Ready to sink it! Carb backfire

The boat.... 1979 Tiara 2000 with a MerCruiser 898.
The problem... Backfire thru the carb after trolling (for hours).
Runs fine on the way out, runes fine trolling all day, get ready to head back in runs like crap.
Backfires thru the carb so bad i cant get more than 2000 rpm.
Things that I have tried... Rebuild carb, checked all fuel lines and water separator, SEVERAL sets of points, caps, rotors.
SEVERAL sets of new plugs. New plug wires. Have set the timing 8 btdc. Have set the points with feeler gauge, have tried with dwell meter. Nothing helps same issue every time!
Yesterday on the water I hooked the timing light to several different cylinders and noticed that the light was not consistently flashing while the engine was in gear and at 700 rpm. What would cause it to not spark consistently?
I have no idea what to do next...
Coil?
Electronic ignition?
Any ideas????????????
Thanks

Re: Ready to sink it! Carb backfire

coil maybe heating up and starting to fail ,wire from coil to cap failing .

Re: Ready to sink it! Carb backfire

^^^x2. Seems to be a heat build-up problem. You've replaced everything else, so try a new coil

Re: Ready to sink it! Carb backfire

Thank you, I will try that.
How do you guys feel about the electronic ignition option?

Re: Ready to sink it! Carb backfire

Is there a difference between a 12v automotive coil and a 12v marine coil?

Re: Ready to sink it! Carb backfire

Clark in Michigan said:

Is there a difference between a 12v automotive coil and a 12v marine coil?

Click to expand...

Many people say no difference, and others say the marine version is better suited for use in a boat. Personally, I would use the marine version

Re: Ready to sink it! Carb backfire

Clark in Michigan said:

Thank you, I will try that.
How do you guys feel about the electronic ignition option?

Click to expand...

Seeing as you now have several sets of points/rotors etc, I would stick with them for now
One other thing you didn't mention is the condensor - did you replace it?

Re: Ready to sink it! Carb backfire

Clark in Michigan said:

The boat.... 1979 Tiara 2000 with a MerCruiser 898.
The problem... Backfire thru the carb after trolling (for hours).
Runs fine on the way out, runes fine trolling all day, get ready to head back in runs like crap.
Backfires thru the carb so bad i cant get more than 2000 rpm.
Things that I have tried... Rebuild carb, checked all fuel lines and water separator, SEVERAL sets of points, caps, rotors.
SEVERAL sets of new plugs. New plug wires. Have set the timing 8 btdc. Have set the points with feeler gauge, have tried with dwell meter. Nothing helps same issue every time!
Yesterday on the water I hooked the timing light to several different cylinders and noticed that the light was not consistently flashing while the engine was in gear and at 700 rpm. What would cause it to not spark consistently?
I have no idea what to do next...
Coil?
Electronic ignition?
Any ideas????????????
Thanks

Click to expand...

Ayuh,.... A Carb Rebuild is a 50/50 option at success in a well equipped shop,...

What do the spark plugs tell ya,..??

Is it runnin' Lean at higher rpms,..??

Re: Ready to sink it! Carb backfire

Seeing as you now have several sets of points/rotors etc, I would stick with them for now
One other thing you didn't mention is the condensor - did you replace it?

Click to expand...

Yes with the set

Re: Ready to sink it! Carb backfire

Ayuh,.... A Carb Rebuild is a 50/50 option at success in a well equipped shop,...

What do the spark plugs tell ya,..??

Is it runnin' Lean at higher rpms,..??

Click to expand...

I understand about the carb, I replaced the basic parts and cleaned it the best that I could.
As for the plugs, I have one cylinder that looks rich after trolling. When it started acting up this past time I changed that plug on the water and it made no difference. They all look good if I keep it at higher RPMs . But the fish have a hard time catching the lure(jk)

Thanks again for your reply's