The Stovebolt Site Forums The Shop Area Engine Shop Won't run...

I have compression, gas, spark, and sputter, but it won't run. The carburetor is pumping gas down to the bottom of the heads and I get some pops and white smoke. Should I choke it? Is the carb putting out too much gas? Help please!

Adam

It sounds like the spark plug wires are out of order. You will need to be sure that the #1 cylinder is at the top of the compression stroke. At that point, known as top dead center(TDC), the rotor should be positioned directly at the #1 plug wire. From that point, going clockwise, the firing order is 1-5-3-6-2-4. Make sure the wires are in that order, or the engine will not run.

If you don't know how to find TDC, waldo53 has written a good method about half way down the page HERE.

Bad timing or plugs wired wrong will spit up thru carb usually. After making sure plugs and timing are correct and still won't start, disconnect input to fuel pump thus no gas to carb, let carb dry out awhile, then pour A VERY SMALL AMOUNT OF GAS down carb throat (teaspoon)(coke bottle cap full)and turn over, should start and run a few seconds. Have fire extiguisher at hand for safety. If it runs, rebuild carb and/or check fuel pump flow. Check float level. Since I don't know what you have or what year, check ballast resistor. Be sure to always include year, model and engine in your posts!!!!!! Remember you must have strong spark not just spark. If it does not run after teaspoon, try a little more than that,(tablespoon) still not start, you have eliminated the fuel portion as the problem. Now it's either spark, timing, resistor, distributor or distributor hooked up wrong, a short or something real big, as in valve train, cracks, etc. Make sure choke is full open during fuel experiment. I don't know if sputter means some firing or spitting up or ?

You shouldn't have gas sitting in the manifold. That indicates that something is wrong with the carburetor. Usually it means the float is set too high and gas is spilling out of the fuel bowl. You mentioned in the previous thread that the carburetor was rebuilt. By whom? And how long ago?

The pops and white smoke you describe are also a concern. Usually those indicate that the timing is incorrect. Before you address the carburetor, I would look into the timing. Make absolutely certain that you have the firing order correct. Then make sure that the rotor is pointing to cylinder one when it's approaching top dead center of the compression stroke.

To determine when cylinder one is approaching TDC, remove the spark plug for cylinder number one, put your finger over the open hole and turn the engine over by hand. You should feel air pushing out of the spark plug hole when the piston is approaching TDC. When cylinder one is approaching TDC, the rotor should be in the proper position to send a spark to the cylinder one spark plug.

If it is not, then the distributor has been installed incorrectly. The firing order for a Chevy six like yours is 1-5-3-6-2-4, so once you've located the cylinder one position of the rotor, the plug wires should be installed in that order in a clockwise rotation. When cylinder one is at TDC of the firing stroke, the rotor should be pointing directly toward the right fender and the number one plug wire terminal on the distributor cap should be the one farthest away from the engine block.

If the plug wires are installed in the wrong order or to the wrong cylinders or the distributor is incorrectly installed so that the rotor is at the wrong cylinder when firing, the result can be pops and white smoke.

All of this needs to be correctly done before you try to start the engine.

Pevious thread? didn't see that.?? I wrote my advice without seeing any other thread, sorry.

Look for his post titled Help!!!.

O I C now. He's got plenty of advice now. thanks Eagle. Very nice 48 and you do good work for sure!!

Thanks, bartamos.

Thanks so much, guys. Again, you all have come through with great advice. I have a 46' chevy 1 ton with a rochester carb and a 235 six cylinder. My firing order is correct and all the wires are running to the correct plugs. I think my mistake is with the rotor/ plug position. The number one plug is furthest away from the engine block, but when my number one cylinder is at TDC, the rotor is dead even with the number one plug. So, should the rotor be just before the plug? Baldeagle clearly explains it should and where it should be, so I'm just double checking. Also, some stupid questions to get out of the way... is the number one cylinder the cylinder closest to the front of the truck and how hard should it be to turn a freshly rebuilt engine (plugs out) by hand. I will give the engine another shot in the morning, but please, baldeagle, let me know for sure about the rotor/ number one plug relationship. Thanks again guys.

