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Post by OMN on Mar 16, 2013 11:49:33 GMT -6
ok got it mostly done. it's running reliably now. still a little bog on throttle, but it's rideable. the float was definitely very high - not sure how long it's been that way, but i assume the old weak fuel pump never got enough gas in there to see there was a problem.
i've got lots of other bike projects to finish up first, but then i'll work on tuning this one better. always something!
thanks, all
ron
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Post by OMN on Mar 14, 2013 16:10:49 GMT -6
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Post by OMN on Mar 14, 2013 15:26:33 GMT -6
i may just be missing it, but what is the proper float height on these things?
thanks
ron
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Post by OMN on Mar 13, 2013 8:10:07 GMT -6
good ideas - i'll try those. thanks!!
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Post by OMN on Mar 12, 2013 23:26:15 GMT -6
hello again, all! well here's another chapter in the saga...
MC-45B; just replaced fuel pump. while running, fuel is now pulsing well, to the point where it fills up the clear fuel filter i have inline just a couple inches from the carb.
on the center stand, scoot will fire right up, idle well. "goose" it, it returns to a strong idle; rev it then hit the rear brake, the engine immediately slows but recovers just fine.
but it still stalls and dies every time i stop! it will even die while i'm rolling but just let all the way off the gas.
i've set the idle while on the center stand and warm; it's around 1800rpm.
here's what's weird: if i start the scoot on the center stand, it idles great. i throw a leg over and sit down, and it idles great. i roll forward to drop the center stand, and the idle drops 200-300rpm. i lean it over on the side stand, it dies.
(this isn't a side stand kill switch thing, btw - it normally runs while the side stand is down...)
any ideas? i've adjusted the valves only a few hundred miles back. i re-adjusted the exhaust tonight to .005 inches (it was very loose, about .012).
could i have a stuck variator maybe? any other thoughts?
thanks mucho!
ron
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Post by OMN on Mar 4, 2013 17:06:44 GMT -6
ok, thanks - that's what i expected. i'll get a new pump ordered. thanks, Alleyoop!
ron
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Post by OMN on Mar 4, 2013 11:56:46 GMT -6
hello, all! quick question: on the MC-54B 250, about how much fuel should be flowing into the carb while cranking the starter?
background: couldn't start it the other day, took a look at the clear fuel filter i installed close to the carb, and it was dry. hooked the mity-vac to the vacuum line running to the fuel pump, and got a couple dribbles to come up.
I took the fuel pump off, took it apart, and found a tiny blade of grass or wood splinter inside. (some may recall i found one of those in the carb a few months ago...) put the pump back together, reinstalled, and now it fires up again.
However, viewing thru the clear filter, it appears that only a trickle of gas is flowing into the carb. shouldn't that filter pretty much stay full of gas? and if i were to disconnect the line, about how much gas should i expect to see pulsing out?
thanks a million!
ron
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Post by OMN on Oct 4, 2012 20:00:41 GMT -6
ok, we may have figured it out. i took the carb off to clean it again, figuring that's about the only thing left. found a 1/4"-long piece of grass in the fuel inlet, between the hole and the needle valve. (see pics) cleaned it up and reinstalled - seems to be idling crazy good. so there you go - great reason to use a freaking fuel filter!!! thanks for everyone's help! ron ;-P Attachments:
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Post by OMN on Oct 4, 2012 9:34:27 GMT -6
thanks for the help so far. any other thoughts?
my plan is to take the carb off and re-clean it, then maybe try a new fuel pump if that doesn't do it. just thought of this - maybe i'll hook up some clear hose to the carb overflow and watch the fuel level, too. any other ideas?
gracias,
ron
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Post by OMN on Oct 2, 2012 21:47:13 GMT -6
here's the video i shot of the idle going up and down on its own...
ron
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Post by OMN on Oct 2, 2012 21:19:57 GMT -6
ok here's what i did tonite:
tried to adjust the a/f screw but didn't have much luck. i couldn't get it to turn more than about 1/4 turn while the engine was running. idle didn't change much. a little, but not much. i was able to rotate the carb (engine off) and adjust it but that didn't seem to change idle speed. which varies so much anyway, it's hard to tell if changing the a/f screw is doing much.
