25 cc weedeater..new carb, new ring and piston, new gaskets, good compression..won't start. when removing plug and looking into cylinder after priming and attempting to start there doesn't appear to have any fuel in the cylinder. plug is new.. other than running over it with a D9 tractor is there any hope..A.T.

Well you certainly have tried a great deal of things, your compression is fairly low, however I would expect it to fire all be it not run too well, initially I would suspect a couple of things, a massive air leak i.e. crankshaft seal leaking or has fallen out, or the flywheel key in the flywheel has sheared knocking the ignition timing way out.

if you have spark and fuel then id be looking at lack of compression.. damaged piston ring or damaged crank seal/gasket

The engine can't run without compression in the cylinders. The plug will still spark, but without a compressed air/fuel mixture to burn and power the cylinder down, the starter will just keep spinning the engine over, cranking forever and not starting.
Check if your timing belts are good and not broke. Cylinder compression is dependent on good piston rings, intake and exhaust valves that open and close at right times and that seal good when closed, and a head gasket that seals up the cylinder from leaks where compression could blow into the water passages, or oil passages, or to outside of engine.
If the timing belts are good, a leak-down test of each cylinder will pinpoint where compression is lost.
Good luck with the Sube, great cars, great engines, but the head gaskets are a common problem.

May be low engine compression. Replace gaskets, piston & cylinder.

check your compression, then make sure the fuel vac pulse line if it has one is not cracked, this creats vacumn when engine is rolled over which in turn pulses your fuel pump to pump fuel through carb. look in the spark plug hole with flashlite and look for scores in cylinder and piston, maybe remove muffler and look at cylinder with flashlite and make sure your rings aren't cooked to piston causing low compression. Sorry I got carry'd away, make sure your fuel filter is clean, fresh fuel and clean your carb and check diaphrams for being stiff if so replace them. Good Luck

Rebuilding the top end on your Ironhead is not really that difficult to do. You start by taking the tank off the frame, then the carb and intake manifold off. With those off, take the four bolts out of each head and remove the heads. With the heads off, take the four bolts out off of the studs to remove the cylinders from the engine cases. One word of caution. When you remove the cylinders, have the piston up high enough in the cylinder so that you can lift the cylinders and stuff shop towels or something into the case before completely removing the cylinder. This will keep bits of carbon, broken rings, or whatever from falling into the case.

Now, that you've got it torn down, no need in doing all this work and not refreshing the engine. I'd have the cylinders checked to see if they needed boring. If not, I'd still put a new set of rings in the engine. They don't cost that much. Have the machine shop break the glaze in your cylinders if you don't have a flexhone. If you have a lot of miles on the bike, a valve job would be in order as well. Clean all the old gaskets from everything. If you have a valve job done on the heads or you've got oil leaks at the rocker boxes, remove them and replace the gaskets. This is a good time to check the rocker arms and rocker arm bushings. Replace them if needed.

Once everything is ready, put the rocker boxes back on the heads. Use good gaskets and a good sealer. Put locktite on the bolts so that they don't come loose. Once you get the heads back on the engine, you probably won't be able to to get to the bolts. Install the base gasket on the cases. Put the new rings on the piston making sure you get the right ring in the right groove and you put them in with the right side up. Refer to the instructions that comes with the rings to determine which side of each ring should be installed in the up position. Oil the rings thoroughly and space the end gaps around the piston at 60° or so apart from each other, do not align the ring end gaps. Carefully slide the cylinder down over the piston and rings. Use your fingers to compress the rings so that the cylinder slides down over the rings easily. Do not use force or you may break a ring. Torque the cylinder base nuts to 35-40 foot pounds. Now, install the other cylinder using the same techniques.

Next comes the heads. Choose the head gasket you are going to use. They come in two thicknesses. I prefer the thicker gasket. It will cost you a bit of compression but they seal better. Spray each side of the copper gasket with CopperCoat spray adhesive and position the gasket so that the oil drain hole is properly aligned. Carefully set the head down on the cylinder without disturbing the head gasket. Install the four head bolts but only snug one of them down. Then install the other head the same way.

Now, the reason you only snugged one head bolt down was you must align the intake ports with the intake manifold. Hold the intake manifold in between the intake ports of the heads. Notice the gap at the intake ports. If it is wider or narrower at the front than it is at the back, you must "rotate" the heads until the gap is even. Once this is done, you can tighten the head bolts. Tighten them in a criss cross pattern to a torque of 60-70 foot pounds.

