Still chasing surging demons

ratface

Member
I've been trying to find the cause of a surging poor running issue on my 1949 front mount 8N . I remember reading here that 90 percent of perceived carb problems are electrical. I think I'm at 100 percent thru the electrical with new, cap, rotor, points, condenser, coil, ballast resistor, and ignition switch. I have a strong blue spark jumping 3/16 gap immediately after surging starts. Have cleaned all three gas filters (weren't really dirty). I get different flow from bottom of carb. With valve two turns out it is slow. With valve all the way on reserve it is about pencil thick and fast. The gas tank doesn't appear to be very dirty inside from what little I can see. Running time can differ from 15 min to one hour before it acts up. Working under load brings it on quicker. The tractor is much harder to start than it used to be. Several years ago I tested my engine and compression was in the 100's. It doesn't burn oil or foul plugs and has good oil pressure. I would say it is a strong running engine.

I'm totally confused in which way to go, I'm thinking it has to be in the carburetor at this point?? My assumption is that since all my gas filters were clean it can't be the gas tank although I think the sediment bowl valve is not working in the 2 turn position. Entertaining any ideas. I have to leave the tractor at it's remote location but thinking I should pull the carb and order some rebuild parts.
 
(quoted from post at 13:22:59 05/15/15) I get different flow from bottom of carb. With valve two turns out it is slow. With valve all the way on reserve it is about pencil thick and fast.
Sounds suspicious.

Here's an experiment. Turn the valve all the way out and work it hard. Does it still surge?

If not, it's the fuel supply to the carb. Something in the sediment bowl assembly or tank is blocking flow when the valve is not all the way open.

If yes, we don't know for sure what it is yet and will have to look further. Don't just jump into changing parts or you may just add new problems.
 
Ratface,Next time it surges,pull the choke out a little and see what that does.If it helps chances are it's a fuel problem and in the carburetor.If it dosen't help or change it's ignition problems.
 
Look for air leaks after the carb - carb to manifold gasket, bushing for throttle valve in carb.

Governor can get sticky if it is worn.
 
I have tried turning the valve all the way out but it still does it. I had thought that was the problem also.
 
(quoted from post at 14:22:59 05/15/15) I've been trying to find the cause of a surging poor running issue on my 1949 front mount 8N . I remember reading here that 90 percent of perceived carb problems are electrical. I think I'm at 100 percent thru the electrical with new, cap, rotor, points, condenser, coil, ballast resistor, and ignition switch. I have a strong blue spark jumping 3/16 gap immediately after surging starts. Have cleaned all three gas filters (weren't really dirty). I get different flow from bottom of carb. With valve two turns out it is slow. With valve all the way on reserve it is about pencil thick and fast. The gas tank doesn't appear to be very dirty inside from what little I can see. Running time can differ from 15 min to one hour before it acts up. Working under load brings it on quicker. The tractor is much harder to start than it used to be. Several years ago I tested my engine and compression was in the 100's. It doesn't burn oil or foul plugs and has good oil pressure. I would say it is a strong running engine.

I'm totally confused in which way to go, I'm thinking it has to be in the carburetor at this point?? My assumption is that since all my gas filters were clean it can't be the gas tank although I think the sediment bowl valve is not working in the 2 turn position. Entertaining any ideas. I have to leave the tractor at it's remote location but thinking I should pull the carb and order some rebuild parts.
Harder to start than it used to be"? Is it still 6v? Are you sure you replacement coil was 6v? What ballast resistor did you use? What other changes have you made, either before or after problems started? After it starts "acting up", can you still finish the day's work with it?
 
JMOR, I think the clue is in that it is now really hard to start and this was a easy starting tractor. I have to use starting fluid to get it going. In answer to your questions, it is a 12 volt system with the ceramic ballast resistor. Since I am using a different coil, condenser, resistor, and push button switch (all the known culprits with "time" triggers) I am leaning toward fuel delivery. Once it surges and dies it will not start again for at least 15 minutes and forget about doing any work with it. It will idle just fine if I can get it started. One day it took me the entire day to get her started again. It is so frustrating to work on a tractor for three days and still not know if it is an electrical or fuel issue. Whatever it is, is intermittent in nature.
 
