I have an older Briggs 5hp flathead in my mini bike. I recently put a new vm20 carb kit from ec carbs on it. The engine will start and idle great. But once I start riding and open the throttle all the way the engine sputters as if it’s not getting enough gas. Then every once in awhile if I roll into the throttle gently the engine will run smoothly but still doesn’t feel like I’ve got full speed. I’ve tried adjusting the carb over and over to no avail. I had this same problem with the pulsa jet carb before I swaped to the vm20. I’m running points right now and have ordered a new pointless ignition from OldMiniBikes Warehouse. But I don’t really think it’s going to fix the issue. The gas tank vent seems fine and the air gap is set to .012. If any one has any advice I’d greatly appreciate it. Thanks!!
Briggs 5hp won’t go full throttle
- Thread starter Emerica1975!!
- Start date
A trick that I learned recently is to install an exhaust valve spring on the intake valve. The exhaust spring is a little bit longer and stiffer, so it lets the engine rev a little higher before the valves float. I would get a couple of new exhaust valve springs and a flathead spring compressor, learn how to adjust the valve clearance,(springs must be removed anyway) and try it again.
You really need to get yourself one of these:
https://www.ebay.com/itm/354638382413
For anyone working on these old Briggs flatheads this is a "must have" in their reference library.
Michael
https://www.ebay.com/itm/354638382413
For anyone working on these old Briggs flatheads this is a "must have" in their reference library.
Michael
I tried starting my engine this morning before leaving for work. I didn’t get a chance to run it for more than a few minutes. But it seemed to run exactly like it did before. Cutting out when I try to rev to wide open. I’m really not sure where to turn to next. Is it possible my points could be causing this. Today in the mail I should be receiving an mag/coil to install and eliminate the points. Maybe this will help??
The valve gap spec is to be set with the compression release “out of the way” so piston at tdc compression stroke. Then follow through till the piston goes 1/4 down into the bore. Stop check valve gap specs with those new valves. next the ol’ 10-20-30
10-magneto gap
20-gap for points
30-spark plug gap.
Go grab the plug out of the push mower and see if it clears up? Or better yet a new plug all together. Next if you can get it to run for any period use WD-40 hose down the running engine in the intake area anywhere there is a gasket. Carb against intake intake against the head spray those gaskets. If there is a leak the bike will try to stall. Cup your hand over the carb with it running but be careful doing this. if it goes to die you cup your hand over the carburetor it rises to life and then tries to die again could be your float level
10-magneto gap
20-gap for points
30-spark plug gap.
Go grab the plug out of the push mower and see if it clears up? Or better yet a new plug all together. Next if you can get it to run for any period use WD-40 hose down the running engine in the intake area anywhere there is a gasket. Carb against intake intake against the head spray those gaskets. If there is a leak the bike will try to stall. Cup your hand over the carb with it running but be careful doing this. if it goes to die you cup your hand over the carburetor it rises to life and then tries to die again could be your float level
Im not a huge electronics fan, kinda bores my head and visual senses, but magnetron ignition (Briggs) or breaker less electronic ignition was one of the best advances on the internal combustion engine by far in my opinion. Even beats fuel injection in my view. I like point systems for nostalgic sake but they are fiddley to keep right. Glad you got it correct.