Air/Fuel Mixture on newly rebuilt OEM Carb... - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 21 Old 09-04-2018, 07:39 PM Thread Starter
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Air/Fuel Mixture on newly rebuilt OEM Carb...

Okay, so did the 'F*&% the .22c mod' to my Carb
(YouTube's "KLR 650 Carby Mods").
It's back on the bike and it was running 'last night (big night... BIG!)...

When setting the Air/Fuel, was instructed to:
'initial setting of Air/Fuel Pilot screw is 2.25 turns out', then
Start motor,
'screw in Pilot screw 'til engine almost dies',
'screw out 'til engine revs too high (counting turns)', and
'screw in half the # of turns you screwed out 'til it revved to high',

and that's how we make our Air/Fuel Mixture.

Having said that, she's running beautifully (no test ride just yet... coupla things to finish off),
idles smoov, sof and silky (12-1300rpm), and
I'm anticipating runs as intended (we'll see this weekend, and I recognize this needs to happen to further 'test' the carb).

My Q is this:
How do I know when I've set the proper Air/Fuel Mixture? It seems to me that MANY settings, albeit all pretty close to each other, would run the carb effectively sitting on the Lift like it is.
I've heard of smelling the exhaust (excess fuel), etc, but I wouldn't really know the indicators of 'too rich/lean'. And I understand 'TOO' of ANYTHING can really put the hurts to a Motor.

SO, how will I know I've "set it right" because, right now, despite my results, I'm not so confident it's correct to ensure no future Motor damage.
Thanks Fellers.
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post #2 of 21 Old 09-05-2018, 11:28 AM
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If you're at 1.75 - 2.25 turns out and it runs fine, you're good to go.


Dave
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post #3 of 21 Old 09-05-2018, 12:31 PM
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I watched that video a couple of days ago. I believe that Glenno (Aussie) is doing this to a Mikuni carb. Not the Keihin that comes on the USA version of the KLR. If that makes a difference I don't know.

Last night I just did the KLX needle, clip set at second notch from top with collar on top of clip, 142 main jet, lightened and drilled slide, three coils cut off of spring, and the air screw set at 2.25 turns out. Still waiting for my Uni filter. I have 6 holes drilled in the air box (2 on top and 2 on each side) and I am running a Big Gun head pipe and muffler with spark arrestor.

When I lived in NorCal I was at sea level and ran a Dynojet needle on 2nd notch with 148 main jet and 2.75 turns out. It ran fine with no popping. But up here in Idaho at 2600 ft elevation it was running really fat, so that was what prompted the KLX needle mod & jet change. Hoping to lean it out just a bit.

I have the Thermo-Bob 2 and will be installing it next.

Last edited by melbakid; 09-05-2018 at 12:47 PM.
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post #4 of 21 Old 09-05-2018, 12:42 PM
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Ain't no thang, AFAIK.

Fuel screw only dominates mixture well below 1/4 throttle, according to, "Care and Feeding of the CVK40 Carburetor."
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post #5 of 21 Old 09-05-2018, 06:44 PM Thread Starter
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CAN'T be that easy... RIGHT!

Quote:
Originally Posted by DPelletier View Post
If you're at 1.75 - 2.25 turns out and it runs fine, you're good to go.
Dave
That doesn't work for me DPelletier... I am an OverThinker and there has to be much more work involved spiced with a little heartache, fear and worry so I'm having alotta trouble with your response...
NOT!
How easy is that?!?!
I'll do it Fri morning (work you know) and run it up and down the street a coupla times to see how it works out.
'Really appreciate that DP!
MelbaKid... it's the same carb as mine though I'll admit that I did double-check!!!
Thanks for the input fellers!
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post #6 of 21 Old 09-05-2018, 09:36 PM
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Quote:
Originally Posted by melbakid View Post
I watched that video a couple of days ago. I believe that Glenno (Aussie) is doing this to a Mikuni carb. Not the Keihin that comes on the USA version of the KLR. If that makes a difference I don't know.

Last night I just did the KLX needle, clip set at second notch from top with collar on top of clip, 142 main jet, lightened and drilled slide, three coils cut off of spring, and the air screw set at 2.25 turns out. Still waiting for my Uni filter. I have 6 holes drilled in the air box (2 on top and 2 on each side) and I am running a Big Gun head pipe and muffler with spark arrestor.

When I lived in NorCal I was at sea level and ran a Dynojet needle on 2nd notch with 148 main jet and 2.75 turns out. It ran fine with no popping. But up here in Idaho at 2600 ft elevation it was running really fat, so that was what prompted the KLX needle mod & jet change. Hoping to lean it out just a bit.

