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Post by crujonesisradd on Jan 9, 2014 16:01:53 GMT -5
Hi all, I've had a Big Chief QMB139 for around a year now. It ran perfect for several months, even reached speeds around 50mph down hills a few times. Now, the scoot starts on command every time and idles perfect, however, it bogs when twisted past 1/2 throttle. I've done tons of research to find an answer to my problems, but nothing has helped up to this point. Here are the things I've checked or changed in hope of solving my issues: -Adjusted valves to .004", and rechecked gap after running -new battery -  jet, tried everything from 60-  -checked diaphragm for damage -new fuel lines, filter, and petcock was checked -new gas, and seafoam -new plug gapped at .3 -new plug wire -tried several cdi -tried stock filter box, pod filter,and no filter , all combinations -6g sliders -cleaned variator, clutch pads, and checked belt -adjusted and re adjusted carb tried another carb and auto choke, with  jet -starts first fire, idles perfect, but bogs on more than 1/2 throttle, stalls and dies if you don't let off back under 1/2 throttle. After warm up, plug is a nice brown, not covered in gas. I tried another carb with an accelerator pump to see if that would help, it made no difference. This scooter ran perfect and even broke 50mph down a few hills using a GPS as a speedo previously , but now won't go over 25, and will barely creep 5-10 mph up hills. I'm at a loss, as I can't think of anything else that could cause these problems. Anyone else have any ideas? |
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Post by alleyoop on Jan 9, 2014 16:29:06 GMT -5
Well it appears it is a Fuel Delivery problem, does the motor make any sounds just past the half throttle position other than the BOGGGGGG sound and if not backed off dies?
What it sounds to me is the Needle is not being raised all the way and just sucking in to much air. Will it take full throttle on the center stand or does it also bog on center stand?
Are there any emissions on the scoot. EVAP, EGR, PAIR systems? A stock 50 139QMB motor usually has a 18mm carb usually comes with a plugged Fuel Ratio Mixture is yours plugged? Also maybe get a Video going of it on the center stand. Also check your CVT, take the cover off and see how the belt is climbing it could also be something is holding it back and that will also cause bogging putting a load on the motor.
Alleyoop
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Post by crujonesisradd on Jan 9, 2014 16:46:46 GMT -5
alleyoop, I agree with you on thinking it's a fuel delivery problem. I get nothing other than a bogging from the motor. On the center stand it dies out just the same as on the ground. I thought the same of the needle, which is the entire reason for swapping to a carb which was on a scooter running correctly at the time. The needles in both of the carbs I have aren't adjustable, so I'm on the lookout for a few small washers I may be able to add to see if it helps. There's no evap, egr, or any type of recirculation emissions parts on this scooter at all. Both carbs were initially tamperproof, both of which have been drilled out and replaced with adjustable parts. I will pull the CVT back off today and see if I see anything strange going on. What would hold the belt from climbing? I may pull the clutch setup from the good running scooter also and swap it to see if I see a difference in performance. The problem I see is that it ran perfectly fine, and pretty much over night decided to start running the way it is now.
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Post by alleyoop on Jan 9, 2014 16:56:05 GMT -5
Then it may be something in the CVT that is holding the motor back and loading it up and with the throttle wide open it the RPMS cannot rise and it will bog and die. You can also take the Variator off and JUST A QUICK test mind you twist the throttle SLOWLY and see if it will take RPMS past the where it bogs. Slowly just in case it is the CVT holding it back you don't want the RPMS to climb out of control. That will tell you if something is holding it back.
Alleyoop
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Post by crujonesisradd on Jan 9, 2014 17:38:15 GMT -5
I'll give all of those a try for sure. Can I start the scooter without the variator and cover on, or do I need to pull them off after I get it running? I've never tried, and it seems like the starter gear would fly out if not held in securely by the cover....
