Briggs opposed twin idle/starting issues

[tkos115]

So I currently have the displeasure of working on my neighbors riding lawn mower that has a Briggs and Stratton twin opposed cylinder engine. (42A707-2238-E1). The problem I'm having with it is it seems to start a bit hard, more so when the engine is hot. (Sometimes it will crank and crank but not start). When it's running it seems to idle pretty high even though the idle screw is set all the way down. It will idle high as well as "hunt" a very little bit but its very slow in the rise and fall of the engine speed. When its above idle it runs perfect and seems to have plenty of power. Because of it idling high I started to check for an intake leak, which as it turned out a bolt on the right intake to engine side was missing. So I put new gaskets in on both sides and it's pretty much the same problem, maybe a little bit better. So next I took some brake cleaner when it was running and started to spray it around all the flanges on the intake. The only place it seemed to have a leak was at the throttle shaft going into the carburetor body. It was a very small change but enough where it was speeding the engine up a tiny amount. Could that be causing these running/starting issues? It almost seems to flood out when I try to start it and it's hot, but starts decent when cold. It also seems to run a bit rich when it's running as well, not enough to make your eyes water but it smells rich.

For the sake of elimination I did take the carburetor apart to see if it was dirty and it was pretty much spotless. But I did clean it some but there was no change in the issues.




Any ideas? Thanks for your time and help!

 

[Rivets]

Have you check the spark when hot starting. Might have a coil going bad.

 

[tkos115]

Yeah I did, it seems to have a decent blueish white spark even when it's hot.

 

[tkos115]

So, just an update... I checked the spark again on the plugs and noticed that the RH side was getting a minimal spark when it got hot. So when it was running I pulled the wire off the LH side and it would stall at idle. Pulling the RH side when running would cause it to keep running but almost want to stall out. So I figured that I had found the problem. I ordered a new coil and installed it tonight... same exact issue. At this point I'm starting to pull my hair out. Everything is good that I can check, valve lash, spark, plug gap, did a leak down test (good), compression (135psi each cylinder), clean carburetor, and new filters. The only oddity I noticed is that when the engine is running even at idle the carburetor seemed to be dumping a fair amount of fuel into the engine. So my next thought was that either the float height isn't right or the float needle isn't sealing correctly. So off comes the carburetor again to check. So on this one the float height isn't adjustable so I do a test on the float needle to make sure it's sealing correctly. I put a vacuum tester on it and it holds vacuum perfectly meaning it's not leaking extra fuel in. So I start to look over the carburetor very carefully to make sure I didn't miss anything like a lose or bad jet. Then I notice it... the throttle flap is bent a little bit causing half of it to stay open a bit on one side. I have no clue how this even happened as prior to this the carburetor has never been taken off or apart. After taking it out and making it flat again and putting it all back together it runs great. Has anyone else ever had this happen? There was no scoring to indicate something was lodged in there at one point or that a tool or something hit it and bent it somehow. the metal flap seemed to be very sturdy still so I'm not sure how this even happened but I'm glad it's finally over..