I have the Thermo-Bob 2 and will be installing it next.
When doing above process, what is the purpose of cutting coils off spring? I also just did KLX needle,142.5 jet, drilled slide, second notch down and 2 turns out on air mix screw, initially I had it at 2.25 but the exhaust smelled peculiar, not like unburned fuel but different from before. BTW the change removed the "rich" smell. Running good now except the flat spot is still there. By raising the needle or lowering clip , I hope to remove the flat spot, and while I am in there should I cut e few coils off as well?? ANYONE? Also air box mod, desnorkled with Lexx exhaust, which I think sounds great , the design is shit at the mid-pipe though
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post #7 of 21 Old 09-05-2018, 09:52 PM
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Cutting coils is done in an effort to improve throttle response.

However, the procedure can be counter-productive.

SHORTENING a spring actually STIFFENS it; greater force is required to displace a shortened spring.

The imagined throttle response occurs because of a change in the OFFSET of the altered spring; once that excursion is taken up, raising the slide required additional force per distance displaced.

Don't believe shortening a spring stiffens it? While the notion may be counter-intuitive, it's valid.

Try it!

Take a spiral screen-door spring, say 2 feet long, and stretch it. Then, cut it in half, and stretch the segments. Cut off a half segment, and stretch it. Cut off a one-inch length, and stretch it. Was it easier, or harder, to stretch the shorter springs the same distance, as you progressed on this experiment?

Formulas for calculating force vs. displacement for springs (found on the Internet) confirm the premise, but . . . YMMV!
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post #8 of 21 Old 09-05-2018, 09:59 PM
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Quote:
Originally Posted by Damocles View Post
Cutting coils is done in an effort to improve throttle response.

However, the procedure can be counter-productive.

SHORTENING a spring actually STIFFENS it; greater force is required to displace a shortened spring.

The imagined throttle response occurs because of a change in the OFFSET of the altered spring; once that excursion is taken up, raising the slide required additional force per distance displaced.

Don't believe shortening a spring stiffens it? While the notion may be counter-intuitive, it's valid.

Try it!

Take a spiral screen-door spring, say 2 feet long, and stretch it. Then, cut it in half, and stretch the segments. Cut off a half segment, and stretch it. Cut off a one-inch length, and stretch it. Was it easier, or harder, to stretch the shorter springs the same distance, as you progressed on this experiment?

Formulas for calculating force vs. displacement for springs (found on the Internet) confirm the premise, but . . . YMMV!
Soooo...shortening spring not needed or not recommended. Thanks D. Youre a scientist or something brainy. hehehehehe that not the first formula you have cited. Right on man, no offense just recognizing
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post #9 of 21 Old 09-06-2018, 01:56 PM
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I shortened the spring as an experiment to see if it would help. But, before doing so I made sure to order a new spring with my KLX needle in case it didn't meet with my expectations. It is an easy enough job to replace the spring if needed.

My Uni filter came in today but, the filter was not oiled. The oil & cleaner did not come with the filter and were shipped separate. So, I will have to wait for that to arrive.

I also will be doing the Thermo-Bob 2 mod on the bike while I have the tank and plastics off. Will also being doing a repair on the broken pegs on the radiator shrouds while the bike is apart.
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post #10 of 21 Old 09-06-2018, 05:22 PM Thread Starter
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Spring cut is indeed to improve throttle response and I do notice it more 'snappy' than before.

Notwithstanding Damocles Engineering Presentation (some-a these guys are just TOO-DANG smart), I've found that I like it mo' betta! I don't know the science of it all, but the cut slide spring sounded reasonable, AND I DID AS YOU DID MELBAKID... had another OEM on standby, JUSTEN KASE you know!!! Trust me, it was a 'measure 23 times, cut once' EVEN WITH THE BACKUP SPRING!

I'm very pleased (so far) with the "Glenno's Garage" version of a 22c mod. "So far" means I've not done a TestRide (tomorrow morning... OhPleaseGod, OhPleaseGod). But it's looking good! More later.

BTW, I've nothing against the work MelbaKid is doing... it's very wise and schmart to check your options. I just don't have the knowledge, time, wherewithal or even confidence to go outside an instruction box (make it up on my own... not with the carb man). I've chosen to make my mods, call it good and just go with it. I don't have 3 Race Teams with Chase Trucks following me every weekend I get to go out on my KLR (DPelletier... SHEESH Therefore I've decided I'm not toooooo terribly concerned about my bike doing very much more than it already does.

More power to ya'll with the knowledge and the abilities! And as I read all ya'll's 'stuff' I'm learning quite a bit here... YaY!
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