Engine Feels Like It's Missing at Medium Speed. Any Ideas?

[Kawinoob217]

Hi Everyone,

I recently just started riding (about 3 weeks ago) and I got a hand-me-down 93 Ninja 250. I'm the third owner of the bike and I've had quite an exciting time trying to get it to run reliably (first owner used it as a track bike). Originally, I knew I was flooding the carb, as I could get it to run and idle, but then after a while it would die. If I let the bike run with the fuel valve turned off, and then only turn it on for a bit when I heard it bog down, I could get it to run indefinitely. After ripping the carb apart, soaking it in Berrymans chem-dip, and replacing the float needle valves, I believe I've fixed the flooding problem. Recently though, as I'm riding at about 50 mph, I feel like the engine is kicking in and out. Holding the throttle at a steady 25 - 30%, I feel power come in spurts. Opening up the throttle any more doesn't help. After getting home I checked the fuel line from the fuel petcock to the carb, and the fuel level inside of my inline filter looks kind of low, so I'm not entirely sure that I'm filling the bowls enough while I ride. I've done quite a bit to this bike so far, as some parts were beyond cleaning / repair. Here's what I've done to the bike so far:

1) Yoshimura RS-3 slip on Exhaust.
2) 112 size main jets (stock ones were beyond recovery).
3) New float needle valves.
4) New NGK Plugs.
5) Oil Change (Castrol 10w - 40)
6) K&N RC-1822 intake filters
7) New Battery
8) New Mid Throttle Needles (e-clip on third notch).
9) Idle screws backed out to 3 turns.
10) Chopped air box (to make room for filters).
11) New fuel petcock.
12) Clear fuel tube with inline filter from fuel petcock to carb.

In the case that I'm not getting enough fuel to the carb bowls, does the fuel petcock use the vacuum that is supplied by the outlet of the carb to pressurize the fuel and push it into the carb, or does it just allow gravity to take hold and fill the bowls? If the former is true, then I might have a bad fuel petcock...which would suck cause it's new. I'm open to any suggestions at this point, as I'm getting kind of frustrated . By the way the attachment is a look at the fuel line from my fuel petcock to the carb after a ride. Went from 50mph, to about 25 (subdivision), to stop.

[Spaghettiknight]

Originally Posted by Kawinoob217

Hi Everyone,

I recently just started riding (about 3 weeks ago) and I got a hand-me-down 93 Ninja 250. I'm the third owner of the bike and I've had quite an exciting time trying to get it to run reliably (first owner used it as a track bike). Originally, I knew I was flooding the carb, as I could get it to run and idle, but then after a while it would die. If I let the bike run with the fuel valve turned off, and then only turn it on for a bit when I heard it bog down, I could get it to run indefinitely. After ripping the carb apart, soaking it in Berrymans chem-dip, and replacing the float needle valves, I believe I've fixed the flooding problem. Recently though, as I'm riding at about 50 mph, I feel like the engine is kicking in and out. Holding the throttle at a steady 25 - 30%, I feel power come in spurts. Opening up the throttle any more doesn't help. After getting home I checked the fuel line from the fuel petcock to the carb, and the fuel level inside of my inline filter looks kind of low, so I'm not entirely sure that I'm filling the bowls enough while I ride. I've done quite a bit to this bike so far, as some parts were beyond cleaning / repair. Here's what I've done to the bike so far:

1) Yoshimura RS-3 slip on Exhaust.
2) 112 size main jets (stock ones were beyond recovery).
3) New float needle valves.
4) New NGK Plugs.
5) Oil Change (Castrol 10w - 40)
6) K&N RC-1822 intake filters
7) New Battery
8) New Mid Throttle Needles (e-clip on third notch).
9) Idle screws backed out to 3 turns.
10) Chopped air box (to make room for filters).
11) New fuel petcock.
12) Clear fuel tube with inline filter from fuel petcock to carb.

In the case that I'm not getting enough fuel to the carb bowls, does the fuel petcock use the vacuum that is supplied by the outlet of the carb to pressurize the fuel and push it into the carb, or does it just allow gravity to take hold and fill the bowls? If the former is true, then I might have a bad fuel petcock...which would suck cause it's new. I'm open to any suggestions at this point, as I'm getting kind of frustrated . By the way the attachment is a look at the fuel line from my fuel petcock to the carb after a ride. Went from 50mph, to about 25 (subdivision), to stop.

what brand/model petcock is it? also is it gravity fed or vacuum fed? I've noticed some aftermarket gravity fed petcocks don't work well with bikes that have stock vacuum fed petcocks like this bike, probably because of ventilation issues.

