engine swap and timing...

[hotmerc]

so i broke down and bought a new 4.3 ltr vortec to replace my older one with a crack in the block somewhere. did the install with a marine mechanic, swapping the parts and all that jazz. we ran her in the shop to time before replacing in boat. was having an issue with keeping it running for more that 30-45 seconds before she conked out. however it would fire back up, not running well when we opened up throttle, but enough to get it timed, or at least close. replaced in boat but it would still not run for more than 45-60 seconds. come to find out the oil pressure switch was bad. replaced that and had no issue with it running, but... when applying throttle it wants to bog down and sputter at between 1500-2000 rpms. could this be bad timing when we tried to time it when it was starving for fuel? its got new plugs, wires, filter, etc...

 

[gettin'even]

Re: engine swap and timing...

Was the carb rebuilt? I had the same condition/issue. A rebuild of the carb using the OEM Merc kit solved the problem.

 

[Don S]

Re: engine swap and timing...

You have an electric fuel pump, and the wiring for pump power comes from the starter solenoid when starting, and through an oil pressure switch when running. Bet the wires are off the oil pressure switch or the switch is bad. It's usually located above the block mounted oil filter.

 

[fishinpa]

Re: engine swap and timing...

so i broke down and bought a new 4.3 ltr vortec to replace my older one with a crack in the block somewhere. did the install with a marine mechanic, swapping the parts and all that jazz. we ran her in the shop to time before replacing in boat. was having an issue with keeping it running for more that 30-45 seconds before she conked out. however it would fire back up, not running well when we opened up throttle, but enough to get it timed, or at least close. replaced in boat but it would still not run for more than 45-60 seconds. come to find out the oil pressure switch was bad. replaced that and had no issue with it running, but... when applying throttle it wants to bog down and sputter at between 1500-2000 rpms. could this be bad timing when we tried to time it when it was starving for fuel? its got new plugs, wires, filter, etc...

don he replaced switch

 

[hotmerc]

Re: engine swap and timing...

i changed the switch so motor runs, but not well. my question was is it possible that when the timing was done with the bad oil pressure switch and the engine would stall out after about 45 seconds, would that give it bad timing, not a good reading because the engine was starving for fuel? motor will run, but rough above 1500 rpms and sputters above that. the carb was rebuilt once before. i can swap carbs with the starboard motor to check, but i dont think thats it...

 

[fishinpa]

Re: engine swap and timing...

engine needs to be properly timed .. regardless .

dont know how you would set timing with a stalling engine .



fish

 

[hotmerc]

Re: engine swap and timing...

i timed the engine this morning and it was dead on, 10 degrees below top dead center. its a 4.3 vortec with thunderbolt ignition and 4 brl carb. it runs great at idle up to 1500 rpm, then bogs down. im gonna swap carbs see if that does anything. like the other fellow said perhaps an issue there, stuck float? anything else i should look at?

 

[180shabah]

Re: engine swap and timing...

Carb swap will narrow things down quickly...

 

[hotmerc]

Re: engine swap and timing...

did carb swap with the same results. for whatever reason i was checking the firing order and saw that the orange main wire that goes to the alternator was broken. would explain why it wasnt charging. i know the fuel pump is indirectly connected to the alternator, perhaps its not getting enough juice? that would be a great thing!

 

[180shabah]

Re: engine swap and timing...

One bad wire, usually means there are more. I think you may be onto something though...

 

[hotmerc]

Re: engine swap and timing...

so i found the problem. when we installed the distributor we were 180 out. when my pal took off the cap instead of rotating the whole distributor, he didnt get it sitting in the notch correctly. so the cap was not flush to the distributor. i sat it flush and re timed and it seems to be fine. will sea trial later on, but glad thats all it was. now to chase down an oil leak. hard to believe i have one of those on a new block...