Sometimes starts sometimes not

[fordmctee]

I am baffled. my 50cc starts only sometimes. Does not seem to matter if it sits for a while or not. When it does start, it runs great. Problem is when I need it to, it doesn't. Have rebuilt carb twice. Sometimes If I clean spark plug that helps for a couple of days. Plug does get wet looking. Was going to try a new ignition coil, but a $50 gamble if that is not the problem. Was hoping for some direction where I should try first.

[jmkjr72]

you need 3 things
fuel
spark
compresion

being this is a every now and then issue i would lean towards spark
next time it doesnt start pull the plug or use a spark checker to see if you are getting spark

i would consider a new cdi and a new coil

[Rebel]

Welcome to the forum.

Have you checked for any bad ground connections?

When the plug is wet, does it look black, or just wet?

And what kind of scooter is this happening to.

[fordmctee]

Thanks for the welcome and ideas so quickly. Well...I have not checked any ground connections, not sure where to look as I am good with anything but electricity. This did cause me to think about checking the brake connection as it needs to be pulled in order to start the scooter. This is a Geely 50 cc. I have kept it running for 6 years which I am told is amazing. Runs great when I get it started. The spark plug is wet and black when I check it. I have tried leaning the carb, but that does not seem to help.

Thanks for the help and ideas.

[Rebel]

wet and black does sound like carbon fouling to me. Does it smoke? If it smokes, what color is the smoke.

[Rocketdog]

I lean in the direction of JMK. Bad ground. However, if the plug is sooty black, it's getting to much fuel and might be fouling out. Check the spark at the plug the next time it won't start and we can go from there.

RD

[90GTVert]

The fact that cleaning the plug helps and that it's wet and black makes me lean toward tuning issues. You said you tried leaning the carb, what exactly did you do? It's not a fix, but if you need it to be more reliable until you get it solved, iridium spark plugs fire more reliably in less than ideal conditions. It's a crutch not a cure, and I can't guarantee it'll help, just putting it out there.

[jmkjr72]

weak spark can also foul a plug too

[fordmctee]

Got a new coil in today. Will see if that works. Will also check grounding. If that is not it, will try a new CDI box next. What is involved in a tune up? Already have rebuilt carb, new spark plug, installed inline fuel filter. Like I mentioned, it runs great when it does start.

[Rebel]

Check the valve lash and air filter and you are about done.

I'd highly recommend another new spark plug once the problem is fixed. It is possible that once it is firing right it could burn off the old carbon, but standard plugs are not very expensive and you only need one. If you put an iridium plug in it you'll spend $10.00 or $12.00 on that plug, might not want to buy too many of those.

Other things you might consider is an oil change and check the tire pressure. Have you ever changed the tire valve stems?

Here is a chart for you

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[fordmctee]

Thanks. Yes, Changed the oil recently and replaced both tubes. You have ESP!! The stems broke off on my last year so had to replace them. The scooter started after I installed the new coil. Will have to see how many times it continues to start. Not sure how to check valve lash, but I am sure I can figure it out. Thanks for all of the help and advise. Cool blog. Where do you buy the good spark plugs?

[jmkjr72]

if you were fouling plugs out with weak spark you will want to change your oil again
the unburnt gas can get down into the crank case and thin the oil out

[Rebel]

You can get your plugs at any auto parts place. You would probably need to pull it out and take it down for them to get the number off, unless you already know them.