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Post by jjoshua20213 on Jan 9, 2014 17:56:33 GMT -5
I'll give all of those a try for sure. Can I start the scooter without the variator and cover on, or do I need to pull them off after I get it running? I've never tried, and it seems like the starter gear would fly out if not held in securely by the cover.... I tried to start a scooter without cover as people told me I could and my starter Bendix like exploded into a million pieces. It was so dangerous. Started scoot and THEN took off the cover and it was fine. After that life threatening experience I always take the Bendix out and start with kick starter, then remove the cover. Also, my clutch got semi-seized after oil got in my cvt and everytime I would gas it, it would bog and die even on the stand like you said. I didnt notice it until I went to put the belt back on the clutch after cleaning it and the clutch would not open and when it did finally it got stuck open (High tension spring should have closed it immediately without hesitation). Replaced the clutch with a used spare and it was like magic, the bike didn't bog anymore. I was like riding with the brake on at some-point.. Rpm's raised drastically after the clutch switch. I was however able to get the bike to accel past the bog but it took forever. It was like being stuck in a high gear. It would take miles for it to reach top speed as if it needed an super extended warmup period |
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Post by alleyoop on Jan 9, 2014 18:03:02 GMT -5
DANG, Sorry I forgot yours uses a BENDIX to start the scoot, well forget about what I said(NEXT..HAHA). Ok but at least take the CVT cover off and see how the CVT is working if something is holding it back causing the bogging I would suspect the CLUCH pulley NOT opening up all the way to allow the belt to climb on the Variator. Here is a VIDEO of what you or someone will have to do to hold the BENDIX straight while you see the CVT working same motor as yours. That is the Mother of the boys scooter holding the Bendix I was the one that got them fixed up and the scoot running great and I asked her to take the Video.  Alleyoop |
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Post by jjoshua20213 on Jan 9, 2014 18:09:58 GMT -5
Ya, everyone I asked said it was ok to do it, and then when I post a forum about how I almost got my eye taken out. Their like you gotta hold it in............................................. Reasons why I consider advise instead of taking it.
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Post by alleyoop on Jan 9, 2014 18:41:11 GMT -5
Yea there are some other Videos of one guy holding the Bendix straight with his Big Toe another used Duct Tape to hole it in place. Video was to show the OP what has to be done with the Bendix there are many ways to hold it in place just got's to use your CABEZA.  Alleyoop Here is one using a piece of wire to hold it in place: |
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Post by carasdad on Jan 9, 2014 21:23:25 GMT -5
I use a long 8mm socket..but ya gotta keep holding it..or the bendix vibrates out..
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Post by millsc on Jan 9, 2014 21:24:25 GMT -5
If you can find a junk cvt case cut the top piece off it that holds the Bendix in place the shop here in my town does that I sold the shop my broken cvt covers.
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Post by crujonesisradd on Jan 19, 2014 17:00:10 GMT -5
Finally have an update. I took everything apart and inspected the CVT, everything acts correctly, cleaned all the surfaces, and reassembled. I still get a pretty good studder when I give it full throttle before it is warm. I have started to notice it wants to die on takeoff now, and when the stalling problem isn't present, it has nearly no power at takeoff, but runs perfectly normal above 10 miles per hour. I got a new plug to see whether I'm running rich or lean, and here is the result of a 20 minute run through the neighborhood. I don't understand how it can be running so lean with a jet, and everything assembled correctly with no issues.  |
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Post by tvnacman on Jan 19, 2014 20:51:34 GMT -5
maybe there is a hole or crack in the air box or cracked manifold letting extra air in .
I would check that the variator weights are in place . You did talk about taking out the clutch when you did that did you also remove the variator ?
John
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Post by crujonesisradd on Jan 22, 2014 17:58:35 GMT -5
Today it started, ran smooth from idle to top end. Now there is absolutely no power from stop, but runs fine past 10mph. I almost have to give it a hard push to go anywhere from a stop sign. I checked the variator and clutch, both look perfect. Took apart the intake manifold today and it looked fine, as well as the airbox. I don't really understand how a crack in the airbox could make a difference while running a jet, when some people run the jet with a pod filter with great results. The pod filter I ran had pretty much the same result as the stock airbox and filter. I've exhausted pretty much everything I can do. Would aftermarket 6g sliders make that much of a difference from a stop? If anything I feel it would accelerate from a stop better than stock rollers. |
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Post by jjoshua20213 on Jan 22, 2014 18:20:49 GMT -5
Running lean on a jet means the carb is adjusted wayyyy off or you have air leaking into the intake manifold. Check for cracks on manifold or broken vaccum tubes. Possibly a faulty egr valve if its still plugged in. If it is check that the big tube coming from the bottom of the valve cover is not kinked. Hows your oil consumption? |
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jet, tried everything from 60-
jet
..BAD TO THE BONE..
