Hey everyone. The 722 that I bought uses the old Ford four cylinder and a Zenith carburetor (13805A without the fuel cut off solonoid). The carburetor is new. Ever since I've owned the machine, it has had an intermittent problem with cutting out, typically when it's on a steep slope. It will only restart after running the electric fuel pump for a minute or so- a few sharp taps on the carburetor also seems to help things. I've done a general tune up (new points, condensor, plugs, fuel filter)- when it runs it runs well and always starts easily. I also replaced the fuel pump with another electric one and added a second fuel filter after the pump and before the carb. When it stalls on the slope, I still have strong fuel flow out of the fuel pump after removing the fuel line entering the carburetor so I've pretty much ruled out any problem with the fuel pickup, fuel filters or fuel pump. I've taken apart the carburetor- it is/was very clean, no signs of any dirt or contamination. The manual that I have specifies a 1.5 inch float height. Interestingly the manual for the 720 (uses the Wisconsin engine but, I believe, the same carb), specifies a float height of 1.125 to 1.1875 and then includes the note "It is sometimes necessary to make the float level 1.250 in rough ground areas". This suggests to me that maybe the Zenith carb in this application is marginal when used on steep slopes. Two questions: does anyone know if the 720 carb float height is the same as the 722? I'm guessing that the 1.5 inch measurment for the 722 is the height from the carb face to the bottom of the float when the float is in the "down" postion. The 722 manual doesn't have a diagram showing the measurment, while the 720 manual shows a diagram showing the float level being mearsured from the carb face to the bottom of the float in the "up" position. The parts manual for the 722 has a note "see BTI 180" next to the carb part number. Does anyone know what this note refers to? I assume it is some kind of a technical bulletin. Thanks in advance for any help. Again, it's a strong running machine most of the time, and an expensive lawn ornament when it acts up....
722 carburetor question
- Thread starter 722bobcat
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I can't comment on the adjustment, but have you pulled the carb down just in case there is some rubbish blocking the jets? I know you said its new, but I'd never trust that there was no obstructions with the fault you are having. Even check the fuel delivery path to be sure.
Yes, I did, thanks. The carb fuel bowl and all jets were very clean and in "like new" condition. I added the second fuel filter just to be sure that there should be no possibility of any contamination from the tank reaching the carb. If it wasn't for the fact that I get strong fuel flow out of the fuel line right at the carb even after it dies (it has an electric fuel pump and not the original cam driven mechanical pump), I'd be getting ready to pull the fuel pickup and have a look inside the tank. I'll probably do that eventually, but I don't think it's related to my current issue.
Its almost like the needle to stop the bowl over filling is sticky with you saying you need to tap it from time to time to get it to work. I never thought you could have so many problems with fuel delivery, but over rough ground i can see the fuel splashing all over the place so the level could be anywhere.
Thanks again. That's what I thought initially as well. The Zenith setup is a bit different from most carbs that I've had experience with. Instead of having the needle connected to the float and therefore pulled opened by the float moving lower, it relies on gravity/fuel pressure to open once the float has moved lower. The needle is a rubber tipped one and there is a lot of clearance between the needle and its housing. Both the needle and seat still look brand new. I'm hard pressed to see how the needle could be getting stuck, but I wish the design was more "standard" where the float provided a positve pull on the needle when it is supposed to open. I'm still leaning towards trying to raise the float level and see if that makes a difference. Some times it will run for hours on end up and down very steep slopes; its making for a very frustrating problem.....
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are you sure that the needle is not supposed to be connected to the float? I've never seen one like that. on mine which does have the cutoff solenoid the needle sits in a clip like on the float and then there is also a light spring to help push the float down which is unusual for this kind of carb. on some there is a small spring clip that attaches the float to the needle to pull it down maybe it got lost at some point. Jiggle the wires on the fuel pump while it is running to make sure you do not have a bad connection somewhere that only shows at times.
Thanks, Jerry. My Bobcat manual doesn't show any sort of a clip in the exploded diagram for the carb. Although, the end of the needle valve does have a machined valley which would sure seem like a place for a clip to attach. I'd bet that Zenith uses the same needle valve in a number of carbs so the valley doesn't necessarily mean that this application uses a clip. My carb also has the light spring. I've emailed a carb specialist who claims to have lots of Zenith parts to see what they say. On the pump, it's loud enough so that I can still hear it running after the engine dies, so I'm pretty sure I'm ok. Again I have strong fuel flow at the carb even after the engine has died. I am going to replace the ignition switch just because the current one has the key jammed in it and can't be removed- makes it too easy for someone to take it for a joy ride. It will remove one more question mark, but I'm pretty sure it's not related to my current issue.
