Farmall cub wont start

[catmotorhead]

We drove it all weekend at a show. It slowly got harder to start. timing is good since it ran great. carburetor is very clean i tore it down scrubed it and put in new gaskets, compression is 90 psi in each cylinder. The spark is fat juicy blue spark on all spark plugs, plygs gapped at .025. valves move up and down freely and the gap on those is .017. I can remove the plug on the manifold and its wet so believe fuel is getting through the carb. Full battery the engine rolls over nicely.

 

[tst]

if it has good steady fuel supply, or give it a shot of carb clean to see if it fires check points condition next, advance weights working correctly?, , if they are in the full advance probably will not start

 

[staninlowerAL]

Ensure there is plenty of fuel in the tank and all valves are open, remove the drain plug or main carb jet (brass nut on the side of the carb) and catch about a quart of fuel in a container to check for a full fuel flow at the carb. Also the OEM fuel cap like yours will not vent properly when they get old so try starting/running with the fuel tank cap removed to see if the vent is plugged. BTW, the rubber fuel line shown in the pic can be a fire hazzard. Do you have any inline fuel filters with it? JMHO Stan

 

[offrink]

Start with starting fluid going into the carb from the air intake side with the choke in the run position (full in). If nothing there then check that you truly do have spark. If you have solid spark do you have the plugs in the correct firing order? If all is correct it maybe that your timing jumped.

 

[Glen]

valves move up and down freely and the gap on those is .017.

Hi,
I don't know what year your Cub is.
The 1950 Cub owner's manual says the valve clearance should be .013"
Below is the page.
https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Owner's Manuals/McCormick Farmall Cub Owner's Manual 1950/Page 39.jpg

The 1947, and 1949 Cub owner's manuals say the same clearance.
I see in your picture the choke shaft in the carburetor looks like it is upside down.
The bottom of the choke arm is supposed to rub on the special flat spring, to keep the choke valve and rod in the position chosen. The spring is small and flat.
Without the arm rubbing on the spring, the rod would just be free to move in or out of the dash.
Below are pictures from TM Tractor Parts of the IH carburetor showing the choke arms.
The 2nd picture is the engine side of the carb.
Both pictures are when the choke is fully open.

 

[catmotorhead]

Yep I had the choke backwards. I don't believe these can jump time, can they? The beginning of the weekend it would start and run like a top. It slowly got harder to start. I would say fuel is the problem. I took the carb off and sprayed starting fluid up the manifold while cranking and got nothing. I pulled the plugs and sprayed fluid in all the cylinders still no fire. The spark is like a lightning bolt, I suppose I could have gotten bad gas at the pump but the other tractors ran off the same fuel.

 

[staninlowerAL]

Yep I had the choke backwards. I don't believe these can jump time, can they? The beginning of the weekend it would start and run like a top. It slowly got harder to start. I would say fuel is the problem. I took the carb off and sprayed starting fluid up the manifold while cranking and got nothing. I pulled the plugs and sprayed fluid in all the cylinders still no fire. The spark is like a lightning bolt, I suppose I could have gotten bad gas at the pump but the other tractors ran off the same fuel.

Did you check the position of the plug wires on the distributor cap? Make sure that #1 cylinder is at TDC on the compression stroke and that what ever position the rotor is pointing to is connected to #1 plug. Firing order is 1, 3, 4, 2. It's cast in the block. As for jumping time, I suppose anything is possible but with a gear drive timing system it's highly unlikely. JMHO Stan

 

[offrink]

Yep I had the choke backwards. I don't believe these can jump time, can they? The beginning of the weekend it would start and run like a top. It slowly got harder to start. I would say fuel is the problem. I took the carb off and sprayed starting fluid up the manifold while cranking and got nothing. I pulled the plugs and sprayed fluid in all the cylinders still no fire. The spark is like a lightning bolt, I suppose I could have gotten bad gas at the pump but the other tractors ran off the same fuel.

If there isn’t any spark then I like to track backwards. Plug wires clean? Both ends? Distributer cap clean on both sides? Rotor? Points, condenser? All free of corrosion and bright and shiny? I’ve found that a brass wire wheel works great to clean things up but won’t remove material.

 

[catmotorhead]

Typically the cub starts easy. I pulled all the plugs and watched them fire out of the engine. It was text book perfect. Gas is getting through to the manifold. If I hand choke the carb, it really draws my hand in, but the plugs still come out dry and no sent of fuel. I think my next step might be pulling the head and taking a good look at the valves.

 

[staninlowerAL]

.........the plugs still come out dry and no sent of fuel. I think my next step might be pulling the head and taking a good look at the valves.

