention that I could have the choke on enough that it'll idle at like 900-1,000rpms, but I don't like it idling that low during warm up.

2. A steady 1,300-1,400rpms

[juliusmichaelhonrada]

its lean bro try holding the choke 1/8 open then rev , it wont die

cold air is leaner because its denser and contains more oxygen molecules for the same amount of space as a hotter air(which is when the engine becomes hotter)

its normal because its not in its operating temp to be called "lean"

[juliusmichaelhonrada]

cv carbs choke does not supply extra fuel instead it dumps the vacuum on the diaphragm slides so the slides wont move up , whack the throttle and the vacuum increase and the slides wont come up , its comparable to covering the mouth of the carb with a hand. this is why the choke is fuzzy on this carbs.

unlike round slides which supply a huge amount of fuel from the choke jets.

[greg737]

The previous answers are pecking around the edges of the actual problem, maybe you'll get there eventually...

I'm betting your carb's low-speed (idle) fuel circuit is not functioning properly (either partially blocked or well on their way to fully blocked).

So "juliusmichael" is absolutely right when he says your engine is warming up lean.

It's a common carb situation actually, and it develops slowly, over time so that the owner/rider hardly notices the start-up getting more and more difficult by degrees as time goes by. It's an easy thing to ignore or find excuses for (like, well it must be extra cold today, or it's because I haven't ridden the bike in a while).

What ends up happening is you have to compensate for the almost complete lack of function in the low-speed idle circuit fuel supply by using the choke lever. But this still leaves you teetering on the edge of "too lean to run" and this makes it easy to kill the engine with any application of the throttle.

This juggling act is neither easy nor fun.

A complete cleaning of the carbs by somebody who really knows what they're doing will give you back that "starts on the button" EX250 that you had when it was new.

Be warned that the idle fuel circuit is the hardest part of the carb to clean, it's the part of the carb that a newbie won't get clean when he first tries to clean his carbs. Then he reassembles the bike and gets the same problem, but now he's convinced that the carbs are clean (because he cleaned them) so now he's looking for other reasons for the problem and he won't even listen to anyone who says the carbs are still the problem.

And on, and on, and on... until the bike gets pushed to the back of the garage or garden shed and forgotten.

[Cra1g]

Originally Posted by greg737

The previous answers are pecking around the edges of the actual problem, maybe you'll get there eventually...

I'm betting your carb's low-speed (idle) fuel circuit is not functioning properly (either partially blocked or well on their way to fully blocked).

So "juliusmichael" is absolutely right when he says your engine is warming up lean.

It's a common carb situation actually, and it develops slowly, over time so that the owner/rider hardly notices the start-up getting more and more difficult by degrees as time goes by. It's an easy thing to ignore or find excuses for (like, well it must be extra cold today, or it's because I haven't ridden the bike in a while).

What ends up happening is you have to compensate for the almost complete lack of function in the low-speed idle circuit fuel supply by using the choke lever. But this still leaves you teetering on the edge of "too lean to run" and this makes it easy to kill the engine with any application of the throttle.

This juggling act is neither easy nor fun.

A complete cleaning of the carbs by somebody who really knows what they're doing will give you back that "starts on the button" EX250 that you had when it was new.

Be warned that the idle fuel circuit is the hardest part of the carb to clean, it's the part of the carb that a newbie won't get clean when he first tries to clean his carbs. Then he reassembles the bike and gets the same problem, but now he's convinced that the carbs are clean (because he cleaned them) so now he's looking for other reasons for the problem and he won't even listen to anyone who says the carbs are still the problem.

And on, and on, and on... until the bike gets pushed to the back of the garage or garden shed and forgotten.

So I actually had the carbs professionally cleaned at the start of last season (it hasn't even been a year yet) and since then I've been extra careful about keeping them clean by making sure I had stabilizer in the fuel at all times.

If I remember right, I didn't have this problem back then, BUT now that I think about it, I installed an aftermarket K&N air filter a few months later and slowly started to notice the throttle issue at start up. I don't know if the air filter could be causing the lean-ness or if it's just a coincidence (I feel like if it was the air filter, the bike would be running lean the whole time, even after warm up).

Shortly after that, though, I had a mechanic look over it and pull the spark plugs, and he said it was running fine; neither rich or lean. But he mentioned something about mixture screws that can be adjusted.

Not sure if any of that info helps, but I really hope it's not an issue where I'd have to pull the carbs out AGAIN..

[greg737]

And that's another syndrome we see here on the forums: "Guy who cleaned carbs a year ago can't believe they may already be gummed up again..."

This is when you find yourself trying to help out another forum member and all indications point to a fuel problem (more specifically, an air/fuel ratio problem) which, of course, points directly at the carbs but the guy "already cleaned them". After 3 pages of posts it comes out that this cleaning took place many months if not over a year prior.

