Engine cranks, but will not fire up

1985 OMC w/ 5.7 L GM Block

First an update...I posted a hydrolock problem about 2 months ago. Finally took it to a mechanic, who told me that my risers/manifolds were shot. Would cost $1000 to fix, unless the hydrolocking had damaged the engine. So I drydocked the project for financial reasons.
Cut to present...I found an identical boat with identical motor (rebuilt). I got a GREAT deal, so I bought it. But I'm now having a problem with the new motor. When I turn the key, the motor turns over great, there is power at the distributor, the rotor spins. But it just won't fire and run. I was thinking fuel pump, but there is gas in the fuel/water separator. Any ideas?
Thanks

Re: Engine cranks, but will not fire up

Do you have spark?

Re: Engine cranks, but will not fire up

When you push the throttle forward, do you get a squirt of gas in the carbs?

Fresh gas?

Do you have spark?

Re: Engine cranks, but will not fire up

Do yourself a favor, get the maintenance manual, it will cover troubleshooting in detail.

Re: Engine cranks, but will not fire up

This will make me sound really dumb, but what is the easiest way to check for spark?

Re: Engine cranks, but will not fire up

The easiest way is to grab a plug wire and crank the engine.
Although not the safest.

Re: Engine cranks, but will not fire up

baurand said:

This will make me sound really dumb, but what is the easiest way to check for spark?

Click to expand...

Pull the coil wire out of the distro, put a screwdriver in the end of it, and set it with the screwdriver a short distance from the block, crank the engine, and look for sparks jumping from the screwdriver to the block.

If you have a spare spark plug, you can use that instead, and just ground the plug to the block, look for sparks...

Re: Engine cranks, but will not fire up

Did you swap a complete motor in? Was it a similar model year? Make sure all of your electrial connections are hooked up. I forgot to plug the coil back in one time after swapping out ignition parts...when I finally remembered I felt pretty dumb about it. Firing order should be the same on both motors but double check that everything is in the right order between plugs and your cap. If you've got spark, it might be way out of time...so much that it won't fire up.

Nubby

Re: Engine cranks, but will not fire up

OK gents, I put a screwdriver in the coil wire and put it near the manifold. Turned the key and got lightning. So I seem to have good spark. Would it pay me to take out the fuel/water filter and replace it? Also, if there was no old gas in the tank, but some was still in the fuel lines, could that be it, and if so, how can I get ALL of the old gas out?

Re: Engine cranks, but will not fire up

As the gentleman up above said, pump the throttle and see if you have fuel squirting in to the carb. You need three things to make fire, fuel, spark and oxygen. You found the spark, the oxygen shouldn't be a problem, you just need to make sure you have good fuel getting to the cyclinders. Of coarse, if you have zero compression it will never start either. Good luck.

Re: Engine cranks, but will not fire up

baurand said:

OK gents, I put a screwdriver in the coil wire and put it near the manifold. Turned the key and got lightning. So I seem to have good spark. Would it pay me to take out the fuel/water filter and replace it? Also, if there was no old gas in the tank, but some was still in the fuel lines, could that be it, and if so, how can I get ALL of the old gas out?

Click to expand...

Since you're getting fire, (assuming your compression is good) you're either not getting fuel, or your fire isn't happening at the right time.

You need to set the engine with the #1 piston at top dead center, at the top of the COMPRESSION stroke. So stick your finger in the spark plug hole, while rotating the engine until you feel it start to push air. Rotate the engine until the timing mark on the balancer is pointing at 0 on the timing marks on the timing cover.

Once you have the engine at top dead center on the compression stroke, pull the distributor cap, and look where the rotor is pointing. Wherever it's pointing is where your #1 plug wire should be connected on the cap (the rest of the wires should follow your firing sequence).

Once you've verified timing and firing order, start looking at the carb. I'm betting your timing just isn't set properly yet.

Re: Engine cranks, but will not fire up

OK, over the weekend I was able to play with the boat again. I replaced the fuel/water filter, pulled the plug wires and checked for spark against the block, and checked all the fuses I could find. But still no good. Maybe I can describe the problem a little better and get some revised options....

When I turn the key to start, the motor turns over great and sounds like it wants to run. But it shuts off instantly when I let the key go back to run. I read on another post that there is a resister wire that supplies power through the distributer when in the run position. If this could be bad, where would I find it? Also, I've described the motor as a 1985 GM with OMC Sterndrive, but I failed to mention that the guy before me had rebuilt the motor and replaced the carb with an edlebrock (sp?). Unlike my other boat of the same vintage, this carb has an electronic firing box mounted on the transom. Could this come into play?

Sorry for continually asking questions, but this is driving me nuts.