BCS 850 fuel problems

cmyoung2 · Jul 26, 2014

BCS850, 14 hp B&S Vanguard. Motor seems to run fine with light loads on level ground, put the 32" bush hog on a slope and it seems to run out of fuel. Let it sit, it will recrank and run for a short period. I thought dirty carb, cleaned, thought kink in fuel line, replaced all the lines. My repair shop was surprised that the motor was gravity feed, he thinks that engine was designed to be on a stationary unit, and he was also thinking vapor lock, so I added a electric fuel pump. Still dies especially on slopes after 10-15 mins. After last shutdown, I opened carb and it was low on fuel. Fuel pump is pumping fine, new fuel filter. Any ideas?? I am getting rather frustrated.

Tbolt76 · Jul 27, 2014

I had an 850 that would act like this if you let it sit all winter with gas in it. Mine was gravity feed, as I thought all of these were, and many other machines were like this as well, shouldn't matter. Bad gas clogs these carbs up unless you put in Stabil or some other treatment, or maybe drain altogether. Find a reputable briggs dealer who can rebuild the carb. It doesn't take much to clog the little passages in the carb with varnish, etc. When my Vanguard engine blew (camshaft came out the back of the engine housing), I bought a Honda 13hp from Earthtools, best move I could've made.
Tom in Raleigh

cmyoung2 · Jul 27, 2014

Tom, Had the carb off, soaked in Chemtrol for three days (at the B&S repair shop) cleaned it completely more than once. I only use non ethanol gas in all my small engines.
I can hear a gurgling noise and see air bubbles in the gas tank between start attempts, but can't figure out how air can get into the lines. All fittings are clamped with screw type clamps, all gas lines are new 1/4" lines made for gas. I like the Honda idea if I could afford it.

Tbolt76 · Jul 27, 2014

Is it possible that the fuel shut off is cracked enough to let air in? I don't think that a second/auxillary fuel pump is necessary. I'd call Joel @ Earthtoolsbcs.com to get his help, he's the biggest BCS dealer in the country. I hope your shop is reputable, I've run into a few here in the Raleigh area that talk a good game, but that's about all they are good for. Maybe the pump is pumping to much fuel compared to demand and flowing back upstream? Sometimes pumps have a vent line of some sort on older cars. I'd think adding a pump could be part of the problem. Are the spark plugs fuel fouled (black)? That would indicate getting too much fuel in addition to rich exhaust. Keep us posted.
Tom

cmyoung2 · Jul 27, 2014

No fuel shut off valve. Fuel pump has no vent. When it dies, carb bowl is almost empty, but when the pump is turned on, fuel flow is good. When the engine runs, it is good, right at 3200 rpm, no sign of running rich I still think a vapor lock issue, but thought the pump should push it through. Did the same thing without the pump.

Tbolt76 · Jul 28, 2014

Are your cooling fins clogged? There are shields around them that can clog if you are doing a lot of mowing. Vapor lock (I assume you already know this) is usually a function of running hot. Mine had clogged with leaves from flail mowing long windrows of them to grind them up for mulch. If not, I still keep coming back to something wrong with the carb or maybe its sucking air---bad gasket from rebuild? Mine had two mounting gaskets with a plastic plate in between, maybe there is something going on there? If you didn't replace those gaskets (which I assume you did-they don't come off intact usually) then maybe they are heating up and leaking?
Tom

cmyoung2 · Jul 28, 2014

Cooling fins are clean, took the cover off and blew everything out. They actually were pretty clean for what I think is a 95' machine.
When I bought it a couple of months ago everything was OEM I think. Gas lines were formed, had the cut off valve and filter. Ran fine for short light work, but when I started mowing it would die after 10-15 minutes, so I figured dirty carb. Took it apart, cleaned with carb cleaner, everything seemed to be open. Inside was tarnished, but not really gummed up like I have seem. No effect, same problem. After a couple of tries at that, took the carb off and had local shop tank clean it just to make sure. They could not find anything wrong. Still same problem. Got to thinking vapor lock because the gas lines do run fairly close to the heads, so I raised the gas tank 1" with spacers to help keep things cooler, and so I could see. Still no good. So I thought 20 year old gas lines might be an issue, replace all, bypassing the shut off valve so they wouldn't kink. Still no good. Took it to the shop, they thought it was a fuel feed issue but could not figure out why, seemed to work better with a full tank of fuel, seems to cut off more on slopes. Have taken the carb apart just after it cuts off, and the bowl is empty, so I still think it is a fuel feed problem. Added a electric fuel pump, 1 to 4 psi, it seems to pump fine, engine runs fine, but still dies when it gets hot. The gasket in the carb is a fiber gasket, does not stick to either side so it is still in good condition. It does seem to die faster on slopes, but that's what I have, very little flat land. And some of the slopes are steep.

farmerboybill · Jul 28, 2014

If I remember right, you replaced the fuel cap? Try running it with the cap loose. Maybe the the fuel tank isn't venting properly. I have a John deere 60 that I've long intended to replace the cap because it'll die after 15 minutes work. Turn the cap, hear a whoosh, and get another 15 minutes run time. If I used it more, I'd change the cap..

cmyoung2 · Jul 28, 2014

Bill, you are correct. I did replace the cap--cheap and easy first

farmerboybill · Jul 29, 2014

I guess I got sick of playing with the finicky Briggs V-twin engine and put a diesel on my machine. It was great when it ran well, but a royal pain when it didn't

Joel likes that engine, he might have some pointers if you give him a call.