5500-7000rpm hesitation

[Mless5]

Warning: newbie needs some help.

I have put my project on the road after cleaning carbs and doing other mechanical work to this $250 gem, circa 2004. Wasn't anything majorly wrong with it I guess, just needed some love. I do have a problem however. When accelerating through first and second gears (haven't gone higher yet) there seems to be a slight hesitation. The bike pulls great other than that. I have taken carbs apart again, boiled jets and cleaned everything once again including setting floats, but the problem is still there. Anything else I could look into as a potential source of this problem? Fresh gas obviously, new petcock.

Thank you

[Ghostt]

Have to checked the valve clearance? Any modifications to the bike, exhaust? Pod filter? Jets? Needles? Vacuum leaks?

At what point does the hesitation happen? What position is the throttle?

If it's happening at WOT then the EX-250's CDI uses a very simple advance curve: 2-dimensions, X and Y, with no compensation for load. It's pre-historic, rudimentary.

At about 4,000 or 4,200 rpm, depending on the year-model of the EX-250, the CDI has the ignition timing at full advance (38 degrees BTDC for the older engines or 42 degrees BTDC for the newer engines).

When you roll-on full throttle at about 4,000 rpm you suddenly make the air/fuel ratio much richer. In a modern car or motorcycle engine the ECU knows when this happens and it retards the ignition a bit because richer air/fuel ratios burn faster than leaner mixtures.

Because the EX-250 CDI has no way to compensate for the sudden rich (faster burning) mixture the ignition advance stays way up there at 38 or 42 degrees and you end up with too much of the burn occurring before the cylinder reaches TDC.

Instead of instantly making a lot more power (as you're anticipating when you open the throttle wide) you make only a little bit more. And the engine slowly lifts itself out of the situation.


If your in need of carburetor services and/or parts PM @ducatiman

[Mless5]

Thanks for your thoughts!

No mods on the bike, bone stock. Have not done the valve job yet.

I would need to ride the bike more to answer your question regarding WOT. What I have noticed is that if I give it good juice at 2K, it pulls even and strong to that point, not as strong 5500-7K and than strong again.

Thanks.

[HoneyBadgerRy]

I'm thinking its a jetting issue/dirty carbs, but it could easibky be a out of spec valves problem. Its hard to tell with the information you gave us.

[Mless5]

Went for a spin today, seems to be doing much better in that range under WOT, but not so great if the throttle is just cracked open.

[Ghostt]

Sounds like the carburetors might need some work?

BUT you need to perform other services first, like valves. Once you have verified the valves are good, air filter? Fuel flowing properly? Inline fuel filter? then you know, don't assume!!!! You can't diagnose that way.

I know with my own experience valves that are out of adjustment will cause issues with idle, etc.....

[HoneyBadgerRy]

Partial throttle hesitation under load sounds like its defintly either dirty carbs or I'll adjusted mixture screws. Its time for a carb cleaning.

[Ghostt]

Was the bike fully warmed up?

[Mless5]

Thanks.

Today's findings include loose clamps on block to carb pipes. After I tightened them up, it seems like the hesitation is only there when the bike is not warmed up.

Ghostt - thank you, this is an excellent diagram that I need to put in my garage!

[SRH]

Although I'm new to this forum, I've owned my '05 Ninja since the 1k mark and bone stock. She now has 13.7K and several mods.
I see no mention of mileage on your bike, so I'll assume based on the age that you're not the original owner, and this bike has more than 10K miles. Correct me if needed because this information needs to be mentioned. If the "EPA" plugs are missing, then the pilot screws have been accessed. The stock 250s exhibited this very symptom due to maladjusted pilot screws from the factory. When I removed the pilot screw plugs from my carbs, the R side screw was set @3.5 turns, and the L side was set to 3/4 turn, just enough to get whatever meter they used to read inside the envelope and move on to the next unit. Also, stock main jets are #105 which is just under what they'll run best with. However, the "anyone will tell you" proceedure for doing carb work ( synching, jetting, etc) is to ensure the valves are properly adjusted first.
I'll spare you any more rambling. A shop manual will help immensely with all this information. The PO gave me one with my bike, and I bought the supplement for my year @ Ron Ayers. I haven't been there in a long while so I can't say if they're still available. When all is well with the Ninja they run great and will provide miles of smiles.

