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I have a 2005 KLR 650 with 25,000 miles. I've had the bike now for 4 years. First time I checked the valves it had all the same thickness shims. After setting the shims it helped the starting. I cleaned the carb and put a kit in it, idle was so so. Sometime to high sometime stalling. Replaced carb with one from ebay.. Cleaned replacement carb and installed kit. Better running but still not right. Now I started out checking the valves again. Intake clearance fine, exhaust both to tight. Installed replacement shims before starting both were .025MM. Cleaned carb again and installed another kit. Now will only idle with choke(enrichment) half on, also backfires. What am I missing? What are the small holes in the area of the throttle plates?



Hate to admit this but I teach a high school auto tech class. By the way this carb is like the Ford Variable Venture carb that was a pain in the butt.
 

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The 3 low speed transition holes get all of their fuel from the Pilot jet as does the external idle mixture screw. All 4 must freely flow fuel when sprayed up thru the pilot passage.
I use a tiny wire bent 90 degrees to poke down thru them before and after soaking, rinsing & drying carb body. Best to close mixture screw to see the flow from the 3 transition holes.
When every thing is clean, exposing 1 & 1/4 of those 3 holes with idle speed screw gets idle speed close for initial start-up.

Read the link in this link and then watch the videos, https://www.klrforum.com/how-tos-tech-guides/45258-care-feeding-cvk40.html
 

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Diaphragm air leak (tear or not assembled correctly) can cause the symptom described.
I really don't think that is correct.

I believe that one could possibly totally remove the vacuum slide & mid-range needle and a properly clean starter jet, pilot jet / low speed system would start, warm-up, idle and respond to the first 1/8th of throttle normally.
Everything above those low rpms would not operate. Would be WAY Too Rich to run in thru the mid-range to build enough rpm to run cleanly on the still functional main jet.

Just read how many owners have accidentally left out the mid-range needle Jet from above the emulsion tube / main jet holder. Too rich at 3/16 - 1/4 throttle & up. But they start & idle & begin to respond to throttle.


With the "back-fires", I should have inquired about a fresh spark plug, mrautoteacher? And I am assuming it has Fresh Fuel.
 

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I really don't think that is correct.
While the contradiction is welcome (as always), respectfully, I am absolutely certain, to the extent of my knowledge and belief, my statement IS correct (YMMV).

Been there, done that. Diaphragm air leak (from faulty carburetor assembly; you, know, the lip around the carburetor casting beneath the 4-screw plastic cap); bike would run only with "choke" (or, if you prefer, enricher) plunger retracted from carburetor orifice (as in, "choke" ON). Assumed: Without adequate vacuum above diaphragm and slide, slide would not rise, preventing sufficient venturi flow for vacuum required for fuel flow from jets. Result: Excessively fuel-lean mixture, without enricher activation.

Or . . . hallucinating, again!

:)
 

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Ah, but there is not enough air flow under the slide to create any vacuum above the slide during cold start enrichment, nor at idle speeds, nor at 1500 - 2000 rpm with No Load on the engine.
(The cold start enricher lets its air & fuel thru from below the diaphragm and above the throttle plate. Vacuum in that area during cold starts should actually try to assist the spring in holding the slide down.)

Next time I have an 'easy access' Bayou 300 carb job, I'll leave the slide & needle out initially to attempt to confirm or disprove my statement. :)
 

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Next time I have an 'easy access' Bayou 300 carb job, I'll leave the slide & needle out initially to attempt to confirm or disprove my statement. :)
I'd think leaving the slide IN, but in its downmost position, would result in a more valid test, because . . . with insufficient vacuum above the diaphragm (as in the case of an air leak), the slide would not rise appropriately.
 

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Useful diagram, Jason!

I see the IMS (Idle Mixture Screw) has influence essentially only up to 1/8 throttle. Makes sense, to me!
 

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From the simple minded...I had some of the same. It was directly related to the "choke". Installed a new cable, set it up properly and...fine now.
 
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