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Post by johnwohl on Apr 26, 2019 15:15:18 GMT -5
Starting off this season with a fizzle. Last year before winter I got a "100cc" bbk but I never got it farther than starting and idling. The starter was beginning to go out when I put it away for the winter so I kept a mental note of that. So far this year I rebuilt the bbk with new gaskets, studs, nuts, washers and a new torque wrench to make sure everything was ready to go, and I changed the battery to an agm, got a taida high torque starter, and a new starter bendix. The problem I am having now is that where before the stock starter would just kind of chug and not turn it over fast enough to start the new starter setup will not engage for tmore than one revolution 95% of the time and when it does it gives only a few revolutions before spinning freely again. See the video: www.youtube.com/watch?v=ToPJek3VEesWhen it does happen to catch, the scooter will start and idle for a while. www.youtube.com/watch?v=8s93XMTpWrEI didn't get a chance to mess with the jets last year so it obviously needs to be tuned, but I can't very well do that if I can only start it 1 out of 100 tries. I don't get it. The starter motor is very beefy and shouldn't have a problem at all, the engine isn't hard to turn over at all, you can turn it through a full cycle by hand pretty easily. The bendix is brand new, the old one gives the same problem. What else is there? Could the flywheel be bad somehow? Here are some pics. Anything look weird?
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Post by FrankenMech on Apr 27, 2019 6:27:26 GMT -5
When the engine fires it releases the Bendix. The engine may not keep running. The Bendix will not reset until the starter stops spinning. Try the old starter Bendix also. Make sure the CVT cover is in place before using the electric start. You can also try kick starting.
I would suggest studying the Bendix mechanism. There should be explanations in many places. Google is your friend.
Your carb idle mix screw should be adjusted 1-1/2 to 2 turns out from seated. I would also suggest increasing the idle speed screw or crack the throttle by hand while attempting to start the engine. Once you can reliably start the engine you can fine tune the carb idle circuit and idle speed.
Also check the carb fuel enrichment system.
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Post by johnwohl on Apr 27, 2019 14:11:14 GMT -5
The starter works and turns the engine over fine with no plug in. I started thinking maybe the compression was too high on the bbk even though it has the cut outs on the head to lower the compression so I got a compression test kit. I'm only getting like 40psi.. WTF. youtu.be/dOQyKmZmdFwI know my rings are on correctly and clocked, the compression test fitting was in tight, I know my cam is lined up correctly. What else? Valves? Now I remember how frustrated I was with this thing.
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Post by FrankenMech on Apr 27, 2019 14:48:49 GMT -5
Make sure the throttle is wide open for compression testing. If the valves are not adjusted properly compression can be low.
If the Bendix kicks out even without the plug in it is bad.
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Post by pinkscoot on Apr 27, 2019 15:29:42 GMT -5
Is that a Harbor Frieght compression Gauge?
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Post by johnwohl on Apr 27, 2019 18:10:26 GMT -5
So do harbor freight compression testers not work?
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Post by johnwohl on Apr 27, 2019 18:17:58 GMT -5
Make sure the throttle is wide open for compression testing. If the valves are not adjusted properly compression can be low.
If the Bendix kicks out even without the plug in it is bad.
I've tried it at all different throttle positions and it gives about the same reading. I did get it to go to 60psi one time but gthats still no where near enough. My valve lash is adjusted to .004" on both sides. I don't know how to tell if the valves are not seating correctly or how to fix it if they are not. The bendix seems to work fine with the plug out. With that low of compression perhaps it isn't enough to keep the bendix extended for more than one revolution?
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Post by GrumpyUnk on Apr 28, 2019 10:02:43 GMT -5
I think your starter(Bendix) kicks out because your battery is not supplying enough amperage. Check that the starter relay is good(look inside at the points), the cables are tight and free of corrosion, and the terminals have good connection to the conducting wires. If you check the voltage when cranking, expect a voltage drop from the fully charged 12.5-12.6V, down to around 10v. If it goes lower(measure in more than one place to detect the spots with bad conduction) your battery is not producing enough amperage. You may have gotten the cam chain/cam gear timing off by a link or tooth. One direction will make starting very hard, the other start well, but have very poor performance. I don't remember... but it could be gutless until high up in the rpm band. Either way, pull the shroud around the blower on the stator end of the crankshaft, and inspect the timing "T" mark position when the cam big hole is topped out, and the two small holes parallel to the cam cover gasket surface. CHECK the T for proper position using a pencil, dowel, screwdriver, etc, rocking the crankshaft back and forth to see when the pencil, etc reach a peak. Wiggle back and forth and determine as best you can actual TDC(Top Dead Center), and compare to the T mark. If on point, great, and if not, mark the flywheel so you don't ever have to repeat the process. Either way, get it to TDC, and check the cam gear alignment. Valve adjustment can make it hard to start if the valves are not seating. Not much else. If they are held open, compression will be low due to leakage, and if too loose, they'll tap, and only in extreme, limit incoming and exiting airflow. If you have a 'performance' CDI, I'd suggest going back to the plain black OEM versions as they seem to keep spark timing from being advanced from startup which the performance CDIs do. If timing is too far advanced when cranking(perf CDI), it makes it harder to start. I still think you have limited starter voltage/amperage, which allows or causes the starter to stop turning, and allows the Bendix to disengage. tom
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Post by johnwohl on Apr 28, 2019 18:29:00 GMT -5
I will do the electrical checks you mentioned.
