1998 43 Mercurser backfiring and poping

"The engine runs great at all

"The engine runs great at all speeds for about an hour. Then it loses power and starts poping and backfiring. Temp, oil gauges all normal. Changed dist cap rotor plugs and wires last summer. This has happened since June. When it cools down it runs perfect again."

"Backfiring is BAD. I had one

"Backfiring is BAD. I had one of my 4.3 engines which was a new replacement engine with 30 hours.
After it Bent an Exhaust Valve, I determined the exhaust manifold/elbow gasket leaked and the engine ingested water. This washed the valve stem and caused it to stick and the piston hit it. This resulted in a complete engine teardown and about $1300 in engine repairs.

Check the exhaust stream for water. You can do this by removing the small brass plug 1/4" or 3/16" from the exhaust elbow and run the engine. If you see water coming out, replace the manifolds and elbows.

I suggest you use OEM parts."

"[b]"Then it loses power a

""Then it loses power and starts poping and backfiring."

Ayuh,... It's going Lean,... You have a Fuel restriction,.. Somewhere..."

Well this is what is going on

Well this is what is going on at this point. The plastic gear on the starter went. I bought an after market starter. Took the boat on the lake and after it started running bad. I let it cool off and went to start it and the starter just spun again. Took the starter apart and it tore up the plastic gear on the new starter. We had to get towed back to the dock. We had the driver in trailer position when it was towed. The company sent me a new starter. The starter cranked the motor real slow and the wires got so hot that it melted the negative terminal on the batterry. This time I thought it was a bad starter motor. I pulled the spark plugs and saw water in there. It was hydro locked. I pumped out the oil and had half a gallon of water in the pan. Now I am really pissed. I lost my job and I don’t have the money for this. Did a compression check and all were between 140-150. I filled with oil and changed the filter. I switched the starter motors and fired it up. Hooked the ear muffs crossed my fingers and fired it up. It ran great and no water in the oil. The next test was to bring it out on the lake for a test. It ran great. No water in the oil. I turned the boat off and sat for a while. Went to start it and the starter just spun again. Got someone to tow me back to the dock. I am using up my tow cards. Thank God there are still good people that are willing to help a fellow boater. Got the boat home. No water in the oil and it wasn’t hydro locked. I guess that is way after market $70 starters are so cheap. I am going to store to buy a $175.00 starter. Please let me know your thoughts. Thanks.

"If your engine had water in i

"If your engine had water in it once and you did not correct the problem, it will ingest water again.
If you only run in fresh water, it may be less likely the exhaust manifolds are the problem. It could be a leaking head or intake manifold gasket, or worse a crack in the heads or block.

I would suggest you check the exhaust stream for water.

As I stated in my previous post, there should be small brass plugs on the top of the exhaust elbows. You can remove them and this is a direct path to the exhaust stream before the water is released into the exhaust. There should be no water, vapor or light spray coming out of the holes.

If there is water, the manifolds and elbows are the problem. They must be replaced.

Fix the water issue before you do serious damage.

Good luck."

I looked at the exhaust manifo

I looked at the exhaust manifold. There are 4 plugs on each side. The plugs are big and not brass. There are 2 on the front and back of the lower one that conects to the engine and 2 on the front of the top part. Which ones should I remove?

"The plug is on the Top of the

"The plug is on the Top of the Elbow, which makes a 90 degree turn and is connected to the Big Rubber Hose in the exhaust system. You would use a hex key to remove it and is 1/4 inch or 3/8", a small plug.

Look at the side of the Elbow and manifold and see what brand is name is cast into it. I know the OEM
Mercruisers have this passage to the exhaust stream. I think on newer models, there was an exhaust gas sensor in that hole.

Otherwise, take a couple of photos and upload them."

""Temp, oil gauges all nor

""Temp, oil gauges all normal". What about the voltmeter? My MC470 started doing the backfiring popping thing and the VM was showing 16 volts. The voltage reg had gone bad, allowing overvoltage, which caused coil secondary voltage to surge, jumping all around in the dist to the wrong plugs. New VR fixed that problem. Perhaps your VR is going bad but runs okay for the first 30 mins while the batt voltage recovers from the starting drain. Can't even guess at the water problem other than what has been suggested. Good luck with the motor and getting another job. DF"

All gauges or normal. I think

All gauges or normal. I think the backfiring problem was due to water fouled pluges. Thanks for the job support.

I called the people that sold

I called the people that sold me the starter. They told me that they had a bad bunch of plastic reduction rings. They are sending me 2 stock Mercurser ones. I hope that fixes the starter problem.

"Your $75 starter does not sou

"Your $75 starter does not sound like is approved for marine applications. The extra cost for the marine version assures that there will be no wayward sparks given off, which could cause catostrophic problems in your bilge (BOOM)!There are a few must's in the engine compartment of a boat. Marine Starter, alternator, carburetor, and distributor. The rest of the engine may fail sooner if not marine quality, but will not kill you."

It is a marine starter. I boug

It is a marine starter. I bought it from DB electric. I think the starter will be fine if the engine is not hydrolocked. My stock starter striped the plastic gear the first time it happened. Thanks for your concern.

I've had fine service from

I've had fine service from DB Electric products.

I agree about DB Electric. The

I agree about DB Electric. They have great prices and they will do anything to make you happy. The starter problem was due to the engine hydrolocked.