Sticky valves?

Don B.

Member
I have a 7hp Briggs L head (made in 1980) that has sat for around 10 years. It is on a snow blower.
Hot spark, starts easy after cleaning up the carb, (was surprised to see it was actually pretty clean to begin with) but bogs heavy, can't find happy medium for hi speed carb adjustment between running full speed under load vs not under load though it does respond as expected to changes in carb adjustment. Doesn't smoke at all whether under load or not. Wondering if the valves could be sticking on account of the bog.
No compression test done because of the compression release Briggs builds into the cam but it does pull over on the recoil with a typical amount of effort to pull vs others I have worked on over the years, no easier or harder to pull over than expected so I believe they are sealing when closed, I have seen much worse carbon build up thru spark plug hole on other engines.
Spark plug itself that came with it nice and tan color, no excessive build up so I am thinking that when it was regularly run it was set up pretty close to right, and is overall a pretty healthy engine.
So what else would cause it to bog so heavy, which is why I was thinking that the valves could be sticking a bit.
Thoughts from the peanut gallery?
 
Don't know model# or which carb so we will guess. Take float bowl off, unscrew unscrew seat for main jet, Now you should be able to get at the nozzle. I am thinking some of the small holes may be plugged of partially plugged.
You probably don't need to remove carb to do this.
If I guessed wrong on your carburetor I could be something different.
 
It's a 2 pc flo jet.

The first thing I did to it upon bringing it home, was to pull the carb, dunk it in my ultrasonic cleaner and put a kit into it. It was surprisingly clean to start with for both the age of the machine (and engine) as well as the length of time it has sat since last used.
The carb does respond as expected to adjustment.
But when I have it adjusted to run good while not under load, it bogs terrible when I try to blow snow with it. I adjust on the fly so it runs as well as I can make it run under load
(Have to richen it about 3/4 turn) and when not under load, it then surges worse than most Tecumseh ones do. I've had my rounds over many years of playing with small engines with this model of carburetor, I don't think the problem lies there. Nor do I think the engine is that tired, or shot at this point.
 
Since you say its a 2 pc. Flo-jet:

1. the vent for the float bowl goes through the gasket. Make sure it doesn't leak. If you can slip a .002 feeler gauge in the side where the vent goes through, its getting outside air and the fuel level is probably too low in the carburetor.

2. If not #1, then remove and clean the nozzle that runs between the two pieces, and remove the idle valve and clean in there again.
 
I agree with the magic of Seafoam.I do not know if it works on the newer BS. But the old stuff you spin the engine backwards and it will rebound hard if the compression is good.(pull the cover off of the flywheel)
 
Are you getting blow-by into the crankcase when you notice bogging under load? Sitting that long may have triggered sticking rings. Soaking with ATF or Marvel Mystery Oil could help.

I agree with the Seafoam approach as well. Can't hurt.
 
haven't yet pulled sheet metal sno gard back off so I can access the carb throat to pour in MMO, but I put ~3-4 oz of MMO in gas tank (1 gallon cap, 3/4 full of fresh gas) and probably 1/3 bottle of Seafoam for good measure. Let it run 10-15 min in driveway earlier, smokes good now with all that in the gas haha.... adjusted hi speed mix to get it to run smooth at hi speed but not under load.... will push it outside and let it run a while tomorrow after work once again. Thurs it looks like Im gonna need this thing if the weather reports arent lying again.... see what happens.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top