help engine problems surge tune up

[sk74991]

Hi everyone i need help.... i thought i had a carb problem,,, As when i started the boat it ran a little rough but then when i add throttle the boat died. I can restart it and same issue.

So i descided to change the spark plugs ,wires, cap rotor and coil. I changed all this and it still seems to run rough. When i add throttle it dies on the hose no load. So then i changed the carb with a brand new unit. The boat seems to run at 2K rpm fires right up seems to run good but on high rpm only. For what ever reason i cant bring down the idle, Seems i cant adjust the idle / fuel mixture on the carb ..with the carb change it runs good at 2K rpm on the hose but every 30 seconds i get a surge from 2K TO 4k rpm AND THEN BACK DOWN. and it runs fine, Any ideas could a spark wire be in a wrong location or the rotor is in the incorrect position ... Im not sure what it could be any assistance would be appreciated ... I belive i got the fire order on the sparks correct. but rotor i wasnt sure on which location to put it in so maybe thats the issue,



Its a 2003 Mercury 5.0 L carb motor. 2 bbl rochester

 

[achris]

Sounds like a vacuum leak.

 

[sk74991]

any ideas where i would look for a vacumm leak i want to try and fix this myself. could the rotor be off and create a hight idle as im not sure i put rotor in same position i might be off by a half inch or so.

 

[sk74991]

by running fine i cant get rpm lower than 2k and i have intermittent surge.

 

[achris]

any ideas where i would look for a vacuum leak ....

Intake manifold or carb... Without us being there, you have to be the eyes and ears...

If the engine runs, likely the rotor is on in the right place. You had the problem before you replaced rotor, so the rotor wasn't the problem.

Chris...

 

[sk74991]

so i have to probably rule the carb out as its new. Is there any way to check for intake issue.

What would cause the motor to start up go to 2K rpm and stay steady at 2k rpm...

So before i did any work everything worked fine started up correct the only issue was that when i added throttle the boat died like it was starving for fuel.. So i decided to do tune up ....first sparks then cap rotor coil and cables.. they i started boat and it started fine ran at low rpm but when i added throttle then it dies again . so i decided too change the carb next.. now with the new carb in it starts up but on startup rpms are 2k and every 20-30 seconds there is an rpm surge to 4k and back to 2k..i cant get idle lower that 2k can the throttel cable be stuck

 

[achris]

Set the idle speed and mixture with the throttle cable DISCONNECTED, then adjust and set the cable up to suit the linkage position on the carb, as per the manual....

 

[Scott Danforth]

so i have to probably rule the carb out as its new.

New does not mean that it is good.

 

[scoflaw]

Maybe have the wrong carb gasket and have an opening in that area.

 

[sk7499]

let me investigate and report back this week... ill check the gasket ill make sure distributor is correct and report back

 

[QBhoy]

Unlikely a distributor problem. More like advised above. Sounds like it’s either intermittent fuel delivery or drawing/strarved of air.

 

[TyeeMan]

With your old carb, maybe the reason the engine died when you gave it throttle was a bad accelerator pump. Try replacing the accelerator pump on your old carb, reinstall it and see what happens.

When the engine is running (with the new carb) spray a little carburetor cleaner around the base, if you have a vacuum leak the engine should respond.

 

[sk7499]

so i got it started looks to run probably need to adjust the air fuel mixture... But i still get an surge every one min or so it runs and idles a oit rough but thats probably do to air fuel/air mixture...i can idle it done the issue is every one min i get a drop and surge in rpm... Can you look at the video and let me know... Not sure if i can post a link.... Thanks so far everyone has been so awesome in helping me troubleshoot.... Next thing is to preform a compression test can that be an issue? Or maybe a fuel pump? its weird because it seems to surge ever 1min or so like its timed or sometiing

My thoughts are if it was vacume leak i would have issue all the time am i correct on this?.. Seems it happens every min or so ...in the video dont mind the loud vacume noise thats how this thing has been since i bought it and it ran fine...

https://drive.google.com/open?id=1G2AcS35L3LRjB-A4se5RnX6Jqn7IFSAv

 

[achris]

Does your trim gauge work? or are you running that engine with the drive fully UP?

 

[sk7499]

Trim gauge doesn't work...drive is in down position

 

[sk7499]

Changed the ignition sensor no dice...now it seems to run real rough..not sure if I need to adjust mixture and idle screw on carb... can I have issue with fuel pump..when I start the boat turn key I don't always here the pump..boat runs just rough..seems rpm move up and down like starved

 

[QBhoy]

Is it possible you are taking water in ? A rotten exhaust and riser just starting to go bad can cause poor idle and other things. Any sign of water on the plugs ? Only takes a little

 

[sk7499]

Is there a way to check a riser...inspection plugs if they look clean then no issues.

 

[sk7499]

so I have it fixed where it idles fine I can accelerate it works normal. But when I move around on the boat there is this intermittent misfire. Look at video

see attched video 10-12 seconds in and at about 39-45s then at 50 seconds the rpms go up higher

https://drive.google.com/open?id=15O...Be1eINQQFyMMsm

Is this electrical ..