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Troubleshooting carbs

Started by Monsterlover, August 06, 2011, 10:25:23 AM

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Monsterlover

August 06, 2011, 10:25:23 AM
First of all, all I know about carbs is that when the bike doesn't run right it's probably a problem with the carbs.

Secondly, I'm having an issue with my KTM 950smr.  I figured id ask here since carbs basically work the same way and I trust you guys more than those guys.

Once it's running, all is well.  No flat spots, no sutters, just the front in the air (if I want) and my eyeballs flattening.  The bike really rips and I get great (IMO) fuel mileage (40 no matter how hard I ride)

However, in the mornings it has become hard to start.  Even with temps in the high 60's i have to use the choke (which I thought was a hot start lever, but dealer said it's a choke)  It will kick on one cylinder, then both and will try to run.  I have to thumb the starter a couple times to get it going.

Once it fires up I can kill the choke, give it a couple quick throttle blip to help clear it out and it's fine.  There's also a grey cloud out the pipes which I'm guessing is unburned fuel.

I have a 40 mile commute one way.  After the bike has been sitting all day I can go outside and start it on the first try with no choke or application of throttle.

I stopped by the dealer and the main guy wasn't in, but one of the other tech minions suggested draining the fuel from the bowls in case there was debris or water in there.

Any ideas on where I might look?

/fuel injection ftw
//carbs = debil
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

CX500

#1
August 06, 2011, 02:20:59 PM
Hey there,
Seems odd that it doesn't want to start cold with the choke on.
If it has a vacuum-operated petcock that went bad, it could cause problems when the bike sits.
It also could be bad gas.  Draining the tank and running new stuff could make a difference.
That would be the first thing I would try -- no wrenching or disassembly.
'96 M900 -- Still get tingles  before each ride.

2-Skinny

#2
August 06, 2011, 02:46:00 PM
Pilot jets...
I don't own a Ducati...but I wrench on one.

Monsterlover

#3
August 07, 2011, 05:36:17 AM
Quote from: CX500 on August 06, 2011, 02:20:59 PM
Hey there,
Seems odd that it doesn't want to start cold with the choke on.
If it has a vacuum-operated petcock that went bad, it could cause problems when the bike sits.
It also could be bad gas.  Draining the tank and running new stuff could make a difference.
That would be the first thing I would try -- no wrenching or disassembly.


I'm pretty sure the pump is ok. Probably not bad gas either. I probably run through 3-4 tank fulls a week from different stations

Quote from: 2-Skinny on August 06, 2011, 02:46:00 PM
Pilot jets...

I'm gonna need more explanation. And, if its a clogged jet why is it only clogged in the morning ?
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

ducpainter

#4
August 07, 2011, 06:13:52 AM
I don't think it's necessarily a carb 'problem'.

If it runs right when it starts it's more likely something simple like an idle adjustment, or a synch adjustment.

How is the idle speed?
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Monsterlover

#5
August 07, 2011, 07:11:01 AM
Idle speed is the same as always afaik. No tach so I go by ear.
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

Monsterlover

#6
August 07, 2011, 07:20:27 AM
Here's a quick phone video

It actually started a little easier this time.

950smr hard start
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

ducpainter

#7
August 07, 2011, 08:13:30 AM
Quote from: Monsterlover on August 07, 2011, 07:11:01 AM
Idle speed is the same as always afaik. No tach so I go by ear.
Say what?  ;D

I'd have the idle speed and synch checked, or find out how to check it yourself, and go from there.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


CX500

#8
August 07, 2011, 10:27:22 AM
To me it sounds like its not even firing right away.  After sitting overnight, you could check the float bowls by opening the drain tubes, and see how much fuel runs out.
I have had a couple problems in the past with both vacuum operated petcocks (I switched to a fuel valve), and with vacuum operated fuel pumps on the monster.
I don't know if you have a fuel pump, but on the monster, it just pulses with the intake vacuum and helps pump fuel to the float bowls.  If one of the diaphragms splits, it allows fuel to seep down the vacuum line straight into the intake for the cylinder.  The result is similar to what you are experiencing.
I guess I am trying to suggest checking the easy-to-get-at components first.  Carb float valves that are not seating are also a common issue, but will probably require pulling the carbs.
Good luck.
'96 M900 -- Still get tingles  before each ride.

2-Skinny

#9
August 07, 2011, 10:34:53 AM
Carbs have lots of small parts, but if you take your time and keep track of your parts they aren't hard to disassemble, clean/check, and reassemble.

As far as why pilot jets would only be when starting- since the carbs work off of vacuum the pilot jets are what run at starting, to "get fuel flowing" so to speak before the bike develops consistant vacuum and fuel flow is handled by the main jets.  There are lots of nooks and crannys in a carb and small vacuum ports that could be clogged in there too. 

This may not be the problem in your case, but the symptoms are similar to other bikes I have dealt with.
I don't own a Ducati...but I wrench on one.

Monsterlover

#10
August 07, 2011, 02:28:00 PM
Just a quick update-

Out of curiosity, about 4 hours after I shot that video I tried again to start it.

Fired up with no choke in about 2 seconds and idled perfectly. It hadn't run today any more than in that video from this morning.
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

koko64

#11
August 09, 2011, 05:00:27 AM
Watching with interest. As mentioned a few things could be causing the problem.
At a guess a gummed up float needle may be clearing itself with a good thrash.

Did it smell rich when it blew grey smoke? A tap on the float bowls with back of a screw driver may help seat those needles if they are gummed up with waxy fuel additives.

Be interesting to see if it starts better or worse with choke when cold.
2015 Scrambler 800

Monsterlover

#12
August 10, 2011, 01:08:54 PM
Hey just a quick carb update.

Now I'm not sure what's up.  The bike seems fine.

I shot that video sunday, then a few hrs later it started with no choke and idled right off the bat.

It sat until this morning where it again started with no choke and idled right off the bat.

I don't know what to think.
"The Vincent was like a bullet that went straight; the Ducati is like the magic bullet in Dallas that went sideways and hit JFK and the Governor of Texas at the same time."--HST    **"A man who works with his hands is a laborer.  A man who works with his hands and his brain is a craftsman.  A man who works with his hands, brains, and heart is an artist."  -Louis Nizer**

koko64

#13
August 10, 2011, 04:05:01 PM
Great to hear.

Just ride and observe. Varnish, gum, etc may have cleared. Float settled. Crap in fuel burned, etc.

She got better!
2015 Scrambler 800

ducpainter

#14
August 10, 2011, 04:07:30 PM
Probly it was the full moon. ;D
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


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