First, Does the engine fire at all using carb cleaner/starting fluid? If so it's fuel related. If not it's ignition related. Second, a compression test is a lot easier than pulling the head and will let you know if you have good compression and leak down. JMHO Stan

 

[offrink]

First, Does the engine fire at all using carb cleaner/starting fluid? If so it's fuel related. If not it's ignition related. Second, a compression test is a lot easier than pulling the head and will let you know if you have good compression and leak down. JMHO Stan

My thoughts exactly. People don’t seem to try starting fluid to see if it will run or not. It can really help isolate the problem.

 

[staninlowerAL]

Did you do the fuel flow check by catching some in a container? The OEM carb had a fuel filter screen in the inlet where the fuel line connects. Something else to check. Stan

 

[tst]

start with a compression check before guessing and taking your engine apart, the test will tell you if it can run

 

[ShawnAgne]

My 300 had an old Rubber fuel line on it when I bought it. Was running then started having issues. Basically the rubber started deteriorating on the inside of the line and it started plugging it shut. On my Cub the liner is pealing off. I started having intermittent issues where it would run fine then stop, sometimes never stop, sometimes wouldn't start. Well there was a flap flaked liner that would giver the fuel inlet. Also had crap get caught in the filter going into the carb which caused issues. As far as jumping time, if the pin on the drive gear shears off it will lose time. That happened spring of 25 on my 300. Here is what I would do
1. Check to make sure you have fuel flow
2. Get an inline spark tester and make sure you're getting spark
3. If you are use starter fluid and see if you can get it to start. You may just be flooding it.
I would be incredibly suprised that something just went wrong internally.

 

[560Dennis]

Yep I had the choke backwards. I don't believe these can jump time, can they? The beginning of the weekend it would start and run like a top. It slowly got harder to start. I would say fuel is the problem. I took the carb off and sprayed starting fluid up the manifold while cranking and got nothing. I pulled the plugs and sprayed fluid in all the cylinders still no fire. The spark is like a lightning bolt, I suppose I could have gotten bad gas at the pump but the other tractors ran off the same fuel.

Nope !

 

[560Dennis]

I try on hard starting engine a teaspoon of gas in each cylinder. If I fire up , then I work backwards to the tank. Or starting over to the last thing that was fiddling with ,cause I did something wrong with it.
I like to remove the sediment bowl assembly from the tank and remove the 70 years of crude that chokes off fuel flow.
I use a slightly smaller drill and hand drill out the encrust sludge in the in ports and out port s .

 

[560Dennis]

If you have magneto do you have copper wires ?
I had old wires with the carbon fiber conductors that would not fire .

 

[Board shortener Tom]

My 300 had an old Rubber fuel line on it when I bought it. Was running then started having issues. Basically the rubber started deteriorating on the inside of the line and it started plugging it shut. On my Cub the liner is pealing off. I started having intermittent issues where it would run fine then stop, sometimes never stop, sometimes wouldn't start. Well there was a flap flaked liner that would giver the fuel inlet. Also had crap get caught in the filter going into the carb which caused issues. As far as jumping time, if the pin on the drive gear shears off it will lose time. That happened spring of 25 on my 300. Here is what I would do
1. Check to make sure you have fuel flow
2. Get an inline spark tester and make sure you're getting spark
3. If you are use starter fluid and see if you can get it to start. You may just be flooding it.
I would be incredibly suprised that something just went wrong internally.

I had a power steering hose on a pickup that had the inside come loose and I had no power steering. Tried 2 other pumps before trying a new supply line. The new line fixed the problem.

 

[offrink]

My dad once had an issue of engine sparatically stop running like it was out of fuel. Never a set time or how the engine was run. Come to find out he lost the cardboard circle in the top of his fuel cap in the fuel tank and every once in a while it would suction down to the fuel hole and kill the engine. When the vacuum was taken off it sloshed away. It took almost 6 months to figure it out.

 

[Glen]

It slowly got harder to start.

Hi,
I would test the power of the spark the magneto or Battery Ignition unit is making.
You didn't say which ignition system the Cub has.
They have said on here that the spark can look good between the electrodes of the spark plugs, when they are out of the engine, but still be weak when trying to fire under compression in the cylinders.
Be sure the Cub doesn't roll while doing the spark test.
Remove the ignition wire from the center post on the distributor cap, and hold the wire by the insulation, with the metal end about 1/4" from bare metal of the engine block.
Be sure the transmission is in neutral, turn the ignition switch to on, and run the starter.
The spark should jump the 1/4" gap, and be blue or white. A yellow spark is weak, and needs improving.
The engine may not run, or run right, with a yellow spark.
Do the test in a building, or not in bright light, so you can see the spark well.
The battery should be fully charged for the spark test. Charge the battery if necessary.
A low output charger is better, it may take several hours to charge it.
The coil may be weak or quitting.
It is sort of common for the old original Cub coils to quit. Some of them work when cold, then quit when warm, then work when cold again.