took the CVT cover off, removed variator. wanted to see if maybe a weak clutch spring was the issue. seems to idle along better, right around 1900-2100rpm. but still varies. sometimes it will rev closer to 3000, then come back down. if i leave it alone, it will slowly reduce its idle speed (like over 3-5 minutes) and then after about 1600 it will slow to a chug and then die.
if i gunned it several times or opened it up to 6000rpm then let off the throttle, it would quickly fall under 1500 and then die.
also sprayed everything with soapy water, as suggested. i don't find any bubbles. sprayed the heck out of it while running at 2000rpm - same story - no change in idle speed. so this makes me think there are no air or vacuum leaks.
i noticed that if i disconnect the air cut-off valve, the rpms jump immediately. same with disconnecting the vacuum line that runs to the fuel tank. could my air cut-off valve be restricting the vacuum and causing the fluctuating idle speed?
so i'm thinking fuel delivery. fuel pump, maybe? it seems like it's not keeping up. though when i used an auxiliary tank the other night, it just flooded.
a couple months ago when we did the PDI, i took the carb off and cleaned all jets and passages, so unless some new chunk of crud worked its way in there, i don't think it's the carb...
any other thoughts? thanks so much for the help! i'm about to try to post a video that i took of the idle speed fluctuating.
thanks,
ron
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Post by OMN on Oct 2, 2012 16:57:02 GMT -6
i like that mini set. may have to go to autozone.
thanks, alleyoop!
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Post by OMN on Oct 2, 2012 15:33:54 GMT -6
sweet - thanks for the suggestions. i'll try these tonite if i can, then post up results. thanks, all!
hey alleyoop - what do you use to adjust the a/f mixture screw? mine is on the bottom of the carb and hard as heck to reach, especially with a hot exhaust... plus my shortest screwdriver is an inch too long to clear. if i can get in there with a screwdriver impact bit, that may do it... is there another trick i'm missing?
;-P
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Post by OMN on Oct 2, 2012 10:56:29 GMT -6
i believe the diaphragm is sealing well and in great shape. the needle feels like the spring is correctly in place. my needle has only 3 clip options. it was in the middle. i moved it to the lowest (richest) setting last nite with not a lot of noticeable difference. any other thoughts, anyone? this thing is kicking my butt! especially since it worked GREAT just a few days ago and i haven't changed ANYTHING. i was thinking maybe fuel delivery so i hooked up an external tank and clamped off the line from the scooter's tank. all that did was flood it. thanks for the input - please keep it coming! :  ron |
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Post by OMN on Oct 1, 2012 21:03:16 GMT -6
ok, just checked. the intake valve is at .005" and the exhaust is .006"
is it a problem that those are both about .001" too loose? i've always heard it's best to err on the loose side.
also i believe the enrichener must be working - it starts right up cold, and holds a strong idle. the enrichener itself also gets very warm.
BUT, here's the wierd deal. on the center stand, it idled strong at about 1800-2000rpm for several minutes after starting. revved it, hit the brakes, etc - all was well. then suddenly after revving and hitting the brakes, it would start lugging and eventually die. it's acting like it's not getting enough fuel to recover from the very low idle that happens when i hit the brakes. once restarted, i had to give it just a little throttle for a couple minutes until it would finally hold itself back at a good 1800-ish idle.
i thought i'd try richening the mixture, so i pulled the carb needle and lowered the clip a notch. it seemed to accelerate a little stronger, but didn't change the low-rpm problems.
i checked for vacuum leaks. pulled and wiggled hoses, visually inspected intake boots, and sprayed WD-40 around all the inlets i could find. during this vacuum test, the engine was idling smoothly at about 2000 rpm. it never changed.
i found a vacuum hose that runs from the RH middle of the carb up to a vaccum thing on the top of the carb (looks like an air cut-off valve). this hose is only about 3 inches long. i found that pulling the hose didn't change anything, but if i covered the hole on the side of the carb body, the engine would immediately bog and die.
there is also a short hose coming off the LH side of the carb, near the top, with a 90-degree bend in it. if i understand correctly, this is a fuel overflow??? i found that when i covered that hole, the rpms went up about 50-100 rpm.
so, what do you think i should look at next? to reiterate, everything has been really great for the last month, or about 850 miles. then suddenly within a week/50 miles, it's back to its old tricks. no changes since about 6 weeks ago when we did a full PDI with new enrichener, valve adjustment, etc.
any more ideas?
thanks for your help, in advance!
ron
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