Adam (the new at everything guy)

To clarify my previous question, when #1 cylinder is at TDC, should the rotor be positioned directly on plug one or just before plug one? I found through another post that #1 cylinder is at the front of the truck, but the turning the engine by hand question still stands. Also, I rebuilt the carb and probably set the float wrong, but just to clarify, there shouldn't be ANY gas in the manifold even though I've been turning it over continuously and it hasn't been starting? Thanks again and I'll check the posts in the morning.

Adam

If you stand in front of the truck and imagine looking down at the engine, the rotor should be at 9 o'clock when the number one cylinder (the front cylinder) is at TDC of the compression stroke. Four stroke engines have two cycles of the piston for each power stroke; compression (moving up), ignition or power (moving down), exhaust (moving up again) and return (moving down again.) You want the spark plug to fire just slightly ahead of TDC so that as the flame front grows and begins to expand, the piston has reached TDC and is in a position to be pushed downward.

Your goal isn't to achieve perfection during the mechanical setup. It's to get the rotor in the right location generally. Perfecting it comes when you move the distributor clockwise or counterclockwise to set the timing according to the manufacturer's specifications.

The precise positioning of the rotor is done with a timing light. From your description it sounds as though the rotor is where it should be, so the rest is timing. When you loosen the clamp that holds the distributor in place you can rotate the distributor clockwise and counterclockwise. That's how you adjust the timing.

Yes, the cylinders are numbered in order from the front on a six cylinder engine. And yes, you should be able to turn an engine over with the plugs out by putting a socket wrench on the harmonic balancer pully nut. Actually, you should be able to turn it over with the plugs in, unless it was just rebuilt and it's a high compression engine.

It wouldn't be surprising for the inside of the manifold to be wet with gas, but there shouldn't be any gas standing in the manifold (like puddles). When a carburetor is working correctly, it sends a mist of gas into the manifold, not droplets (ideally - they're never perfect). That mist should be taken in (for the most part) by the cylinders and not left in the manifold, even if the engine isn't firing. The spark plugs would be wet from the gas (if the motor isn't firing), but the manifold should not have puddles in it.

Float level is critical, so make sure you follow the instructions in your kit precisely. Also verify that the float moves freely and does not hang on anything. And make sure that the inlet valve is seating correctly and closing correctly when the float reaches its top position.

Thanks, baldeagle. I have the rotor exactly on plug one when at TDC, so I'll try to move it a little ahead. And, I will check the float level according to the shop manual specs. I'll let you know what happens. Are there any signs that make it obvious whether the distributor should be advanced or retarded? And sounds or indications (engine backfiring through carb)?

Adam

Side note on setting the float level - The first time I rebuilt mine, I set the float level too high(to the top of the housing inside the carb). It wouldn't start. I took it back apart, and set the float level from the bottom of the housing.(the seam around the carb. where the gasket goes) It started right up after that. I don't know how yours is, but mine was set way too high at first.

The carb kit directions should show you how to set the float level properly. If they don't, look up your carb online and see if you can find the adjustments manual.

Timing - if you set the timing too far off the engine can be very hard to crank. The battery might not even be able to turn it over. The engine can rattle or knock or spit back through the carburetor. I wouldn't fiddle with the timing until you get the motor running. Make sure you use a timing light (borrow one from a friend if you don't have one) and set it to factory specs. You can fiddle with changing the timing later - after you've got the truck back together and you want to test some things to see if you get better performance.

Timing can either be advanced, neutral or retarded. Advanced means firing earlier in the compression cycle. Retarded means firing later in the compression cycle or even after the piston has reached TDC. Too much advance and too much retardation can both cause lots of problems, even going so far as to mechanically damage the engine.

