Need help with 351 Merc

"Hi all,

I am new to this f

"Hi all,

I am new to this forum and new to the boating scene. I recently purchased a sea-ray which I use for Lake MI. salmon fishing. It has the 351 ford with a rochester 2 barrel carb. The boat ran great at idle for hours and at high speed. Latly within the last couple weeks the idle has been giving me fits. It will run great for about an hour and then the engine starts surging and running rough and eventually will quit. When it first started doing this it would restart right away, but last week it would take longer each time. At one point I was bobbing around the big lake 6 miles out at 10 o'clock at night for a half hour trying to get it started. I did all the usuall things such as fuel filter and what not. It has great spark and the timing is correct.

So this week I performed a experiment. I hooked the hose up in the driveway and let her idle for about a hour and a half. After that it started acting like it does out in the lake. Finally it quit. I pulled a spark plug and the tip was white. A friend told me I had better get the carb rebuilt which I did. So last night I bolt the carb back on and let it run for about an hour. It seemed like it was running well, but when I turned the key off and tried to restart, it would not, nor would it even sputter. I sprayed some gas down the throat and tried again....No luck. I am very baffled on this one."

"I pulled a spark plug and

"I pulled a spark plug and the tip was white."

It was running lean then. What color are the plugs now? They should be tan or light brown. Do you run the blower all the time? Did you check for spark when it quit? Is the coil getting hot? If it is then change it and the condenser; they are notorious ignition killers. You could install a spacer between the carb base and intake to reduce heat gain on the carb.

"Guy,

I checked the plugs l

"Guy,

I checked the plugs last night after idling for an hour. Even though the engine would not start they were brown which is good. However....when I am out trolling on the lake I rarely use the blower. I figured that was only for startup??? I ran it in the driveway for an hour this morning and it was running good. I shut the key off and could not get it to start for the life of me. I waited about a half hour and she took right off. I did notice the coil was really warm. It wasn't so hot that I could not hold on to it, but you get the picture. So I took it off and pulled it away from the engine and restarted it. After 15 minutes of idling I shut the key off and she restarted instantly. I hope I am on to something with the coil. We'll see??? I did close the engine hatches and turned the blower on too."

"I dismounted the coil and pul

"I dismounted the coil and pulled away from the engine I also ran the blower. I ran the boat at idle in the driveway for about an hour to simulate trolling on the big lake. She ran fine and I could shut it off and restart it again without any problem. So is that SOP to run the blower 100% of time while motoring? I just have not quite figured out if it a ignition problem or fuel though. I should have refastened the coil and tried to run again, but I ran out of time."

I think you just proved you ar

I think you just proved you are causing a heat gain issue by not running the blower. Fuel is boiling and causing vapour lock.