chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
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Post by chris962 on Dec 10, 2014 1:47:54 GMT -5
Does anyone know how to troubleshoot a no-start issue after doing 72cc BBK for a Taotao 50cc scooter? My scooter was running fine with my stock engine, but have tried 4 times to take apart the engine and figure what was wrong with it, but each time all it will do is crank when pushing the start button. After the 3rd attempt, it managed to nearly turn over, but let go of the start button and the next time all it did was keep cranking. Thanks!
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Post by Clank on Dec 10, 2014 1:50:24 GMT -5
Do you have fuel? Do you have spark? Do you have compression? Did you install the kit yourself?
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Post by birdman on Dec 10, 2014 5:58:09 GMT -5
Spark, fuel, compresion, correct timing, the thing will not have a choice except to run.
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Post by blaq on Dec 10, 2014 7:19:36 GMT -5
I'm having same problem the mechanic seems to get it running but I guess once it gets cold a day later after only a few short trips here and there it doesn't start he says he's got everything right n he don't know what's wrong I'm not the smartest person in the world but I get my hands dirty with this thing somebody
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Post by Clank on Dec 10, 2014 7:23:00 GMT -5
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Post by 90GTVert on Dec 10, 2014 13:00:39 GMT -5
Hey Chris. See, pretty much the same response you got from me on YouTube. You really do need to verify all of the basics (fuel, air, spark, compression, timing).
There have been a lot of long messages over a long period of time, but if I'm correct you know it is getting fuel, you've checked and it gets spark, you've made sure nothing is clogged in the air inlet path. It's been sitting for how long now though? Hasn't it been a couple of months? I don't trust gas at that point, and at very least I'd smell it to see if it smells sorta like varnish. You've never done an actual compression test have you? I know you've tried to check valve timing multiple times. Really wish there was a compression test so we know 100% you don't have a mechanical issue with a valve or that nothing is out of time far enough there that you are losing compression that way.
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 10, 2014 13:13:00 GMT -5
take the intake manifold and carb off , while cranking dribble some fresh fuel down the hole . See if you can get it to run for a short stint .
John
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chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
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Post by chris962 on Dec 10, 2014 23:12:46 GMT -5
Thanks John, sounds like a good idea. @ Clank, I did the installation myself, first time and no experience as a mechanic, but did have a number of videos, tutorials to do a BBK, and pictures, so think I got it mostly right other than while I could get the two small holes of the cam to line up in a perfect 180 degree angle with the engine case, and the one large hole perpendicular to it, and also was able to keep it that way with the chain on the cam, but once I put the rocker arms assembly flush against the head, the two small holes would move a bit off parallel, maybe 1 to 3 degrees?, then after torquing down the rocker arms it moved a bit more. I tried over and over again moving the cam on the chain to get a better position, but only went to 180 degrees in one scenario and each time I slid the rocker arms assembly over the camshaft, it would 'move'. I purchased the 72cc BBK, which came with a new head, piston, cylinder, etc., but my stock head had 69mm valves and got damaged after the 1st installation whereby I was tired when re-installing the spark plug and cross-threaded it causing metal shavings to drift into the combustion chamber, so got damaged. I didn't like the new head as 1. it had 64mm valves, a different set-up than the stock head, and 2. I didn't realize that the head of this BBK was 'different' when I purchased the BBK, so therefore my stock rocker arms were of no use with the new head. Thus, I had to buy 'new' rocker arms for the new 64mm head, so maybe the new rocker arms don't fit the new head right? As you can see from the operator of this site, I've done several checks on it, but the scoot has been sitting for maybe 2 months now, so the premium gas that used to be good,...well it could be stale now. @ Brent, I think I went back and forth with you online for maybe a week or so before I decided the new head with smaller valves wouldn't damage my engine, plus it probably took a week for the new rocker arms assembly to arrive in the mail, and probably waited until the end of the week to do the 'second' attempt at the BBK installation, plus I forgot on the 2nd attempt about the need to switch the exhaust manifold studs from the stock head to the new head, didn't have the right tools, so these studs were damaged when I used regular pliers to get them off the old head in the 2nd attempt. Thus, I couldn't finish the 2nd installation attempt that night and had to go buy two new exhaust studs at the hardware store the next day. Therefore, it's possible I waited for up to 3 weeks before I did the third attempt, whereby I was successful in reassembling the entire scooter. I guess in that time frame my premium gas could have become 'stale', but my gut says that is 'not' the problem, then again my gut is wrong sometimes, so I'm taking your advice and getting a fresh 1/2 gallon of premium gas to add to the old gas in the tank to see if it makes a difference in starting. After reading about how the 4 stroke, 4 cylinder Wright brothers first airplane worked last night on a NASA website, I'm starting to think that perhaps I'm not getting the explosion, or combustion, in this new engine simply due to the old gas in the tank and gas line. I'm also going to first try John's idea above and pour a little of that new premium gas directly into the intake manifold 'hole'. John's idea just might work. I wish I had one of those devices to check compression levels, but don't have much money this month to go buying such a tool as they sound expensive. Yes, it would be nice to know the compression is good in the new engine, but I just don't have the money for this sort of tool.