All points distributors have mechanical advance weights that advance the timing as the RPMs increase. This is because there is a delay between the time the spark plug fires and the time the fuel mixture fully ignites. As the RPMs increase, the piston reaches TDC faster, so the spark plug has to fire sooner in order for the engine to run properly.

If you think about that, it should tell you something about timing. You need the fuel to fully ignite just as the piston reaches TDC. Too soon and the fuel explosion will be pushing against the piston as it is still rising, fighting against the movement of the piston, reducing power and potentially damaging the rods, pistons and/or bearings. Too late and you lose power because the piston is already going down, increasing the total volume of the compression chamber and therefore reducing compression (which reduces power.)

For most older motors the timing is set somewhere between TDC and 10 degrees advanced. The sweet spot is where the fuel has fully ignited and is beginning its explosion at the exact moment when the piston reaches TDC and is ready to move downward and the compression chamber is at its smallest possible volume. You can imagine that with all the variables involved (weight of the pistons and rods), friction in the engine, condition of the ignition wiring system, etc., etc., the perfect timing for each motor will be similar but not exactly the same. The factory selects a timing setting that will work well for all motors, but your motor might work better with another degree of advance or a degree or two less advance.

Gatsby---In addition to what 54Tow and Baldeagle/others have said:

As long as you have the rotor pointing directly at the passenger fender when #1 is TDC, just make sure that the clips that hold the distributor cap on are directly straight with the firewall and radiator(the flat parts of the clips should be facing the radiator and firewall). This will get you well within the ballpark for getting your truck started. If your truck still doesn't start, something else is wrong. This is how I tuned in my motor to get it running and I just barely rotated it counterclockwise to get it running the best I could without tuning the carb. At this point, as the others have said, timing with a light is not necessary. I probably just restated everything that baldeagle has said but I thought it might help...

When the engine is turning over, should I be able to see a continuous mist of gas when I look down the carb? Right now I smell gas, but don't see any.

And thanks again for the advice.

I wouldn't look down the carb when the engine is turning over. If it is backfiring that's a good way to get your eyebrows burnt off or something worse.

jdl is correct. Don't do that. You could get a nasty surprise. Why don't you update us on the status? What does the engine do now when you turn it over? Does it still pop and send smoke signals?

You won't see a continuous mist at all. These sixes like lots of choke to start.

Timing: if the motor has been worked on then at some point the timing needs to have an initial adjustment. The oints should just be opening when the UDC triangle, just after the ball, is at the pointer.

It shoudl be possible with some effort to turn the engine by hand. I usually do this using the fan and fan belt. However, make sure that the ignition is off!

Hey guys. Here is the latest: the engine backfires through the top of the carburetor when it is turned over. I just don't know what to do at this point. At TDC on cylinder one, I've tried the rotor dead on plug one, and a little before plug one so it fires on the down stroke. Everything I've tried makes it seem like the plugs are firing too early.

When cylinder one is TDC, the rotor should be pointing toward the front passenger tire, the distributor cap clips should parallel with the motor, and plug one tower should be furthest away from the engine block, right?

Should I mess with the retard/ advance setting or is it too early for that? It is almost like it's too advanced. PLEASE HELP!!! I'll try anything, and thanks for sticking with me guys. Don't give up on me.

Adam (26 years old and losing his hair over this)

Are you sure that you're on TDC on the compression stroke? You may be 180 out. Try taking off the rocker cover, turn the engine over while watching the rocker arms. Both valves will be closed on the compression stroke. Check th rotor to where it is pointed, then install the cap and wire it from that point. The distributer doesn't realy care where the rotor is at, only that the rotor and wire fir at the right plug.
I wouldn't mess with the advance/retard just yet. Get it running first.

Yes. The rotor, when #1 is at TDC, should be directly beneath the tower that's connected to the spark plug for #1. Are you certain you have #1 at TDC of the compression stroke when the rotor is directly underneath that tower?

Usually, when an engine backfires through the carb, the timing is way too far off to correct by moving the distributor. It's either 180 degrees out plus a little or correct but off by a little, because the plug is firing while the intake valve is still open.

