Need some help diagnosing an engine missing problem on my Pregen.

[Wanderer]

I bought my 2007 Ninja 250 F Series a month or so ago. I'm trying to figure out an engine missing problem with the bike. The problem didn't show up during my purchase test ride unfortunately, so I suspect that the last owner knew it and never said anything.

Here are the symptoms:

- The bike starts every time, idles perfectly, comes off from a start great and has plenty of power(for a 250 anyway).

- Once I am out on a longer stretch of road and I am up to the local street cruising speed, say 40/45mph and I cut back on the throttle a little to hold my cruising speed, the bike starts to miss badly like it is about to die. When I first had it happen, I thought I was out of gas but I wasn't.

- I pull to the side of the road and surprisingly the bike continues to idle fine. The throttle revs up fine and I am able to start off again with plenty of power like nothing was ever wrong.

- I get back to cruising speed again, cut back a little on the throttle and the same thing happens. It feels like it is going to die and leave me stranded, but when I pull over again, it idles fine as before.

The bike appears to be stock. The airbox/air filter has not been modded, the exhaust is stock, the carbs may have been out at some point because the carb rubber boots don't have springs, but have hose clamps on them.

What I have done so far:

Replaced the petcock with a new one.

Checked for vacuum leaks.

Flushed out the tank with new fuel.

That's about it.

Can anyone give me any ideas what I should try next? I suspect this may be a fuel issue, but I guess that it could possibly be electrical(spark plugs?)

Any help would be greatly appreciated.

[Wanderer]

Just to add, when I am going up through the gears from a start, the bike runs great.

When it starts to missing like it is about to die at cruising speed, I can hit the throttle and the bike picks right up and accelerates without any problems.

It has never left me stranded, but I have expected it to many times.

How do I troubleshoot this issue?

[Triple Jim]

It could be one of a few things. To start, your gas cap vent could be clogged. See if opening the cap cures the problem. It that's not it, I'd check the needle jets and see if there's a little varnish in them. The engines run lean in the midrange anyway, and anything that makes it even a little leaner would do what you're describing. Other things like low float level could cause or contribute to the problem.

[Wanderer]

Since it only happens at cruising speed and then idles fine once stopped, how do I do this?

It never dies or refuses to start after I stop the bike on the side of the road.

[Wanderer]

Originally Posted by Triple Jim

It could be one of a few things. To start, your gas cap vent could be clogged. See if opening the cap cures the problem. It that's not it, I'd check the needle jets and see if there's a little varnish in them. The engines run lean in the midrange anyway, and anything that makes it even a little leaner would do what you're describing. Other things like low float level could cause or contribute to the problem.

That makes sense. That is why I suspected an intake air leak or maybe a vaccum leak, but I haven't found one.

I am a little intimidated about taking the carbs out. I have never done any carb work before. But, I don't want to take it to a shop. I want to learn to fix the bike myself, even if it takes me longer and I make some mistakes.

[jkv45]

It sounds like a fuel starvation problem to me as well. As Jim said, when it happens pull over and open the gas cap. Listen for air rushing in. That would tell you it's not venting properly.

Have you checked the inline filter at the carb inlet for obstruction?

You could also drain the floatbowls to look for signs of debris or water in the gas - just to confirm the system is clean.

If that all checks out, I would try running a strong fuel system cleaner like Techron Concentrate at 1oz per gal for a tank of 2.

If none of that helps, it may be time to pull the carbs and go through them. I believe a damaged carb diaphragm might cause something like you described.

Check the clamps on the carbs, but usually a vacuum leak will give you a hanging idle or a slow drop in RPMs back to idle when you open and close the throttle.

[Triple Jim]

I'd unlock the cap and go for a short ride, but I understand that could be dangerous and wouldn't suggest someone else do it. jkv45 gave a good alternative.

If you take the carbs apart, be gentle with the rubber diapragms!

[Wanderer]

Originally Posted by jkv45

It sounds like a fuel starvation problem to me as well. As Jim said, when it happens pull over and open the gas cap. Listen for air rushing in. That would tell you it's not venting properly.

Have you checked the inline filter at the carb inlet for obstruction?

You could also drain the floatbowls to look for signs of debris or water in the gas - just to confirm the system is clean.

If that all checks out, I would try running a strong fuel system cleaner like Techron Concentrate at 1oz per gal for a tank of 2.

