75 Merc. 850 WOT problems

[marktwain85]

Hey guys, I've got a 1975 mercury 850 that has a WOT problem. I just bought the boat and had to put an internal harness, and a distributor cap in. It starts on the first crank and idles great. It is a little sluggish if you ease the boat on plane which I know it is a comprimise between smooth idle and smooth acceleration. The motor runs great up to about 3/4 throttle then if you ease the throttle much farther it starts to surge a little then cuts out and dies. I have noticed just a little bit of surging while at 3/4 throttle, but it isn't too bad. I had my wife pump the bulb while I accelerated past 3/4 throttle and the engine automaticly bogged down. So I am thinking it is running just a little rich at high throttle settings. What do you guys think? Anyone had this problem before?
Thanks,
Michal

 

[Laddies]

Re: 75 Merc. 850 WOT problems

If the timing is right then clean the carbs install new inlets an ck the float hieght.

 

[marktwain85]

Re: 75 Merc. 850 WOT problems

When I put the distributor cap on i noticed that the rotor had one side that was worn quite a bit. I probably need to get a timing light to see if that is the culprit. The problem may be happening about the time that the timing starts advancing.

 

[Chris1956]

Re: 75 Merc. 850 WOT problems

The high speeds jets are fixed, so it isn't likely that it si running too rich because of them. Check the plug wires for arcing, as well as the other things Laddies recommended.

 

[marktwain85]

Re: 75 Merc. 850 WOT problems

Well I rebuilt the fuel pump and discovered that I had a hole in the diaphram. I figured I would go ahead and clean the carbs while I had it apart. I was wondering if any of you guys know the correct way to set the float height on these carbs. I am waiting on my manual to come in the mail, and this is the only thing that has me stuck on dry land. Any help would be appreciated.

 

[emckelvy]

Re: 75 Merc. 850 WOT problems

Hole in the fuel pump diaphragm will make 'er run a bit rich!!!

This should help with the carb adjustments:

http://www.maxrules.com/oldmercs/carburetors/1966c/6.pdf

Cheers.........ed

 

[marktwain85]

Re: 75 Merc. 850 WOT problems

Thank you so much for your help!! I am going to try and get her out on the lake tomorrow to see how she runs. Yeah she was running just a little bit rich, haha. I'll let you know how the old thing runs. Thanks again

 

[marktwain85]

Re: 75 Merc. 850 WOT problems

Well in finally got to take it to the lake, after running the boat in the yard a little. I got it in the water, and pumped the ball. Started right up, and ran for about a min then died. When I pumped the bulb again to prime it the primer bulb wouldn't get pumped up hard, and I noticed the sound of air coming from the motor. I finally got enough fuel into it to get it started and it did the same thing. I was able to pump the bulb to keep it running then it died again. I took it out of the water and pulled the fuel pump to check the new diaphram, and it all looked good. When I put the pump back on I was able to pump the bulb up tight again. Went to the water, same problem. Then I noticed the air sound was coming out of the carb. float bowl vent. So I am thinking the needle isn't seating, and I am wondering about the fuel pump check valves since they didn't come in the kit.

 

[Chris1956]

Re: 75 Merc. 850 WOT problems

You sould be able to get a kit with the check valves, although they usually do not go bad.

 

[marktwain85]

Re: 75 Merc. 850 WOT problems

I finally got it fixed, tracked it back down to the gas tank pick-up tube. It had about a two inch crack on the top, so when I accelerated the gas would shift back and the line would break suction. It's kind of frustrating thinking that all I had to do was switch tanks to fix the idleing problem. Thanks for your help guys!