[DannoXYZ]

Have you done the gas cap mod?

During this mid-range stumble, if you drop down a gear or two to increase RPMs, does it run smooth again?

[Kawinoob217]

Originally Posted by Spaghettiknight

what brand/model petcock is it? also is it gravity fed or vacuum fed? I've noticed some aftermarket gravity fed petcocks don't work well with bikes that have stock vacuum fed petcocks like this bike, probably because of ventilation issues.

When I bought the petcock, I was under the assumption that it was an OEM replacement. Getting it, it came in a "Kawasaki genuine parts" box, and seemed good. Is there anything in particular that I can look for on the petcock to validate that it is a Kawasaki original?

[Kawinoob217]

Originally Posted by JacRyann

Have you done the gas cap mod?

During this mid-range stumble, if you drop down a gear or two to increase RPMs, does it run smooth again?

I'm not entirely sure what you mean by the gas cap mod, but everything looks stock up top on the tank. Dropping down a gear does not seem to give me back my throttle response. I do find, however, that if the bike starts to miss at around 50 mph, if I pop the clutch in, rev a few times and hit the bogging point, the bike seems to open up again and I have proper throttle response. For kicks, I also rode around my neighborhood with the fuel valve shut off in order to see what the bike feels like when it's starving for gas. It feels very similar to what's happening at 50 ish mph. Also, from a stop sign or stop light to acceleration, if I'm pulling on the bike decently hard, say 8k to 10k rpm, the bike never bogs during that time and will bog directly after if I try to drop to just a cruising speed.

[Triple Jim]

Is it possible the problem depends on the position of the twist grip, and not engine RPM?

From what I'm reading, it's starting to sound like you have a lean region somewhere like 1/2 throttle, maybe from the non-stock air filters and needles that may not be the right ones, or set to the correct position. You could try raising the needles a notch and see if the problem changes.

[Ghostt]

Have you serviced the spark plug caps and renew the HT leads?

Write up

Even bad plugs should do something, unless they are totally shot.

Did you renew the HT leads, and disassemble the caps?

Make sure you disassemble the caps, and clean them, and yes the caps get cruddy.

Here my write-up,

Short explanation: The inside of the hard plastic caps accumulate crud the can short out the spark. This can cause rough running or failure to start. Every time you do any work on the bike: remove them disassemble and clean them and renew the wires or at least the connections.

The long Explanation, Warning engineering information can cause Drowsiness.
The ancient cylinder design of the engine dictates that the spark emanate form the center of the combustion chamber. In order to get it there, the plugs had to be located down deep in a well between the cams. This well is a perfect place for dirt and moisture to accumulate. Then because there is no cooling water at this point the metal around the plug runs very hot. Surround this with the large amount of cool metal and you have a recipe for condensation. Now K did drill a drain hole between the fins to help (a little) but it often gets plugged up.

The moisture boils off the base of the plug and the vapor condenses on the cool plastic cap and the plug insulator. This moisture forms a easier path for the electrons to ground than jumping the gap at the plug to make a spark. Misfire.
This issue is right up there with Pilot jets as a cause of trouble.

Here's some pictures that might be helpful. I took these when I replaced the wires themselves, as it was a good time for a write-up, and the wires were OEM from 1998.

Wires are just 7mm copper core, with clear silicone jacket









IMPORTANT NOTICE: make sure to use a proper screwdriver, make sure it fits, as the parts are made of brass inside the spark plug caps





Important notice: the wire must be screwed on the spark plug cap, note the screw like object inside the spark plug cap?



Important notice: be careful to not loose the ferrules on the HT leads, these keep the wire from falling out of the coil. Below is an example of ferrules on a pressure fitting, looks familiar?







The gas cap mod is as follows,


Sounds like it could be a venting issue, no worries it's a free and easy fix,

You need you to disassemble the gas cap and remove the two small red diaphragms, assuming this is your only problem.

The diaphragm gets hard and losses it's flexibility and gets stuck, and doesn't allow proper venting.

IMHO this modification should be done regardless to prevent future problems whatsoever.

They are ment to vent the tank, but in the case of an accident not allow gas to leak out, but more often cause problems then they fix.

Here are some pictures to help you.

The plastic piece houses the two small red diaphragm pieces, this one being mine, they are already gone, and you can leave the plastic piece out all together, as I'm going to do now.

Some things to watch out for are, there are 5 small springs under the round collar, and a small round collar as well on the locking mechanism, don't lose any of them.

Good luck.

[A.J.]

