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Discussion Starter · #1 ·
Heads up: This is a 250 Ninja, and the 500 that everyone on the forum is used to. However, I think the problem is pretty generic across all bikes, let alone the big brother/little sister Ninja.

I posed this on the ninjette forum because there are the technical ninja's of the littlest ninja. :) But I'm double-posting over here on EX, as there are some seriously clever mechanics on this forum.

The bike is a non running 2007 250 bought at the start of the year as a project rebuild. The tank and bodywork, as well as the rest of the bike in general, is in pretty nice condition for a non-runner.
Other than a good head-to-toe cleaning of the frame, wheels and plastics, I was hoping it would just take a good carb strip/rebuild/clean, new oil, new spark plugs and we'd be good to go.

Not so much. The bike simply won't start. I confirmed that both cylinders are getting good spark, and just to prove it I was able to start the bike on some starter fluid. I pulled the airbox off the carbs and was able to start the bike by placing my hands over the carb intakes. It would die if I moved my hand away completely. It would restart easily if I covered the carbs with my hands again.
I was starting the bike from an auxillary fuel source, so the tank and petcock (which are very clean) are not part of the equation.

So, what do you think I'm possibly dealing with here? I thinking the choke circuit on the carbs could be a problem. Also the pilot jets. I originally cleaned the carbs in an ultrasonic cleaner, and was sure to make sure the all the holes in the main jets, pilot jets, and emulsion tubes were clear by using a fine guitar wire. I've done a few sets of these in the past, so I'm fairly confident navigating my way around these carbs. But there's always a firs time to screw things up....

Planning to pull and strip the carbs again, and pay extra special attention to jets and the choke circuit. Anything else I should really be looking at here?


TIA.
 

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Lemme start with the fact that I’m not a carb expert. I’m sure @ducatiman will chime in with some sage advice.

That stated, it would appear to me that your engine is in a lean condition, hence it runs when you reduce the amount of available air.

I dunno if that means the intake valves are not opening enough or your carbs aren’t set rich enough, but that’s what logically makes sense to me based on your description of events
 

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yeah I would tend to lean (no pun intended !) to a weak mixture. what your describing is getting it started by applying a manual choke (your hand) instead of relying on the enrichment system. so probable cause. could be too much air not enough fuel. any number of possible causes there,, air leak. fuel levels. restricted jets. carb vents. we all know the 500 doesn't like airbox removal. although it should start even if it runs crap.
being a accomplish spanner man. you will no doubt have made sure you have the correct grade of plugs the timing is correct. the carbs have the correct jets installed and the choke plungers are working. all have for now.
 

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Discussion Starter · #4 ·
Thanks fella. Definitely lean!

Few extra nuggets of info I missed from my original post:

  • Valves were a tad on the tight side, adjusted to middle of the range specified.
  • Float levels are good, verified by checking the height on clear vinyl tubing attached to the float bowl drains.
  • I cleaned and assured smooth operation of the choke plungers.
  • Plugs are good.
  • Timing is good.
  • New air screw/spring/washer/o ring, set to 2.5 turns out.

I'm 99% sure that the jets are good, but I will reinspect and correct as necessary when I pull the carbs.

I've been thinking about this, and I'm leaning heavily towards the choke pickup tubes. Whilst I made certain the plungers were good, I neglected to confirm the pickup tubes were clear using air and carb cleaner. I used air and carb cleaner on the jet passages, making sure that they were clear, but think I may have missed the choke tubes.
 

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Within my carb service, I use a guitar string (much larger that pilot jet .013" size, maybe .016 or .018?) to assure choke pickups are, in fact, clear. Also, be aware of clarity within the pilot/transition ports as well.
 

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Discussion Starter · #6 ·
Within my carb service, I use a guitar string (much larger that pilot jet .013" size, maybe .016 or .018?) to assure choke pickups are, in fact, clear. Also, be aware of clarity within the pilot/transition ports as well.
I got the carbs off the bike, stripped them down and went through the inspect/clean process again. Pilot jets were good as I expected. The internal circuits were also clear, carb cleaner sprayed cleanly through everything tested (pilot jet port / AF screw port / carb body tiny hole on engine side of butterfly).

I poked wire through the choke circuits, and didn't seem to dislodge any crud that I could see. Carb cleaner was flowing cleanly after I finished. The one thing I did discover was a blocked hole halfway up the choke circuit tube inside the float bowl area. I poked out the crud and got carb cleaner spraying cleanly through it.

So, I did find some stuff to clean. But, I'm not confident it was enough to make the difference that I think is needed.

I'll put the carbs back on and give her another whirl....
 

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Discussion Starter · #7 ·
Well, as small as the changes I made seemed to be, they were all that was needed to get the bike running again. Started quickly and easily, settling into a nice idle. Synced the carbs when the bike was warm, good to go.

Likely issue....choke pick tube.
 

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Discussion Starter · #9 ·
was it just 1 or were both pick ups clogged?
Not sure....thinking just 1. Only 1 was blocked for sure at that little mid-point hole up the choke tube.

I wasn't confident it was enough of a fix to cure the problem, but apparently it was.

Spent some time putting stuff back together tonight. Only things left to do are fit the tank, the front faring, front turn signals, mirrors, side panels, belly pan, and seat. About 1-2 hours work depending on how much I take my time.
 

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Discussion Starter · #11 ·
You did post you had "cleaned your carbs" prior to the problem. I'd suggest, going forward, that clearing choke pickups become standard procedure during the process.
No kidding! I was so focused on clean jets and passageways that I mistakenly overlooked the choke pickups. I also falsely assumed the US cleaner would fix all ails, which is not the case. It really helps the job, but you also need the traditional air/wire/carb cleaner combo to make absolutely sure.

Lesson learned....
 
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