But you don't have to take my word for it, there are other opinions out there. In fact, right now, right here on Ninjette.org you'll find a thread where the "carbs are better and more reliable than fuel injection" guys have just proven that carbs don't gum up when the bike is stored without "winterization".

Regarding the K&N filter installation, there are lots of guys here who will tell you that to dramatically affect the air/fuel ratio (causing it to go lean) you have to do both the intake and the exhaust (installing some higher-flowing exhaust, like the AreaP system I have on my EX250).

[Cra1g]

Originally Posted by greg737

And that's another syndrome we see here on the forums: "Guy who cleaned carbs a year ago can't believe they may already be gummed up again..."

Haha, well said

However, isn't it a common belief that once you clean the carbs and get them running great, then you shouldn't have to mess with them for years down the road as long as you do some basic maintenance?

[greg737]

Like a lot of things in life, you're right and you're wrong.

Yes, the basic carb function can go along fine for years without problems if you take certain precautions. But making this a "blanket statement", something that is meant to cover any and all brands of carbs and types of carbs is a mistake.

The EX250's Keihin carbs are relatively small items, with small passages, and the passage that feeds idle fuel is both the smallest (at its most narrow point) and the longest passage in these carbs.

So while most of your EX250's carb's functions are clean and ready to rock, it sounds like the idle fuel supply isn't.

[jkv45]

Originally Posted by greg737

But you don't have to take my word for it, there are other opinions out there. In fact, right now, right here on Ninjette.org you'll find a thread where the "carbs are better and more reliable than fuel injection" guys have just proven that carbs don't gum up when the bike is stored without "winterization".

What - who said that?

I said the opposite.

And I never said carbs are better than F.I either, like you suggested I did (in the other thread)...

[jkv45]

I don't think you have a problem.

You have to look at how it acts when it's completely warm. If you have the idle mixture screws adjusted properly (start about 2.5 turns out) and it idles smoothly at 1300 when fully warm, your idle circuit is fine.

Because you changed the air filter to a less restrictive one, you may need to make some adjustments. The idle mixture may need to be richened and you may want to shim the needles to get a richer mixture sooner. Running ethanol-free gas will help to richen the overall mixture as well.

Try running the idle speed at 2000 or slightly more when it's on "choke" (enrichener). That's about where you want it to be IMO. You be able to ride it safely before it's fully warm, but don't expect it to run perfectly.

[Cra1g]

Originally Posted by jkv45

..and it idles smoothly at 1300 when fully warm, your idle circuit is fine.

This is what I'm thinking. If the jets were clogged or there was some other issue with the carbs, then the bike would still run poorly in some way no matter if the engine was cold or warm--like I said in my OP, the bike idles perfectly fine when warmed up and all throttle and RPM levels run great.

Originally Posted by jkv45

Running ethanol-free gas will help to richen the overall mixture as well.

How do I know if I'm getting ethanol-free gas at the gas station? I feel like most gas in the US uses ethanol..

[jkv45]

Originally Posted by Cra1g

How do I know if I'm getting ethanol-free gas at the gas station? I feel like most gas in the US uses ethanol..

If it's priced normally - it's not ethanol-free.

The cost will be significantly more than normal E10 (10% Ethanol), but you do get some of the cost back in increased mileage. Sometimes you have to go to Premium (91 octane) to get away from ethanol. That reduces some of the benefit in a non-high performance engine - but it's still worth using IMO.

This website lists ethanol-free gas by location - http://pure-gas.org/index.jsp

I have ethanol-free 87 octane less than a mile from work, so I'm lucky. I use it in all of my small engines and cycles.

[greg737]

Glad to see you guys have it all solved.

My posts were directed toward this paragraph of your Original Post:

When I took it out of winter storage today, it acted extra fussy and I had to give it more choke than usual to get it started at all, but I was able to back it down fairly quickly. Granted it was a bit colder outside than usual (low 50s compared to at least 70s during the spring and summer). I had to let it run for a couple minutes without it completely dying with throttle, but I was able to take the choke off completely after a few minutes of riding. Once I was on the road after those first few minutes, the bike sings!

Maybe I gave this paragraph more weight than it deserved, but if there was no problem to begin with then the whole post was really just a red herring.

[Cra1g]

Originally Posted by jkv45

This website lists ethanol-free gas by location - http://pure-gas.org/index.jsp

Looks like there's only one station in my area that carries ethanol-free gas, according to the map. And it's 20 minutes away..

[jkv45]

Originally Posted by Cra1g

Looks like there's only one station in my area that carries ethanol-free gas, according to the map. And it's 20 minutes away..

I'll admit - I'm an ethanol hater.

In your case I would fill up the bike with ethanol-free, then plan to go back with the car and a 5 gal gas can at a later date. Add Stabil to the gas in the can and keep it in the garage to top-off the bike when needed.

I keep 5 gal of fresh ethanol-free 87 (with Stabil) at home all the time, and run it in everything except the car. Engines always start immediately after storage and I'm never cleaning carbs. It's worth it to me.