[Ghostt]

Originally Posted by Mless5

Thanks.

Today's findings include loose clamps on block to carb pipes. After I tightened them up, it seems like the hesitation is only there when the bike is not warmed up.

Ghostt - thank you, this is an excellent diagram that I need to put in my garage!

Your very welcome. Especially check the airbox to carburetor boots, they are a PITA to seal properly.

The slight hesitation while it's not up to operating temperature is normal. Your next job should be to check valve clearance, once you've verified those you can move on to other items.

Like spark plugs, replace?, servicing the spark plug caps and HT leads accordingly.

Then once you've got all that sorted, then you can fine tune the idle mixture screws.

If you need any help let me know, write-ups available apon request.

[Mless5]

Thanks a lot!

Spark plugs were already done, the bike runs much better once I tightened up those clamps. Now onto valve adjustment once I get the feeler gauges. The bike is stock, I've verified yesterday that jets are stock size. I set mixture screws to 2.5 turns for now. 12800 miles on the bike btw.

Airbox to carb junction that you mention: I struggled really bad coupling the 2 back together until it dawned on me that the spring around the tube needs to slide back in order for the proper seating of the box to carbs. Doh...

Thanks again!

[Ghostt]

Did you renew the HT leads, and disassemble the caps when you changed the plugs? What? Huh?

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











I have since done the CoPs modification, Kawasaki ZX Ignition Coil Pack modification.

[Mless5]

Many thanks for the write up, I will be sure to do that as I haven't addressed it yet.

[Ghostt]

Did you or the PO do the plugs?

[Mless5]

I did. I bought this bike "as-is" from somebody who picked it up as a "project" so I did not know what I was getting into. Started with basics like fresh gas, plugs, oil change, coolant flush, brake work, chain, petcock (was bad) carb clean up and other standard bits. Got it running now, time to dive in a bit deeper and take it to the next level.

[Ghostt]

Okay just making sure, trust no one!! Especially the PO.

Doing the caps not only eliminates another possible cause, but insurers their proper operation which makes for a happier rides, and ultimately safer.

You trying to eliminate as many variables as possible.

[Mless5]

Happy is good, we like happy! Many thanks again for your detailed write up!

[SRH]

Now that you've experienced carb removal that way, take a look at this mod. It makes carb work/removal MUCH easier. Ask me how I know.

http://faq.ninja250.org/wiki/Battery...r_carb_removal

[Mless5]

Thanks. This was the first thing I did after initial 1hr length assault. Can get it out to my work table in 7 minutes flat now

[Mless5]

This past weekend I decided to get back into it. I bought some shims for both needles and popped them in - just one per needle. The bike seems to be running hella rich and anything under 4K feels like it is being overflown. It takes off like a rocket after 4K however ::buttrock::.

The question I have is this: when I placed a washer of the specified size under the head of the needle, I noticed that it would not fit into 4 legged plastic spacer that sits under the spring. That doesn't look right to me, any feedback?

[csmith12]

Then it's too large. #4 in the variety pack from radio shack is perfect and you can pick them for $2 any day of the week.

[Mless5]

Originally Posted by csmith12

Then it's too large. #4 in the variety pack from radio shack is perfect and you can pick them for $2 any day of the week.

Thanks, I thought it didn't look right. Everything is already apart, going to get some more washers tomorrow.

It is interesting though how the original issue has gone away, which proves that it is most likely caused by fuel supply issue. We shall see tomorrow.

Thanks for your help!

[Mless5]

Well who woulda thought... that one single washer under each needle will fix this issue?! Bike runs smooth like butter through RPM range with no hesitation - an absolute blast!