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Post by zummerp on Mar 17, 2018 17:04:09 GMT -5
I keep thinking I have it nailed and then I get a setback with my carb tuning. First off, anyone recommend a good set of pilot jets to play with? I ordered a new 20mm Keihin clone and it was working great. Starting today, the idle slowed to an uncomfortably low level so I opened up the idle screw a couple turns and it improved. It still isn’t doing great during initial acceleration so it seems like maybe the pilot isn’t quite big enough, which seems odd since it’s a #38. One thing I haven’t touched at all is my needle - could that be contributing? Is it easy to adjust assuming I have an adjustable one?
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Post by jackrides on Mar 17, 2018 17:45:31 GMT -5
Needle probably not the issue. Miles since last valve adj?
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Post by zummerp on Mar 17, 2018 18:10:00 GMT -5
Needle probably not the issue. Miles since last valve adj? Never adjusted them that has always really intimidated me. I guess it’s time to try!
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Post by jackrides on Mar 18, 2018 11:21:04 GMT -5
Go to Four stroke engine tech sub-board for videos on how to. If the valve cover doesn't come off after unbolting, rap it once with the plastic end of the screwdriver. Flywheel; when the 'T' is lined up, be sure it is at the top of the compression stroke, not at the top of the exhaust/intake stroke (if it is, you will see one or the other valves move of you rotate the flywheel 30 degrees either way; if that happens, rotate the flywheel one full turn). Find the best angle to hold the gauge. When it is adjusted right, a smaller gauge has no resistance to push or pull, a larger gauge has a lot of resistance. Note, when you lock down the nut, the clearance will change a little, that's fine, just compensate with a small fraction of a turn, tighten down, and measure again.
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Post by zummerp on Mar 18, 2018 12:21:27 GMT -5
Go to Four stroke engine tech sub-board for videos on how to. If the valve cover doesn't come off after unbolting, rap it once with the plastic end of the screwdriver. Flywheel; when the 'T' is lined up, be sure it is at the top of the compression stroke, not at the top of the exhaust/intake stroke (if it is, you will see one or the other valves move of you rotate the flywheel 30 degrees either way; if that happens, rotate the flywheel one full turn). Find the best angle to hold the gauge. When it is adjusted right, a smaller gauge has no resistance to push or pull, a larger gauge has a lot of resistance. Note, when you lock down the nut, the clearance will change a little, that's fine, just compensate with a small fraction of a turn, tighten down, and measure again. Just finished - took 2 tries. The first time I had a pretty obvious rattle so tried again and got it to a good place. It didn’t solve my issues but I have another maintenance routine under my belt now I’m getting frustrated so I think I’ll pause for a couple days so my hobby doesn’t become a chore.
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Post by 3strokeengine on Mar 18, 2018 18:16:55 GMT -5
I keep thinking I have it nailed and then I get a setback with my carb tuning. First off, anyone recommend a good set of pilot jets to play with? I ordered a new 20mm Keihin clone and it was working great. Starting today, the idle slowed to an uncomfortably low level so I opened up the idle screw a couple turns and it improved. It still isn’t doing great during initial acceleration so it seems like maybe the pilot isn’t quite big enough, which seems odd since it’s a #38. One thing I haven’t touched at all is my needle - could that be contributing? Is it easy to adjust assuming I have an adjustable one? Get a can of carb spray and spray it around the rubber intake manifold and see if the idle changes, it sounds like a typical vacuum leak. Another thing worth testing is seeing if the automatic choke plunger is fully extending, if its not it will cause lots of idle problems
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Post by zummerp on Mar 18, 2018 18:52:20 GMT -5
I keep thinking I have it nailed and then I get a setback with my carb tuning. First off, anyone recommend a good set of pilot jets to play with? I ordered a new 20mm Keihin clone and it was working great. Starting today, the idle slowed to an uncomfortably low level so I opened up the idle screw a couple turns and it improved. It still isn’t doing great during initial acceleration so it seems like maybe the pilot isn’t quite big enough, which seems odd since it’s a #38. One thing I haven’t touched at all is my needle - could that be contributing? Is it easy to adjust assuming I have an adjustable one? Get a can of carb spray and spray it around the rubber intake manifold and see if the idle changes, it sounds like a typical vacuum leak. Another thing worth testing is seeing if the automatic choke plunger is fully extending, if its not it will cause lots of idle problems I hadn’t considered a vacuum leak but that actually aligns with my symptoms (and explains why I’m having similar problems with 4 different carbs). Thanks!