If none of that helps, it may be time to pull the carbs and go through them.

I didn't even know that there was a carb inline filter.

How do I remove this filter? Link?

Good advice about the gas cap from both you guys. I'll do that.

Thanks.

[jkv45]

Originally Posted by Wanderer

I didn't even know that there was a carb inline filter.

How do I remove this filter? Link?

Good advice about the gas cap from both you guys. I'll do that.

Thanks.

There's a photo of it about 1/2 down the page - http://faq.ninja250.org/wiki/How_do_...fuel_filter%3F

[Wanderer]

Originally Posted by jkv45

There's a photo of it about 1/2 down the page - http://faq.ninja250.org/wiki/How_do_...fuel_filter%3F

Thank you Jay!

[Wanderer]

Originally Posted by Triple Jim

I'd unlock the cap and go for a short ride, but I understand that could be dangerous and wouldn't suggest someone else do it. jkv45 gave a good alternative.

If you take the carbs apart, be gentle with the rubber diapragms!

Good advice. I'll do that.

[Triple Jim]

Installing an inline fuel filter is a good idea, and one that I always do on my motorcycles. But I strongly suggest using the paper element type, not the sintered metal type. I've had particles get through the sintered type, big enough to clog a main jet!

[Wanderer]

Originally Posted by jkv45

There's a photo of it about 1/2 down the page - http://faq.ninja250.org/wiki/How_do_...fuel_filter%3F

Can you guys tell me if this inline fuel filter is on the left side(petcock side) of the bike or on the right side.

I don't think that the inline filter is there at all. But, I'll check closer tonight at home.

[jkv45]

Originally Posted by Wanderer

Can you guys tell me if this inline fuel filter is on the left side(petcock side) of the bike or on the right side.

I don't think that the inline filter is there at all. But, I'll check closer tonight at home.

Left side.

[Triple Jim]

My '05 didn't have a filter when I got it last year, and I don't think it ever did before, but I added a pleated paper one.

[Wanderer]

Ok, I went for about a 7 mile ride and when it started missing, I stopped and opened the gas cap. No hissing like a vacuum was heard and I then rode the bike another couple of miles with the gas cap open.

It started missing again with the cap open.

I also checked for an inline carb filter as suggested, but there wasn't one.

I will add one later once I figure out this issue.

Any other ideas?

[Triple Jim]

The next idea I had was to check the needle jets, and probably the needles too, for any sign of varnish buildup.

[Wanderer]

Originally Posted by Triple Jim

The last idea I had was to check the needle jets, and probably the needles too, for any sign of varnish buildup.

Yeah, I was avoiding that one to be honest. I have never carbs off of a bike before and taken them apart. I guess that I had better start preparing myself to learn how to do that.

I need to learn how to do it sooner or later anyway. I guess that I should consider doing the airbox mod to make getting the carbs off easier. Right?

I am not in any hurry and plan to take my time learning to do this.

I suspected that I was going to have to do this anyway.

Thanks.

[RacinNinja]

I would disconnect the petcock vacuum line from the carbs. Disconnect the fuel line to the carbs and run it into a clear container. Suck on the vacuum line and plug it with your tongue while watching the fuel come out of the fuel line.

If it slows or stops, the petcock diaphragm may have a leak, thus causing a vacuum leak and your cabs to run out of fuel. If the fuel flow is slow, the fuel valve may be plugged or the filters in the tank attached to the petcock are plugged. Is the inside of the tank rusty at all?

If it checks out OK, I would take the black rubber hoses off the bottom of the carbs. replace them with clear lines about 2 feet long. unbolt the fuel tank but leave it sideways on the frame so the fuel line is still connected. Run the hoses out from under the carbs and then vertical up and out of the frame, lay them over the fuel tank. Loosen the float bowl drain screws so the hoses fill with fuel. Suck on the vacuum line again until the fuel level in the hoses stabilizes. This is the float bowl fuel level. It should be approximately level with the seam in the float bowl to carb body. If it's not, the float level will need adjusted.

[Triple Jim]

Wanderer did say he replaced the petcock in an attempt to cure the problem.

[RacinNinja]

Originally Posted by Triple Jim

Wanderer did say he replaced the petcock in an attempt to cure the problem.

Genuine or knock off though?

