742 Melroe Bobcat Back fires after running for 5 min and dies

[m_espn]

I recently purchased this 742 9 months ago and was running great up until a few weeks ago. It has the 1.6 ford motor and at high idle starts to back fir and then cuts out and dies. I have replaced the fuel filter, fuel pump, fuel solenoid, and rebuilt the carb. Also added new spark plugs and wires along with a new cap and rotor. The timing seems to be correct. What would cause this to be cutting out at high idle? Any input would be great as I would like to start using the bobcat this week again.

 

[OldMachinist]

Sounds like a bad condensor or ignition coil ether one could do that if they're going bad. I'd replace the points and condensor and see if that fixes it.

 

[m_espn]

Sounds like a bad condensor or ignition coil ether one could do that if they're going bad. I'd replace the points and condensor and see if that fixes it.

I changed the points and condenser. I set the points to the .025 specs from Bobcat. Now it will run full power for about 3 mins and then loose power and die. No back fire this time. I am running out of ideas on what it could be now. It runs smooth at any other power setting than full power.

 

[OldMachinist]

I changed the points and condenser. I set the points to the .025 specs from Bobcat. Now it will run full power for about 3 mins and then loose power and die. No back fire this time. I am running out of ideas on what it could be now. It runs smooth at any other power setting than full power.

I can't remember if your ignition system has a ballast resister or not. It would look like a white ceramic block that the battery wire to the distributor comes from. Sometimes they cause problems like this. But the coil can do it too. Do you have a dwell meter so you can see whats going on when it dies?

 

[m_espn]

I can't remember if your ignition system has a ballast resister or not. It would look like a white ceramic block that the battery wire to the distributor comes from. Sometimes they cause problems like this. But the coil can do it too. Do you have a dwell meter so you can see whats going on when it dies?

There is no ceramic block. No I do not have a dwell meter. I ordered a coil this morning from Bobcat. Only $40. for it. I will try that when it gets in. The Bobcat will start fine and run great at idle up to 3/4 throttle. When I hit full throttle it runs great for about 3 mins then it losses power and either dies right away or the power goes down like it is a low idle then picks back up again to full throttle then goes to low idle then just dies. The coil is the only thing have not replaced yet. Unless you have any other ideas. You have been a great help!

 

[skidsteer.ca]

There is no ceramic block. No I do not have a dwell meter. I ordered a coil this morning from Bobcat. Only $40. for it. I will try that when it gets in. The Bobcat will start fine and run great at idle up to 3/4 throttle. When I hit full throttle it runs great for about 3 mins then it losses power and either dies right away or the power goes down like it is a low idle then picks back up again to full throttle then goes to low idle then just dies. The coil is the only thing have not replaced yet. Unless you have any other ideas. You have been a great help!

Also pehaps check you fuel pressure (I see you installed a new pump and filter) and your fuel tank venting.
Ken

 

[m_espn]

Also pehaps check you fuel pressure (I see you installed a new pump and filter) and your fuel tank venting.
Ken

By chance, what is the settings for the Zenith Carb I have on this Bobcat. I was told with the needle in the closed position open it up 1 turn then another 1 1/4" turn. The idle setting they could not tell me. I have left the idle setting alone. At the needle setting recommended it seems like it is getting alot of gas so I set it down to only 1 1/4" turn.

 

[jerry]

By chance, what is the settings for the Zenith Carb I have on this Bobcat. I was told with the needle in the closed position open it up 1 turn then another 1 1/4" turn. The idle setting they could not tell me. I have left the idle setting alone. At the needle setting recommended it seems like it is getting alot of gas so I set it down to only 1 1/4" turn.

it does sound like a fuel flow problem, have you disconnected the line and just let it run into a container to see if it is a steady stream for a while , run a gallon or so out? Is the .025 point gap from the book? seems like a lot. You could take the bowl off the carb and make sure there is nothing like varnish in there slowing down the float reaction also. I think you are right on the 1 1/4 turn.

 

[OldMachinist]

it does sound like a fuel flow problem, have you disconnected the line and just let it run into a container to see if it is a steady stream for a while , run a gallon or so out? Is the .025 point gap from the book? seems like a lot. You could take the bowl off the carb and make sure there is nothing like varnish in there slowing down the float reaction also. I think you are right on the 1 1/4 turn.

Initial setting for the idle fuel adjustment is 1 turn out and then with it warmed up and running you turn the screw in until the engine starts to run rough, then turn it out until it's running smooth. Next adjust the idle spped to 850-950 RPMs. Initial setting for the high speed screw is 1 1/4 turns out and then with it running at governed full throttle(2900-2975 RPMs) turn the screw in until speed drops, then turn out just until it's running smooth.
The service manual says there's a resister in the primary circuit to the coil and the ignition specs lists a Ohm value for it.
It's along shot but the other thing to check is if the oil level in the governor is correct.
Tune up specs for the Ford engine

 

[craigb93]

Initial setting for the idle fuel adjustment is 1 turn out and then with it warmed up and running you turn the screw in until the engine starts to run rough, then turn it out until it's running smooth. Next adjust the idle spped to 850-950 RPMs. Initial setting for the high speed screw is 1 1/4 turns out and then with it running at governed full throttle(2900-2975 RPMs) turn the screw in until speed drops, then turn out just until it's running smooth.
The service manual says there's a resister in the primary circuit to the coil and the ignition specs lists a Ohm value for it.
It's along shot but the other thing to check is if the oil level in the governor is correct.
Tune up specs for the Ford engine

The External Resistor referred to is actually a resistive wire that is part of the harness. There are two wires on the coil primary terminal. One is the resistive wire and the other is 12 v. from the starter solenoid applied during cranking only. It could have been a ceramic block resister on low serial numbers. I would look at low fuel volume--dirty tank sock filter or bad fuel pump or worn fuel pump eccentric on the cam (quite common) My machine has a fixed main jet and safety shut off solenoid. As I've posted before, keep the fuel loaded down with Stabil-Marine Formula. Government gas is a fuel pump killer.

 

[craigb93]

The External Resistor referred to is actually a resistive wire that is part of the harness. There are two wires on the coil primary terminal. One is the resistive wire and the other is 12 v. from the starter solenoid applied during cranking only. It could have been a ceramic block resister on low serial numbers. I would look at low fuel volume--dirty tank sock filter or bad fuel pump or worn fuel pump eccentric on the cam (quite common) My machine has a fixed main jet and safety shut off solenoid. As I've posted before, keep the fuel loaded down with Stabil-Marine Formula. Government gas is a fuel pump killer.

Tried to post in HTML editor. This must be an Internet Explorer only forum. HTML Editor will not work in FireFox.

 

[skidsteer.ca]

Tried to post in HTML editor. This must be an Internet Explorer only forum. HTML Editor will not work in FireFox.

Yes it butts heads with other browsers, IE works the easiest
Ken