Thread: 250 only starts if intake covered.
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Old May 3rd, 2021, 06:51 AM   #2
jkv45
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Name: Jay
Location: WI
Join Date: Jul 2013

Motorcycle(s): '06 SV650n, '00 Derbi GPR, '64 CA77 Dream 305, '70 CL450 Scrambler, numerous dirt bikes

Posts: A lot.
MOTM - Jun '18, Oct '16
Quote:
Originally Posted by davenay67 View Post
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.
Yes - something isn't right with the carbs.

Did you remove the idle mixture screws and make sure the passages are clear? O-rings can break and get lodged in the passages also.

Float levels correct? Bench sync the carbs, then confirm with vacuum gauges?

Set the idle mixture screws at 2.5 turns out for starters, and tune precisely when running and fully warm.

Make sure the gas is fresh and the tank is clean.

Some tips in this section - https://faq.ninja250.org/wiki/Intake
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