Bobcat 722 fuel problem

Shuttlebug

New User
First time posting. I've got a Bobcat 722 (Ford 1.6L Pinto-style engine with Zenith carb) which seems to be running too rich. The plugs come out black and sooty, sometimes there is gas overflow when cranking the engine, and it stalls and dies whenever it encounters the least load. After it dies, I have to cut off the fuel and crank for about 40 seconds to get it restarted, during which time the exhaust smells like raw gas, which is why I think it's flooding. I flushed the gas tank and it's got fresh fuel, and a new high-capacity fuel filter with water trap, a new fuel pump, a new fuel pressure regulator set to the minimum 3.5 psi listed in the manual, new carb floats set a bit lower than listed in the manual, a new carb kit with new fuel inlet needle valve, and the carb is clean and there is no blockage in the bowl vent. It also has new spark plugs and new electronic ignition, timed spot-on. I'm running out of ideas for things to try. Anyone else ever run into this problem? I think this could be a nice little loader if I could just get the engine running good. Thanks, Nick
 
Shuttle bug, Sounds like the float is full of fuel making the carb ask fot more fuel. If the float is set correctly and the needle and seat is right, the one thing left is the float, Either draging or full of liquid(fuel). LOU
 
A lot of questions .Why the new float assembly, Was the original damaged? was the replacement float correct? Settings right on the money?If as you state, all; new parts. carb cleaned and it still floods out,can only be with the needle/seat/float assembly.we have the same unit as you do.722 Bobcat. I would re work the float measurments and check the seat where the needle goes in ,to make sure the needle is seating properly. Seat in the body of the carb is not worn out(highly unlikely) But if it was rusted badly or varnished to not allow the needle to seat properly,could cause it to flood over.Hope you find the cause of the overflooding. LOU
 
I think Lou is right, sounds like a needle and seat problem. Causes are easy, trash blocking it open, incorrect float setting, needle/seat worn out or float being too heavy (on brass floats a leak allowing it to fill with fuel and on composites old and has absorbed fuel to the point of being too heavy). My outboard (83 merc 50hp) had bad composite floats this spring making it flood.

Rick
 
To fill in some of the details: the previous (brass) floats looked good and I couldn't hear or feel any fuel when I shook them, but I also couldn't find a weight specification to rule that possibility out. The Bobcat dealer in the nearest major city also didn't have the weight, and could only suggest buying new floats to go with the carb kit, (which would also avoid a separate $10 shipping charge if I later decided I needed them). The new floats were the same weight and shape as the old ones, but since I had new floats, I decided to use them just to eliminate those as the problem. "Correct" float position is ambiguous because the manual specifies three different height settings, one of which is impossible with the bowl I have. The mechanic at the dealership said to just set the tops of the floats level, and they are currently tipped slightly leaner than that. It looks like there is lots of room between the floats and the bowl. And when I flip the carb dry so that there is the weight of the floats against the needle valve, I can pressurize the inlet to about 45 psi air pressure before there is any leakage past the needle, with no noticeable leakdown at lower pressures, so I think that should rule out alternate fuel routes. And the gas that comes out of the bowl when I disassemble the carb appears clean, and it's the same gas that works great in other machines here. I'm also thinking a grit problem should be intermittent, whereas this problem is highly consistent.
Logically, it doesn't seem possible that the bowl could be overfilling, but if it isn't that, the only alternatives I can think of are that it is somehow sucking too much gas despite correct fuel level, or else there is some other problem which can have symptoms that look just like flooding. But I've got no ideas for either of those alternatives.
Nick
 
Is that one of the engines with a timing belt? If so check your valve timing. Ma want to check that anyway even if it's a gear of chain system. If everything is right in the carb and the ignition timing is good thats about the only thing I can think of short of worn/burnt vlaves and or low compression problems due to ring/cylender wear.

Rick
 
Just a couple more thoughts,1- Could the float be twisted on the float pin (when it was set for float height) so it will not raise or lower with the gas level? 2. Could the choke not be operating right, could it have been moved to closed position when you put it back together and causing the engine to run rich?Don't know,but just a few more possibilities.
Reguards
LOU
 
Thanks for the suggestions guys. Regarding the choke, it's a kind of primitive control linkage, operated by twisting a bent rubber hose, but it seems to work, and the choke is definitely wide open. The float hinge pin is shiny new (came in the carb kit) and slips in and out easily, and the floats have a bit of play on it, so there doesn't seem to be any binding there. I don't know how to check whether it's running the correct jets. I can't find anything in the shop manual on that, but since the engine is badged as a rebuilt engine, I'm assuming that much, at least, is not original. And this machine was previously owned by a contracting company which operates a fleet of loaders, so parts swapping certainly could have taken place. I'll see if I can track down what jets it's supposed to have. The valves are timed by a short chain, which is apparently at least still in place, for it to be running at all, but I've never had the chain cover off to check the timing marks, so I'll get into that when the rains stop here. Valve lash was okay a couple of months ago, but I'll recheck everything there too. I'm not sure if a valve problem could cause dripping gas at the carburetor, but for all I know about it, maybe it could create some sort of abnormal venturi condition. It's something to hope for anyway. I'll post a follow up if I can find anything.
Nick
 
If, as you say everything is correct with the carb and ignition timing then there are only a few options left.

1. Fuel pressure too high.

2. Low compression.

3. Valve timing that can cause poor compression.

4. Bad or burnt valves.

Rick
 
Old Tanker has a good idea, about fuel pressure being too high.We have the same problem on the OC 46. It takes only 2-3,5 psi fuel pressure and with the electric pump that came on it 4.5psi, causes the carb to flood over.We're changing the pump back to 2-3.5psi electric.Hope this helps.
Reguards.
LOU
 
I was able to check the valve lash between rains, and all were spot-on according to the manual. If I can find where my compression gauge got off to, I'll check that next, but just putting my thumb over the spark plug holes, it felt like pretty good push-pull turning the engine by hand, and the engine oil is still pretty clean. Checking valve timing requires a bit of engine disassembly, so that'll have to wait for drier weather. The fuel pressure regulator I mentioned is Mr. Gasket brand, which is supposed to be a reputable unit, but I don't have a way to check that it's actually doing what it's supposed to. The manual lists 3.5 psi as the minimum, but I'll try dropping it below that to see if that does anything helpful. Still haven't found a way to ckeck what jets the carb is supposed to have, but I'll keep asking around. Again, thanks for all the suggestions guys. Nick
 
I have a similar problem on a bobcat 720. The fuel problem was that the float was set wrong. Bend the float tang so that the float will shut off fuel sooner. After reassembling carb, hold upright and blow through fuel line connection, is it open? Now turn the carb upside down and blow, is it closed? If you have low compression and backfiring you won't completely fix this problem until you fix the leaky valves. Also these engines run hot and you may have fuel boiling in carb. Are all the shrouds on engine present? Is the screen clean in front of flywheel fan? Are all the manifold gaskets good? Is the exhaust pipe extended far enough so that the hot exhaust is not flowing back into the engine compartment? Is timing correct and timing advance working?
Did you make the factory recommended metal cut between the exhaust and intake manifold with a hack saw for hot weather operation? I have a VH4D WISCONSIN.
 

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