Bobcat 742 Stalling

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pconn171

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Joined
Jun 23, 2015
Messages
16
I recently picked up a Bobcat 742 (Ford gas engine). When I went to see the unit, it ran out of gas when the guy was showing it to me (may or may not be relevant). He said he only runs it for about 30 minutes at a time so he only keeps a couple gallons in it at a time. After re-fueling we were back to running and I test drove it myself. Everything seemed normal. When I called to arrange for me to pick up the unit, he said that he was just about to call me because he had a project he needed to finish with the unit and while doing it, the unit started to run poorly. He said that he understood if I wanted to back away. We agreed to take $300 off the price with the assumption that I would probably need to clean the carburetor. He swore to me that it's never done this before and that he would have told me if there was something wrong. I believe he was pretty honest, but you never know. After owning it for 2 weeks, I can tell a little bit more about the behavior. It seems to run "okay" when you first start it and leave it on choke. I can get about 30 minutes out of it before it really becomes unusable. What happens is that when the unit gets under a load, it coughs, sputters and eventually backfires out of the pipe if I don't relieve the engine by pulling the throttle back to idle quickly. At this point, it doesn't care if it's choked or not. Under no circumstances can you "goose" the throttle...you always have to roll it on slowly to get the engine up to speed. It's manageable for about 30 minutes, but I can never put it under full load like during a counter-steer or even full stick. I also can't lift the bucket while moving. When it really starts acting up, it becomes so bad that it's hard to get the unit limped around to a safe parking position. The things I've done so far are... Bypassed the pick-up tube by placing an external tank on and tried - no improvement Replaced the fuel filter - no improvement Removed the air filter - actually seemed to get worse Re-routed the coil wire because it was restricting the governor movement - seemed like it was fixed and then all hell broke loose again after the unit got good and warm Added some seafoam to the fuel tank (haven't even go through half of a tank yet) - no improvement Checked the diaphram on the vacuum advance in the distributor by sucking on the vac hose and seeing it if held vacuum...worked fine even though not a quantifiable test Removed the carburetor and cleaned everything (checked the float heights too) - just tested tonight and may have actually made the unit run worse I've been avoiding the electrical system because it seems to run fine when it's unloaded, but maybe I'm overlooking something. On thing I keep thinking about is that the unit coughs almost immediately when it's under load, but in my mind there should be enough fuel in the bowl to keep it running. This makes me start to think that it could be spark or oxygen that's missing for proper combustion. Things that seemed a little strange... I did take the pick-up tube out and somebody removed the bobcat tube and replaced it with some brake line. I don't think this is relevant, but never-the-less somebody more educated than me might see some relevance. When I was cleaning the carb, I found it strange that there was carbon inside it. I haven't really torn down that many carbs in my life to know if this was normal or not, but it was mostly just a film that wasn't restricting anything. When I put the carb back on, I was have having trouble figuring out how much the choke should open and close. It seems that I can put it in a position that it doesn't open fully but closes fully or doesn't close fully but opens fully. I chose to position it such the that the choke opens fullybut doesn't close fully which may have contributed to the worse running condition after testing tonight. Either way, it's still not right. I haven't looked at the fuel pump yet because not only is it running smooth when it's not under load, I'm still convinced that there's enough fuel in the bowl to compensate and not cough and sputter immediately. Any input is appreciated at this point. I've done quite a bit of searching but I haven't come across a solution that works for me. I'm not a mechanic, but I'm certainly mechanically inclined and not afraid to try some stuff. I don't have all the tools that I will need to do compression tests or timing tests, but if that's what I need to do next, I'll certainly borrow or buy them. Thank you in advance. Pat
 

craigb93

Well-known member
Joined
Nov 9, 2010
Messages
163
Mine has done that before. Start with checking the point gap. Next a new condenser. Be sure the governor has the correct oil level. Plan at some point to pull the fuel tank and get the years of accumulation out of the bottom of the tank. The 'fuel filter' is a metal screen so removing and blowing it clean backwards is all that is needed, not a new one. After that buy ethanol free gasoline. If the fuel pump ever falters replace it with an electric such as a Carter P 4070. The mechanical pumps wear the cam eccentric to the point that little pump stroke is left even if the pump is good. Bad part is the pump diaphragm material seems to get really brittle from ethanol fuel. Mine can sit for a week or two or three and start effortlessly after the electric pump comes to pressure. In my experience the factory carburator float level setting is ~1/16" too low for good start and run. More than you wanted to know. -Dick
 
