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Old September 20th, 2019, 11:26 AM   #1
GAU-8
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Student 250, turned to personal ride: a few Qs

Hey y'all. Been quite some time since I said hello.

Hello!

So here is my dilemma, a private 250 with mods, was sold to the school a few years ago. It has mods. ( the rest of the bikes are bone stock) because of this, if I did carb work on this 250, I cleaned all carb stuff, but adjusted nothing. Unfortunately I have lost the "dark arts" to aftermarket jetting tuning. Anyways, we have updated our fleet of bikes, and this 2008 ninja 250 was offered to me for a very attractive price.

The issue: 20 to 30 minute warm up time, with choke on.
When warm, is a banshee right out of the gates from your sweeetest nightmare. It's really strong/crisp accelerating for a 250!

Now that it's mine, a few Q and A.

It has an aftermarket exhaust. ( yoshi triangular exhaust)
Stock airbox
Aftermarket needles/jet kit. ( i can get jet numbers in a few hours)

I can't quite tell if this is a full system, or slip-on, by looking at the headers) if this is a full system, i would THINK that the airbox would be removed, and an alternate filter/pod would be in place?

Mixture screws out 3-1/2 turns
Needles have clip 3rd from top, the plastic spacer, then two washers on top of the spacer.

That doesn't look/sound right to me, but always ran fine after warm up. I also don't know a good baseline to start.

Sorry if there is too much "TL.DR" but offering up what info I know, at the start.

Thx for any help identifying any issues.
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Old September 20th, 2019, 11:44 AM   #2
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Quote:
Originally Posted by GAU-8 View Post
The issue: 20 to 30 minute warm up time, with choke on.
When warm, is a banshee right out of the gates from your sweeetest nightmare. It's really strong/crisp accelerating for a 250!

Now that it's mine, a few Q and A.

It has an aftermarket exhaust. ( yoshi triangular exhaust)
Stock airbox
Aftermarket needles/jet kit. ( i can get jet numbers in a few hours)

I can't quite tell if this is a full system, or slip-on, by looking at the headers) if this is a full system, i would THINK that the airbox would be removed, and an alternate filter/pod would be in place?

Mixture screws out 3-1/2 turns
Needles have clip 3rd from top, the plastic spacer, then two washers on top of the spacer.

That doesn't look/sound right to me, but always ran fine after warm up. I also don't know a good baseline to start.

Sorry if there is too much "TLR" but offering up what info I know, at the start.

Thx for any help identifying any issues.
That's crazy! Does it have a thermostat installed? You should be able to start it using some choke, but back it down quickly to hold about 2500 RPMs until it will stay running with no choke - which is usually in a minute or 2.

Something isn't right in the carbs. 3 1/2 turns out on the idle mixture is more than any of ours ever needed, and near that amount they didn't run well as they were overly rich.

Is the air filter in good condition and not breaking-down or overly oiled?

Check what the jets are, but normally a "jet kit" is overly rich. DynoJet kits use their own numbering system that isn't the same as OEM jets. The OEM Main Jet is already rich. The needle clip position is on the rich side, and then there are shims raising it more?

I'd also check for a vacuum leak and maybe pull the plugs to get a better idea of what's going on.

Seems like the carbs may need to be gone through (cleaned, adjusted, synced) and maybe the jetting corrected.
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Old September 20th, 2019, 01:37 PM   #3
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Check out this thread for photos of factory exhaust compared to other aftermarket offerings: an exhausting tale!!!

Even with full exhaust, there is no need to increase fuel. It's already too rich in factory configuration (+25-30% too much fuel), with slight mid-range lean spot. I have full exhaust, free-flow air-filter and snorkel-delete and Spears Racing still downsized main-jet on dyno-tuning. Along with DynoJet needle which removes even more fuel in high-end, and more importantly, adds fuel in lean mid-range. Clip is at top position on needle.

Yes, check that you have proper thermostat in place.

Thoroughly clean carbs with flossing of all jets and passages. Ultrasonic soaking and micro soda-blasting. Revert back to factory 38 pilot and 98 main jets. Set clip to top position and set pilot screws to 2-1/2 turns out. Leaning out mixtures from current too-rich settings will make bike even more responsive and faster!
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Old September 21st, 2019, 04:35 PM   #4
GAU-8
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Thanks for the info. I'll be following up on that for the next two weeks.

