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Post by bigmac on Jul 19, 2014 0:56:51 GMT -5
The engine (a 50cc gy6) has fuel and compression and a proper fuel/air mixture but the engine acts like it doesn't spark at times. The valves are set well (I can hear them ticking) and it runs and sounds normal when on the go. However, it's hard to start, stalls at an idle and bogs down and stalls while going up long hills.
It's like the ignition coil is off the plug half the time while starting, but will randomly begin to ignite the fuel, and eventually start. Once started, the engine will occasionally "hiccup", making a soft thump sound, as if the spark plug didn't go off correctly during the power stroke. I have to hold the throttle open a little to keep it from stalling because of this. Sometime when going down a hill with the throttle closed I'll hear a loud crack sound, like the fuel never ignited in the engine, causing a backfire. Sometimes when going up hill the engine bogs down and stalls and refuses to start for about 10 minuets. I will push the kick start lever by hand during those 10 minutes to see if the compression feels normal, and it always does.
I have already replaced the ignition coil and the plug. Is there anything else that could be causing a problem with spark? Maybe a bad CDI box or stator coil?
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Post by geh3333 on Jul 19, 2014 2:14:12 GMT -5
Sounds like the cdi to me . They are cheap so won't hurt to try a new one . I would have started at the coil and plug " you know it's neither " so I would try the cdi . I would also check your valves just to be sure .
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Post by rockynv on Jul 19, 2014 4:24:51 GMT -5
A number of things starting with a loose spark plug or spark plug cap. The spark plug cap just screws onto the end of the wire with a sheet metal screw that goes into the center of the wire from inside the cap and will come loose over time so you do have to occasionally give the a few turns to tighten them back on.
Ignition pickups do send intermittent signals to the CDI when they start to fail, get out of alignment or the magnets in the flywheel get a bit too rusty so you need to check them for cracking, alignment or rust and act appropriately. It could also be a defective CDI or bad ground connection.
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Post by gy6fandan on Jul 19, 2014 12:41:25 GMT -5
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Post by bigmac on Jul 25, 2014 15:56:06 GMT -5
Thanks for the replies. I had some Sea Foam in my gas tank and wanted to wait until my next fill up to see if it would run any differently before getting anything replaced. It still runs the same. I guess I'll start with a new CDI box.
I noticed today that I can actually feel slight power loss at times, even on flat roads. The problem seems to be getting worse.
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Post by savy09 on Jul 25, 2014 18:24:00 GMT -5
How recent did you replace the wire and coil? I wouldcheck your wire for any cracks and loose connect to the plug or check the plug for cracks and proper gap. Next, check for old or bad gas or sediment in your tank… if gas flow to filter is good. Check for any residue in your float bowl. Did you check for cracks in your intake hose or cracks or vacuum leaks at all your hose connections, I replaced those butterfly clips with plastic quick ties, found leaks with engine idling and spraying carb cleaner by all the hose connections. Clean or replace your air filter...CDI is also suspect.lol
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Post by alleyoop on Jul 25, 2014 19:11:58 GMT -5
Sounds more like you need to adjust the valves, set them both to .003 inchs. If you don't have feeler gauges to to your friendly auto parts store and get a set with feelers .003 and .004 some sets start at .008 for cars.
Alleyoop
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Post by geh3333 on Jul 25, 2014 19:43:03 GMT -5
Sounds more like you need to adjust the valves, set them both to .003 inchs. If you don't have feeler gauges to to your friendly auto parts store and get a set with feelers .003 and .004 some sets start at .008 for cars. Alleyoop Advance auto by my place only had ones that started at .004 no lower . But .004 is fine to set both at . |
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Post by alleyoop on Jul 25, 2014 20:33:43 GMT -5
Sounds more like you need to adjust the valves, set them both to .003 inchs. If you don't have feeler gauges to to your friendly auto parts store and get a set with feelers .003 and .004 some sets start at .008 for cars. Alleyoop Advance auto by my place only had ones that started at .004 no lower . But .004 is fine to set both at . I guess they should change their name to NOT SO ADVANCE AUTO PARTS(HAHA). |
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Post by geh3333 on Jul 25, 2014 20:37:49 GMT -5
Yes they should , LOL .
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Post by bigmac on Aug 10, 2014 14:57:15 GMT -5
After I put in a new CDI box, it shook badly while trying to start. I thought it was sparking before the piston fully compressed the air and gas or something. But then it started after a few tries. However, it still ran like before. So today I removed all the brittle plastic body panels so I could get the valve cover off. What a shocker, both valves are set EXACTLY as they were when I last set them, .003.
I will try them at .004 and .002 and see if it makes any difference. I doubt it will since I have tried every setting in the past and noticed no difference at all, aside the amount of tapping noise they make.
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Post by alleyoop on Aug 10, 2014 15:16:50 GMT -5
Have to ask do you know how to set the valves, we do not know how mechanical you are, you may be doing it wrong?
So explain to us what you do to set the valves. Also what if anything have you changed or put on or taken off the motor?
Alleyoop
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Post by bigmac on Aug 10, 2014 17:31:48 GMT -5
I've left the motor completely stock. The only thing that has changed is my valve stems are a different length. I replaced the cylinder head while doing a top end rebuild, but the new head had 64mm valve stems installed into it instead of 69mm. I had to get new rocker arms to work with the shorter valves but besides that, everything else was compatible.
To set the valves I take the cover off, position the large hole in the camshaft gear so that it's facing outwards from the cylinder head while the two smaller holes in the camshaft gear are level with the cylinder head. Then I slid the feeler gauge between the adjustment screw on the rocker arm and the top of the valve stem to check the gap.
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Post by alleyoop on Aug 10, 2014 21:01:09 GMT -5
Great, just wanted to make sure, now bring it up just like that and check the timing on the flywheel, if the woodruff key is damaged the flywheel will rotate on the crank and will change the timing on you(just to make sure that all that is okie dokie).
Also since you put on a new head, when you put the chain on the cam did you make sure the chain was loose the top and tight on the bottom, If not the chain may jump a tooth and there again you timing would be off.
Alleyoop
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Post by bigmac on Aug 13, 2014 15:41:10 GMT -5
I made sure the timing was correct while reassembling. It worked fine for several months after the top end rebuild. Unless the flywheel has changed its position on the crankshaft, I don't know how the timing would have gotten off.
I tried loosening and tightening the valves, but no improvements were made. I also checked for vacuum leaks using propane gas but didn't find anything.
What I find most confusing is the way it reacts during start ups. It stalls at idle and won't start without some throttle given, so I'd assume it needs an idle speed adjustment. With the engine on and warmed up, I placed a clamp on the throttle so that it kept the engine on and at a normal idling speed. Once I shut it off, it wouldn't start up again. The flap in the carburetor is open the same amount as it was before, so I don't know why it doesn't start up and resume idling like it was just seconds earlier. Meanwhile, it seems like it's randomly not sparking as it attempts to start.
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..BAD TO THE BONE..