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Post by Moat on Sept 17, 2014 21:47:25 GMT -5
Sounds to me like you might be facing more than a single issue...
1) Yes - having it accept WOT better after taping off the air snorkel inlet holes would indicate that it's too lean at full throttle... i.e - likely needs bigger main jet (as long as there are no other air leaks, such as caused by a split intake manifold, leaking manifold gasket, cracked vacuum hoses, etc...)..
2) The mixture screw is in reality an idle mixture adjustment screw, and is designed as a way to dial in the idle mix so as it idles smoothly, starts easily, and comes down from throttle into a smooth, consistent idle. It has little effect at high throttle openings, and playing around with it to address an issue at WOT will only serve to screw up that otherwise smooth, consistent idle. So once the idle is dialed in... don't mess with it - the WOT problems need to be be properly addressed elsewhere... and not with an idle mixture screw adjustment.
3) As long as it's not too restrictive and not capturing any large air pockets/bubbles, a larger fuel filter will be no problem at all (in fact, beneficial if anything - with it's larger surface area to catch more debris before plugging, as well as often using a paper filtering media, which is far more effective at catching small debris than the fine plastic screen that typically comes stock). Some visible bubbles inside the filter are normal, but fuel delivery can act a little "wonky" if they get sizeable. An air pocket can usually be cleared by tilting the filter - bubble up towards the fuel tank - whils sucking on the petcock vacuum hose, opening the petcock's valve and allowing the bubble to rise up into the tank.
I have a big John Deere paper filter on my ATM... works a treat.
4) The white smoke at idle... does the smoke itself smell more like fuel, or more like oil? I'm guessing that it may very well be oil, as if an engine is otherwise idling normally, the mixture would be close - certainly not rich enough to produce a cloud of smoke without stumbling/faltering/stalling. A tiny visible bit of smoke, maybe - but not any substantial amount (i.e. - cloud). If oil, then...
5) Check compression, if at all possible. Significant oil smoke out the exhaust could mean broken ring(s), which might be the cause of the difficulty in getting the engine started (low compression).
6) Do use feeler gauge on the valve adjustment - they're only a coupla' bucks, and should last many years/uses. These little GY6's can be a bit finicky when adjusting things... just as well get it right and avoid the possibility of improper clearance contributing to some other running or tuning issues, downstream.
7) Did you check/set float height when you replaced the float/needle/seat?? If incorrectly set, that could easily be a cause of the WOT troubles (as well as others).
8) You also mention replacing "the needle that goes into the diaphragm" - do you mean the slide needle? If so, that's normally not a regular replacement item (too risky matching it's taper profile from other than the original carb manufacturer), and should only be replaced if damaged or for more extreme (un-common) fine-tuning purposes. Also make sure it's installed correctly, with the needle's clip in the proper groove and the retaining cap right side up. And while buttoning up, make sure the delicate slide diaphragm and cover are installed correctly with the diaphragm's edge bead properly seated in the carb bodies' groove! A little tricky, but paramount!
9) And yes - flooding. With their auto enricheners - and often being a bit finicky to start in the first place - it seems that if these motors don't start on the first try, they tend to flood - as the enrichener continues to deliver too much fuel to an already "wet" combustion area. Holding the throttle wide open and continuing cranking to clear it is about the best (but still sucky) way to get 'em to fire, at that point, it seems.
FWIW... just some stuff to consider...
Bob
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Post by Moat on Sept 16, 2014 21:45:44 GMT -5
Like one of these - Intake Manifold Insulator - if it doesn't already have one (and not a bad idea, anyways, if it doesn't). Of course, you'd need enough clearance beneath the crossmember for it all to fit properly. And likely longer mount studs. Intake pipe/bracket looks nice!  Bob (oops... missed Alley's post...) |
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Post by Moat on Sept 15, 2014 20:08:30 GMT -5
Oh, good! Glad you are making progress - a bit of fine-tuning of the jetting, and you just might be good-to-go.
BTW - the pics earlier in this thread show the intake pipe/filter supported by white zip-ties, wrapped around frame members. Was that just something temporary? The engine on a GY6 scoot is part of the rear suspension, and moves up and down (and a little forward and backward) relative to the frame - those zip-ties would be tugging back and forth/up and down on your intake tube as you're bouncing down the road... i.e. - not Kosher!
A simple support bracket bolted to the CVT cover might be a good alternative.
