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blow back through the carb

N

newatrebuilding

New User
I have a 12 HP Briggs and Stratton L-head engine. I broke the connecting rod. I have never worked on one of these before. Replaced the rings and the connecting rod. It ran fine before I broke the rod.
Now I get blow back through the carb when it turns over. I checked the valve timing and it is dead on. did nothing to the valves, except that when I took the camshaft out the lifters fell out and I have no idea which one was which. When I check the valve clearance I don't have any clearance. I am mystified about what could have made it change. Is there anything else that could cause the blow back?
 
Lifter have to be intake and exhaust and if switched can cause funny problems. Also the PVC valve many have gotten metal etc in it and that too would cause that problem
 
The tappets should be the same,you can easily check this by going to partstree.com or jackssmalleng.com & looking up assembly draw/parts list for your mod/type number eng,pn for tappets should be the same.

IF you are losing clearance on both valves you probably are 1/more teeth out on crank/cam gear timing or timing set incorrectly.

Due to fact you didn't post mod/type numbers of eng & weather plain bearing or ball bearing crank/cam timing is set differently.On plain bearing eng the crank/cam timing marks are set dead on.If a ball bearing eng,timing is set when crank pin almost at TDC and timing mark on counterweight/cam are out from behind/slightly below bearing.If you're loseing clearance only on one valve & crank/cam timing set correctly I would suspect an acr problem depending on which valve acr on.
 
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