Stoopid air bleed/ T mod Tube - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

 
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Old 04-12-2015, 10:56 PM Thread Starter
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Stoopid air bleed/ T mod Tube

Bike's been on the fritz last 4 work commutes backfiring and stumbling really hard n' bad around
5 g's rpms under acceleration.


I did the twist on the carb and took off both ends and did a cleaning, fine wire thru
the jets n' passages, etc. No improvement, even slightly worse. Pinched just a touch
of the diaphram which explained the "worse". I noticed this after pulling off the carb this time.
I have the paint can type carb solvent kit with the basket thingie ya drop in there for 10-15 minutes.
Did that with every piece removed. Nearly naked casting. All the brass
bits dunked in the basket and swished around. The diaphram was held up to the light and gently manipulated
for a full, thorough inspection. Perfect. With the choke cable clearance issues for reattaching the needle
and nut I had the tank off, and of course the sides and seat to get to the tank bolts.
Same problem as when it started.

"Bout this time the Cheapster's gettin' confused cuz it's a lean backfire (blue) and not an ignition issue.
Now the carb has been fully rebuilt. WHAT THE FLIP?????????????

While cruising to work two weeks ago the front T-mod line was swinging loose
in front of the tank behind the radiator. (I had noticed a lean surge at highway rpms a few
years ago and moved the line while riding and the problem stopped.) I stuck the line into a
gap but pinched off the line without knowing it. Today was warm and I'm farting around on the bike
recreating the stall under full throttle 5th gear, etc etc, and it was doing it repeatedly. Drop to 4th
and roll thru the bad spot, the thing catches and runs right up the tach the rest of the way to 6k which is my redline usually.
The lightbulb FINALLY flashes and I yank out the tube and run it down next to the top of the radiator
where originally installed and the problem disappears right then in mid-ride.
It hasn't returned.
I sucks the hours put into repairing a non existent problem due to whether that
line needs to be sucking or blowing, and I am very curious as to how the T-Mod can
affect whether which end of it is doing the emulsifying. I almost wanna
go back to the pink straw running up the inside of the tank after all of that.
All of that, combined with post-addict/alkie memory issues. LOL

There's something to learn here but I'm not sure what. Something about
the tube needing fresh air, but which direction does it flow? Two tubes split
from one makes it better (creating the t-mod)?

That's been my riding life last two hundred miles,
Cheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeea p

This is my son, with whom I am well pleased." ----God
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Old 04-13-2015, 03:44 AM
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Hard to diagnose, whether examining on-site or remotely from the description . . .

All the following may already be known; regrets if I'm telling something already obvious.

My understanding only; could be in error.

Basically, the carb vent line provides atmospheric pressure to the underside of the diaphragm, and, I think, to the surface of the fuel in the float bowl (so fuel can flow through the jets from venturi vacuum). Don't know if you have a Generation 1 or 2; Generation 1 carb vent line opening was about 10" above riding surface; left in stock configuration, subject to flame-out when water crossing level was deeper. Solution: Tee mod, providing alternate path to atmosphere when tube bottom was submerged.

Generation 2 carb vent opening is about 30" above riding surface; less likely to stop up from water crossings up to that depth. Tee mod not so vital for this model.

As to which way air flows in the carb vent tube, the answer is: BOTH ways. When venturi vacuum raises the slide, air flows IN; when venturi vacuum falls and the slide lowers, air flows OUT. Not a lot of flow, in either case; as mentioned, only enough to maintain atmospheric pressure on the underside of the diaphragm.

Given this scheme, an occluded (as in, submerged, stopped up, or pinched) carb vent hose will honk up your carb's ability to deliver mixture proportional to venturi vacuum.

Corrections and clarifications welcomed; regrets if I merely state the obvious and known.

-----------------------------

Alternate cause of symptoms described: Stopped-up fuel tank cap vent; impedes fuel flow into carb by restricting air flow to replace fuel used from tank.

Another thing to check: Petcock fuel flow. Since the problem occurs at higher rpm, the petcock may not be delivering at the desired flow rate.

Regardless: You now have a CLEAN CARB!

Last edited by Damocles; 04-13-2015 at 03:48 AM.
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Old 04-13-2015, 09:18 AM Thread Starter
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Gonna go with a single line up the top tube under the tank but a lil' longer than stock


Thank you for taking the time to reply, Damocles.

Fuel flow is vigorous. Full flow petcock, lines clean, float level good, and it screams
at higher rpms than the stall rpm speed. I think we're good now.........

It used to easily do an indicated 100 mph. It's falling asleep at 90 now leading me
to believe both T-lines are catching negative or positive airflow at speed and not a
two way flow then as much as is needed for a full slide of the piston.

I don't drive 100 but it lets me know it's close but not dead on yet as far as
mixing and airflow. Especially WOT airflow as it seems the slider isn't getting
fully out of the way. The wind blast as we know comes upwards in front of the tank.
I need to try sideways rather than up or down next on this now annoying lil' hose. LOL

The rain is present and steady today so a test'll have to wait till after works n' sleeps.

This is my son, with whom I am well pleased." ----God

Last edited by CheapBassTurd; 04-13-2015 at 09:47 AM.
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Old 04-14-2015, 02:43 AM Thread Starter
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Been thinking on it a bit.

