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Old July 4th, 2022, 12:41 PM   #1
gravitationaldef
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Topping out at 85?

Hey guys this will be my first official post although I’ve been lurking for a while so thanks for all the information you guys have posted it’s greatly helped me with this bike… This is not one of those “how fast can a 250r go” posts. Had the bike for about 6 weeks…rebuilt carbs using 6 sigmas kit and procedures. 105 main and 40 pilot(I think). Have done runs with the airbox, the airbox and the snorkel removed, and then finally where I am at now running pod filters… I have never owned a 250 before but I must say that I am really impressed with the performance of this machine and throttle response and acceleration is very impressive. The continual issue that I’m running into is that the bike maxes out around 80 to 85 mph… The strange thing is that it will actually rev higher and reach higher top speeds when you do not have WOT… now I don’t have it pegged to 12 or 13 K in all the gears often but from what I recall a couple weeks ago when I was running tests and reving it out that it is doing this in almost every gear. My question is do you think someone regeared the bike? I really don’t wanna go to counting teeth unless someone thinks that may be what it is, or is this the result of poor carb tuning? I can say that from running the complete factory set up to what the set up is now is it night and day difference… Like the bike performs almost twice as well which is what has me confused… Fuel issue? Gearing issue? CDI issue? Or a combination? Thanks in advance guys and happy fourth
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Old July 4th, 2022, 01:05 PM   #2
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Quote:
Originally Posted by gravitationaldef View Post
Hey guys this will be my first official post although I’ve been lurking for a while so thanks for all the information you guys have posted it’s greatly helped me with this bike… This is not one of those “how fast can a 250r go” posts. Had the bike for about 6 weeks…rebuilt carbs using 6 sigmas kit and procedures. 105 main and 40 pilot(I think). Have done runs with the airbox, the airbox and the snorkel removed, and then finally where I am at now running pod filters… I have never owned a 250 before but I must say that I am really impressed with the performance of this machine and throttle response and acceleration is very impressive. The continual issue that I’m running into is that the bike maxes out around 80 to 85 mph… The strange thing is that it will actually rev higher and reach higher top speeds when you do not have WOT… now I don’t have it pegged to 12 or 13 K in all the gears often but from what I recall a couple weeks ago when I was running tests and reving it out that it is doing this in almost every gear. My question is do you think someone regeared the bike? I really don’t wanna go to counting teeth unless someone thinks that may be what it is, or is this the result of poor carb tuning? I can say that from running the complete factory set up to what the set up is now is it night and day difference… Like the bike performs almost twice as well which is what has me confused… Fuel issue? Gearing issue? CDI issue? Or a combination? Thanks in advance guys and happy fourth
Welcome to the forum!

It is popular on the 250's to go to a 13 tooth front sprocket. I would expect to see that from what you said, and I am sure you were probably expecting to hear that. I personally don't expect the other potential issues you listed to reduce top speed.

I think you may need some larger jets, I have not gotten into pods and a more open exhaust, as I bought a bike once that had both, and found the experience sub-optimal, so please don't take what I say as definitive. No low end power, and the exhaust in my opinion sounded too brappy/buzzy. You may be too lean from what I see according to your numbers. Have you pulled the spark plugs at all to make sure they are looking good?
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Old July 4th, 2022, 01:23 PM   #3
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Reading plugs is ancient art-form, like reading tea-leaves. It's an average of every single combustion event plug has experienced from 1st installation. So to do it accurately with useable results, you must install new plugs on side of road, do ONE SINGLE WOT run and immediately pull over and chop throttle and shut off engine. Then pull plugs right there on side of road before they cool off.

Modern dyno and wideband O2-sensors give so much more accurate results because they give you instantaneous AFR at exact RPM zones, not averages. This data will tell you that mixtures are both too lean AND too rich. Something impossible to discern from reading tea-leaves.

Your carbs are not factory fresh clean without ultrasonic soak and micro soda-blasting. Factory mixtures way too rich as it is.

My race bike was dyno-tuned with full Tyga exhaust by my sponsor Spears. Very 1st thing he did beforehand was downsize main-jets down to 96. Then we went down one more after dyno runs. Result as +24% more power than stock with smaller mains.

