Help needed diagnosing carb issue

[gitter]

Hey all,
Havent been on here in a while, but currently have a couple of 250's in the garage and one of them needs some carb work.

First off a little back ground on the bike:
2006 with 1304 miles on it. Owner let it sit outside for a few months and I bought it as a non starting project.

I can get it to start with the choke on, but once the bike warms up (and it takes a little longer than it should) the idle is rough, dips, hangs if you rev it, sometimes it will rev fine, other times it will stumble and not go past 5 or 6k rpm. Also when i took the carbs off, i noticed there was a decent amount of gas in the boots between the carbs and the motor.

So far ive broken the carbs down and cleaned them, replaced the main and pilot jets with fresh 105/35 jets. Idle screws are 2.5 turns out. checked the diaphragms and they look like theyre in good condition.

In any case, I could use some help diagnosing what could possibly be wrong and where to go next.

Thanks
Gitter

[Ghostt]

Did you check the float height? Replace the float valves? Verify all fuel circuits are clear with an air compressor?

[gitter]

Haven't checked float height yet. I think I have a spare set of valves I'll drop those in and see how it does. Also, is there a list or maybe some picture ls that show the different passages that need to be checked? I got the obvious ones where the jets are but simply for the sake of being thorough I want to make sure I didn't miss one

[csmith12]

Welcome Joel!

Why 105's? Stock airbox and exhaust?

[gitter]

Yeah everything is stock, that's why I decided to go with the stock 105 jets.

[Ghostt]

Good call on the jets.

As far as passages goes, the jet holes, also make sure the emulsion tubes part# 13091 are clear as well.

Make sure the idle circuit is clear, from the jet side, idle mixture screws, and inside the carburetor, check any hole as well.

Make sure you've assembled them correctly. Common mistakes are the assembly of the diaphragm, and needles, and the other is part # 16017. Also the small washer and O-ring on the idle mixture screws.

If your in need for carburetor services and parts PM @ducatiman, his prices are extremely affordable.

[gitter]

Emulsion tubes are clear, pulled them out and checked when i replaced the jets.

Did a quick google search- would a good step be re-clean and blow out all these spots with compressed air? http://n4mwd.blogspot.com/2013/10/se...-passages.html

As far as making sure theyre put together correctly, I'll break them down and put them back together again. This is the first 250 ive had that the carb problems havent been solved by swapping in clean jets and cleaning the jet holes.

For adjusting the float bowls, is there a walk through somewhere? I found the one in the how to section but i was hoping to find one with pictures

[gitter]

Also, just to rule it out, at only 1304 miles, valves being out of spec should be a non issue right?

[Ghostt]

Here's a link
http://faq.ninja250.org/wiki/How_do_..._the_floats%3F

And picture

Float height is very important for the tuning, and one of the most overlooked.

[HoneyBadgerRy]

Stock Pilots are 38s that could be a cause of your problem.

[rojoracing53]

Hanging idle is a sign of an air leak in the carb system. A simple vacuum leak will make it impossible to get a consistent idle.

[Ghostt]

I agree, but without being 100% sure the carburetors are right, you'll be chasing your tail.

You need to cover the basics, carburetors are correct, petcock, tank vent, spark plugs, and caps, and valves adjusted.

[HoneyBadgerRy]

Originally Posted by rojoracing53

Hanging idle is a sign of an air leak in the carb system. A simple vacuum leak will make it impossible to get a consistent idle.

Not necessary a air leak, it just means its lean. Which could be caused by his small pilots.

[gitter]

didnt even think to double check the pilot jet size before i ordered

took the carbs back apart, blew everything out, checked the floats, put everything back together. Also forgot to add in the original post that i put fresh plugs in.

With the idle screws turned out three turns, it will idle fairly well. Seems to pull decently well at neighborhood speeds. Has a bit of a flat spot around 3 or 4k rpm. Gonna let it sit over night and check it again in the morning to make sure it will warm up properly before i button everything back up.

I'll post back and let you guys know how it goes. Should i order 38's or just stick with the 35's if they seem to be working?

