Briggs & Stratton Compression

[lefty]

Thank you.

So after cleaning the carb she fired right up. Thanks very much.

[KE4AVB]

Just wondering why such a low compression reading. The next time I get a 09P in and no telling when that will be, I will check with my compression gauge. Meanwhile I only seen one engine that would start with only 45 psi and that was a Tecumseh use on a shredder with an extremely heavy flywheel effect of chopper assembly. And it was very slow to start up, by gradually increasing speed until it finally took off to idle speed.

[lefty]

Could the low compression be due to intake valve clearance being a little too tight? Now that I have the right specs, it looks like the intake could use a little more room. I believe you had mentioned that the ACR is on the intake. Not sure if a couple of thousanths would have that sort of impact but I also noticed that it runs a little rough after warming up. I plan on adjusting that soon.

[KE4AVB]

I wouldn't be surprised if a couple 1000ths too close wasn't the culprit. Just my opinion.

Normally once the engine is operating speed the ACR will rotate out and become ineffective. Now valve stems and push rods due lengthen as they heat up so too little clearance can become no clearance.

This property is taken advantage by some us to install bearings and bushings by either freezing or heating if not both depending on what we working on . Either way got to work quickly. I have done this for years install rear axle bearings especially when I was in my teens and just recently last week on a Yanmar tractor front 4 wheel drive hub. Bearing was heated to get it on the bevel and that assembly was frozen so it could be installed in hub which I had sitting in the sun on a 100 degree day.

Lately I have working where bearing clearances of a .001 makes a world difference but I am talking about ball bearings where the manufacture has the spindle a .001 undersized and the inner race is slipping and wearing out the spindle shaft. I end up having the spindle shafts knurled by a machine shop.

[Arkie]

Sometimes you can manually spin a small engine backwards to the compression stroke just to get an idea by feel the difference in forward de-compression and reverse no de-compression when the decompression is built into the cam grind.

(just to get a fast idea about compression vs de-compression)

[lefty]

I adjusted the valves to spec and guess I got this thing running but I'm still having this pulsation problem. It starts first pull and after about 20 seconds I get this fast pulsing. It then levels out for a while but begins again...broom broom broom. I got a new spark plug, clean air, good valve clearance. I've removed and cleaned the carb twice. It looks spotless. This has one of those plastic jobs. I removed that little white plastic piece and disassembled it, cleaned it all out. I checked the tank and cleaned that out and made sure I have a good flow. The main jet is tiny but it is clean. I don't know why I'm so obsessed with this little thing but I got it for free and would love to have it around as a backup. It's so small and small and light.

[bgsengine]

One thing - when you had the center plastic main jet piece out, did you also have air cleaner body removed from carb and maybe see if the plastic venturi in carb body might have been loose? Ive had a couple mowers do that - venturi popped loose (it should never come out, its supposed to be very tightly and permanently fitted to carb body, if it's loose it can leak air past venturi) might also want to check intake gaskets (air leaks) - what you describe is what we call a lean surge (which can also be a governor adjustment problem in rare cases) , lean surge is caused by too much air, not enough gas and since you mention it comes and goes, seems to me the problem just might be the venturi portion of the carburetor being loose. (I had one that seemed to fit fine, but fell out when the carb was warm and I popped the main jet out) Also be aware there's an updated version of the main jet - they had problems with the first versions (gumming up) and that issue could not be cleaned since the jet was press fit deep inside the plastic main jet, but it was in a location that was prone to drying out (newer version keeps it immersed in fuel) If your venturi is loose, you need a new carburetor. Otherwise, might be worth trying a new main jet (although there's now cheap china copies of the OE carburetor that are going for less than the dealer cost of the main jet)

[lefty]

I took it apart for a much closer inspection but couldn't find anything out of wack. But I take your point. I just found a kit with the carb, spark plug, air filter, fuel line and some hose clamps for $15.98. Given this is going to be my own machine, I think it's worth taking a chance on some cheap parts. Going to need all that stuff anyway. Thanks for your help.