Hi everyone,

I have a 1986 YFM225 Moto4 that had been sitting in the shed for about 12 years due to a stripped rear axle. This year I finally got around to fixing it. Overall here is what I did:

• Replaced rear axle
• Cleaned carb (multiple times, it's definitely clean)
• Adjusted valves

Now, when it is cold, it can't idle. It will run for a couple seconds, I will hear a click somewhere under the tank it seems, and it will die. When revving and driving when it is cold, it will also click but it won't die, but it will have a momentary loss of power.
Also, when driving and it is cold, it coughs/spits through the intake, enough that the filter will often be wet if I check it.
When it is warm/hot, it will stop coughing/spitting, and when driving it won't click and lose power. But when idle it likely will click and die... Most of the time. Sometimes when it is hot, it will seem to run perfect, no click, good idle, easy to shift to reverse etc. I checked the compression (cold) and it was good (120 I believe).

So, needless to say, I am out of ideas... Has anyone seen this before? Any insight into what the clicking could be?

 

Are you running on choke when engine is cold? most engines spit back a bit when cold, nor will they idle properly, especially if you don't use choke when they need it. Spitting back is fairly normal, but excessive can be a sign of the valve timing a tooth or two out, so check valve timing if it isn't just needing choke.

 

I have been running with choke when it is cold, except in warmer weather it was able to start without choke. I did check the timing and it did seem to line up (arrow at the top, T in the hole). Otherwise, there doesn't seem to be any missing teeth or anything.
Also, I can't believe I forgot to mention this. The engine was a little seized up too. We used a deep penetrating oil in the spark plug hole and gently used a breaker bar on the flywheel nut to go back and forth until it came free and started to spin freely.

 

A valve may have been open and rusted up like the cylinder, it may just need use to make it seat again but, if you adjusted it when it wasn't properly seating, you will lose clearance once it does.

 

try simply replacing the spark plug yet?

 

Any way I can check if it is seating properly? Aside from tearing it all apart... I have replaced the spark plug, and I have new spares I can test with as well. I wonder if it would be worth while to replace the valves as a winter project...

 

Also, would it be worthwhile to get an engine cleaner of sorts and spray it into the intake?

 

Could try engine cleaner, but my advice is to use it for a while, let things bed in, rings will be sticky, valves too, just using an engine improves performance. Like I wrote above, check valve clearance again once you have run it for a while.

You may have the cracked inlet manifold problem, common on Yams, if it is, replace it.

 

How long do you think it would have to be used? I have probably put about 10-12 hours on it so far since the end of rebuilding everything and it still acts up. I have checked the valve clearance recently (at about 8 hours). I will double check the inlet manifold. Although, if it is the inlet manifold, wouldn't that show in compression tests?

 

"if it is the inlet manifold, wouldn't that show in compression tests?"

No.