Quote:
Originally Posted by Thumper
A respected guru recommends 0.002" clearance on 172-FMM engines. Who is this? Joe Henner. No one checks the valve clearance when the engine is hot, but that would be the best time to verify that the gap hasn't closed.
A fully closed gap when the engine is HOT is no problem, as long as the valve is not slightly open. The main reason for a gap is to assure that the valve CLOSES when the engine is hot. Escaping gases burn through the valve seat. This is bad.
So I will stick with 0.001-0.002" on intake, and closer to 0.002 on exhaust. Do I have evidence for this? No. I just pretend to be a guru 
After a lengthy session of valve adjustment, I discovered that about 1/8th turn loose from snug is about 0.002" or a little less. At least this was true when I did this. One of these days, maybe I will do a hot check  |
Another respected source who recommends setting 172-FMM valve clearance to 0.002" is Zongshen. They allow +/- 0.001" on that so anything between 0.001-0.003" is in-spec. I am in 100% agreement with both Zongshen and Joe Henner on this.
Thanks for the 4 stroke 101 re. burnt seats. The only reason I checked my valves after only 50 miles. Just in case they weren't set right, they were.
I saw that you had some problems after adjusting your idle mixture screw. I got around to changing my idle air screw yesterday. Originally I set it to 2-out because I couldn't remember which way was richer. I googled it and the first hit said that most commonly the idle mixture screw controls fuel so clockwise is leaner and counter clockwise is richer. On the Templar you can't adjust the idle mixture without loosening the carb and wiggling it around so I can't adjust it on the fly. This being the case I opted for 1/2 turn richer initially which turned out to be leaner when I later confirmed that these carbs are the opposite. In fact I learned something very useful. When the idle mixture screw is located on the air filter side it controls air volume and when on the intake side after the slide, fuel. I used to just adjust it to the fastest idle and then 1/2 turn richer but I've never had a carb sitting snug against the frame with no access to the idle screw before...
...So, back to the story, I tried 1-out but it seemed a bit too rich so I'm currently testing 1.5-out. It starts without any choke and idles great. I'll check the plug someday, the exhaust smells splendid! Methinks 1.5-out is very close for me. Sorry for any confusion caused by my poor memory. I've already corrected the resource guide.
