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Discussion Starter #1
Just bought a 93 CT70, and it wouldnt start. Cleaned the carb, blew out the jets, checked the spark and it was weak. Assuming it's the ignition coil. Are there any other ignition parts that could cause the weak spark? Also, do you have to drop the motor to get to the coil? Thanks!
 

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Discussion Starter #3
Thanks. Any idea how to test the ignition coil and CDI unit to see if they are working? Also, the ignition coil doesn't appear to be under the seat. I'll have to research that more today.:confused:
 

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I think you'll find the CDI box and the ignition coil mounted to the frame under the fuel tank.
 

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Someone come along and correct me here if I'm wrong, because I am, after all, a points guy, not a CDI guy.



But if the CDI unit was bad, wouldn't that result in no spark, instead of a weak spark?



If you can get to the little primary wire that feeds the coil to unplug it, you could test the coil in place. You need to simulate the magneto's little on/off pulse of primary current to the coil while observing for spark at a known good spark plug, plugged into the spark plug wire and laying on the engine where it's grounded.



That bike will be 12V, so any 12 volt DC source, briefly touched and pulled away from the coil's primary wire, should cause a spark to jump at the plug gap. A battery charger set to 12V, with the ground clamp on the engine and the positive clamp brushed momentarily against the end of the primary wire, should do it.



Of course it may be impossible to reach or unplug the coil primary wire without removing the tank or engine. But that's the way I know for testing coils.



If the spark is weak, but steady, you might look at ground connections and wire connectors, clean 'em up and see if you just have a bad ground somewhere?
 

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Discussion Starter #7
Thanks Mexicanyella, great info. Trying to figure out the best approach to access the coil with either gans tank or engine removal. I thought I read somewhere where you had to remove the engine.
 

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Discussion Starter #8
Well, I finally got to the coil. If anyone has this problem in the future, you have to drop the engine (remove the carb, muffler from the shock, and two bolt rods), the coil is mounted with two small bolts on the right side of the bike between the the gas tank and engine. I can't imagine reaching it by removing the gas tank--dropping the engine was the right choice. I'll order a new one and see how it goes. I appreciate everyone's help.
 

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How long is the coil wire from coil base to the plug boot? Maybe an aftermarket one (or a used one) from an XR/CRF50 would work for you.



Here's the OEM Honda part number: 30510-GJ1-405
 

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Discussion Starter #10
its about 12 inches. I just ordered an after market one from retrobikes.com



I've ordered from them before and they are pretty good. Thanks
 

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Discussion Starter #11
just installed the new coil, have great spark, but now no fuel...at least the spark plug isn't wet. I took the carb completely apart, blew out all of the jets, and still no luck. Any ideas?
 

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Well, glad to hear you have spark, and this is interesting news also because in my experience, spark problems are almost never the coil; I always suspect it but always find the problem elsewhere...like, say, the points. Now this is twice this summer I've had reason to continue suspecting the coil...an old points Tecumseh lawnmower I rescued, and now your (non-points) bike.



Re: your fuel issue...start by checking if fuel is getting into the carb's float bowl. Fuel in tank, fuel lever "on" at carb, open bowl drain screw at base of float bowl. Is fuel coming out? Either in the "on" or "reserve" position?



If yes, suspect an incomplete job of clearing jets and passages.



If no, pull the fuel lines and verify that fuel is/is not coming out of them. With that goofy CT70 fuel system routing, you may have a pinched or kinked line or something. Or a dead gopher blocking the in-tank fuel strainer thingy.



If you've got no fuel coming into the bowl but fuel at the fuel lines, your float needle is hanging up in the seat due to varnishy residue, or there's a blockage in the petcock or something.



It's just tedious stepping through the various connections to see how far the fuel is getting from the tank, but be patient and you'll get it sorted out.
 

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Discussion Starter #13
Thanks yella...I have fuel getting to the bowl,. I'll recheck the jets and take the float off for a closer inspection. It appears to move freely, but could be hanging up after reassembling the float bowl. Will let you know. I appreciate your help.
 

