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Post by truebluethecat on Aug 7, 2015 1:15:56 GMT -5
Ok so I did a 100cc bbk on a 139qmb. Everything mostly went well. Started fine and everything. Was letting her idle for 5 mins and talking to a neighbor at the same time when the scoot died. Turned around to look and found a nice puddle under her. Seems I tore a gasket during install and didn't notice. Any ways she didn't freez all looks good except the piston rings.... I think. The bottom rings (the two with the mesh between) look very nearly flush with the side of the piston. Now when I start her (yes replaced the gasket) she runs fine until she starts getting to temp (about 10 mins or so). The dies and won't start again for like 30 mins and during that time if I try to start her its as if the spark plug wasn't in. So what do you guys think? New rings? Or do you think there's another issue I'm over looking? I installed a new coil, cdi, rocker arms, a9 cam, exhaust, iridium spark plug and carb with a  main jet. |
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Post by lain on Aug 7, 2015 9:08:52 GMT -5
Did you adjust the valve gaps and idle mix screw? It sounds like it could be a mix problem, maybe too rich. I would mess with needle position and idle mix screw. I actually have a 100cc bbk with scored cylinder and piston from a ring coming out before, it has a tendency to spin the rings after install because the hone did not remove the scratches, but it runs just as well as a new bbk with perfect installation just needs oil every few weeks.
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Post by truebluethecat on Aug 7, 2015 10:20:53 GMT -5
I set the valves to .005 while cold. And I've adjusted the idle but it didn't seem to die at idle, its dieing out while riding. Maybe to little air flow? I'm using stock filter bix but have a cone like filter that came with the kit that I haven't installed yet
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Post by lain on Aug 7, 2015 10:33:25 GMT -5
I set the valves to .005 while cold. And I've adjusted the idle but it didn't seem to die at idle, its dieing out while riding. Maybe to little air flow? I'm using stock filter bix but have a cone like filter that came with the kit that I haven't installed yet Maybe not enough air flow, I was not able to use anything higher than #  with the air box, but with the foam filter like the uni filter I have I can go up to 100 and still with stock muffler/exhaust. Could also simply be tuned by moving the needle to a leaner position. It's not always the same from scooter to scooter, I definately had to tune my needle position after installing the bbk though. I also had to shape the accelerator pump bracket thing that gets pushed by the throttle butterfly, you know that piece of metal the throttle slides on that pushes that diaphragm on the bottom of the carb? That piece of metal controls the diaphram ont he bottom of the carb that essentially pumps tiny bursts of gas when you pull the throttle to allow more gas for the sudden change in air in the venturi. You can shape it to pump later or earlier in the throttle range or you can pull it back and eliminate it to provide a leaner transition in throttle change. .005 may be too big, but wouldnt cause you to stall out, I set mine to .003, at .005 I could hear clatter from the valve tappets while running. |
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Post by truebluethecat on Aug 7, 2015 12:17:51 GMT -5
Ok so I'll swap out the air filter. The one that came with the kit is like a foam uni filter. And just to clarify the needle you talking about is the one in the diaphragm? (Fist time adjusting one of these carbs, I'm more experienced with lawn mowers and weedeaters/chainsaws a bit different lol)
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Post by truebluethecat on Aug 7, 2015 12:36:17 GMT -5
Oh and what did you do with the cam ventilation hose? Mine hose to the air box. Dose it need the air pulled in or is it fine being zipped to the frame? I was thinking if that's the case I'd put a small air filter on it form a old gas rc car I had.
