Ok, Z425 with Briggs 23HP OHV engine. Model 445577-0122
Checked flywheel keyway. ok
Replaced carb with new. ok
Checked coil gap. ok
Spark plugs. ok
Adjusted valves, 1/4 inch past TDC ok (twice)
Run like a top before shutting it down last time. Pops and backfires through carb trying to start now.
Checked compression in both cylinders today. 180 on one and 120 on the other. 180 seems awful high to me.
I did all the things above and it still backfires through the carb when trying to start.
Before I rip into the low compression cylinder, is maybe the valves still out on the low compression cylinder?
Forgive me but it has been 50 years since I worked on these small engines at this level. HELP?
Thanks
#2
ILENGINE
the side with the 120 seems more realistic for that engine. I think I would be looking into the cylinder with the 180. Maybe a valve issue, along the thought of the cam lobe is worn down and the exhaust valve isn't staying open long enough to exhaust therefore you are getting pressure push back into the carb when the intake valve opens.
Pull the valve covers and spark plugs and rotate the engine over by hand and make sure all the valves are opening the same amount.
First trick i to remove both of the kill wires form the coils.
Problem goes away = wiring fault
No joy then then remove the plugs, one at a time.
If when you take the 120 psi one out the popping through the carb stops then suspect a loose valve seat on that side
Ok, had visitors today so didn't get much done. I did first thing this morning recheck the valves and the 180 cylinder was out of tolerance loose. Badly I might mention. Still don't know what I could have done wrong. Readjusted the 180 and the 120 cylinders and guess what? I reversed the compression between the cylinders. Now 180 is 120 and 120 is 180. Rechecked the new 180 cylinder and readjusted and it still reads 180. I guess I must not be getting something right when I adjust that cylinder.
I will wait till tomorrow and see if I can figure the 180 cylinder out. At least now I know I must be doing something wrong.
Remember it is a 4 stroke engine and the valve lash has to be set on the compression stroke.
A common mistake is to set one side on compression & the other side on exhaust
Remember it is a 4 stroke engine and the valve lash has to be set on the compression stroke.
A common mistake is to set one side on compression & the other side on exhaust
Thanks sooooo much for the reminder. You were spot on. I adjusted one cylinder on compression and the other on the power stroke just thinking both valves needed to be closed. Been a long time.
PITA to get the compression tester in one cylinder as the engine is still in the Z turn frame but I got it done. Both showing around 120 now and she fired and runs.
We have all done it at least once so don't feel too bad about it.
Glad to hear you are up & mowing.
And thanks for the closing post it helps other who might be looking at this thread in the future to actually know what the problem actually was.
