860 STILL won't fire! What have I missed?

My 1956 860 usually runs great, but started misfiring a couple of weeks ago, then wouldn't start at all. Battery is fully charged, wiring is good, has new coil, points to 25thou, condenser, rotor, rotor clip, sandblasted plugs, and I have a good 1/4" white/blue spark.
I have overhauled the carb carefully, used choke cleaner and compressed air in all it's passages, and put a new O ring on the throttle shaft to ensure no air leak.
So I have good spark and gas, but it won't fire. Could this be an air leak, a timing issue, compression problem or what? I've worked on my 8N and this 860 for 20 years and have not seen this before.
What have I missed? Or what has happened? Thank you in anticipation.
 
Easy enough to do a compression test on each cylinder but I suspect possibly pulling air someplace therefore not drawing from the carb. I have an 860 and am trying to remember where a vacuum test could be performed. The tractor is 30 miles from home so not as simple as walking out the door. In any event it is very possible that it could be the manifold gasket or the manifold itself.
 
Did you check spark at a plug or just out of coil? I notice you didn't say you replaced cap.

If spark to plugs, if you shoot some starting fluid into carb intake (air tube removed) does it fire? If so fuel starvation, check fuel flow to carb and if good go over carb again.

If not fuel starvation are plugs wet (other extreme - flooding).

If nothing out of the ordinary with fuel check compression and timing (something awry with basic engine condition?)

I assume you have checked that you didn't run out of gas (only kidding)
 

It would help if you described what good spark and gas means to you. Carburetors passages are usually cleaned by pushing appropriate sized wires such as O/A tip cleaners through them.
 
It has got to the point a lot of condensers are bad the day you buy them and half the others are bad within a year. Fast and dirty test for condenser is put new/spare condenser wire under screw at coil or where wire from coil enter's distributor then clamp jump wire from battery ground post to condenser case. While you have jump wire handy,go from battery hot to coil.
 
sandblasted plugs
since you're having this trouble I'll suggest you install a set of new plugs - I've had a lot of trouble with spark plugs the last few years, they stop working and sandblasting won't bring them to service - I've given up and just keep extra new plugs around and install a new set when an engine starts missing - I'll run thru a couple of sets a year on the more heavily used tractors
 
I have overhauled the carb carefully, used choke cleaner and compressed air in all it's passages - So I have good spark and gas, but it won't fire.

What Showcrop said. Your method may work for some carbs but for these you want to chase each passage with a small gauge wire or torch tip cleaner to ensure the path is open.

Will it start with starting fluid?
 
Yep, gas is good - I've made that 'Operator Error' a few times before.
Will run these tests on Saturday - thanks for your help.
 
Good spark is a quarter inch strong white spark on a plug, opened to quarter inch and grounded to the body.
Plugs don't seem saturated, so may have an air leak. Will check on Saturday. Thanks for your ideas.
 
If you put your hand over carb when cranking, does it flood? The air cleaners fill up with water when sitting out in rain. If you see oil on the outside of the bottom cup thats water pushing the oil out. You can also get a birdnest in the top of the cleaner if you dont have that hood funnel going to it.
 
Starting fluid doesn't make a difference.

An internal combustion engine needs three things to work - Fuel, Fire, Compression. You have eliminated two out of three. If you have good ignition and it won't fire with starting fluid (ether) then it's time for a compression test.
 
(quoted from post at 16:10:44 12/14/17) Starting fluid doesn't make a difference. Will try other ideas and keep you posted.

David, Please advise what "starting fund doesn't make a difference" means.
 
That's exactly what I am going to check next - I've got good gas and spark and compression, so it could be blocked exhaust or
leaky manifold.
 
(quoted from post at 00:45:00 12/15/17)
Starting fluid doesn't make a difference.

An internal combustion engine needs three things to work - Fuel, Fire, Compression. You have eliminated two out of three. If you have good ignition and it won't fire with starting fluid (ether) then it's time for a compression test.

Bill, I am still convinced from his answers and lack of answers that he simply is not getting gas. I think that he is determined that it is a very unusual problem instead of commonplace.
 
Bill, I am still convinced from his answers and lack of answers that he simply is not getting gas. I think that he is determined that it is a very unusual problem instead of commonplace.

You're probably right - Will be interesting to hear final outcome.
 
Yep, I think you're right about this. Compression reads between 105 - 115psi on cylinders, on a cold engine. I have spark, but
it's interesting that the plugs are not soaked if I run the starter with the choke out. This must mean it's not getting fuel,
which could be 1) blocked exhaust, 2) air leak on manifold intake, or 3) blocked carb. Thoughts?
Will check all these tomorrow. In the meantime, here (photo) are my 1952 late 8N, 1956 860 and 1954 Fordson Major, all fitted
with rollbars for this hilly Kentucky country.
a250858.jpg
 
(quoted from post at 18:16:37 12/18/17) Yep, I think you're right about this. Compression reads between 105 - 115psi on cylinders, on a cold engine. I have spark, but
it's interesting that the plugs are not soaked if I run the starter with the choke out. This must mean it's not getting fuel,
which could be 1) blocked exhaust, 2) air leak on manifold intake, or 3) blocked carb. Thoughts?
Will check all these tomorrow. In the meantime, here (photo) are my 1952 late 8N, 1956 860 and 1954 Fordson Major, all fitted
with rollbars for this hilly Kentucky country.
a250858.jpg

Or, instead of rare unlikely things, like blocked exhaust or carburetor, or a leaking manifold, how about simply checking the flow of gas to the carb. Note I said FLOW not presence.
 
If you have spark at the plugs and it won't fire on starting fluid, check timing and distributor components. Loose rotor, worn shaft, bad gear, etc will all affect timing. Firing but at the wrong time. Not likely, but, could have sheared timing gear key and altered timing. Sometimes don't take much.
 
I have spark, but it's interesting that the plugs are not soaked if I run the starter with the choke out. This must mean it's not getting fuel, which could be 1) blocked exhaust, 2) air leak on manifold intake, or 3) blocked carb. Thoughts?

Very much like Showcrop, I'm thinking you have a fuel delivery problem. To isolate this possible cause; with fuel valve off, remove the float bowl drain plug from the bottom of the carburetor then open the tank valve and allow it to flow for 30 seconds. You want to drain the float bowl and evaluate fuel flow through all of the tank screen and sediment bulb.

Just out of curiosity, where were you spraying the starting fluid?
 

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