Factory too-rich jetting


Actual top-speed went up from 97-mph to 106-mph on calibrated Vapor digital dash (117-mph on factory dash). Don't forget that all important '60s hot-rod saying...
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Old July 4th, 2022, 01:40 PM   #4
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Quote:
Originally Posted by gravitationaldef View Post
Hey guys this will be my first official post although I’ve been lurking for a while so thanks for all the information you guys have posted it’s greatly helped me with this bike… This is not one of those “how fast can a 250r go” posts. Had the bike for about 6 weeks…rebuilt carbs using 6 sigmas kit and procedures. 105 main and 40 pilot(I think). Have done runs with the airbox, the airbox and the snorkel removed, and then finally where I am at now running pod filters… I have never owned a 250 before but I must say that I am really impressed with the performance of this machine and throttle response and acceleration is very impressive. The continual issue that I’m running into is that the bike maxes out around 80 to 85 mph… The strange thing is that it will actually rev higher and reach higher top speeds when you do not have WOT… now I don’t have it pegged to 12 or 13 K in all the gears often but from what I recall a couple weeks ago when I was running tests and reving it out that it is doing this in almost every gear. My question is do you think someone regeared the bike? I really don’t wanna go to counting teeth unless someone thinks that may be what it is, or is this the result of poor carb tuning? I can say that from running the complete factory set up to what the set up is now is it night and day difference… Like the bike performs almost twice as well which is what has me confused… Fuel issue? Gearing issue? CDI issue? Or a combination? Thanks in advance guys and happy fourth
Are they aftermarket jets? Many kits contain parts that are not 100% correct - even though they look right.

105 Kehin jets should be good with an airbox. Stock 38 Pilots are fine. Basic idle mixture adjustment is 2 turns out.

They usually run best with an airbox. Make sure the filter is in good condition and not over-oiled.

You could look at the plugs for an obvious rich/lean condition.
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Old July 4th, 2022, 01:47 PM   #5
gravitationaldef
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Thanks for the information guys… I do have a 100 Main that I could put in and try that… I’ll also count the teeth on the front sprocket and see if somebody did indeed swap that… That’s very interesting information I definitely don’t know everything but I’ve been around bikes my whole life and I’ve never heard of doing one dry run on new plugs to read them but it makes perfect sense… I’ll do these things and report back… Oh and I forgot to add earlier that I punched out the main catalyst and there is a slip on pipe in place of the stock muffler… Thanks again
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Old July 4th, 2022, 01:56 PM   #6
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@jkv45,

Yes they are aftermarket jets… The tough thing about my situation and what makes it hard to describe to you guys I really don’t have a baseline of “expected performance “other than when the bike was factory and I barely rode it like that before I broke into the carburetors and the exhaust so I don’t really know what the performance level ““ should be for this bike… As was mentioned above and I was hoping wasn’t the case but I suspected it was regeared so it’s going to be quicker up to top speed regardless(right now a mundane 80-85)… I’m gonna try a few of the suggestions you guys mentioned and see if I can increase the performance of this thing… Like I said I wish one of you guys could ride it you’d be able to tell me if it’s at optimal performance or not.
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Old July 4th, 2022, 02:31 PM   #7
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Note jetting for pre-gen bikes is completely different than new-gen. There's two performance variables you may be able to distinguish:

acceleration - function of torque vs. weight. IF bike had factory-level output, having lower gearing would give you better-than-factory acceleration. As baseline, factory bike did 0-60 in about 7-sec. If your bike can't match or beat factory speeds, it's not gearing issue.

top-speed - function of power vs. aero drag. Max-power is generated at about 11K-rpm, so you'll want to select gear that places RPMs right in that range to coincide with top-speed.

What RPM and gear are you in when you hit your observed top-speed? Even IF your bike was geared lower, you'd still hit 105mph in 6th-gear instead of 5th. Your overly-rich mixture will rob you of about 3-5mph top-speed, not 20-mph.

So I suspect your carbs may need deeper cleaning with scrubbing out of hidden secret passages and bleed holes poking out with soft copper wire. Carb-cleaner spray no longer work due to removal of chlorinated compounds. Might as well use pee as at least it's got some ammonia in it.

I would put everything back to factory OEM bone-stock condition and get some baseline performance numbers for future comparisons. You'll find add fuel will just make bike slower.

I use one of these to measure changes AFR with each mod: http://wbo2.com/2y/default.htm . Max-power is made at ~13,5:1 AFR on NA engines (dashed line on dyno above). And one of these accelerometers to measure actual changes in performance since butt-dyno is hugely inaccurate. Measures 0-60 and 1/4-mile very precisely and actually gives fairly accurate Hp estimates based upon your entered weight parameters.