(quoted from post at 09:39:14 05/16/15) JMOR, I think the clue is in that it is now really hard to start and this was a easy starting tractor. I have to use starting fluid to get it going. In answer to your questions, it is a 12 volt system with the ceramic ballast resistor. Since I am using a different coil, condenser, resistor, and push button switch (all the known culprits with "time" triggers) I am leaning toward fuel delivery. Once it surges and dies it will not start again for at least 15 minutes and forget about doing any work with it. It will idle just fine if I can get it started. One day it took me the entire day to get her started again. It is so frustrating to work on a tractor for three days and still not know if it is an electrical or fuel issue. Whatever it is, is intermittent in nature.
hose "ceramic resistors" have a value range of "all over the map", so should never be trusted. You need 4 to 5 amperes through the coil primary when engine stalled/points closed. It is just a fact of life (& physics) that coil current will decrease as the copper windings warm up, & result in lower HV to plugs & if this gets low enough, crappy/non-running. Try shorting around your ceramic resistor next time you have this problem. It will probably run.
 
You have to narrow it down when it acts up. When it acts up with no power or dies, and without the engine running, remove the plug on the carb and see if fuel runs out fast enough to fill a pint jar quickly. Let it fill the jar and see if, before it does, the flow rate decreases. That would rule out fuel delivery and allow you to get a sample of gas to evaluate. I would not guess here. You need evidence to determine your next step. Post back. Gerard
 
(quoted from post at 14:39:14 05/16/15) JMOR, I think the clue is in that it is now really hard to start and this was a easy starting tractor. I have to use starting fluid to get it going. In answer to your questions, it is a 12 volt system with the ceramic ballast resistor. Since I am using a different coil, condenser, resistor, and push button switch (all the known culprits with "time" triggers) I am leaning toward fuel delivery. Once it surges and dies it will not start again for at least 15 minutes and forget about doing any work with it. It will idle just fine if I can get it started. One day it took me the entire day to get her started again. It is so frustrating to work on a tractor for three days and still not know if it is an electrical or fuel issue. Whatever it is, is intermittent in nature.

SOUNDS LIKE CARB REBUILD IT! IF YOU GET A NO GO YOU CAN DO A FEW SIMPLE TESTS IN ADDITION I WOULD CHECK YOUR VALVE LASH AND LOOK FOR A STUCK VALVE OR BROKEN VALVE SPRING YOU CAN ALSO CHECK YOUR COMPRESSION IF YOU DONT HAVE A COMPRESSION TESTER IF IT BLOWS YOUR HAT OFF ITS PROBABLY GOOD.

You should also test your wires you may or may not have solid core wires you WILL need to know the spec on the wires measure the length of each wires in inches measure the ohms divide ohms by the inches wire is long. This will give you ohms per inch. times the ohms per inch by 12 to get ohms per foot. If it less than the spec on the wire it is really good. Example the spec may say 30k to 40K note: 28K would be even better. You just don't want to see it over the spec for the wire in the example over 40K would be no good. IF YOU HAVE SOLID CORE WIRES YOU WOULD HAVE VERY LITTLE MEASUREABLE RESISTANCE.
I HAVE ADDED SOME IGNITION TESTING AS WELL AS COIL TESTING AND PLUG TESTING VIDIEOS. PARTICULARLY CHECK THAT YOU DONT HAVE A PLUG THAT IS LEAKING SPARK TO GROUND.

There are some tests you can do that MAY HELP FIND the problem for you THIS IS THE SAME ADVICE I GAVE TO ANOTHER FELLOW WITH A NO START CONDITION.

https://www.youtube.com/watch?v=bl0Z6kbyI0c

https://www.youtube.com/watch?v=e66tA43wsNo

https://www.youtube.com/watch?

This fellow is a little long winded so skip to around 7 minutes if you can stand it!
v=h8vSwfnX3Xc&list=PLskh86IwPs9AeFOBgzy2oSzzvzXG1D0c4

https://www.youtube.com/watch?v=-vdC2rwclGo

http://www.yesterdaystractors.com/articles/artint131.htm

If it help YOU great if not maybe it will help some one else.
HOPE IT HELPS BYRON
 

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