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dentwizz

Briggs flathead twin IC issues

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dentwizz
I have a 1984 JD 116 with a Briggs IC twin in the shop and it has an electrical device with three hose ports that connects a single wire into the harness. The one hose goes to the pulse drive hose that drives the fuel pump and the other two go from the other end of the cube up to a pair of ports on the air filter base(one with a pop up valve). What is it for? The other flat twin is a 14hp IC twin II series that has been rebuilt. Last year I got the whole machine for $25 because the PO ran it for most of a summer on one cylinder(broke rod 1). I took 50 peices of rod out of it but the rest was alright, and put it back together. The problem is it runs rather lopy. Key is fine, valves are clearanced and lapped, ignition coil is new(PO did that). It did seem to "spit" a lot out the intake even after I lapped/ground the valves. Could that be a cam thing?

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dentwizz
Wierd thing is the Deere still does a Kholer-esque backfire after shutdown. Runs good otherwise so the owner accepted for the time being(didn't want a lot of R&D time). The still somewhat vexing one is the other twin. Today I got new fuel pump diaphragms and it helped a hair but not a ton. Then it occurred to me to try taking the exhaust headers off. It ran decently. So I cut the muffler open and found nothing odd but cut a larger hole in the internal baffle, welded it back together and now it runs. Not perfectly but it does at least run and mow now. Still skippy at times for some odd reason. The flywheel key is good too(first thing checked and rechecked) and the coil mount does not allow re-timing(grr).

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1Litre
Be sure you have the valve clearance set correctly. That may cause the valve not to seat if there in not enough clearance . There is a way to check valve timing if you are interested.

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1Litre
4 strokes have a valve overlap period when both IN and EX are open at the end of exaust stroke and beginning of intake stroke. This happens with the piston just approaching TDC thru TDC to just after. Most engines will have split overlap ( when both valves are open the same amount of lift ) at TDC or + or - 2 deg. which still lookd like TDC at the piston . If you are off a tooth the split overlap will be before or after TDC and that is a quick way to identify the error in valve timing. This also places the ignition timing off spec for those engines with points operating off the camshaft .

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D-17_Dave
Odd air flow through the engine and sometimes back pressure coming out the carb are all indications of the cam off time. This can be checked just as 1litre stated. He is spot on and this is true for most L head engines, and all Briggs Lhead's. Both valves open the same amount at TDC of the dead stroke. You can pull either head off and check this without tearing the engine apart until you have to.

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dentwizz
Took it apart today and it was in fact the cam. It was offset by about 3 teeth, and it was during reassembly of the oil pan that it happened. To avoid the jump(due to wobble and valve springs) took a rather lot of creativity to keep it in place. Now it runs much better.

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dentwizz
With the cam adjusted, I did more extensive testing today as to why the cyl 1 exhaust temp was a lot colder than cyl 2. They were both still hot after a couple minutes but the 1 temp was readily touchable and the 2 was typical temp. That was also with new RJ-19 plugs. Upon reinspection, the intake manifold gaskets were good and sound, pcv and valves were intact and clearanced but the cyl 2(the good one) exhaust valve was leaving an imprint on the cylinder head. Wierd. Would that be from a bent cam?

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dentwizz
Still dissatisfied, I took the cam out today(What a chore on a twin, had to take the valves all out and everything) to see if it was bent. Sure enough, it was way bent! I little time in the arbor press and voila it's straight. Too bad it took so much time to get it apart, because now I didn't have enough time to get it running before the noise 'curfew'. Have to test tomorrow, but I have a good feeling about it.

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