BTW - you are redlining every gear on way to top-speed right? Due to reduction in on-the-ground torque at contact-patch with each higher-gear, you won't be able to accelerate up to a speed that'll allow continuted acceleration in next gear if you shift too soon (this chart came from car, but same idea).

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Old July 4th, 2022, 03:10 PM   #8
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BTW - overly rich fuel-mixtures, in addition to robbing you of power, quenches and cools combustion and gives smoother output. Which lots of people think is more powerful. Nope...

When tuned for max-power @ 13.5:1 AFR, bike will run rough, raw and temperamental. It will make the hairs on back of your neck stand up when you mount it. Such bikes demand respect and attention, you can't just ride it, you have to manage it.

Throttle has to be precisely controlled at all times or it'll just stall or turn tyres to dust, pretty much very little in between. Anyone's who've ridden such bikes will only speak of them in hushed voices. Such as when they downshifted to 4th gear on freeway and bike screamed and wheelied over lazy Corolla hogging left-land ahead...
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Old July 5th, 2022, 06:51 AM   #9
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Quote:
Originally Posted by gravitationaldef View Post
@jkv45,

Yes they are aftermarket jets… The tough thing about my situation and what makes it hard to describe to you guys I really don’t have a baseline of “expected performance “other than when the bike was factory and I barely rode it like that before I broke into the carburetors and the exhaust so I don’t really know what the performance level ““ should be for this bike… As was mentioned above and I was hoping wasn’t the case but I suspected it was regeared so it’s going to be quicker up to top speed regardless(right now a mundane 80-85)… I’m gonna try a few of the suggestions you guys mentioned and see if I can increase the performance of this thing… Like I said I wish one of you guys could ride it you’d be able to tell me if it’s at optimal performance or not.
I would suspect the carb/jetting then.

It should run close to 100 MPH indicated, given the time.

Because you said it revs higher when you back-off the throttle from wide open, it tells me it's most likely a carb/mixture/jet issue.

That's assuming the gas is good and fresh. I've had similar issues with a cycle that had old gas. Drained and refilled, and it ran fine.
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Old July 5th, 2022, 11:38 AM   #10
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@DannoXYZ,

It’s a new gen (2008). Stripped off passenger seat, passenger foot pegs, airbox, any mounting brackets not needed, coolant reservoir, mirrors etc. I am running the bike naked right now so I know that will slow it down some. I weigh 190lbs.
I will need to time it but it definitely is faster 0-60 than 7 seconds. 80-83mph @10k. It’s maxing @10k in all gears like it’s bouncing off a rev limiter. In neutral it will rev above the redline on the tach…not any loud noise but a soft “pop” with a blue flame coming out of exhaust after reving up and letting off throttle or downshifting before going into a turn. Went one turn in yesterday on A/F and went and fueled up(ethanol free 90) and granted I’m not driving slow at all but you can watch the fuel gauge dropping. I am swapping to either the 100 or 102 today and doing the plug test you mentioned.
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Old July 5th, 2022, 11:41 AM   #11
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@jkv45,

I suspect so as well. I haven’t counted the teeth yet but based on my experience on my 600 race bike this thing is too quick down low , at least what I would suspect(wish it was that quick with factory gearing
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Old July 5th, 2022, 01:34 PM   #12
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You can't use plugs to gauge jetting with unleaded fuel. You will only see any worth while difference if its really rich or really lean, anything else & it looks the same. My ZZR250 is good for an indicated 95mph, probably a true 90mph whilst dragging my heavy arse along & the newer 260 has less power.
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Old July 5th, 2022, 04:15 PM   #13
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Quote:
Originally Posted by gravitationaldef View Post
@DannoXYZ,

It’s a new gen (2008). Stripped off passenger seat, passenger foot pegs, airbox, any mounting brackets not needed, coolant reservoir, mirrors etc. I am running the bike naked right now so I know that will slow it down some. I weigh 190lbs.
I will need to time it but it definitely is faster 0-60 than 7 seconds. 80-83mph @10k. It’s maxing @10k in all gears like it’s bouncing off a rev limiter.
You'll want to time 0-66mph on dash to account for speedo error.

You might have other issues. Redline is 13k on this bike...
What's part# on ignition box?
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