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mercruiser 4.3lx surging

Z

zuki1000r

New member
first this is my first post, and a thanks in advance for responses. well today i took my 20 foot caravelle out for first time of the year. had rebuilt carb last year and motor ran well. well not this time. i did change plugs and compression test and was 150 across the board. went out and ran good for 30 minutes with temps at 160. then started to surge and would barely run past idle, any more throttle and would nearly die. i got back in and checked pump filter and was dirty but not bad. checked carb filter and same thing dirty, not bad. not real sure if that fixed but may try again tommorrow . any other things to try. on land it revs like a bat out a hell.when loaded it surged.
 
fuel pump giving what psi. Choke opening all the way. Scrren on the pickup tube and ant-syphin valve looked at cleaned? Filter in the fitting at the carb ?

Vent clear ?

Timing good ? Got points ? They clean run sandpaper on the contacts, rotor and cap shine them up also.
 
well cap and rotor new last year,i just did filter in carb and fuel pump and havnt tried to take out yet. has thunderbolt ignition. will look at screen on pick up tube and clean siphon valve today. thanks and will repost results if i can take it out today. also i dont have way to check fuel psi is there a decent way to check without a gauge. thanks choke is wide open. i checked timing last year and was ok. havent checked this year as it did well last year. but im sure you know boat good one time then bad next time.haha oh yeah i will also make sure vent is clear.
 
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May sound trivial but after 30 minutes of running the tank can form a vacumn if spiders/bugs build a nest that blocks the overflow hose. Back blow will clear it out. The $450.00 it cost a friend to have his carb(Quad) replaced could have been avoided.
 
well i cleaned carb filter, pump filter, blew out overflow, blew out dip tube, cleaned anti-siphon,and put new gas and went out and it ran fine.still having trouble with idle as it wont idle below about 900 without stalling when shifted int gear. but overall its running.
 
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