bc119
Scoot Junior
Posts: 5
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Post by bc119 on Apr 18, 2014 18:47:53 GMT -5
Hey everyone, I'm a new member, but I've been browsing the forums for about 6 months now, after starting the rebuild on my Tao Tao Scooter. It ran before I took the top end apart, and I have kept everything constant except for the motor work. I decided to partake in the rebuild because I wanted a little more power, and the jetting and CVT were in pretty rough shape from the original owner. I am pretty mechanically inclined but this thing has me stumped.
To start, I have checked and doubled checked everything on the 47mm cylinder and "performance" head from Scrappy Dog Scooters and it is put back together the way the original came apart. The marks on the flywheel match the position of the piston, and the timing is dead on, as long as the markings on the cam are correct. I have great spark, with a new plug and NGK boot checked against the engine. Currently, the compression is at 120 PSI, I have heard that the compression should be between 150 and 200 psi. However, I am not running the stock head, so I don't know if these numbers are accurate for my setup. I have been trying to get it to start on starting fluid, and it refuses to even hiccup like it wants to start. It turns over and theres a strong push of exhaust gas out the back as the piston cycles up and down.
I am up to try anything, so any advice or thoughts are welcome. I am going to tear it down and put the stock head back on and see how much that raises the compression. This thing has been a pain since the beginning so please, any help would be greatly appreciated!
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Post by Upgrayedd on Apr 18, 2014 19:02:18 GMT -5
ok so 47mm piston and sleeve, and a 47mm head?
there are 2 different length valves, 64mm and 69mm. if you got a new head to go with yours, did you get the right length valves in your new head? Is your motor the 139QMB, 1P39QMB?
did you set your valve lash?
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Post by 49cc High Country on Apr 18, 2014 20:35:57 GMT -5
Here's a look at a head with 64mm valves (right) and another with 69mm valves (left).
Have tried any adjustments on your carb yet? What jets are you running on your carb?
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nightriderrv
Scoot Enthusiast
Never Give Up- Ride all the time !!!!!
Posts: 177
Location: Western mountains Nebo NC
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Post by nightriderrv on Apr 19, 2014 10:29:19 GMT -5
Check everything again make sure your on the correct mark on the flywheel and the cam lines up. Also make sure the kill switch is not on killing the starting (ask me how I know that)
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bc119
Scoot Junior
Posts: 5
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Post by bc119 on Apr 19, 2014 11:32:05 GMT -5
I have a 1P39QMB engine. It is the 47mm cylinder and head. The original head had the 69mm valves, but the aftermarket head came with 64mm valves. I switched the longer stock rocker arm assembly for a shorter aftermarket set that work with the shorter valves. The valve lash is set to .004 intake and .006 exhaust. Right now I'm running a 95 main jet, but I havent looked at the needle position or pilot jet sizes. It should still start for a few seconds on starting fluid if everything is good right? I also have an aftermarket air filter and I removed the PAIR system, how crucial is having the correct vacuum line routes for these machines? The only thing requiring vacuum hoses now that I could find is the petcock. Lastly, can anyone confirm that 120 psi is good compression for this set up?
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Post by 90GTVert on Apr 19, 2014 17:52:46 GMT -5
How did you deal with the crankcase vent when switching to a pod filter? That needs to be vented. 49ccscoot.proboards.com/thread/997/crankcase-ventingIf you don't have emissions stuff, then your only vacuum line probably leads from the intake to the vacuum petcock. Without that it won't get fuel to the engine. If it fires up on starting fluid and not without it, you probably aren't getting fuel to the engine. You can look at the spark plug after a failed starting attempt and it should be wet if it's getting gas. 120psi is OK. Enough for it to start. May wanna see more for a strong engine, but sometimes testers don't seal well and read low.
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bc119
Scoot Junior
Posts: 5
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Post by bc119 on Apr 22, 2014 12:49:27 GMT -5
I figured 120 was enough for it to at least start. It won't even start on starting fluid, so I will check to see if the plug is even wet after I attempt to start it again. I ran a bit of hose from the crankcase vent port and tied it to the frame, and just let it hang. I figured once it started I would make a custom catch pan. I have setup the inline petcock, so now all the vacuum lines aren't necessary, correct? I have been using vacuum caps from auto-zone to block these off, that wouldn't affect anything right?
If it won't even start on starting fluid, what other problems could there be, other than the valves being out of spec or timing being off? Leaking valves would produce low compression, but since 120 psi should be enough for it to start, what else could there be?
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Post by 90GTVert on Apr 22, 2014 13:13:28 GMT -5
With no emissions and no vacuum petcock you shouldn't need vacuum lines. Those vac caps should be just fine as long as they're snug.
I suppose a mildly leaking valve could still allow compression but cause starting issues.
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Post by scooterpimp on Apr 22, 2014 19:25:53 GMT -5
Careful with the starting fluid , compression will increase as the rings seat. If all is well elsewhere.
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bc119
Scoot Junior
Posts: 5
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Post by bc119 on Jul 1, 2014 13:04:06 GMT -5
Finally got her up and running! I had one of my friends who works at vespa get me a kick start gear and shaft, and after putting the stock head back on with the aftermarket cylinder it started first kick. I need a larger pilot jet but it ran really well on the 95 main that was in it. It electric starts fine when it is warm, but refuses to electric start cold. Is there an obvious reason for this that I'm missing?
Thanks everyone for your time and help!
I can now hit GPS speeds of 40-43 on flat ground!
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Post by 90GTVert on Jul 3, 2014 16:40:11 GMT -5
Possibly lean and the starting condition will improve with the larger pilot.
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