Bob
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Post by Moat on Sept 13, 2014 15:43:22 GMT -5
hmmm...here's what I just did....I pulled the check valve out of the compression tester and applied 30 psi to the engine at TDC and it would not hold any air. It just came out the carb along with fuel. So I'm gonna go ahead and pull the head and check the intake valve. It can't hurt at this point just to check it out. Even if I did this "leak down" test wrong...I'll let you guys know. Thanks Whoa, there! No need to pull the head off yet - like alley said, your compression is fine. You were likely on TDC of the exhaust stroke during this 30 psi test - not the compression stroke (although there's the remote possibility a valve was sticking open). Bob |
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Post by Moat on Sept 13, 2014 1:08:27 GMT -5
Will install it tomorrow and just for yuks see what happens... Well, ya never know... could very well cure it! Please keep us posted on how it does... Bob |
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Post by Moat on Sept 13, 2014 0:49:18 GMT -5
The problem is, that by the time you may have noticed some degradation in performance due to a too-tight valve, the damage (i.e. - burned/eroded exhaust valve face/seat/sealing surfaces) is quite likely to have already begun. Sure, if caught in time, any further "damage" will likely be prevented - but that effortless starting and idle you mentioned will be among the first things to go.
Yes - there is some risk involved in doing the work yourself, as a first-timer - but you've gotta jump in at some point, right? Just take your time, follow the directions, be as clean as possible, and make especially sure the adjustment screw's lock nuts are appropriately tight before buttoning things up.
At least you'll know exactly what's been done in there... something you can't say if you have someone else (noob? hack?) do it for you. And that in itself is quite satisfying and re-assuring. If you have the time and general mechanical competence... well worth it, IMO.
Bob
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Post by Moat on Sept 11, 2014 13:01:42 GMT -5
Yes - bad ignition misfire or way too rich (which you've already mostly ruled out).
Intake tube or air filter collapsing (or other major intake restriction) under load, is another thing that comes to mind in looking at those pics... how are they? All clear, stiff-walled, well supported, etc? Didn't leave a rag in there or something, while it was apart (known to happen... don't ask!)?
Bob
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Post by Moat on Sept 10, 2014 23:44:33 GMT -5
5. Attempted to get a strobe timing check, but the timing light wouldn't fire. Checked it on my Goldwing and it worked OK. Maybe the voltage in the scooter isn't high enough of the inductive pickup ... Could be a clue, right there (weak spark). i.e. - coil, plug wire and plug cap. A simple test might be to temporarily reduce the plug's gap to, say, half (.015" or so) and see if it affects the stutter symptom. A weak spark will have an easier time jumping a reduced gap, somewhat resisting being blown out under power. Not having lapped the valves may explain the slightly mediocre compression (and it may well resolve itself with time/miles, as it breaks in) - but again, would not be the cause of the stuttering/misfire issue. Hard starting, hunting idle and a slight lack of overall power/torque, maybe... but not the stutter/surge/falter under power, as you describe. Coil grounded to the frame good? Wiring OK? Plug wire and cap connected together and to the coil securely? Not crushed/cut/yanked during the engine work? Many plug caps (like NGK) have a threaded brass screw fitting up inside, which secures a resistor and spring - sometimes those internal components fail, becoming burned/cracked and causing an insufficient spark. Bob |
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Post by Moat on Sept 10, 2014 23:16:42 GMT -5
Time for a valve adjustment! Service the air filter while you're at it...