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Post by GrumpyUnk on Mar 19, 2018 14:10:13 GMT -5
If it was working well previously, you should not have to change the mix or speed adjusting screws. Something else has changed. Either fuel flow is restricted or otherwise compromised, or the amount of air being introduced has changed flow. A vacuum or intake leak would explain, as would a loose clamp on the air tube, or loose mounting fasteners. Things can loosen up with vibration and use, especially if they were not torque checked after delivery. Things could have been loose from the assembly line, and gotten looser over time. If it seems the mix is too lean, you could also have gotten a chunk of 'something' that is partially clogging the jet or jets. Worthwhile to check fuel flow also, as restricted flow would definitely affect operation. tom
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Post by zummerp on Mar 19, 2018 15:07:15 GMT -5
So this thread has me thinking - I have been tightening the clamps on both the intake and air sides VERY tight... I’m theorizing that I’ve caused holes in the intake manifold. Got a new one from a store down the street and I’m checking when I get home. Fingers crossed!
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Post by zummerp on Mar 19, 2018 17:28:37 GMT -5
Ok - replaced the intake manifold, my air filter with a torn rubber boot, and went back to a #30 pilot and I'm running again! Now to tune the main jet and hope it runs reliably...
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Post by GrumpyUnk on Mar 20, 2018 10:18:11 GMT -5
zummer:I have been tightening the clamps on both the intake and air sides VERY tight...
The clamps on the 'rubber' portions do not need to be tightened very tight. The rebber fits pretty snugly, and the clamp is more or less just to 'make sure' things don't rotate and fall off. The effort to fit the rubber tube over either end of the carb is indicative of how much effort it would take to remove it. I think the clamp is more to help limit rotation of the carb from horizontal. May be incorrect, but to seal, it doesn't take a lot of force. I'd use a 'screwdriver' type tool, i.e. a Philips bit screwdriver, to tighten, not a wrench of any sort. Hand tighten and walk away. tom
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Post by zummerp on Mar 20, 2018 19:35:29 GMT -5
Ok - so without overtightening, new intake manifold, new 39mm cone air filter, and a #30 idle / #90 main, I’m performing relatively well. I sensed some bogging after 1/4 throttle so I’m guessing my needle needs a little adjustment. I’m also considering trying a #32 pilot since my mixture screw is out more than 2 turns. Anyone else with a similar setup have advice? I’m getting really good about changing the carb, outside of regularly spilling gas everywhere!
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Post by GrumpyUnk on Mar 21, 2018 11:46:22 GMT -5
Have you tried the drain hose on the side {at the front of the CVT case, more or less}? You should be able to open the fitting and catch all the fuel in the float bowl(majority, anyway) into a tin can or glass jar. You may have to open the fitting screwed into the float bowl to enable the drain fitting. If you don't have the 'armored tube with the metal fitting' and have just a plain hose for draining the float bowl, you could swap one from another carb that was so equipped, or, just use the screw on the float bowl to open the drain hose. I have swapped carbs w/o doing the drain thing myself, but immediately flip and turn them over a cottage cheese sized plastic to slurp out all the fuel I can and avoid having it dribble into my lap as I fiddle. tom
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Post by zummerp on Mar 21, 2018 17:52:50 GMT -5
Good progress today! I kept my #30 pilot and #90 main and adjusted the needle up 2 positions (which I guess is leaner). No bogging and feels pretty good. Now I guess my best bet is to start looking at plug color? I’m getting so close!
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Post by zummerp on Mar 21, 2018 18:33:10 GMT -5
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