Spark, compression, fuel ... nothin!

I have hooked up a temporary gas tank - a clear vinyl tube about 1 ft long and 5/8 inch ID, so I can troubleshoot problems without the hood and gas tank in the way.

Naturally, the tractor won't start. The muffler is not connected to the manifold yet. When I turn the key and press the starter button on the dash, the engine turns and the cylinders fire (I think). Bluish grey smoke (mostly blue) comes out of the manifold (would go out the tailpipe if the muffler was connected) and I hear the popping of the cylinders. It sounds pretty good, really. But when I release the starter button, she just won't run on her own. Usually she stops popping right away. At best the engine turns on its own for a few pops. I don't think I can get her to pop all four cylinders more than twice without the starter button pushed.

I have seen the spark. I have measured the compression. I can see and hear evidence of combustion in the cylinders (blue smoke and popping). I can even see that fuel is being consumed (thanks to my see-thru gas tank - no leaks, by the way). The thing oughtta run!

The archives point me in the direction of two possibilities. Could I have screwed up the wiring such that the ignition circuit is only connected when the starter button is pushed? I have compared my wiring to the diagram several times, but...

The other possibility is the carb. I did not rebuild it, or for that matter, even touch it. Even though my cylinders are firing (I think), could the air/fuel mixture be wrong and causing this thing to not run on its own?

I was VERY careful to make sure my timing marks were lined up when I re-installed the crankshaft and camshaft. But... could this be the problem? The camshaft gear is new. What if it is marked wrong? (nah, that couldn't happen, could it?)

By the way, I have not yet checked the voltage at the coil. Need I do this with nice blue spark?

As always, any and all comments and suggestions are appreciated. If I've left out something important just mention it and I will fill in the blanks.

Thanks,

Ron

If you still think you have wired it this way, pull a plug, and then jumper from one side of the relay over to the other, but don't hit the thumb switch....that should be fairly decisive.

Your ignition should be powered via the key switch. If you made your own harness, or point to point wires, just trace them down to see what goes where.

Since you say it is 12v, I'll assume an alternator, and that means negative ground, and also will mean you are using 1 or more resistors, depending on whether you have the side or fornt mount ignition.

Next guess would be fuel or timing.

Can you get a good stream of fuel from the bottom plug of the carb?

As for timing, from what I hear, it pretty hard to put the front mount in wrong, but the sidemount can be put in 180 out.

Guess the rest would be the points, etc.

Some other more knowledgebal person will most likely fill in other tidbits, or correct any mistakes if I have misquoted something.

Soundguy

Theres been a spate of miss-marked camshaft timing gears. Its a major mis-match, not something so subtle that you have to micrometer it. ok? It actually sticks out like a sore toe if you're looking for it. And actually, your low compression readings on a new engine rebuild support this problem.

Only way I know to identify and fix this camshaft gear mis-match is to dis-assemble the engine a little. I know, just what you wanted to do isn't? Take the cylinder head off. Watch your #3 valves as you hand crank your front pullynut untill BOTH #3 valves are up and overlapping. Go ahead put your finger on both of them and rock the crankshaft back and forth. Both #1 & #3 pistons should be top of stroke at top of block. If not (I'd almost bet on it) you need to pull your engine frontcover and re-index your camshaft/crankshaft gears.

Unbolt your camshaft gear and slide it off end of camshaft without rotating camshaft, understand? Then rotate your crankshaft until pistons # 1 & #3 are at top of stroke. You can use your finger to feel it.

NOW heres the tricky part, slide the camshaft gear back on, so it bolts up to camshaft without moving anything very much, ok?. IGNORE ALL CAMSHAFT INDEX MARKS. Once you've gottitt back together, check as before. #3 valves both wide open, and #3 & #1 top of stroke. If'n you're satisfied, then remark your camshaft gear witness to match your crankshaft witness mark and deface your old camshaft gear index mark (for the next poor ol'mechanic that opens up your engine, tnx)

Now then put yer new engine back together. Yes, I'd re-use the headgasket..... ....Dell

When Dell said #1 and #3, he meant #1 and #4.
Just look at the shape of the crankshaft in the I&T manual and you'll see that pistons 1 and 4 move up and down together, and 2 and 3 move together.

When Dell said "#3 valves both wide open", he meant to say "#4 valves both slightly open"
-- as in exhaust valve almost closed and intake valve just opening. Valve overlap on the 8N engine is almost zero degrees -- you really shouldn't see both valves open very much on any cylinder at any time.

A possibly easier way to check the cam timing might be as follows:
1) Remove the manifold and valve covers.
2) Rotate the engine (CW facing the crank pulley -- the normal direction of rotation) until #1 is coming up to TDC on the compression stroke. Feel the compression build with your finger. If you have timing marks (side mount distributor), watch for zero degrees. Otherwise you can do a crude but good enough TDC locator with a pencil down the spark plug hole feeling the piston rise, then start to sink again.
(Side note: It's a good idea to make your own TDC mark on the crankshaft pulley and timing case as you assemble the engine. Useful reference and/or check on the flywheel marks.)
3) With #1 at TDC on the compression stroke, rock the engine back and forth. 10 degrees each way is enough. You should see the valve springs on #4 alternately compress -- facing the crankshaft pully as you turn CCW the exhaust valve spring compresses, as you turn CW the intake valve spring compresses.

I propose this method as it avoids draining the block and fussing with the head and head gasket.

Personally, I'd be surprised if cam timing was your problem. Maybe its one tooth off, but I doubt it is way wrong.

My engine did the cough sputter "only runs with the starter" thing on initial startup as well -- new Don B "clone" carburetor put on out of the box.

The engine finally started and ran once I tweaked the main power screw to a setting that would work. Easiest way to do this is to start at the reference point (1.25 turns), and go out 1/4 turn at a time as you keep trying it. The "clone carb" requires brief full choke for every start -- doesn't start the same way as the 2N I drove 30 years ago.

One more thing to try is running on starting fluid. Ether allows a much wider mixture ratio than gasoline, and you can confirm that you have good spark, compression, and valve timing.

Good luck!