Slap these puppies on that bike so you don't have all the fluid reservoirs showing and hanging out. You can look and get them much cheaper. Does wonders for the looks too. If that's your bike in the pic of course. As far as your issue definitely look into what ghostt posted. That's some valuable info.
http://m.ebay.com/itm/1998-Kawasaki-...%257Ciid%253A1

[Kawinoob217]

Originally Posted by A.J.

Slap these puppies on that bike so you don't have all the fluid reservoirs showing and hanging out. You can look and get them much cheaper. Does wonders for the looks too. If that's your bike in the pic of course. As far as your issue definitely look into what ghostt posted. That's some valuable info.
http://m.ebay.com/itm/1998-Kawasaki-...%257Ciid%253A1

I do have these side fairings for the bike I'm just keeping them off as they're a hassle to take on and off of the bike constantly when I'm working on it. As for all the other suggestions, thank you all so much for the help! I haven't done the gas tank mod yet, but I do plan to, and I should definitely check out the the HV leads on my coil packs. I didn't end up shifting the needles up, but I might as I'm still having a little bit of a problem. What ended up fixing it was taking the carb back out, and blowing compressed air through the fuel rail right after the fuel tube, before the carb bowls. I think what happened is that after soaking my carb in Berrymans Chem Dip (which is great stuff by the way I highly recommend it), I forgot to blow out anything that might have been loosened up by soaking it. I think that at a certain throttle position, I was plugging the fuel inlet and not letting the vacuum pull gas up. Makes me wish I had an ultrasonic cleaner big enough to shake this thing up for an hour or two. I'll let everyone know if the bike starts acting up again, as I'm being cautious in telling you guys that everything is all good with the bike. Thank you for all of your help!

[Kawinoob217]

So as it turns out, I didn't solve the problem. I did the aforementioned items with the gas cap and spark plugs, but that hasn't fixed the problem. Cruising along at 50mph with the throttle maybe at about 35%, I still feel power cutting in and out. As you can see from my profile photo, I don't have a windshield, and so when it's really windy, it gets worse. I'm wondering if this is due to my needle height in the carb? I'm guess I'm asking you guys to tell me if this is a bad assumption to make based on the evidence I have. From what I've read, 35% throttle is in the ballpark of percentage where the carb is switching from pilot jets to the mid-needles. Along with the larger main jets that I installed, I put in the needles with adjustable e-clips. I'm guessing that when switching to the needles, the needles are seated too deep which starves fuel and causes me to run lean. Is this logical troubleshooting thought?

[Triple Jim]

I'm not saying you should assume you need to do this, but I had steady throttle surging on my pregen until I shimmed the needles about 1/2 mm. Maybe Ducatiman can comment.

[Ram Jet]

Originally Posted by Kawinoob217

So as it turns out, I didn't solve the problem. I did the aforementioned items with the gas cap and spark plugs, but that hasn't fixed the problem. Cruising along at 50mph with the throttle maybe at about 35%, I still feel power cutting in and out. As you can see from my profile photo, I don't have a windshield, and so when it's really windy, it gets worse. I'm wondering if this is due to my needle height in the carb? I'm guess I'm asking you guys to tell me if this is a bad assumption to make based on the evidence I have. From what I've read, 35% throttle is in the ballpark of percentage where the carb is switching from pilot jets to the mid-needles. Along with the larger main jets that I installed, I put in the needles with adjustable e-clips. I'm guessing that when switching to the needles, the needles are seated too deep which starves fuel and causes me to run lean. Is this logical troubleshooting thought?

Adjustable jet needles? I didn't know you could do that. Anyway, drop the "E" clip one notch - might work. #112 main jets should be plenty big enough. I run #110s.

Bill

[DannoXYZ]

Originally Posted by Kawinoob217

Along with the larger main jets that I installed, I put in the needles with adjustable e-clips. I'm guessing that when switching to the needles, the needles are seated too deep which starves fuel and causes me to run lean. Is this logical troubleshooting thought?

Without actual wideband datalogging to determine if the symptoms are caused by lean or rich condition, you can do a 2-step test.

1. adjust needles one setting towards richer and see how bike responds. If it's better, it was lean

2. if not better, it was too rich already, so adjust needs one setting towards leaner from original position and see how it runs.

This was the '60s method for carb-tuning before EFI and electronic datalogging was available. The process was to initially add too much fuel for safety so you know for sure it's too rich. Then gradually lean it out until HP-improvements level off. There was a saying that goes along with this process, anyone remember it?

[Triple Jim]

You can also make a quick stab at the enricher lever for the same purpose. If it helps, it's too lean.

