2008 Mercruiser 4.3 L/H alpha not starting and backfiring out the carberator.

[Jayrock1]

I went to start my boat engine 2 weeks ago, to winterize it. The engine turned over, but wouldn't start and backfired out the carburetor. It eventually started briefly, but it sounded very underpowered, and it stalled out. Any attempts to start since have only resulted in some backfires. It did the same thing when I used starter spray. The gas is only 2 months old and didn't look bad in the has filter. I have just replaced the distributor and the ignition sensor in the distributor. The engine still does the same thing. I have checked all spark plug wires with a timing light, and they are all sparking. The coil has 12v DC on it's terminals. The carburetor is pumping out gas when the throttle is moved, like it should. It seems like a timeing issue to me? Im at a complete loss, of what do next. I was leaning towards the ignition module has posably gone bad, but I was told that they rairly fail! Any help would be greatly appreciated!7

 

[bman440440]

did you recheck your firing order? and when you did the distributor did you set the firing order for clockwise or counter clockwise distributor rotation?

 

[Jayrock1]

I removed each plug wire one at time and installed each one at a time on the same number on the new distributor.

 

[Blueghost924]

I would charge the battery up fully, hook up the timing light to #1 wire and turn the motor over (and hopefully to get it to start for a few secs) and shoot the timing marks. Real good chance the timing is off (you just replaced the distributor).

 

[Rick Stephens]

Agree with the sentiment that your timing is off. Firing out the carburetor is a sign the timing out.

 

[alldodge]

What is your engine serial number?

 

[Bondo]

The engine turned over, but wouldn't start and backfired out the carburetor. It eventually started briefly, but it sounded very underpowered, and it stalled out.

Ayuh,.... Welcome Aboard,..... How long ago was the motor run,..??
Did it run Ok when it last ran,..??

Before ya started swappin' ignition parts, it sounds like a fuel problem, as a lean condition also induces backfirin' through the carb,...
​Ya say the carb is sprayin' liquid, but is it clean fresh gasoline,..??

 

[crazy charlie]

Pull the disrtib cap off and check it for condensation on the inside.Charlie

 

[Jayrock1]

Thanks for the responses. I agree it definitely seems like a timing issue. The gas is only 2 months old, and doesn't look like it has any contamination when I poored out the fuel filter gas. The last time I had the boat on the water, the engine was dieseling after I turned the key off. I don't believe that it has a condenser in the distributor. I will have to get some timing readings this weekend with a timing light. I will need to check on the engine s/n. Is it common for the timing to drift off over time? I guess I will need to check for any slop in the timing chain? Thanks

 

[Bondo]

and doesn't look like it has any contamination when I poored out the fuel filter gas.

Ayuh,.... Unless ya poured it into a clear container to look for separation, ya didn't check it,....

No, timin' doesn't move by itself,.... a timin' chain problem is doubtful,...

'n the dieselin' could also be a carb problem,....

What color are the spark plug tips,..??

 

[Lou C]

If it dieseled its possible it could have sucked in some water, and that could have rusted valve stems. Backfiring through the carb, can be a sign of an intake valve stuck slightly open. I'd try a compression test even though the engine is cold, if a valve is sticking open the comp test results on that cyl could be close to zero...If need be you can remove a valve cover and if a valve is not closing all the way you will see it if you can rig a way to turn the engine manually...

 

[Jayrock1]

The spark plugs don't look fauled up. They have a little black carbon on them. I will take another fuel sample later today in a clear container.

 

[crazy charlie]

. I don't believe that it has a condenser in the distributor.

I didnt think I had condensation under the cap either when my SeaRay was doing same as yours.I pulled the cap after running crappy and backfiring a few times and it was wet inside.Wiped it out ,put back on and was on my way with no further issues.I repleced my canvas screens with clear plastic and never had the issue again.

 

[Jayrock1]

Here is my motor serial number 1A307623. Today I took a gas sample in a clear glass from just before the carberator, and the gas looks perfect, no contamination. I tested the timing chain for any excessive play, and I only had 4 degrees of play, which is not an issue.

 

[alldodge]

Disconnect the wires going to the shift interrupter, see if bad idle stops

Assuming timing is set at 10 BTDC with White/Purple wire grounded for base timing mode

Firing order 1-6-5-4-3-2 distributer rotation clockwise looking down on top of it



If all that checks out, suggest compression test

 

[Jayrock1]

Thank you sir. I did disconnect the shift interrupter wire before, and it had no effect. As of now the engine will only back fire, and not start up. The fuel pump seems to be pumping, but I am wondering if I should check the fuel pressure, just in case the pump is on the edge? And how I should do this? Thanks

 

[Jayrock1]

One more detail, before I had all these issues I changed the fuel filter. I normally would fill the filter with gas and install it, but Installed the new fuel filter empty, because I was out of gas in my gas cans. Could this be a issue? The filter is full of gas now from the pump, and the carbs are pumping fuel out the jets when the throttle is advanced. I am just wondering if there is a sensor in the carb that is causing an issue, because of air in the line?

 

[alldodge]

Since it's backfiring, not start and prior it was running ruff (on muffs), I don't see it being the fuel pump or carb. If the TKS carb was lean or flooding motor it should not backfire. It ran good the last time it was used and now has this issue.

In post 1 the distributer and components were changed after this issue started, but post 9 states you need to check timing. Dieseling is caused by to much fuel and/or idle is to high.

While if the plug wires were not installed in the correct order would make things worst. I'm thinking a valve issue from water ingestion (dieseling can do this) or something else which is keeping some valves from not closing.

 

[alldodge]

One more detail, before I had all these issues I changed the fuel filter. I normally would fill the filter with gas and install it, but Installed the new fuel filter empty, because I was out of gas in my gas cans. Could this be a issue? The filter is full of gas now from the pump, and the carbs are pumping fuel out the jets when the throttle is advanced. I am just wondering if there is a sensor in the carb that is causing an issue, because of air in the line?

No there is no sensor and what you have done would have no effect

 

[Rick Stephens]

Use a timing light and get an idea of where the spark is. Should be in the neighborhood of 10? BTDC and a powered timing light will show a good flash even while cranking.

If timing seems good, you may be opening up the carburetor and checking it for cleanliness. You might also try a spark gap testers that show how strong a spark you are getting from the coil.