Fix or Replace

Jeff Rhode's picture

Hey everyone.
I have a 1969 G series with a 1983 Briggs IC that has been running faithfully since I put the motor on in "83. The carb crapped out this spring. I am no mechanic, and the guy I brought it to rebuilt the carb and it ran fine for a cut or two, but is sputtering and misfiring now.
I love the engine and to feels like it has plenty of compression. I don't want to replace it, but i am not able to troubleshoot. Any thoughts? I have parts to trade for fix's, including another original 3.5, deck, wheels, handles. This is not a disposable motor or motor...I don't want to lose a piece of history that works better than any "homeowner" machine I could buy now.

NOO!!! Do not get rid of that engine unless you want to sell it to me:) I have that same engine on my sensation mower. It has to be the best Briggs ever made. Nobody makes a good small engine anymore that will work even close to as long as the old Briggs I/C's. Between the cast iron bore and the simplicity of it there is not a lot that can go wrong. Make sure that the carb is mating flush to the gas tank. If it is not this will cause and air leak throwing everything off. Luckily these gas tank carbs are pretty easy to find so you could probably order a whole new carb. No engine of today will come close to the awesomeness of yours. Post a video of it running and send some close ups of the carb and I can then help you out more.

By Jpethan
Jeff Rhode's picture

I know...I want to keep it. I think you are right though-there is a little gas on the tank after it runs for a little while. The engine starts and the longer it runs the more I have to turn the air screw in to keep it going. After 10 min or so the screw is all the way in and it is sputtering. The first cut after the guy rebuilt the carb it was fine. Next cut it ran like that-maybe the mounting screws for the carb to take vibrated loose. I'll check that. Thanks!

By Jeff Rhode

That sounds to me like the top of the gas tank has warped a bit. I had this problem on one of my old Briggs. What I ended up doing was taking the tank off and sanding the top of it with 800grit sandpaper on a flat surface. Take your time when doing this because you need it to become flat. Also there is a gasket between the tank and the carb, with time the rubber breaks down rendering the gasket useless. Most small engine shops have these gaskets in stock or you could make your own. If all else fails you should be able to just order a new tank and carb assembly.

By Jpethan
Jeff Rhode's picture

Thanks for the suggestion!

By Jeff Rhode

I need time to get my shop in order, I'm currently running low on parts but this winter I should be doing motors again.

By Rocco
Jeff Rhode's picture

I snugged up the screws between the gas tank and the carb and got 1/8 turn on each. I took the engine cover off and the large tube that goes to the top of the engine from the back of the carb was really loose-so I tightened the 2 screws on top of the engine. I started it up and adjusted the carb and it was running great. Still a little gas on top of the tank when it was running, so maybe the gasket or warped take, like Jpethan suggested. I can't see where else it would be coming from. While I was cutting though I had to close the air screw on the carb a half turn 2 times because it was losing power and not running smooth. Any thoughts what to try next?
Thanks!

By Jeff Rhode

What I would try next is to take the carb off the tank and use some rtv gasket maker to seal it up. Be sure not to get any on the carb diaphragm (the black membrane thing with a spring coming out of it) because that could affect performance as well. Just make a small bead all around where the carb attaches and see what happens. If this fails and you have determined that your tank and carburetors mating surfaced are flat I would then buy a new carburetor. If you could post some pictures close up of the carb. I can look at my engine and compare to make sure there is nothing obvious.

By Jpethan
Jeff Rhode's picture

Thanks. This weekend I'll try and send the pictures and take a look at the gasket.

By Jeff Rhode
Jeff Rhode's picture

So 2 months later (after using a cheap mower and cursing at it every week) I had time to put it up on the bench and take a look. It turns out the gas tank has a crack in it-I assume that would cause the same behavior as a leak at the gasket, since the fuel pump is between the tank and carb....right? I have another old engine I can pull the tank off of to try.

By Jeff Rhode
Kopfjaeger's picture

Yes, if you are sucking in air at the carb base, it will act like a ruptured diaphragm. Did it crack at a screw hole? Nice catch!

By Kopfjaeger