Bill, there is only one clip position, but you can use one or more washers (shims) under the clip to raise the needle.

[Ram Jet]

Originally Posted by Triple Jim

You can also make a quick stab at the enricher lever for the same purpose. If it helps, it's too lean.

Bill, there is only one clip position, but you can use one or more washers (shims) under the clip to raise the needle.

Well, I know about the washer thing but I thought he was able to purchase jet needles with notches and an "E" clip. As Gilda Radner would say "Nevermind".

Bill

[Triple Jim]

I'm the one who speed-read the post, Bill. I missed that he had adjustable needles.

[jkv45]

A 112 Keihin Main Jet might be too rich. What do the plugs look like?

3 turns out on the idle mixture screws is unusual. Most of the time 2 to 2.5 is optimum.

I would move the clip on the needle 2 spots leaner (up) and see how it runs.

Another possibility is a damaged or misaligned carb diaphragm. Did you remove the idle mixture screws, clean the passages, and look at the condition of the o-rings before replacing the screws? Did you remove and clean the Pilot Jets?

What gas are you running? How old is it?

[Kawinoob217]

It's not a Keihin 112, it's a factory pro 112. I'm not sure if they're different, but I know that some jet brand sizes don't compare. The reason that I originally put it in was because the stock ones were corroded and far past saving. I'm trying to mod the bike around that, so i bought Yoshimura pipes and have been trying to tune ever since. Any idle screw setting under 2.5 won't let me start the bike even with full choke on. A while ago I tried one clip level up, and the bike in neutral would bog and die at anything past 1/4 throttle. I did not remove the idle mixture screws before cleaning, but I did remove and clean the pilot jets. Before I had the bike, I have no idea what gas was being run though it, but I stick with 91 octane ethanol free gas.

[jkv45]

Originally Posted by Kawinoob217

It's not a Keihin 112, it's a factory pro 112. I'm not sure if they're different, but I know that some jet brand sizes don't compare. The reason that I originally put it in was because the stock ones were corroded and far past saving. I'm trying to mod the bike around that, so i bought Yoshimura pipes and have been trying to tune ever since. Any idle screw setting under 2.5 won't let me start the bike even with full choke on. A while ago I tried one clip level up, and the bike in neutral would bog and die at anything past 1/4 throttle. I did not remove the idle mixture screws before cleaning, but I did remove and clean the pilot jets. Before I had the bike, I have no idea what gas was being run though it, but I stick with 91 octane ethanol free gas.

Factory Pro uses Keihin jets, DynaJet does not.

That tells me something isn't right with the carbs. Partially plugged idle mixture passages, or damaged o-rings, may be some of the problem.

Most likely the carbs need additional attention as well.

Check around for more info, but I still think a 112 Main Jet is too much. We ran pods, a leaky factory system (that was loud), and 108 Keihin Mains and a shim or 2 on the factory needles. Pulled strong and clean all the way to redline, where it spent a good amount of time. We were running 87 octane ethanol-free. Gas without ethanol does give you a slightly richer mixture than gas with ethanol.

[Kawinoob217]

I'll see if I can open up the carb on the weekend and check out the idle screw passages. Shouldn't be anything some compressed air and some new gaskets couldn't fix. I'm a college student so time is scarce. I'm not sure what I've got on hand, but I think I've got 110 jets sitting in the jet kit I received with the bike. Assuming that I'm running lean right now, and I switch out my 112's for 110's, would I have to shim (or shift my eclips down), even more? It's to my understanding that the needles even though the 25% to 75% throttle range still pull gas through the main jet. In this case am I right to assume that less gas will make it though? I do believe I'm running lean as, shifting my needles down really killed my throttle response last time I tried. I know for sure that I'm running rich on idle, as blipping the throttle at idle, the tach dips below idle before returning to normal. Also, I've never had to use choke on a cold morning. I'll play with idle screws a bit more before I decide to totally take them out and screw up any gasket I might have left in there.

[jkv45]

Originally Posted by Kawinoob217

I'll see if I can open up the carb on the weekend and check out the idle screw passages. Shouldn't be anything some compressed air and some new gaskets couldn't fix. I'm a college student so time is scarce. I'm not sure what I've got on hand, but I think I've got 110 jets sitting in the jet kit I received with the bike. Assuming that I'm running lean right now, and I switch out my 112's for 110's, would I have to shim (or shift my eclips down), even more? It's to my understanding that the needles even though the 25% to 75% throttle range still pull gas through the main jet. In this case am I right to assume that less gas will make it though? I do believe I'm running lean as, shifting my needles down really killed my throttle response last time I tried. I know for sure that I'm running rich on idle, as blipping the throttle at idle, the tach dips below idle before returning to normal. Also, I've never had to use choke on a cold morning. I'll play with idle screws a bit more before I decide to totally take them out and screw up any gasket I might have left in there.