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Post by lain on Aug 7, 2015 14:01:40 GMT -5
Oh and what did you do with the cam ventilation hose? Mine hose to the air box. Dose it need the air pulled in or is it fine being zipped to the frame? I was thinking if that's the case I'd put a small air filter on it form a old gas rc car I had. I actually added an extra crankcase vent by adding a vent to the dipstick port as well (due to too much crankcase pressure), and both are connected to an oil catch can that looks like a small muffler sort of and pointed behind the back wheel. You can essentially leave it connected to the valve cover but unplugged from anything else, but face the end of the hose towards the rear because if it faces forward dust can get pushed in by passing air. You can also put a small gas filter like from lawn mowers on it, in fact a lot of lawn mower parts work with scooters, I've even used a lawn mower solenoid in a pinch.  As far as the needle, yes I am talking about the one in the large diaphragm in the carburetor. If you unscrew the top 2 screws from the cover looking thing ontop of the carb you can access the diaphram and needle. The needle if adjustable should have a C clip on it you can pull off/put on with pliers (be very careful not to lose it, it's very easy for it to fly off!!!), and it should have 5 slots on the top of the needle for the clip to go on. Moving the clip adjusts when the gas is introduced from the main jet, or in other words tunes the middle end of the carb to be richer or leaner. Moving the clip up makes the needle drop down which closes the main jet sooner/opens later, which essentially leans the middle end. Moving the clip down will raise the needle up in the diaphragm and allow gas from the main jet to be introduced sooner/in effect longer which essentially richens the middle end. What you want is for there to be no hesitation from idle all the way up to top revs. You may find there is no hesitation but after moving the needle may find snapier response and faster ability to reach the top end. If it pops or hesitates move back to the last clip space you had good results on. When you installed the BBK, did you torque the bolts to the right amounts? If they are too tight it may make starting hard, like it will turn really slow until it starts. It will also make all the pieces too tight when it warms up, which could also cause stalling. How new is your ignition coil and CDI? There are soooo many things that can cause stalling it is rediculous, one of the hardest things to resolve. |
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Post by truebluethecat on Aug 7, 2015 14:28:47 GMT -5
Ok sounds like my little rc car air filter should work then. It's essentially a micro uni filter. About a inch and a half tall and about as big around as a quarter.
I did not think to torque the bolts so you may have actually pinned it. I had not thought about it but what you say makes sense. I'll do that tonight first thing. I'll have to look those numbers up.
My cdi and coil are new. Came with the kit.
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Post by lain on Aug 7, 2015 16:28:50 GMT -5
Ok sounds like my little rc car air filter should work then. It's essentially a micro uni filter. About a inch and a half tall and about as big around as a quarter. I did not think to torque the bolts so you may have actually pinned it. I had not thought about it but what you say makes sense. I'll do that tonight first thing. I'll have to look those numbers up. My cdi and coil are new. Came with the kit. I believe the 4 nuts that hold the rockers on the cam should be at 14 ft/pounds and the 2 on the side should be at 8 ft/pounds which is essentially hand tight. Yeah it sounds rediculously low torqued but that's how they are. |
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Post by truebluethecat on Aug 7, 2015 22:36:20 GMT -5
Well after adjusting the torque. Putting the new air filter on and adjusting the needle she still died BUT I believe I have found the problem, actually I'm 99% sure its the problem. The intake valve is getting stuck. I just pulled the cover off to check the rockers and noticed that it was already at tdc and the valve was still down and rocker hanging in air. Gave it a couple small taps and it popped back up That explains the feeling of no compression. Any suggestions?
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Post by truebluethecat on Aug 8, 2015 0:30:40 GMT -5
Just doing some thinking. The sticking valve I'm pretty sure means its likely bent. Now I haven't compared the two physically yet, been googling lol. But dose any one know if the 50cc head is any different from the 100cc? If so what about the valves them self. Thinking if the heads are the same then just swap back to the old one. Failing that if the valves are the same then swap those?
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Post by lain on Aug 8, 2015 0:48:22 GMT -5
Same? Well, mostly. The smaller valves on the 50cc head will decrease performance though. You are going to need a new head gasket if you do that so might as well order a new head or try to get a replacement if the head came preassembled with valves, might be a defect.
Are you sure the new cam was installed while at TDC? Like did you install the cam while the flywheel was at the timing mark and did you make sure it didn't move? Sometimes it can move slightly without noticing and when you assemble it again it can be very slightly off and cause valves to stay open or open at wrong times. Have you tried with the old stock cam, maybe the performance cam doesn't have good timing for your engine, I've heard mixed results about those.
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Post by truebluethecat on Aug 8, 2015 0:59:15 GMT -5
Yeah I was very careful with the timing its dead on. I don't think it's the cam there was at least a quarter inch of play between the top of the valve and the rocker arm before I tapped on the valve and it popped back up. Unless your saying the cam is pushing the valve too far in? And yeah I'm going to check on what it'll take to get a new one in the meantime
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Post by cyborg on Aug 8, 2015 9:17:07 GMT -5
valve stem is slightly bent
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Post by truebluethecat on Aug 8, 2015 14:15:45 GMT -5
Yeah that's what I'm thinking. If using the old 50cc head is safe then I'll use that in the meantime. A loss in performanc till I get a new head is acceptable to me. The real question is though is it safe? The old head is flat mostly till you get to the valves. The new one is slightly dished just large enough to see where the piston should in theory go. While I don't see how the piston could hit it, I'd still prefer a more experienced opinion ha-ha. Also by safe I mean any long term damage that could happen doing this?
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main jet.
with the air box, but with the foam filter like the uni filter I have I can go up to 100 and still with stock muffler/exhaust. Could also simply be tuned by moving the needle to a leaner position.