[Wanderer]

Originally Posted by RacinNinja

Genuine or knock off though?

New Kawasaki OEM petcock. Same issue before and after change.

[RacinNinja]

Originally Posted by Wanderer

New Kawasaki OEM petcock. Same issue before and after change.

Good!

Ruins my train of thought for flow though. Still, I'd check the float levels and drain the carb bowls in case there's water in them.

[Wanderer]

Originally Posted by RacinNinja

Good!

Ruins my train of thought for flow though. Still, I'd check the float levels and drain the carb bowls in case there's water in them.

Yeah, I'm preparing myself mentally for my first carb removal and complete carb cleaning. I guess that I have eliminated all of the other stuff like petcock, vacuum leaks, plugs/spark, sea foam carbs.

Time for me to learn how. I'm sure the previous owner had the same issue. He only had the bike for about 2 years and only drove it a few miles to work each day, never above 30mph. The bike had sat for a year or two previous to him buying it.

So, I guess that dirty carbs are the issue here.

[RacinNinja]

Originally Posted by Wanderer

Yeah, I'm preparing myself mentally for my first carb removal and complete carb cleaning. I guess that I have eliminated all of the other stuff like petcock, vacuum leaks, plugs/spark, sea foam carbs.

Time for me to learn how. I'm sure the previous owner had the same issue. He only had the bike for about 2 years and only drove it a few miles to work each day, never above 30mph. The bike had sat for a year or two previous to him buying it.

So, I guess that dirty carbs are the issue here.

I would confidently say you're on the right track!

Not as scary as they seem if you're just disassembling and cleaning. Take lots of pics with your phone or camera.

While you're in there, I'd replace the float needles and DEFINITELY the bowl gaskets. Get those parts on hand before you even start. Shoot, @ducatiman even sells complete rebuild kits for what you'd pay for just those. Ask him about them...........

[Wanderer]

Maybe a dumb question but, when I go to take the carbs out and to clean them, is there a carb kit needed for these carbs? In other words, do I need any replacable parts or gaskets for the carb cleaning?

[RacinNinja]

Originally Posted by Wanderer

Maybe a dumb question but, when I go to take the carbs out and to clean them, is there a carb kit needed for these carbs? In other words, do I need any replacable parts or gaskets for the carb cleaning?

You were typing as I was posting. The one above has the answers you seek and a very reasonable supplier of said parts!

[Wanderer]

While I'm waiting for my carb kit parts, I think that I should go on and remove the airbox out the rear of the bike and do the airbox mod so it will be easier to get to the carbs next time.

Maybe look for old or cracked vacuum hoses while I have the room to look around.

[ducatiman]

Wanderer-

follow the Custom Carb Service thread link in my signature, post #3 shows the kit you require, follow the thread for some basic info.

Sufficient orings, float valves and replacement screws for both carbs are contained within the kit.

Please PM me for Paypal info and we'll get them to you quickly, all are on hand here.

Keep in mind another option...I can perform the carb service for you, if you desire, at any point if you run into difficulty or complication.

[jkv45]

You are absolutely, positively, sure the gas is good? I know you said you drained it, but you did go and get new gas and not use something you had at home in a can - right?

If there is any possibility it's not fresh I'd drain it again before moving on. 87 octane without ethanol is the best choice if it's available.

[ducatiman]

"I'm sure the previous owner had the same issue. He only had the bike for about 2 years and only drove it a few miles to work each day, never above 30mph. The bike had sat for a year or two previous to him buying it."

^ current issues a cumulative effect of prior history?
I'm amazed this bike is even idling or remotely capable of being ridden. Unfortunately, repair path a little more complex beyond a simple fuel purge, IMHO.

[Wanderer]

Originally Posted by jkv45

You are absolutely, positively, sure the gas is good? I know you said you drained it, but you did go and get new gas and not use something you had at home in a can - right?

If there is any possibility it's not fresh I'd drain it again before moving on. 87 octane without ethanol is the best choice if it's available.

Yes, in fact I have drained and refilled the tank with fresh fuel three times because I was removing the old petcock and then installing a brand new one. I put in fresh gas from a gas station each time.

[Wanderer]

Originally Posted by ducatiman

"I'm sure the previous owner had the same issue. He only had the bike for about 2 years and only drove it a few miles to work each day, never above 30mph. The bike had sat for a year or two previous to him buying it."

