3.0L Mercruiser starts hard, backfires-FIXED

[glastron1989]

Ok, here arethe symptoms: 1989 mercruiser 3.0L in a 1989 Glastron Sierra 199CC Won't start unless forced, misfires and backfires at anything less that half throttle, won't idle at all and runs rough at over half throttle. Was running like a swiss watch one day, next day this. Cleaned choke, replaced plugs, no help. Besides a mechanic, what next?

Points had zero gap. Reset points, back in business. Starts and runs fine. Thanks for all the suggestions that gave me the backbone to go ahead and try to fix it.

 

[havasuboatman]

Re: 3.0L Mercruiser starts hard, backfires

Re: 3.0L Mercruiser starts hard, backfires

backfires how?
Thru the carb? or thru the exhaust?
If thru the exhaust, you have a lean fuel problem check and replace your fuel filters, check problem. If it still exsists, look to fuel pump. Check pressure and volume.
If it is thru exhaust, look at timing, valvetrain.

 

[cr2k]

Re: 3.0L Mercruiser starts hard, backfires

Re: 3.0L Mercruiser starts hard, backfires

Other possibility is that it jumped a tooth or more on the cam timing. Or the distributor. Check dist. for dirty cap or tracks in the cap. Point gap.
Loose distributor. And as noted above carb problems.

 

[Bondo]

Re: 3.0L Mercruiser starts hard, backfires

Re: 3.0L Mercruiser starts hard, backfires

Won't start unless forced, misfires and backfires at anything less that half throttle, won't idle at all and runs rough at over half throttle. Was running like a swiss watch one day, next day this.

Ayuh,... My guess is, ya got a dose of Water in your fuel....
Change the fuel filters,+ Look for water....
If it got into the carb, a Rebuild Kit will allow you to Clean out the idle circuit, which is plugged,...
As well as the rest of the carb...

 

[fat fanny]

Re: 3.0L Mercruiser starts hard, backfires

Re: 3.0L Mercruiser starts hard, backfires

Welcome aboard. Start going through all the above as the fellas said and if that doesn't help go through everything and keep track of what the change was to what you did start with all the things you can do without spending first cleaning all electrical connections cleaning filters anti siphon valve fule lines fuel pressure tests compression tests then move onto things such as carb job timming and correct advance tests go to the stickies @ the top of this forum you suold find what you need there to help get you started. good luck