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pconn171

Member
Joined
Jun 23, 2015
Messages
16
Mine has done that before. Start with checking the point gap. Next a new condenser. Be sure the governor has the correct oil level. Plan at some point to pull the fuel tank and get the years of accumulation out of the bottom of the tank. The 'fuel filter' is a metal screen so removing and blowing it clean backwards is all that is needed, not a new one. After that buy ethanol free gasoline. If the fuel pump ever falters replace it with an electric such as a Carter P 4070. The mechanical pumps wear the cam eccentric to the point that little pump stroke is left even if the pump is good. Bad part is the pump diaphragm material seems to get really brittle from ethanol fuel. Mine can sit for a week or two or three and start effortlessly after the electric pump comes to pressure. In my experience the factory carburator float level setting is ~1/16" too low for good start and run. More than you wanted to know. -Dick
I should clarify that the unit starts effortlessly even after it stalls.
 

reaperman

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Joined
Dec 18, 2011
Messages
598
I should clarify that the unit starts effortlessly even after it stalls.
Did you check or replace the points? They are very fussy on this engine, the gap is .025. I had the same engine on my old machine and it would act up, sputter, etc when the points needed adjusting. I think it wouldn't hurt to give it a old fashion tuneup with points, rotor, cap and condenser, and perhaps plugs/wires. As far as the carbon in the carburetor, have you checked the chock cable to make sure it is opening the chock all of the way and not just partially? If its partially closed it could explain why its running poorly after it warms up.
 
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pconn171

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Joined
Jun 23, 2015
Messages
16
Did you check or replace the points? They are very fussy on this engine, the gap is .025. I had the same engine on my old machine and it would act up, sputter, etc when the points needed adjusting. I think it wouldn't hurt to give it a old fashion tuneup with points, rotor, cap and condenser, and perhaps plugs/wires. As far as the carbon in the carburetor, have you checked the chock cable to make sure it is opening the chock all of the way and not just partially? If its partially closed it could explain why its running poorly after it warms up.
I took distributer cap off today and the points weren't even opening. I don't know how it was running at all. I'm going to set the gap and try again. If this improves or fixes it I will do the tune up as well.
 
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pconn171

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Joined
Jun 23, 2015
Messages
16
I took distributer cap off today and the points weren't even opening. I don't know how it was running at all. I'm going to set the gap and try again. If this improves or fixes it I will do the tune up as well.
I think this may have fixed it. I couldn't run it real long to get hot because I was busy and it's really sloppy wet around here. I ran it for a little while and when I would "goose" the throttle, it would still cough a little, but then as it got a little warmed up it seemed like it was gone so I put it through it's paces a little with full stick forward while raising the bucket and it didn't stall and then I did some full counter steers as well and it seemed to be doing fine. I've been fooled before though, but after that 30 minute mark, if it's still working okay, I think I'll feel comfortable in saying that it was the issue. Thanks for the help and I'll try to follow up when the weather dries up and I can complete my project.
 

reaperman

Well-known member
Joined
Dec 18, 2011
Messages
598
I think this may have fixed it. I couldn't run it real long to get hot because I was busy and it's really sloppy wet around here. I ran it for a little while and when I would "goose" the throttle, it would still cough a little, but then as it got a little warmed up it seemed like it was gone so I put it through it's paces a little with full stick forward while raising the bucket and it didn't stall and then I did some full counter steers as well and it seemed to be doing fine. I've been fooled before though, but after that 30 minute mark, if it's still working okay, I think I'll feel comfortable in saying that it was the issue. Thanks for the help and I'll try to follow up when the weather dries up and I can complete my project.
It sounds like you have it. I remember a bobcat tech telling me anytime that engine starts acting up, start by adjusting the points. He was dead on!
 

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