^ current issues a cumulative effect of prior history?
I'm amazed this bike is even idling or remotely capable of being ridden. Unfortunately, repair path a little more complex beyond a simple fuel purge, IMHO.

The previous owner told me that when he bought the bike, it wouldn't start or idle. He said that he got it running by spraying sea foam into the airbox. I think that he had been trying to fix this missing problem at cruising speed issue himself also and never was able to, so he just sold it without telling me about the problem. I know that he never took the carbs out himself.

I know that he checked to valve gap, new plugs, fixed a couple of vacuum leaks and sea foamed the carbs. He then only drove the bike about 3 miles each way to work and back and I suspect just lived with the missing issue.

Can you give me any ideas what part of the carbs you would suggest that I pay special attention to with a problem like this?

[jkv45]

Originally Posted by Wanderer

Yes, in fact I have drained and refilled the tank with fresh fuel three times because I was removing the old petcock and then installing a brand new one. I put in fresh gas from a gas station each time.

OK - you should be good then. Just a basic thing that some people overlook, and it will never run right if the gas is bad.

There is another thread here somewhere that is similar - engine runs fine most of the time except when cruising or a slight roll-off of the throttle. I remember adding a comment about the carb diaphragms being something to look into, but I don't think we got any definite answers.

[Wanderer]

Originally Posted by jkv45

OK - you should be good then. Just a basic thing that some people overlook, and it will never run right if the gas is bad.

There is another thread here somewhere that is similar - engine runs fine most of the time except when cruising or a slight roll-off of the throttle. I remember adding a comment about the carb diaphragms being something to look into, but I don't think we got any definite answers.

Thanks Jay. If you find that old thread would you link to it here for me?

Thanks

[jkv45]

Originally Posted by Wanderer

Thanks Jay. If you find that old thread would you link to it here for me?

Thanks

This is the one I was thinking of - https://www.ninjette.org/forums/showthread.php?t=272674

[Wanderer]

Originally Posted by jkv45

This is the one I was thinking of - https://www.ninjette.org/forums/showthread.php?t=272674

I read through this thread and he seemed to have a problem when the bike was under load. My problem is actually when you cut back on the gas at cruising speed to stay at a constant speed. As soon as I cut back on the throttle a little to cruise at a steady speed, it starts to cut out and acts like it is dying.

If I get back on the throttle, it picks back up as normal. If I stop, it idles fine.

[jkv45]

Originally Posted by Wanderer

I read through this thread and he seemed to have a problem when the bike was under load. My problem is actually when you cut back on the gas at cruising speed to stay at a constant speed. As soon as I cut back on the throttle a little to cruise at a steady speed, it starts to cut out and acts like it is dying.

If I get back on the throttle, it picks back up as normal. If I stop, it idles fine.

Sorry - maybe that's not the right one then...there are soooo many carb-related threads going that I may have gotten them mixed-up.

I'll look again and see if i can find the one with a similar problem.

[Wanderer]

OK, I think that I found the problem.

Once I had gotten the carbs out of the bike and on the bench, I removed the Pilot Mixture screws. Someone else before me had drilled the plugs out(Doing a TERRIBLE job of it I must say!). Anyway, the Pilot Mixture Screw steel washer was missing in one of the carbs and the o-ring was torn in to.

The fool that did this had the mixture screw on this carb almost completely closed, I assume to control the o-ring being damaged. Whoever opened these carbs previously did a shoddy job of it.

The carbs weren't dirty at all. I didn't find any clogged ports or openings, so I suspect this was the whole issue. I just sprayed everything well with carb cleaner. Looks like new inside, except for the Pilot Screw problem.

To get the carbs out, I decided to go on and remove the old airbox and to add a K&N dual pod air filter. I cut off the battery box to be reused alone. I didn't do this for more hp, but to make any future carb work much easier.

I have new #108 main jets on order also and of course new Pilot Mixture o-rings and steel washers for both carbs. (I still have a stock exhaust.) I am adding 2 washers under the needle at this time also. And reset the Pilot Mixture screws to 2.5 turns to begin with.

Everything else looked great and didn't need to be replaced.

Once I get the parts and the bike back running I'll let you know how it is running.

Thank you all for your help troubleshooting this problem.

Peace