ATV Forum banner
1 - 5 of 5 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter · #1 ·
I have a 1986 YFM-225S that runs great with a new NGK-DPR-7ES spark plug. But only for about 30-40 miles, and then it gets harder and harder to start, and eventually won't start. Then I put in a new plug, and it's like a new bike again.

Any idea why? It appears to be getting carboned up, but eventually, even if I clean up the plug, it won't spark.

What else should I check/replace?

Frank
 

·
Registered
Joined
·
3 Posts
I have a 1986 YFM-225S that runs great with a new NGK-DPR-7ES spark plug. But only for about 30-40 miles, and then it gets harder and harder to start, and eventually won't start. Then I put in a new plug, and it's like a new bike again.

Any idea why? It appears to be getting carboned up, but eventually, even if I clean up the plug, it won't spark.

What else should I check/replace?

Frank
Hey Frank,

I have a 1987 YFM 100 that is doing the exact same thing. Did you ever figure out what the problem was?

Thanks
DJ
 

·
Registered
Joined
·
261 Posts
So the new plugs turn black quickly ? A dark plug is either fuel fouled or oil fouled. Next time you pull the plug see if it looks wet. Sniff it. Does it smell like gas ? If so you have a very rich carb. Maybe dirty air filter or float level is too high. If the plug is a dry black, you have oil entering the combustion chamber. Either a bad valve guide seal or possibly a broken ring.

Mad
 

·
Registered
Joined
·
3 Posts
Hi Mad,

Thanks for the reply. The plugs turn black right away. While I was trying to figure out why it wouldn't start (the plug was still sparking so I didn't realize it was the problem) I switched out the carb. It's still happening with the 2nd carb so I'm guessing it's an oil fouling problem. I tried to adjust the 2nd carb in the hopes that both carbs were running rich but either I'm doing it wrong (very possible) or it's oil fouling. The plug doesn't smell like gas, another sign of oil fouling. I'm not sure I have the know how to try to tackle the valve guide seal or the rings on my own. Might be time to get someone who knows what they are doing involved, unfortunately. But thanks again for help.

DJ
 

·
Registered
Joined
·
261 Posts
Yeah sounds like oil to me. To change the valve stem seals you have to pull the head. If you're going to do that you might as well pull the cylinder too and give it new rings. It's not a hard job on a single. Plenty of videos that can help
What you can do to narrow down where the problem is is to try this.
Get a fitting that will screw into the spark plug hole that you can attach an air supply to. Some compression testers work. Turn the motor over so it's at TDC on compression stroke. You'll need to hold the crankshaft from turning. Put the fitting in and add air. Keep the pressure fairly low. Open the throttle. If you hear air in the carb throat you have intake valve problem. If you hear air out the exhaust, it's a exhaust valve. In your case listen at the crankcase breather. If you hear or feel air there you have worn or broken rings.

Mad
 
1 - 5 of 5 Posts
Top