I DO. have a correction though. On the needles, both have two washers ABOVE the E-clip. Not below as I stated.

Anyways... I do know the airbox is clean, dry. Airfilter is....surprisingly intact, clean and dry. Becaaaaause....

Unfortunately, had an event. The fuel diaphram (?) That prevents the tank from filling up the carbs without suction..didn't. Left side intake and valves, was FULL. Oil sight glass..FULL. Carbs FULL. Garage floor had a nice puddle, and eye burning gas fumes, when I walked into the garage this morning.

-----Here it is as sitting------

There will be NO riding. Whatso ever. ( "meh good enough, lets see how she runs" none of that. Especially with fuel tap in place.

- Gas tank has inline ball valve in fuel line.( tempory fix until rebuild/new unit) Tank is off the bike.

- Carbs fully drained and loosely "installed" on bike.

-Oil was immediately drained.. ( crankcase was FULL of gassy oil).. Currently have fresh pan under it for any additional seepage overnight. Bike is on rearstand to drain forward slightly.

- Pulled spark plugs ( wet of course)

- siphoned out intake valves( left side valves were open, right side intake valves were closed)

- Both cylinders syphoned out.

Anything I missed, or should check?

In the mean time, (probably tomorrow) I will re-dismanle carbs, Berryman carb dip them, blow everything out again ( and get numbers for ya) and benchseat the mixture screws/synch butterflies.


Sorry for typos/odd speech. I'm tired.

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Old September 21st, 2019, 05:26 PM   #5
GAU-8
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In a month or so, I'll probably opt for a full system, and new jet kit, filter, so I know exactly what I am dealing with ( plus the Yoshi can is FUGLY, from students dropping it.)
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Old September 21st, 2019, 10:12 PM   #6
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Quote:
Originally Posted by GAU-8 View Post
I DO. have a correction though. On the needles, both have two washers ABOVE the E-clip. Not below as I stated.
That's better. Stuff above clip makes no difference in needle height. Stuff above just helps spring seat better and prevent needle bouncing. Best to remove everything and set clip on top position.

Quote:
Originally Posted by GAU-8 View Post
Unfortunately, had an event. The fuel diaphram (?) That prevents the tank from filling up the carbs without suction..didn't. Left side intake and valves, was FULL. Oil sight glass..FULL. Carbs FULL. Garage floor had a nice puddle, and eye burning gas fumes, when I walked into the garage this morning.
You've got two problems:

1. First, petcock diaphragm is not sealing. Without vacuum to open it, it should stop all fuel-flow regardless of position. Will need rebuild-kit with new seals. Or new petcock.

2. Second issue is float-valves in carbs aren't sealing. Even IF petcock is leaking fuel into carbs, proper float-valve operation will stop fuel-flow.


Good idea to fix everything before riding. Carbs need complete refurbishment to factory-fresh condition, not just some surface cleaning with dip. Thorough disassembly of every last nut and bolt into individual components. Everything scrubbed and flossed; all jet holes, bleed-holes, fuel-circuit passagesways. Ultrasonic soaking in caustic radioactive solvents. Micro soda-blasting at 100000psi. Only when carbs are factory-clean like when they left factory with 0-miles, will bike run as brand-new.

Riding bike with leaking carbs can be very dangerous.
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Old September 22nd, 2019, 04:16 AM   #7
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Check the tank for rust, and check the screens and inline filter at the carb inlet.

The petcock needs rebuilding or replacement.

Float valves need replacement, but a full carb rebuild kit is in order.
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Old September 22nd, 2019, 11:22 AM   #8
GAU-8
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Danno,

I have found the ultrasonic tub for a good price. But the caustic radiation, only comes in unshielded pellets. With an extremely hi entropy count. Can i get the generic shielding at JcWitney, or shouldI get a well known/reputable Auxiliary Shield Booster? Either way, I'll have to ensure my home is capacitor stable...or i need to buy some CAP charges.
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Old September 23rd, 2019, 08:41 PM   #9
GAU-8
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Got it all rebuilt, back together. Let it run for about half hour. No riding done yet. A few things here n there to tweak. Im sure when I get it driving, probably a few more tweaks after that. No immediate issues as of now.

I'll get through the details, and findings tomorrow. For most part, it's fairly crisp and clean. (Again just sitting, not riding/or moving) Just wanted to thank you guys, and let ya know the current status.
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Old September 24th, 2019, 05:50 AM   #10
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Good job!!!
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