I'm probably going to end up taking everything apart and putting it back together again. I need to figure out the compression issue before the starter maybe?
Is there anything I might have missed that would cause low compression like that?
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Post by pinkscoot on Apr 29, 2019 10:41:28 GMT -5
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Post by GrumpyUnk on Apr 29, 2019 12:06:27 GMT -5
I bought a china compression tester, in a blow-mold red plastic case, that would not show proper PSI. The gauge needed more air pumped on each cycle than a 50cc engine could produce, spinning at normal cranking speed. I attached my old JC Whitney compression tester(made in USA, FWIW) that I have had for 40 years or so, and it seemed to display consistently higher pressure. The old gauge was fine, but I needed a 10mm(?) plug adapter to connect to the 139. The china gauge had a connector that allowed me to use the old gauge, and I was happy with that. I suspect you will need to get a 'name brand' gauge to get accurate results on a small displacement engine, but the china gauges will likely work reasonably well on larger displacement cylinders, such as auto and truck engines. Perhaps HD v-twins, too.
IF the engine will start and idle, then it has compression. That will not go away unless there is something holding a valve open, or the engine gets hot with the valve clearance set too close, and things expand, taking up all the clearance and holding the valve open slightly. That said, I think you should check the starter wiring. A quick check of the wires is to bypass them completely. Using jumper cables, to the scooter battery terminals or to an auto battery, clamp onto the cable terminal on the starter with the +/red connector. Clamp the black to the auto or scooter '-' terminal. Find a good bare metal spot, such as the kick starter, or the transmission gear case(final drive gearbox), and you should get a good spark, and direct full connection to the starter. If it cranks well with the jumper cables, you have problems with your large gauge wires on the scooter, or the relay had poor contacts internally. Jumpering provides full battery power to the starter, and bypasses all the other bits.
tom
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Post by johnwohl on May 1, 2019 19:05:17 GMT -5
Oh for cripes sake: That problem being nonexistant, what gauge would you recommend for new starter wires? What are the stock ones, like 16ga?
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Post by FrankenMech on May 1, 2019 19:14:07 GMT -5
10AWG would be good. Pay particular attention to crimping the new terminals and securing the wire near the starter relay and on the engine so the connections do not flex with suspension movement. Make sure the wires are well insulated and do not chafe on any moving component.
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Post by GrumpyUnk on May 3, 2019 10:09:05 GMT -5
What is the situation now? I figure you got a compression gauge that indicates good compression from the 'cripes' comment & picture. Remember, this thing is about the size of a small push mower engine. They generally should start with the 1st or second kick, IF the carburetor is not hokey, gummed up, or mis-adjusted. ANd, there is fuel in the tank(FRESH), the petcock, filter and fuel lines are connected and functional, AND the fuel gets to the float bowl.
IOW, they will start readily if things are right. It should not take more than a couple revolutions of the crankshaft to get them going. Were I trying your machine, I'd get some starting ether, and squirt a snort into the air cleaner, and then give the starter motor a whirl. If you were experiencing no-start, ether would rule out lack of spark, and generally point to a fuel problem. If there's no POP with ether, pull the plug, ground the threads/shell, and crank it over watching for spark. SOME have a safety built into the kickstand that disables spark if the stand is extended. The switch on those can become 'touchy' and cause a no-spark. tom
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Post by johnwohl on May 4, 2019 21:11:10 GMT -5
I don't have it all figured out yet but I do have some observations. I replaced the wiring comepletely with 10 gauge for the starter.
I am using a 20mm carb and I hadn't changed the jets that were in it, they were 28 idle 95 main.
With the 25 idle even with the wiring upgrade and a full battery it will not turn over with the electric start unless the throttle is held open, but it will not start. I read on another post that someone else had used a 38 idle jet so I decided to try that.
with the 38 it turned over very easily and started with a bit of throttle. it ran very high and rich 10:1 afr and died when the auto choke started to come off
I worked my way down and each step down the afr came closer to 12.5 and each time the starter has a bit more trouble turning it over.
im at a 30 now and afr is around 12.5 but it will die off after a few minutes of idle, no idea what thats about.
its at the point now where its hard to turn over again without a freshly topped off battery.
I haven't meddled with the main jet yet, hoping to get it idling reliably at a good speed first.
also its noisy. are my valves too far at .004"?
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