Surge sickness

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
I am still experiencing the surge sickness on my 1987 Mercury 25 serial OB213279. I have rebuilt the carb , have a new fuel line assembly and new fuel tank and have installed new plug wires. Both cylinders are firing and the compression is 128 on the number 1 cylinder and 127 on the number 2 cylinder.
The motor starts and idles fine and takes partial throttle before showing any sign of problems. I can accellerate up to a certain point then the motor starts surging and will not stop until I back the throttle off. If I go to full throttle the motor sounds like it is bogging out and loses rpm. I cant give any rpm readings because my boat doesnt have a tach .
Any advice will be greatly appreciated.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Surge sickness

fuel pump, or link n sinc. seeing you rebuilt the carbs, voting link n sinc. synchronizes, the spark and carbs so they work together properly. covered in the manual.
 

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
Re: Surge sickness

I have the manual but I swear I'm blind or something. It tells me the timing pointer is on the starter housing but I cant find it . The fuel pump is integral to the carb and I put the kit in it as well but it does seem to sound like a pump issue .
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Surge sickness

not familar with the engine, so i'm at a loss there. you can use a pencil, thru the plug hole, and rotate the engine, to find tdc. and go from there.
 

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
Re: Surge sickness

I think I have found the problem but want some insight before I jump to conclusions since I dont know Mercs. I opened the throttle up with the remote to see if the throttle plate was fully opened , it was perhaps open 1/3 of the way . I then disconnected the linkage to see if it might possibly be misadjusted . With the linkage removed the throttle shaft roller will not move to the upper range in the cam without me actually moving the throttle shaft with one hand and the cam with the other. I tried adjusting the cam but it makes no difference. There is a rough spot in the cam or the roller itself that will not allow the roller to go full travel . I believe I can work on the cam by smoothing the slot somewhat with a rotary file , will this cause any problems ?
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Surge sickness

yep. that linkage has to open that plate, so the engine gets enough air to burn the gas cleanly. the engine has been being partially flooded by not getting enough air.
 
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