Now you can install and adjust your pushrods. Use new O-rings on the pushrod tubes. Bring the front piston to Top Dead Center. Use a common drinking straw in the spark plug hole to determine when the piston is at it's highest point. Do NOT use anything that is hard or that will break. You could damage the piston or break the tester off in the cylinder making you have to pull the head off again. With the piston at top center, adjust each pushrod longer until you can't turn it with you fingers, then back off until you can just turn it freely. Lock the locknut down tightly. It's better to leave the pushrod a bit loose than a too tight. Do the same with the other pushrod. Put the pushrod tube into it's proper position. Now, bring the rear piston to top center and install the pushrods and tubes on that cylinder. It makes no difference which pushrod goes in what position as they are all the same length on the Sportster.

Now you can install the carb. Use new "rubber bands" on the intake clamps. Make sure you position the intake so that the carb is level. Position the clamps and "rubber bands" so that you won't have any vacuum leaks and tighten them down. Once the carb is installed on the intake, check the throttle for proper operation. You don't want to start your bike only to find out that the throttle is wide open. Install the fuel tank and you should be ready to go.

Good Luck
Steve

Basics to check:
1) Spark plug - brown or dark brown - OK
- aluminum or silver - piston/cylinder scored
a) is it carbon or fuel fouled
b) is there spark

2) Compression - 125 to 150 psi

3) Muffler remove for inspection
a) exhaust screen clean or plugged
b) inspect cylinder wall/piston as the flywheel is slowly rotated

Fuel starvation - 'lean fuel' condition
Basic things to check:
1) spark plug
2) spark arrestor in muffler
3) fuel lines and tank filter
4) turn adjustment needles out (counterclockwise) 1/4 to 1/2 turn
*if all of the above are OK and/or do not improve performance then:
Remove Carburetor
5) replace gaskets/diaphragms
b) use a spray carb cleaner to clean jets, holes, and body of carb

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

Pull the spark plug after pushing the primer bulb and cranking a few times...if the plug is "wet" (indicating fuel is present in the cylinder) then the next step will be checking the compression...compression should read above 90psi (preferrably 100-125psi)...if compression is below 90psi, the most likely culprit will be a stuck piston ring.

If you have a compression gauge, check the compression. Anything under 90psi is too low.

Check your flywheel key. If it is broken the flywheel will move and not fire at the correct time.

Note: if it does not sputter with carb cleaner then it's not your carb.

Next:
Remove your exhaust manifold. Look into the cylinder with a flash light. You are looking for scratches. Anything larger then a light fingernail is definite proof you need a new cylinder/piston assy.

If it passes that test do the following:

Pour mixed fuel straight into your cylinder until 1/4 full. Slowly pull your saw over while looking into the cylinder. If you see bubbles after the ring/rings go by then you need a new cylinder/piston assy. On rare occasions if no scratches are present on the cylinder wall or piston, you may be able to change just the rings.

Four things I can think of:
1) There is a short in your spark plug wire. When you bend it to connect the plug in the machine it allows the exposed cable to contact the engine block. Examine the wire all the way to the coil.

2) Flywheel key is sheared ( you obviously know how to take off the flywheel since you checked the seals).

3) Flywheel air gap is not set correctly. Loosen the coil. Put the cover of a notebook or the cardboard piece of a cigarette pack between the magnetic portion of the flywheel and the coil. Tighten the coil down. This will get you the proper gap.

4) Your cylinder/piston or rings are scrubbed out. Even though it passed a compression test, on rare occasions it will loose compression only when it fires. So do the following:

Remove your exhaust manifold. Look into the cylinder with a flash light. You are looking for scratches. Anything larger then a light fingernail is definite proof you need a new cylinder/piston assy.

If it passes that test do the following:

Pour mixed fuel straight into your cylinder until 1/4 full. Slowly pull your saw over while looking into the cylinder. If you see bubbles after the ring/rings go by then you need a new cylinder/piston assy. On rare occasions if no scratches are present on the cylinder wall or piston, you may be able to change just the rings.

First if you can get a inline spark tester so you can see if your getting spark with the plug installed.