If you are running lean anywhere, it's due to an issue with the carbs I would say. With a 112 Main Jet and the needles adjusted where they are, you should be plenty rich.

I think the carbs may need more than just carb cleaner and compressed air to be right, especially because you said the Main Jets were beyond cleaning when you got it.

Overall, a few things don't make sense to me.

I would consider shipping the carbs off to ducatiman to have them gone though thoroughly if you don't have access to proper tools and have limited time.

[DannoXYZ]

Yeah, the not starting with mixture screws in more than 2.5 turns even with choke is clue that some of circuits are clogged.

[Ram Jet]

Originally Posted by JacRyann

Yeah, the not starting with mixture screws in more than 2.5 turns even with choke is clue that some of circuits are clogged.

Agree.

Bill

[Ceeloo Yello]

Not sure this applies to you but recently my bike started bogging, kept cleaning the carbs and playing with the jetting but nothing worked. Ended up that some of the vacuum lines on the carb had cracks in them. Replaced all the vacuum lines on the carb and the bike was good to go.

[Kestrel]

The amount of air passing through the carb at idle is significantly less than that at 35% throttle. Gut feeling tells me that even with a screwed up idle circuit, that's probably not the smoking gun.

Often, aftermarket exhausts combined with different air boxes / filters can be a real bear to jet correctly. I had some serious surging issues at cruise RPMs when my jetting wasn't sorted out, and I bet you do, too.

[Kawinoob217]

Whelp given the time of year the bike is back home in the garage while I'm off at university. For a bit, getting it to start in the morning took about a minute of cranking, which isn't good. Kestrel you are correct in that I get surging issues when it comes to cruising RPM's. I'm not sure why it took so much cranking at cold to get the bike running. It felt as if I was getting combustion, and I just needed to hold the starter down long enough for the combustion to warm the block so that it could self sustain. Yesterday I prepped the bike to be stored for the winter (took all the fuel out and drained the carb bowls), and I decided to take the plugs out. The left plug (left if you're sitting on the bike) was covered in oil....uh oh. The right plug was white on the tip (makes no sense since I think I'm running really rich). I've definitely got some work cut out for me. I think I'm going to try a couple of different things with the carbs, but if I can't come up with anything I'm going to send the carb off to ducatiman. Also, does anyone know a good resource for learning the tear down process of the engine? I'm guessing that I need to replace piston rings if I'm seeing oil on the plug. I'm sure I can get the engine apart, but I'm not so sure that I would re-assemble it correctly. I'm not to keen on the whole timing chain and cam shaft positioning when assembling the upper.

[Ram Jet]

Originally Posted by Kawinoob217

Whelp given the time of year the bike is back home in the garage while I'm off at university. For a bit, getting it to start in the morning took about a minute of cranking, which isn't good. Kestrel you are correct in that I get surging issues when it comes to cruising RPM's. I'm not sure why it took so much cranking at cold to get the bike running. It felt as if I was getting combustion, and I just needed to hold the starter down long enough for the combustion to warm the block so that it could self sustain. Yesterday I prepped the bike to be stored for the winter (took all the fuel out and drained the carb bowls), and I decided to take the plugs out. The left plug (left if you're sitting on the bike) was covered in oil....uh oh. The right plug was white on the tip (makes no sense since I think I'm running really rich). I've definitely got some work cut out for me. I think I'm going to try a couple of different things with the carbs, but if I can't come up with anything I'm going to send the carb off to ducatiman. Also, does anyone know a good resource for learning the tear down process of the engine? I'm guessing that I need to replace piston rings if I'm seeing oil on the plug. I'm sure I can get the engine apart, but I'm not so sure that I would re-assemble it correctly. I'm not to keen on the whole timing chain and cam shaft positioning when assembling the upper.

This is a MUST! Just consider it another text book.

https://www.ebay.com/itm/Kawasaki-Se...tY5oww&vxp=mtr

It's a good price too. Kawasaki wants about $50.00 for the same thing.

Bill

[DannoXYZ]

Oil leaking into cylinders can come from multiple sources. Aside from rings, it can also be from valve-guide seals. Which can actually be replaced without tearing down the engine or even removing the head! Do a leakdown test to determine if it's rings or valves that's leaking.