4.3 v6 backfiring

Hi, the port engine is constantly backfiring thru the carby. It does run ok at slow speed on flat water. When you try to accelerate it starts popin.
Both engines are remans about 60 hrs old, look to be in as new condition.
problem seems intermittent.

Mark.

http://www.marineengine.com/boat-forum/attachment.php?attachmentid=9825&d=1410060572

First confirm plug wires are on the correct plugs in the correct firing order!!!!!

If that is all ok

Next if they are NOT efi Swap timing modules and see if the problem moves to the other motor.

If that does not work then remove the valve covers and see if there is a broken valve spring or something not right mechanically.

make sure each and every rocker arm is moving the same..........If the cam was not broken in or maybe bad you might have rounded a exhaust lobe.

Ok willlook tomorrow.
like to add troubles started after mech removed engine to fit a new transom assembly and out drive. Cant go back to him, in dispute after spending $10k with him, says engine performance ain't his issue. Dont want to get into what he should be doin etc, just want find the wire or plug he left loose, fix it, and go fishin..

if it worked before he pulled the engine and now it dosent, I`d be looking at the dist cap for a crack

Ok plug wires in correct order, swapped thunderbolt modules no change, swapped leads no change, swapped dissy cap no change, both coils are new thats the first thing mech did no change, removed primary filter/water sep, half full of water. Secondary filt/sep clean.

strbrd engine both filters half full of water but its running ok (for now).

Both secondary filters look fairly new, im sure they were changed at last service and probably had water in em. I think I may have water or corrosion in the Weber 4 barrel.

I think you have water in your gas tanks..........I would get that out first, flush the lines, install new water separators and then re run and hope the water in the carbs works its way out but if not then a quick service to clean and de-water them.

There really is no reason for water in the tanks at least not enough to cause a problem.

Nasty job...best of luck!

tuna_man said:

Ok plug wires in correct order, swapped thunderbolt modules no change, swapped leads no change, swapped dissy cap no change, both coils are new thats the first thing mech did no change, removed primary filter/water sep, half full of water. Secondary filt/sep clean.

strbrd engine both filters half full of water but its running ok (for now).

Both secondary filters look fairly new, im sure they were changed at last service and probably had water in em. I think I may have water or corrosion in the Weber 4 barrel.

Click to expand...

Ayuh,.... Ya found yer skippin', Right there,...

Water don't burn, yer gettin' a lean skip, 'n possible detonation,.....

The Good thing is, those carbs are easy to work on,....
Go to Edelbrock for parts, Way cheaper than Merc, 'n the same parts,...

and you wanna check the fuel tank plumbing to see if the water enters that way.....o-ring on the filler neck and the vent not being shielded are common issues..