Rolled it into the garage/shoppe and capped off the rear tube.
That's all so far. It's very much turbulent between the tank and fairing
and I feel the line needs to end in "dead air". I'm thinking top tube under the tank
or going further forward behind the instrument cluster. Got tomorrow off to play
with myself, er, the bike.

This is my son, with whom I am well pleased." ----God
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Old 04-16-2015, 04:25 AM Thread Starter
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Ran the batcycle hard today.

The back t-mod tube is plugged up and the front one along the frame rail protruding
in front of the tank about 8 inches flops in the wind blast or can be pinned a few places
and angles to the upwards blast. (if you so choose to run yours that far)

Running it down and left against the radiator cap: normal with a slight stumble at
a steady 60mph. Accelerated thru it easily. Topped at indicated 90 mph.

Straight down along the radiator: No stumble, 93 mph.

Straight up into the risers and cables: Ye-friggin' ha !!!!!
Pulled hard from idle to 6400 rpms showing 94 and still climbing when I let off.

This location of the tube-end seemed to be in a dead spot just missing the rush
of air. My opinion formed is that neither positive pressure nor vacuum at the
emulsion tube helps performance. The carb works best balancing the slide piston
height with the butterfly position without our interference. The T-mod isn't necessary
on gen 2's unless you cross water as deep as the tops of the tires.

This was on 15/42 sprockets, snorkel gone, cored exhaust, stacked needle, and 150
main. Wind was from the side a bit. Nice repaved Indiana 6 mile straightaway.
(yes there's crazy twisties too where I live near the big lake.)

Have an emusified day,
Cheeeeeeeeeeeeeeeeeeeeeeeeap

This is my son, with whom I am well pleased." ----God
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Old 04-16-2015, 01:03 PM
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Damocles,
I beg to differ about the 'pink vent hose' supplying Any Air to either side of the throttle slide diaphragm. It only supplies atmospheric air pressure to the Float Chamber!

The 'eye-brow' shaped vent at the top of the carburetor intake bell throat supplies Filtered air to the underside of the throttle slide diaphragm. The small hole ahead of the mid-range jet needle, supplies filtered negative pressure (vacuum) to the top-side of the diaphragm.

CBT,
On the '08 and up KLR's, I always pull the pink hose out from along side the frame rail and route it 'up and over' the Large frame spine. Then Down alongside of the 1/4" Black rear fuel tank vent hose to near the top of the shock. Just don't let the blunt end rest on top of the shock adjuster, cut it at a 45 degree angle.

If I do the 'T-mod', the top hose is routed forward under and alongside the frame spine to the rear edge of the 'steering head gusset', and tucked Back into the L.H. Front corner of the tank puck mount.

These 2 different ways make a 'sink trap', to keep any water out and in calm air.

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 84,000+ miles & counting
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Old 04-16-2015, 01:25 PM
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I like Damocles could be wrong, but I had my carburetor apart last week and am fairly certain that the area under the diaphragm is connected to the intake manifold side of the carburetor throat. The float bowl vent of course connects to a nipple on the left side of the carb and is ported across the the right side also and both sides have openings into the area above the float bowl to provide atmospheric pressure to the fuel in the bowl.

I wonder why your vent is run up under the tank instead of back over the fender next to the battery like on the stock gen2 KLRs.
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Old 04-17-2015, 02:42 AM Thread Starter
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This is getting weird.

The tube connects to a nipple above the fuel line. There doesn't seem to be a float
tank vent but one of the many interior passages could be doing that job. I moved the hose
a few times on the way home from work and got it to stumble again, and also found
the sweet spot again.

At this point I feel that the mentioned spot behind the steering head gusset sounds
like a great spot for permanent mounting. Interesting topic as it hasn't been talked
about nor tested much. We can learn from each other which is one reason I posted
the steps I was taking and each result.

Still, this only happens at speed. First 3 gears run perfectly all the way up the tach.
Once it gets windy things start to change if our hose is out flopping in the breeze. LOL

This is my son, with whom I am well pleased." ----God
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Old 04-17-2015, 09:06 AM
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Quote:
Originally Posted by GoMotor View Post
I like Damocles could be wrong, but I had my carburetor apart last week and am fairly certain that the area under the diaphragm is connected to the intake manifold side of the carburetor throat.
Maybe so; I thought manifold vacuum above the diaphragm, and atmospheric pressure on the underside of the diaphragm, raised the slide.

Thus I thought (perhaps incorrectly) manifold vacuum was routed to the mixing chamber area above the diaphragm, and the area under the diaphragm vented to atmospheric pressure.
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Old 04-17-2015, 10:33 AM
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Quote:
Originally Posted by CheapBassTurd View Post
This is getting weird.

The tube connects to a nipple above the fuel line. There doesn't seem to be a float
tank vent but one of the many interior passages could be doing that job......................
The nipple above the fuel line nipple is the float bowl vent connection. You say the line connected to that nipple runs forward under the tank. I am curious about that. On all other KLRs I have heard of (many) including my two, that carburetor vent line runs toward the rear. Did you change the routing of the carburetor vent line or did a previous owner?
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