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Sometimes the float moves fine but the float needle itself stays stuck up in the float needle seat, when the float drops. The sides of the needle and the insides of the seat get crusty enough to hold it there, even against the fuel flow.
 

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Discussion Starter #15
Took the float off, everything seems to be moving freely, took the carb apart again and blew everything out with an air compressor...no luck, still no gas getting to the cylinder--have a dry plug. I'm at a loss. Could the carb be shot?
 

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Not likely. You didn't mention using any carb cleaner spray or soaking the carb in any kind of cleaner, and you didn't mention removing the jets. My guess is there's still something clogged; likely the pilot jet. You can always check yourself by squirting a small amount of fuel in the carb throat, to verify the saying "90% of carburetor problems are electrical," but I'd guess in your case it's the pilot jet.
 

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Discussion Starter #17
I didn't soak it, but did use a lot of carb cleaner on the initial cleaning. Are there any hidden jets I'm not seeing? I took out and cleaned/blew out the two in the float, I removed the air mixture screw, cleaned and blew that out, I removed the idle screw, cleaned and blew it out.
 

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Discussion Starter #18
still can't get it to fire up. have spark, clean the carb and jets several times. The plug is never wet when I check it. This doesn't make sense, but could it be a compression problem?
 

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What's it feel like when you kick it over? Do you feel distinct "pulses" of comression through the kickstarter? If you remove the spark plug, put a thumb or finger firmly over the plug hole and kick it over, is there enough pressure to make a sharp "pop" sound as the pressure spikes and escapes?



Assuming you don't have a bent or burnt valve and/or incorrect cam timing, and your spark is in fact healthy, and your carb is in fact delivering fuel, you can try this...



Sometimes when they sit without running for a while you lose some of the oil film on the cylinder wall, which is crucial for the rings to seal. You can squirt a bit of motor oil (or ATF, or power steering fluid, or two-stroke oil) in the plug hole and kick the motor through slowly a few times so the piston can distribute it on the cylinder wall. With the throttle open, kick it a few times sharply for good measure to blow any excess oil out the plug hole, reinstall the plug and try it. If a dry bore or worn rings are your problem this will temporarily help the compression so it can start.



I've had to do the oil squirt thing AND push start my Z50 a couple of times, using 2nd or 3rd gear. They're pretty easy to push-start in the higher gears; nice feature of the semi-auto clutch that it transmits power from the rear wheel to the engine!
 

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Discussion Starter #20
mexicanyella said:
What's it feel like when you kick it over? Do you feel distinct "pulses" of comression through the kickstarter? If you remove the spark plug, put a thumb or finger firmly over the plug hole and kick it over, is there enough pressure to make a sharp "pop" sound as the pressure spikes and escapes?



Assuming you don't have a bent or burnt valve and/or incorrect cam timing, and your spark is in fact healthy, and your carb is in fact delivering fuel, you can try this...



Sometimes when they sit without running for a while you lose some of the oil film on the cylinder wall, which is crucial for the rings to seal. You can squirt a bit of motor oil (or ATF, or power steering fluid, or two-stroke oil) in the plug hole and kick the motor through slowly a few times so the piston can distribute it on the cylinder wall. With the throttle open, kick it a few times sharply for good measure to blow any excess oil out the plug hole, reinstall the plug and try it. If a dry bore or worn rings are your problem this will temporarily help the compression so it can start.



I've had to do the oil squirt thing AND push start my Z50 a couple of times, using 2nd or 3rd gear. They're pretty easy to push-start in the higher gears; nice feature of the semi-auto clutch that it transmits power from the rear wheel to the engine!


It doesn't really feel like adequate compression, so I need to check it with a compression tester. The one I have doesn't have an adapter to fit this size. I did squirt some oil in and it didn't feel much different (using the thumb over the hole approach), Perhaps the the valve is stuck? This bike only has 389 miles on it so I'm surprised it would be something serious. thanks again for your great advice
 
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