Hello, I'm in the same situation with my 742 skidloader. I've replaced everything I could think of. I even pressurized the fuel tank to get the needle to open. I then replaced the mechanical fuel pump. ($46.) FYI, it crossed over from a Pinto. I've taken the tank out and cleaned everything. Replaced every hose. Eliminated the electric shut-off. I rebuilt the carb twice. This actually helped for a couple months. The motor shuts off so quickly that I thought it was electrical. I then changed everything. Points, condensor, wires, plugs, coil, cap , and rotor. It made no different!! I then pulled the carb back apart again. Everything still real clean. I also noticed that there is NOTHING that connects to the needle. My diagram from the carb kit shows no clip. After getting it back together, everything works great. The machine is very hesitant if I jerk it hard. SOMETHING IS STILL WRONG. I've had this machine for years. It really has a mind of its own. There are times that I can make it stay running if you pull the choke. This is telling me that it is starving for fuel. Is there anyway to modify the needle? Is there a better carb I can put on this thing? Please advise if anyone has any more suggestions. Thx
This is the same problem that has shown up with my 632 the last couple months. If I go over rough ground and it jerks it will die unless you choke it but if you choke it and keep it running and purposely bounce it then it will clear up and run good. New fuel pump also. I think it has to be the needle hanging up. If I can't fix it soon it has to be replaced with a diesel. I had a 610 gas before this and never had a problem on rough ground. Maybe that is what is needed is the carb from a v4 wisconsin. After the new fuel pump it seemed to run better for a month or so also.
By the way I did get the fuel pump from Bobcat and learned that the extra thick gasket is there to position the pump arm on the cam correctly.
I thought its to keep the pump from hitting the breather that BC added.??
No breather in that area on mine but it is a lot older than yours also. The carb on mine has a electrical solenoid valve in the bowl also but that is working as it should. Older ford tractors used the marvel carb so I may look into making a different carb fit.
Bobcat added a breather, the early ones didnt have one,mine also has a solenoid on the carb.but it has been removed so its pluged.I have not started it yet and Im hopeing the carb works.Maybe that solenoid is droping out causing it to stall????
I just put my carb back on again, will try it tomorrow. It is the 13805 with the electrical bowl solenoid which seems to be working o.k. The needle on mine is connected to the float by a spring clip and there is a coil spring on the float shaft to help the float drop down. I could not find and dirt in it at all, removed everything I could and cleaned it made a new gasket and reassembled. All last winter it ran fine but nothing but trouble now. If I can get it to stall I will stop right there and check for current at the carb solenoid.
Ran the bobcat today, same trouble, hesitation and even a backfire when shutting off so I checked the point gap and it had closed up to almost nothing. Reset the gap, ran it about two hours moving dirt with no trouble at all, time will tell though.
Hi all from a new guy. Been reading here for years. Thaought I could offer some insight on this issue. So here is my story. Had this issue with mine. I bought my machine in pieces. Rebuilt the engine and had it running. Then it began to do the same things yours was. The issue was dirt in the carb. The machine had been in a flood and the tank was full of crud. Should have cleaned it out before I ever ran the thing. Mine has an aftermarket electric fuel pump. Now, after two attempts to clean the carb out, soaking it and blowing every passage I could never cure the problem. So I finally found a guy in Los Angeles who had new carbs. I bought one and it has run perfectly ever since. Paid about $180 for the carb. The new carb had no provision for the cutoff solenoid. So I left that off. I also had to switch the side that the linkage connected to. It was the opposite of the original. Perhaps if I had asked I could have got the carb with revesed linkage. My 722 is at a vacation home and sits for at least 6 months a year. But I did this project 5 years ago and it starts right up every year. I always put Stabil in the fuel when I store it. The bottom line here is that I think you have dirt in the carb somewhere. Once it gets hot the dirt somehow totaly plugs the carb. Hope my description helps some. I felt the carb was expensive but worth the investment. I bought my machine in pieces for $2500 with a perfect hardly used backhoe and 2 buckets. I have spent about $1600 more on it for engine parts and a few hoses plus machine shop work. Considering my total investment, the carb was well worth it.
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