1997 7.4 keeps backfiring
 

I had a issue with one engine.... was able to get it fixed. Went out then the port side started acting up. Would pop sounding like its backfiring. Then shut off. Wait a minute then turn it back on and it ran good for a few minutes then did the same thing... pulled the carb off and hope its just dirty.

Its sounds like a fuel delivery issue.
Check the lube in the seawater pump housing. Pull the plug and if it runs out fast its full of fuel and you need a new pump

I don't understand. The lube and seawater pump?

Being a 1997 (did not list serial number) you should have a belt driven raw water pump, and the fuel pump is mounted on top of it. The raw water pump has either one or two plugs on it. The pump is filled with gear lube and this is the lube which the fuel pump arm floats it. The top plug is removed and filled with Merc gear lube until it starts to run back out

If the fuel pump diaphragm leaks it will leak fuel into the lube area. So if the top plug is removed (which should be done yearly) and any lube runs out, this means the fuel pump is leaking

If fuel pump is leaking then it may not be supplying enough pressure. Could also put pressure gauge on pump outlet to measure (3 to 7 psi)

Pic shows 2 ports, many only have the top fill, and not the lower drain


https://cimg8.ibsrv.net/gimg/www.off...3b5170e5d1.jpg

i have seen ignition coil cause it.

Carb can do it for sure. Ignition issues too. Need more info and better description too. Also, what was the other engines issue ?

x 2

Also weak battery and have one this week a bad alternator. Charge voltage bounces around but keeps battery charged enough to start boat. This was a weird one.

Dump your water separator (fuel filter) into a glass jar and allow it to sit. What you describe can be the result of water in the fuel. Watch to see if any water blobs form at the bottom after a while.
Replacement filters are inexpensive. Put on a new one..

Thanks I looked up a 97 but typed 93