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B&S carb headaches

occidental_tourist

14 years ago

Have a 21 horse V-Twin I/C B&S Engine Model 4045A7 on a Murray 465306x8 garden tractor.

If it matters: type is 0211 E1 and Code is 031103YG

I'm having constant starvation problems when the tractor has not been run in a while and occasionally during start and stop engine operations.

Always starts with starting fluid and when it does run off the gas tank it runs smooth and never quits. When it is not starting I often seem to able to solve the problem by tapping the carb with a hammer that makes me think the pin is hanging up in the seat.

I've seen some carbs do this, but obviously it doesn't happen every time.

Don't know if this just says replace the needle and seat anyway. Or if there is any additive I could put in the gas to minimize sticking of the needle on the rubber seat or?

Would also be interested to find out if anyone makes a permanent or test bowel for these carbs that is clear. Then I could actually observe what the hell is going on. (Kind of like a temp plexiglas door for a dishwasher which is how we figure out performance problems with dishwashers).

Also, I can't help but be interested in the theory of ops for these carbs with some kind of magnetic solenoid where the jet adjustment screw used to be. I have several of these in service and don't think that carb adjustment or the functioning of this solenoid has ever been a problem but the whole thing is kind of black box to me at the moment compared to the accessibility of the old adjustment screws. So some kind of primer on what this is actually doing. Is it some kind of fuel shutoff or a governor . . . ?

Thanks,

Brian

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Comments (2)

mownie
14 years ago
Try adding a bit of Seafoam (additive for fuel) to help remove any varnish deposits that "might" be sticking the needle to the seat. Also, add a bit of Marvel Mystery Oil to the tank, it will serve to protect against corrosion, give a little lubricity to the fuel, and also help prevent against an intake valve sticking (and the intake valve alone is reason enough for the MMM).
The solenoid valve you asked about is to minimize the occurrence of "afterfire" (the bang aka "backfire") when the engine is shut off hot. The solenoid only controls fuel flow through the main jet. It DOES NOT stop fuel flow through the pilot (idle) jet. It WILL NOT protect against fuel overflow from a defective carb in conjuction with a gravity fed fuel system (where tank is elevated higher than the carb), for gravity fed systems, an inline fuel cutoff valve is neccessary to protect against fuel drowning.
Transparent bowl?? My guess is that IF such an animal exists at all, it would be found in the respective laboratories for R&D at carb designers such as Mikuni, Nikki, Walbro etc. And if they actually did offer one for sale to public, they would probably price it at $200 or more.
occidental_tourist
Original Author
14 years ago
The last time I had this trouble with a float needle and seat on a Tecumseh on an Ariens snowblower, it didn't really turn out to seem to be varnish or any build up of contaminants. As I recall the seat for the needle was a rubber ring, can't remember if it was a small flat rubber washer similar to a hose washer although smaller or an o-ring. But the needle was just hanging up in the rubber.

I think eventually I just bought a new needle and seat. Now in this case it seems it could be either the anti-backfire plunger or the float needle. I don't know if the float needle on these carbs has a rubber or brass seat.

Seafoam certainly seems sensible and I had forgotten the old sticking valve and using a little marvel oil.

That same old ariens snowblower had a sticking valve one season and I had to pull the head. so a little prophylactic mystery oil sounds good.

While I've been trying to reason through this problem I've gotten the mower started enough to run down the full tank of gas and I think at this point the level is below the carb so I and pull the carb without having to go too crazy to keep gas from running all over and that will allow me to test what seems to be a vacuum operated fuel pump as well.

Once I break it down, maybe this weekend, I'll let you know what I find.

Thanks,

Brian
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