Bob
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Post by Moat on Sept 10, 2014 1:37:37 GMT -5
And yes - as you mentioned in your first post - fuel pump or vacuum petcock (whichever one you have) could be a possibility. If it's a vacuum-operated petcock, a simple test to eliminate it would be to temporarily bypass the thing using a small barbed hose union (like one of these thingies - link ) - using it just long enough for a good test run down the road. The same could be used to temporarily eliminate the fuel filter as a suspect, too. It's a good idea when troubleshooting, though, to pay particular attention to every single thing you touched while working on it, just prior to when it began acting up. Usually there's a pretty darn good chance that that's where the problem originated. FWIW! Bob |
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Post by Moat on Sept 9, 2014 20:24:50 GMT -5
130-140 psi is OK... not great, but OK. And anyways, compression a bit on the low side won't produce the symptoms you describe (bucking/missing at WOT). Again - try a new, known good plug (and cap - or even coil, if you have one) - and check all of the associated ignition wiring, connectors and grounds. That will at least rule those things out, without costing any $$. At idle, the strobe should illuminate the "F" mark on the flywheel when aligned with the pointer (looking thru the rubber plug-covered hole in the fan shroud). That mark is before (when turning in a clockwise rotation) the "T" mark. Even so, ignition timing itself being a bit off, too, won't cause those symptoms - less power or overheating/detonation rattle, yes - but not bucking/missing. Although - if it's a 12V timing light and you can rig it up to watch it while riding the scoot, it very well may visibly show the stutter while it's happening, if it's a failing spark. A weak spark, caused from, say, a dirty primary coil connection, insufficient ground connection or bad plug or plug cap - can actually be "snuffed out" by the increased combustion pressures that come from opening the throttle further. So it may run fine at lower throttle openings, but "snuff out" and misfire at big throttle openings. Maybe not what's wrong, but just some things to chew on.  Bob |
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Post by Moat on Sept 9, 2014 19:13:45 GMT -5
And, remember - this all started suddenly .... It's common for electrically-related problems (i.e. - a weak spark) to present themselves "suddenly". I'd try a new plug, check all connectors/kickstand switch/kill switch/ground points (engine especially), swap CDI's if you have a spare, etc... If it was running acceptably before - and you know the carb didn't suck a plug of nasty goo or something into the float bowl, and diaphragms are OK - you're just wasting time chasing your tail with mixture settings/jet sizes/idle mix screw adjustments/etc. Follow the most logical explanations, first - all of those things didn't just suddenly change. Bob |
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Post by Moat on Sept 8, 2014 21:47:57 GMT -5
... it seems to have good compression. How much is "seems"? Can you do a compression test? Did you leak-check the valves before installing the head? If you've got a good spark at the right time, cam timing is correct, fuel in the (clean!) carb - and it still won't fire on ether... looks to me like it's just not quite making enough compression. Bob |
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Post by Moat on Sept 8, 2014 7:33:02 GMT -5
The "CV" in a "CV carburetor" stands for "Constant Velocity". This type of carb design more precisely controls fuel flow over varying throttle by attempting to maintain a constant airflow velocity across the narrowest portion of the venturi... which is right at the bottom of the slide, where the needle and needle jet reside. Maintaining a constant airflow velocity provides a steady reference of pressure/vacuum over the fuel delivery ports - that steady reference aiding in more precise control of fuel delivery over the carb's operating range (i.e. - lower emissions, lower fuel consumption). To do that, CV's incorporate the flexible diaphram (seal) as a means of moving the slide up/down, via the pressure differential between the (more or less) atmospheric pressure in the airbox and the low pressure (vacuum) that exists right there, at the very bottom of the slide (narrowest point of the venturi). The top of the diaphram "sees" that vacuum via a hole (port) in the bottom of the slide - and that vacuum is thus applied to the entire (otherwise sealed) topside diaphram/slide chamber. That vacuum is what lifts the slide against the slide's spring, and gravity. In an enclosed tube, as airflow velocity increases, air pressure decreases proportionally (Bernoulli's Principle). So as you open the throttle (butterfly valve), the airflow velocity through the carburetor increases, pressure at the bottom of the slide drops (vacuum), and that vacuum is applied to the top diaphram chamber - lifting the slide, and pulling the tapered slide needle further out of it's opening (needle jet) to deliver appropriately more fuel. Of course, the bottom chamber side of the diaphram must not be sealed off, in order to allow it to move freely and find it's steady, proper "place". So the lower chamber has to be open to somewhere - and since the engine's entire process of "breathing" is dependent on the environment's atmospheric pressure in which it's operating... then atmospheric it is. That's what the elliptical port is that Ally circled in the pic above - the lower-side diaphram's reference port to the atmosphere. So the slide's position at any given engine intake demand is determined by the balance between vacuum at the bottom of the slide and atmospheric pressure at the carb mouth inlet - and to a lesser degree, the weight of the slide assembly and the slide return spring. That balancing act of pressures is what maintains something close to a constant airflow velocity across the narrow point of the venturi. A simple feedback-based governor system, really. For most CV carbs, a quick and easy check of the slide diaphram for sealing integrity is to gently push the slide all of the way up with an index finger, and then tightly close off the elliptical port with the thumb of your free hand (lick your thumb first, for a good seal  ). Then release the slide - it will drop part way, but then should hang partially raised, more or less until you remove your thumb to uncover the port. A leaky diaphram will continue to drop when the slide is released. Bob |
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Post by Moat on Oct 27, 2013 23:04:10 GMT -5
On closer look of the last pic, it just looks like a corner of the attach flange gasket folded up, instead of a chipped flange...
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