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5 hp briggs

Geo-TH,In

Geo-TH,In

Well-known Member
I had trouble starting my old 5 hp briggs flat head. Took breather off and added a little gas. When it started, for about 15 seconds the intake valve didn't close all the way and it would blow gas out the carb, miss and blow black smoke. I didn't add that much gas to create the problem. I'm wondering, do the old flat heads use the intake valve as a decompression valve?

Is it possible rust or carbon didn't let the intake valve to close?

Or is it possible I have a case of intake valve set recession?
George
 
I would pull the head and see if you can tap that valve lightly to see if it will close. It may have some carbon or rust causing the problem. Squirt some engine oil around the stem. If it will close I would rotate the engine several revolutions to make sure it keeps closing. Hal
 
El Toro
After looking at old cams, there is no decompression valve. That leaves carbon and rust. Motor doesn't get used much. Once it got over the spell, motor seems to be better.
If it does it again I may pull carb and spray valve stem. If that doesn't work pull head and check valve clearance
Thanks, George
 
Old gas caused it to stick. Been there before. It usually starts for me but as soon as you shut it down it sticks.

Take the head off and spray some miracle juice down the valve guide. Work the valve a few times and have at it.

The older flat heads had "Easy Spin Starting". Never thought about it at the time, but it may have been a compression release. Either way, probably old fuel.
 
Common carbon problem or if your real unlucky the valve seat is coming loose which I have seen.
By the way got the timer yesterday but not had the chance to work out the wiring of it. Also have not found that cam found the head to that engine but so far not the rest of it
 
I do have staybil in gas. It sure acted like it may have a compression release on intake. Once it cleared up it was fine for the half hour I used it.
 
You should be able to figure out wiring with the instructions I sent.

If you find engine numbers, I can look it up to see if it's the right cam.

The numbers on timer may not be the same, but the location of termials is all that counts.
 
I found some numbers on one engine but did not get a chance to write them down due to a guy who has a vette in my shop coming in to work on it today
 
I have never seen,nor do I believe you will find a compression release on the intake valve. This would cause blow-back or backfire through the carburetor, which can not only cause problems but is dangerous. If you have ever seen an engine blow fire back through the carburetor, you will know what I mean. The compression release lets the compression escape through the exhaust valve.
 
ShadetreeRet
That's what I thought until I lost the cam on an 18 hp briggs. Decompression release was on the intake, yes intake. My 13 hp honda the decompression release in on the exhaust.

My 5 hp was blowing gas out the carb at least 8 inches, yet no back firing even though the engine was running extremely rich. That means the intake had to be closed when engine was firing on the power stroke while the intake was open during the compression stroke causing blow back through the carb. Sounds to me like there is decompression happening on the intake valve. I'll do some research on the engine.
George
 
George, I stand corrected. I will admit that I am not up to date on the newer engines, but to me it doesn't make sense to put the compression release on the intake. I guess some, just out of engineering school pencil pusher, decided he knew better. Go figure.
 
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