[HoneyBadgerRy]

Originally Posted by gitter

didnt even think to double check the pilot jet size before i ordered

took the carbs back apart, blew everything out, checked the floats, put everything back together. Also forgot to add in the original post that i put fresh plugs in.

With the idle screws turned out three turns, it will idle fairly well. Seems to pull decently well at neighborhood speeds. Has a bit of a flat spot around 3 or 4k rpm. Gonna let it sit over night and check it again in the morning to make sure it will warm up properly before i button everything back up.

I'll post back and let you guys know how it goes. Should i order 38's or just stick with the 35's if they seem to be working?

In the end you will probably be better off with the idle screws screwed in and bigger pilots, but before you buy the pilots try to shim the needles to see if it helps the 4k flat spot. I know on my bike the needles are very sensitive very early.

[ducatiman]

the difference between 35 and 38 may seem insignificant, but its not and is very likely causing your issues.

In doing others carbs, I routinely "index" (measure) the pilots...can vary wildly even though marked a given size. "Hogging out" jets is, evidently, a fairly common practice and can reveal causes for weird symptoms.

Back to OP's case...the factory called for #38....I'd strongly suggest to get them back in there.

[gitter]

I have some spare 38's from previous 250 projects. Do these look too beat up to use?

[ducatiman]

Though not pretty, yes, they CAN be used. The actual metering orifice lies deep within the jet, not affected by the mauled head. If you choose, you can order new ones for next time you go in there.

Just one note...if the outer circumference of the mauled head is nicked (deformed out of round), jet removal may be problematic....high spots may cause interference... not allow the jet to "drop out" of the pilot orifice when loosened. There is not much clearance there. You can carefully file any nicks causing high spots.

Correct fitting screwdriver for soft pilot jets essential, using plenty of downpressure during removal....mauled heads are the aftereffect if compromised.

[jkv45]

Installing new oem jets always gives you peace of mind and a good starting point for tuning. On a used cycle, that's obviously been worked on, you never know if someone has reamed 'em out.

It's just not worth messing around with questionable parts when you are going through a carb. That, and make sure they are totally, completely, absolutely, clean before you call it good.

[ducatiman]

indexing (measuring) immediately separates the good from the bad....

agree with automatic replacement of hogged out or badly mauled pilots...

but if found to be unbastardized nothing wrong with reuse (after thorough clean)

[HoneyBadgerRy]

Originally Posted by ducatiman

indexing (measuring) immediately separates the good from the bad....

agree with automatic replacement of hogged out or badly mauled pilots...

but if found to be unbastardized nothing wrong with reuse (after thorough clean)

How would a normal person measure and index a jet. I have way more tools than the average person, and If it was even in question the jets weren't genuine I would just bin them and buy new ones.

[gitter]

Originally Posted by HoneyBadgerRy

How would a normal person measure and index a jet. I have way more tools than the average person, and If it was even in question the jets weren't genuine I would just bin them and buy new ones.

I'm also curious how this is done. On a side note, put those 38's back in, bike warms up and idles like a champ now. still a bit of a flat spot around 4k, but it lessens once the bike is warm

[HoneyBadgerRy]

Originally Posted by gitter

I'm also curious how this is done. On a side note, put those 38's back in, bike warms up and idles like a champ now. still a bit of a flat spot around 4k, but it lessens once the bike is warm

I'd say for sure shim your needles, sounds lean at 4k.

[ducatiman]

Originally Posted by gitter

I'm also curious how this is done. On a side note, put those 38's back in, bike warms up and idles like a champ now. still a bit of a flat spot around 4k, but it lessens once the bike is warm

a hobby drill set aka "pin drills", using the dull shaft end, optionally can use various sized guitar strings (must be ID'd with correct size)

examples
#35 jet is .35mm= .0137"
#38 jet is .38mm= .0149"

using drills or guitar string as a "go, no go" reference...kinda like feeler gauges whilst checking valve clearances

Impossible to confirm by eyeball...hogged out jets will stand out like a sore thumb using this method.

PS I always stock a set of *new* 35's and 38's just in case, along with usable accumulated spares, offering folks the choice.

Merry Christmas and Happy Holidays , y'all!