888 backfire

[Tipsy]

Hi! Wondered what you thought about my problem. Got a 1975 Sea Ray with a Merc 888 only 500 hours on the reman engine. Rochester 2GC carb. Changed out the water sep filter a week before I rebuilt the carb two weeks ago. Went out first weekend after rebuild-she purred like a kitten all day! Sweet! Went out the next weekend and rode around for a half hour or so, everything was fine! Then all went bad. Started backfiring on acceleration. Doesn't do it at idle but when I accelerate or when I'm going full speed it backfires. I've pulled the top off the rebuilt carb and checked for water and dirt and all seems OK. I checked carb filter and it looks new because it is. Plenty of pump delivery pressure, replaced it last year. New valve cover gaskets this year, everything looked clean and new under the covers when I replaced the gaskets. I'm planning on replacing the filter again tomorrow and trying a test run with the cap loose to see if maybe my vent line is clogged or restricted. Any other ideas?
Thanks!

 

[Coors]

Re: 888 backfire

do you have a water/fuel seperator? It may have crap in it'

 

[Tipsy]

Re: 888 backfire

Yes. Changed it the week before I did the rebuild.

 

[Coors]

Re: 888 backfire

Did it have water, or crap in it?

 

[Tipsy]

Re: 888 backfire

I don't normally look at it. I routinely change it every start of the season. I've had this boat for 15 years. Had the engine replaced about 12 years ago. I've tried to be very meticulous about all the routine maintenance, but it seems to be catching up with me the last few years. Anyway, I was gooing to change it again today but it's storming here so it may have to wait. We'll see.

 

[Bondo]

Re: 888 backfire

Ayuh,.........

I believe you're still experincing Fuel Starvation...........

If by chance you've picked up a load of Water,......
You may need to change the Filter several times.........

Or,.......
You have some Other Issues with the Fuel System,........
And that includes Everything, from the Tank to the Carb............
Somewhere,......... There's a Restriction.............

 

[Tipsy]

Re: 888 backfire

Thanks Bond-O, Thanks Coors, That's what I've been thinking too. I just needed to know where to look. I'm going to replace my plugs just to be safe. I've got several water sep filters, so that I can replace them several times. I'm going to open the newly rebuilt carb and clean it again. Last Fall I replaced the o-ring on my gas cap...now that it has a good seal maybe it's not venting properly. Maybe my tank vent has been clogged but I never knew it because the cap was not sealing tight and now with a new o-ring it's not getting air. Although, when I disconnected the fuel line at the carb it had a good strong stream of fuel pressure. My carb filter is brand new every Spring and it's still clean. When I push the throttle linkage I get two good shots of gas into the throat. Thought I'd try a test run with the gas cap loosened.
Got any other troubleshooting ideas for me?
Thanks!

 

[Haut Medoc]

Re: 888 backfire

Inspect your distributer cap for moisture or cracks....
Hook up a separate tank , (six gallons or so) & see if it will show the symptom after two minutes at 3000 rpm.....
Of course do the filters first & see if it goes away.......​

 

[Tipsy]

Re: 888 backfire

Thanks everybody! Haut Medoc-I did check all of my ignition components first and eveerything was clean and clear.
At this point it seems to have been fixed. I replaced my water sep filter and although the gas in it looked clean as a whistle, I guess you can never tell. I also changed my plugs even though the old ones were only a few weeks old and probably most importantly, I blew out and then shop vacced my tank vent line and while it did not seem clogged the one thing that seems to have stopped the backfire was when I opened the gas cap during a test run. Shortly after doing that the backfire went away. So that's when I decided to try and clear that line. Seems like it's been just fine all day today. However, that is what happened last ime. It was good for a day or so after I rebuilt the carb and then it started to backfire. So, we'll see what happens after next weekend.
Thanks again to all!