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 10, 2014 23:41:11 GMT -5
autozone , pepboys , advance auto parts loan tools . You don't need higher than 87 octane fuel 91 in china standard is like 85 or 86 in comparison to USA standards . Are you getting strong cranking ?
John
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Post by Clank on Dec 11, 2014 4:52:35 GMT -5
Metal shavings in the cylinder is very bad. You could've damaged the cylinder, piston, and rings. Those shavings could eventually work their way into the crank case and damage your crank bearings. I would highly recommend changing your oil immediately. When you get it running run it for ten or fifteen minutes and change the oil again. Post your results also. Fyi if you have a O'Reilly's close by you can rent a cylinder compression tester for free. They just require a $40deposit which you get back when you return it. Or they let you use it in the parking lot w/o deposit so long as you have an I.D. and can get the scoot there.
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Post by scooterpimp on Dec 11, 2014 5:36:44 GMT -5
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chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
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Post by chris962 on Dec 11, 2014 8:45:28 GMT -5
@ John, yeah the cranking is strong, installed a new starter motor myself in maybe April of 2014. Btw, I took your suggestion and also sprayed in first some starting fluid, then cranked it while dribbling in a little fresh premium gas and while I noticed that I did get some 'smoke' rising from the engine below, I still didn't get any fire!
@ Clank, thanks for the warning! I got rid of that old head after I noticed the shavings in the combustion chamber and the first thing I did was inspect the cylinder and didn't really get in there, but there was definitely 'some' shavings on the 'top' of the piston. I cleaned that off first, then checked inside the cylinder and what I noticed is that the cylinder was 'very' clean, so simply put some more lubricant inside the cylinder and tried to install the new head with a new NGK plug. I figured at the time that since only the combustion chamber above and the very 'top' of the piston had shavings in it, while the cylinder below was super clean, spotless, I figured the top of the piston had shielded the piston rings and the entire cylinder below it,...but now I'm not so sure! I'm starting to think maybe I once again have to take apart the whole engine again and even take off the jug to inspect the piston rings. What do you think the odds are that the rings got shavings in/around them? I know I did a good job on ring placement, so figured the rings and piston was what kept the cylinder so clean.
What if it turns out that the piston rings are just as clean as the cylinder? Do I really need to change the oil then? I was hoping that I'd get the engine to turn over before I went about the drudgery of changing the oil. I'm new at installing a new engine, but it just doesn't seem to me that the old oil has anything to do with the ability of an engine to fire up, or not fire up. I guess it all depends on whether or not those piston rings got shavings on them or not. I figured when placing the rings that these would shield anything from the combustion chamber getting below the cylinder as it was pretty difficult to get the rings compressed enough to fit inside the new cylinder, so figured it was a pretty good seal and like I said the chamber was filthy, but the cylinder below was pristine. Anyway, I've been changing oil on my car for about 3 decades and am very good at it and do a better job than mechanics and know what I'm doing there, but thanks again for that warning because I suppose some shavings could have got into the 1st or 2nd ring and that's 'not' a good thing, didn't check though!
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tvnacman
Scoot Enthusiast
Posts: 408
Location: NYC
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Post by tvnacman on Dec 11, 2014 8:52:47 GMT -5
are you getting spark ?
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Post by Clank on Dec 11, 2014 11:36:13 GMT -5
Did you run it after stripping the plug? If not you could be safe but I personally would dbl check. Check the oil filter to see if there's shavings in it. IMO I'd rather spend $6 on two $3qts of oil vs coming up with $400 for a new engine.
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chris962
Scoot Member
Anyone out there good at diagnosing a no-start when doing a 72cc BBK on a Taotao 50cc scooter?
Posts: 24
|
Post by chris962 on Dec 11, 2014 21:49:28 GMT -5
Yes, I checked for spark and it was good. No, it wouldn't turn over after I stripped the plug. I guess you're right, maybe should change the oil right away. I was looking at a compression test video today and while this guy's scooter later started up with 90psi of compression, in the video it cranked for quite a bit and it wouldn't turn over and sounded just like the continual cranking on my scoot. I'm starting to think my engine just won't start with this new head with 64mm valves. Maybe there is something 'different' in the BBK head, so the top end isn't sealing in the same way as the stock piston/cylinder and head, so thereby there has been a big loss in compression.
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