At least you know you have ignition. If it's backfiring the fuel is igniting, which is a good sign. Don't give up now. You're close.

Make sure you are looking at the outer edge of the rotor and not the top of it.If you are at TDC and the rotor is not pointing at number one spark plug wire,pull the distributor and reset it in the right position.

Again, guys, thanks for responding so quickly. So, to tell whether cylinder one is on compression stroke, the cylinder should be at TDC and I need to remove the valve cover and make sure both valves over cylinder one are closed (up). My next question scares me: if the valves on cylinder one are both closed, and the cylinder is not at TDC, then is the crank/ cam timing off? Is that what you guys mean by 180 off?

What is the best way to check that the valves on one are closed? If say the valves are closed and the cylinder isn't at TDC, would one more rotation through cure that or is there a cure? Sorry for all the questions. Please let me know?!

I'm scared and confused, too (a somewhat normal condition for me).


180 degrees out - referring to the cam
360 degrees out - referring to the crankshaft/flywheel

You might be a full rotation of the crankshaft off from the compression stroke.

http://www.animatedengines.com/otto.shtml

In the original thread that you started you wrote that you had "just rebuilt my 46 Chevy one ton with a 235 and I can't seem to fire it up the first time." Did you mean that you rebuilt the engine? If that is what you meant, did you mean that you rebuilt it yourself? Or you had someone else build it for you?

If the crank/cam timing was off, you would probably have broken at least one valve by now, so I doubt that.

If you take the valve cover off and turn the engine over while watching the valves, you'll see how they work. Each exhaust valve and each intake valve opens once every other revolution. If you look at the exhaust and intake manifold, you can figure out where the intake and exhaust valves are. #1 exhaust is the first valve at the front of the engine. #1 intake is the next valve in order. When you see the #1 intake valve open and then close, #1 piston is approaching TDC.

If you have the motor at TDC to fire on #1, the two rocker arms on #1 will be at their maximum clearanc and you can feel that by wiggling them. The exhaust valve on # 6 will have lots of clearance and the intake will be tight and atrting to open.

You can't set your timing precisely by where the rotor points. You need to have the points just opening at Upper Dead Centre on the flywheel. You said that you tried moving the distributor to fire just before. That would be advancing the timing. If the timing is too advanced, it can stop the starter dead. When you are close to starting, you will here the starter speed up as the engine is helping it out.

I did rebuild the engine myself and I triple checked that the cam/ crank were timed correctly. I've just been second guessing myself lately. So, when cylinder one is on compression cycle the piston will be at TDC and the both the exhaust and intake valves will be closed? Please stick with me. I am starting to figure this whole thing out.

Yes. Don't loose your confidence. If it helps at all, I'm 14 and have had to do the timing thing all the way through short of the cam/timing light stuff. You'll get it sooner or later.

gatsby46,
that is correct, both valves would be closed. Cylinder #1 and #6 have pistons that are at the same position only #6 is on the intake cycle of the four cycles.

OK. I think I got it now. I'll give it a try now and let you guys know.

Adam

Here's the deal: when the number one cylinder is at TDC, neither the intake or exhaust valves have any play (I can't wiggle the rocker arms. But, the number six cylinder's exhaust and intake valves have plenty of play. I rotated the engine all the way through and found that the number one cylinder intake and exhaust valves never have play. It's like they are always slightly open. Is there a way to go through and adjust all the rocker arms to correct position? Is there another way to figure this out? Again, please help!!!!

Adam

here is the procedure for adjusting the valves, as outlined in the Techtips:

http://www.stovebolt.com/faq.html#valves

Now, #1 and #6 pistons are always at the same position in the stroke. With the motor at TDC either #1 will be ready to fire with #6 on intake, or vice versa. This is where your rotor needs to be pointing at the proper plug wire. The distributor turns around once for every two revolutions of the crankshaft.

Also, you need to make sure that all your valves are set properly or you could burn some out when the motor starts.