Toro Mower

[lefty]

outta do a leakdown test - possible burned exhaust valve, or check valve clearances

stray air being sucked back in through exhaust could do that too.

Sounds like a logical step. I need to pick a tester up. Any recommendation for a reliable one that won't break the bank? I'm a hobbyist at this point. I've been meaning to add one to my tool box but it's not like it's going to be earning for me anytime soon. But I don't want to go too cheap and end up with a poor tool.

[bgsengine]

Only ones Im familiar with would be the ones from Briggs and Kohler which are pretty pricey - but there's a couple regulars on here that I believe have plans or instructions and sources for a D.I.Y. leakdown tester kit ( You'll want to be able to measure flow rate as well as control pressures ) - some can be as simple as an air hold fitting but it gives you no leakdown rate measurements (but it would work for testing for valve leaks and the like, just don't over-pressurize and blow out seals, etc)

[lefty]

In the mean time, I checked the compression with a compression tester and it shows just under 40psi. Not sure if there is any type of compression release on this machine so not sure exactly what that means. This is a cheap tester from Harbor Freight so just to get a benchmark, I tested my snow blower which has an 11 HP tecumseh engine. The blower is an Airens 1128pro. The Airens is about 10 years old and I keep it in great condition. It came back with about 70psi.

I'm having trouble finding compression specs for this exact briggs motor on the toro mower. Do these numbers tell us anything?

[bgsengine]

40 is definitely low even with compression release - you ARE cranking it over with throttle wide open and choke open and crank until needle stops moving, right?

[lefty]

40 is definitely low even with compression release - you ARE cranking it over with throttle wide open and choke open and crank until needle stops moving, right?

I am. Both wide open. I've done it several times now with readings between 35ish and 40. Nothing ever over 40. Pulling over about 6-10 times to be sure the needle is stopped for good. I think the next step would be the leak down test?

[Fulltilt]

40 is definitely low even with compression release - you ARE cranking it over with throttle wide open and choke open and crank until needle stops moving, right?

I am. Both wide open. I've done it several times now with readings between 35ish and 40. Nothing ever over 40. Pulling over about 6-10 times to be sure the needle is stopped for good. I think the next step would be the leak down test?

As bg alluded to, you can get by with judicial use of a rubber tipped blowgun ( not no sissy osha one) applied to the plug hole. SECURE the flywheel at about 1/4" past TDC on the comp. stroke.
Loosen/remove the dipstick, best to pop muffler off( but not necessary) pop air filter/cover off open choke/throttle. I usually put my thumb over the crankcase breather tube, or make up a stopper hose.
Gently apply air, and listen for any serious leakage. should not be any leakage at the valves, and minimal leakage at the oil fill tube.
The key is don't go ape on the air pressure.
I have a good OTC leakdown tester, but I usually do the air trick on the small units.

[Arkie]

Remove the valve cover and disengauge the exhaust valve rocker or take out the exhaust valve push rod so as the exhaust valve stays closed and do the compression test. This will dis-able the compression release. On a OHV engine you can do this by just pushing down with finger pressure since the valve springs are weaker as compared to a L head valve spring. Do not let the push rod fall into the block.
While you are in this area check the valve clearances.

Also adding some choke at idle and the surging and hunting decreases indicates the engine is running lean. (too much air or not enough gas)Some of the idle jets have several small cross drilled holes and a center hole. All the little holes have to be very very clean. Just one of the itty bitty holes restricted will cause such. May have to use a torch cleaning tip tool or carb type jet cleaning tools instead of just air cleaning.

Send KE4ABB a PM about his recipe for resizing just a itty bit. If you don't find valve issues.
I've done such also to some carbs with real good results, but nuff said.
I've also seen some of the low emission Briggs carbs with a low speed adjustable idle jet that would idle OK but hunt and surge at medium throttle or off idle speed and just a 1/8 turn of the idle jet would correct the H roughness or surging. (then check the critical L adjustment at both cold startup and warm engine)

[KE4AVB]

L-head...I like to see you disengage the rocker and if wish to remove the push rod you're need to drop crankcase cover, pull the cam, to get the pusher (lifter) out, then re-install the cam (timed correctly of course) and the cover.

[Arkie]

L-head...I like to see you disengage the rocker and if wish to remove the push rod you're need to drop crankcase cover, pull the cam, to get the pusher (lifter) out, then re-install the cam (timed correctly of course) and the cover.

Well it is a L head. (with 40 psi comp ) I was thinking OH valve.

Better get the comp corrected first. (might just be a head gasket but don't forget loose valve seat that has not completely popped out yet. With compression that low He should be able to ear test with a low pressure leak down, listening to the intake/exhaust and around head.

[38racing]

remove the breather cover (probably the carb first) and check for valve clearance.L heads apparently lose clearance over time. You might have to remove a valve and grind some off the stem.