Merc cruiser 5 0 backfire

[Lancerdad34]

My 5.0 has been running pretty good except I have noticed when I go to WOT the last couple of times I have am getting backfire from the carb. When I back off it goes away. Is this a timing issue?

Thanks,

Brian in Mi

 

[Scott06]

I suspect its probably a lean sneeze. if you haven't done much to it would start with a compression test to verify good mechanical conditin. certainly verify timing and empty contents if fuel filter into container and see if there is anything other than clean gas. What do the spark plugs look like? Susoect they may show you are lean and probably have a fuel delivery or carb issue

 

[Lancerdad34]

I suspect its probably a lean sneeze. if you haven't done much to it would start with a compression test to verify good mechanical conditin. certainly verify timing and empty contents if fuel filter into container and see if there is anything other than clean gas. What do the spark plugs look like? Susoect they may show you are lean and probably have a fuel delivery or carb issue

Thanks for the reply! Engine only has 150 hrs so it is one of the other things. Just filled up fresh gas so I guess that narrows it down.

Thanks,

Brian

 

[stresspoint]

check and clean the grounds on the back of the motor , some have a small ground the attaches to the distributor that looses continuity .

 

[Bondo]

My 5.0 has been running pretty good except I have noticed when I go to WOT the last couple of times I have am getting backfire from the carb. When I back off it goes away. Is this a timing issue?

Thanks,

Brian in Mi

Ayuh,..... Backfires are usually from a lean condition,.....
Pull the fuel filter, 'n inspect it's contents in a clear vessel, for anything but clean fresh gasoline,.....

 

[Lancerdad34]

Is it time for seafoam?

 

[QBhoy]

Is it hitting the rpm limiter perhaps

 

[alldodge]

Is it time for seafoam?

snake oil

 

[Scott06]

Is it hitting the rpm limiter perhaps

Good thought it does sort of sound like a popping...

 

[Scott06]

Is it time for seafoam?

if you have an issue with the carb or contaminated fuel you need to take those items apart clean them and reassemble. Running seafoam through a carb wont clean it out, just like topping off bad fuel with new only makes more bad fuel..

Do some diagnosis and see what's going on.

 

[QBhoy]

Good thought it does sort of sound like a popping...

Yeah. The carbs that have a limiter do exactly this for sure eh. Like a popping. Be about 5000 rpm as far as I’ve seen.

 

[Lancerdad34]

Yeah. The carbs that have a limiter do exactly this for sure eh. Like a popping. Be about 5000 rpm as far as I’ve seen.

Thanks for all the replies! I guess I have to get into it deeper to find out!

 

[Lancerdad34]

One critical thing I forgot! When I test drove the boat in late July it did not do that!

Thanks,

Brian

 

[alldodge]

Don't see popping/backfire when rev limiter is reached. It kills spark a bit

TBV limiter is in the 5K rpm range

 

[Scott06]

Don't see popping/backfire when rev limiter is reached. It kills spark a bit

TBV limiter is in the 5K rpm range

mine will seem like a popping for sure when i hit it. If you don’t know what it is or not experienced could be confused with a back fire easily. Big difference between a lean condition is the boat will run perfectly until 4900 + depending on tach accuracy

 

[Lancerdad34]

mine will seem like a popping for sure when i hit it. If you don’t know what it is or not experienced could be confused with a back fire easily. Big difference between a lean condition is the boat will run perfectly until 4900 + depending on tach accuracy

Thanks did not know there was a difference.

 

[Scott Danforth]

the rev limiter is set at 5200 or so

at what RPM are you getting the backfiring thru the carb?

as stated above, most likely a lean sneeze.

what were the compression numbers?
what is the fuel pressure to the carb/
what were the results of checking the fuel filter contents?

 

[Lancerdad34]

the rev limiter is set at 5200 or so

at what RPM are you getting the backfiring thru the carb?

as stated above, most likely a lean sneeze.

what were the compression numbers?
what is the fuel pressure to the carb/
what were the results of checking the fuel filter contents?

If it did not do it when I test drove the boat why now? Have not been back to boat yet to check all that. Can check fuel filter then. Compression check will have to wait. That is a major undertaking I can hardly get my arms under to even feel the plugs!

 

[Bondo]

If it did not do it when I test drove the boat why now? Have not been back to boat yet to check all that. Can check fuel filter then. Compression check will have to wait. That is a major undertaking I can hardly get my arms under to even feel the plugs!

Ayuh,..... My guess is, the filter got to critical level of plugged in the mean time,....

 

[Scott Danforth]

If it did not do it when I test drove the boat why now? Have not been back to boat yet to check all that. Can check fuel filter then. Compression check will have to wait. That is a major undertaking I can hardly get my arms under to even feel the plugs!

because 3 months has past from July to now and you could be getting moisture in your tank from summer humidity or you could have had enough gunk in the fuel system plug up the carb

because 3 months has past and you added fresh fuel which could have had high moisture and crud in it which plugged your filter

because your tank could be full of crud and you just now plugged your anti-siphon valve

because you could have been running lean the whole time and now tuliped the valves

stop living in July, bring yourself to the present and start troubleshooting.