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Post by rtonelli on Oct 14, 2018 18:45:20 GMT -5
So I bought this scooter off a neighbor after he had issues with it. He had a valve adjustment done on it and then it quit running. I tested compression and it was 30psi. I went ahead and got a full top end kit, piston, rings, all gaskets, and a new head. While I was at it I bought a new carb with upgraded jets, and installed that. I’ve rebuilt both small and bigger engines before so I have experience and I also double checked everything. The issue is when I try to start it with the electric start, it wants to start, and basically sounds like it is running while the starter is spinning but it just won’t get going. If I give it that extra power by kick starting it I can get it to run. When it runs if I take it down the street for 30 seconds it begins to cut power heavily and eventually bring me to a stop where it just stalls. Not like hogs down and stalls almost like spark is cutting out. This is what my neighbor said it did before he adjusted the valves. It seems to be getting fuel, and for the $8 I just bought a new Cdi just to try it and it didn’t change a thing. Any thoughts?
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Post by tortoise2 on Oct 14, 2018 19:08:31 GMT -5
Year, brand, model, engine cc's, modifications? What are you now seeing for cylinder compression? When engine quits, are you testing for spark? |
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Post by rtonelli on Oct 14, 2018 20:10:13 GMT -5
Year, brand, model, engine cc's, modifications? What are you now seeing for cylinder compression? When engine quits, are you testing for spark? Yes still has spark when it dies, it’s a 2016 Tao Tao 50cc |
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Post by GrumpyUnk on Oct 16, 2018 11:41:33 GMT -5
RT:"The issue is when I try to start it with the electric start, it wants to start, and basically sounds like it is running while the starter is spinning but it just won’t get going."
If it will not start without you fiddling with the throttle control, your idle is not adjusted properly. It may be you need to diddle with the idle mixture screw. When adjusted, the engine should fire right up, within a second or two of cranking. If longer crank time is needed, adjustments to the carburetor are likely needed.
To beat a dead horse, did you check the cam timing after reassembly? Pull the shroud around the blower, and crank the flywheel around to where the "T" mark aligns with the casting line(just about 9 o'clock, should be a bit lower than the rubber inspection port if viewed through the shroud). Then look at the cam sprocket. THe large hole should be at noon, and the two smaller holes align with the gasket plane on the top of the cylinder head. A tooth in either direction can change timing such that the engine will not want to run slow or will not want to run fast. Once at TDC, re-check the valve clearance. You should have at least .0015 I and .0020 E, some suggest more. I took those numbers from a 139QMB shop manual PDF online. You can choose .002-.004" for both and should be OK. There will be more noise, but for sure the valves will be closing.
You could be losing vacuum to the fuel petcock diaphragm. If so, the diaphragm will move back under spring pressure and cut the flow of fuel If you lose vacuum once you open the throttle, the engine would consume the fuel in the float bowl, and come to a stop. I dunno if it would hesitate much before stopping, but my one experience with consuming all the fuel in the tank was coming down hill, and I just felt the engine shut down, and coasted into the driveway. They do seem to cut off quickly.
tom
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Oct 19, 2018 8:47:29 GMT -5
When you rebuilt it, did you stick with stock parts or did you go to a big bore kit? The way I read your post, it sounds like you might have kept the orginal cylinder. Before you installed the new piston and rings, did you hone the cylinder? ( new rings with out honking the cylinder will do little good). You said you measured the compression before the top end rebuild, have you checked the compression since? Before you installed the new head, did you loosen the lash adjusters? These little guys tend to run hot, so I always set my vale’s at .004”. If your valves are too tight, it is possible to get an engine running, and when it warms up, the valve are so tight that they hold the valve open just a bit and of course the engine will loose power and stall. When it cools down, you can start it again, but again when it gets warm it quits again.
If the bike was sitting a while, it’s very possible the battery has gone bad. If you have a battery charger, hook it up to the bike and after a few min. Try to start it with the charger still attached.
Does the bike have a stock cdi ( or is the cdi you bought a stock replacement item? After market “ preformance “ cdisvare famious for causing starting problems
New carb setup that I would be to screw the mixture screw all the way in, then back it out 1 1/2 turns ( and leave it). Take off your air cleaner boot and look down the carb. Now adjust the throttle stop screw so the butterfly is all the way closed. While watching the butterfly, screw in the throttle stop screw until the butterfly starts to open again, the give the screw 1 1/2 more turns. ( replace the boot)
You did replace the spark plug, right?
When you adjust the valves, take off the flywheel cover (engine side cover) and make sure you are at top dead center on the compression stroke. Remember there are 2 top dead centers, if you are on the intake stroke, the valves will still have pressure on them. You want to make certain that you are on the compression stroke, and the valves should have just a little bit of play. While you are there, double check the cam timing. If you have a stock cam, you should see a big hole in the cam gear. Then check for the two little holes. The two little holes should be even with the top of the head. If you look exactly from the side, the top edge of the head should exactly cut the holes in half.
On the bottom of the float bowl there is a small drain screw. Get ma screw driver and and open that screw. You should get gas pouring out the bottom. Meet that handy because if you can get it started, and it runs and quits, you can open that screw right away to see if you have gas in the bowl.
I have the same bike ( well really my Nephew has). This is the best way I have found to start it. First open and close the throttle quickly a couple of times. The leave the throttle closed, grab the break, and oust the starter. This should get the bike running. Keep you hand off the throttle. Everyone of these things I have touched are very cold blooded. You have to let them idle for a few min before you can open the throttle. It will tell you if it’s not warm enough. If you twist the throttle and it stalls, it’s saying I’m not warmed up enough!
You did drain mall the gas out of the bike and replace it with new fresh gas , right? Most of the gas we buy at the pump is E10. If it sits a while the
“E” will turn to water. So it’s very important to get all the old out and put fresh in. Bayou didn’t mention it, but you did replace the fuel filter, right?
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