1971 Mercury 800 starts wonbt run on low idle or in gear

"I just bought my 1971 Cee Bee

"I just bought my 1971 Cee Bee Avenger with the original engine '71 Merc 800 from the original owner - my friend. He serviced the motor well. He had just replaced all the fuel lines and filter last season. I just put in new plugs. Couple of days ago we were running on the lake full throttle and the boat worked great then hit a few large wakes/waves and then the engine started to fail. It would run and then get weak, I'd give it more throttle it would die. I managed to bring it in to shore on a slow pace. The lower end is smooth, no drag, fresh fluid end of last season. It pumps water just fine. Not knowing what caused it to run poorly, I replaced the 5 year old plugs. Let the engine sit out in the hot sun for 2 days to make sure plug wires and everything is dry - took it out on the lake again and it still won't run right. Only other thing I know I messed with is that round knob on the control box - I don't know what it does, but I turned it a few times both directions and seemed to do nothing at the time, but maybe it is the cause of the motor not running now?
I am totally new to this web site and came across this thread because I need some advice - what do you guys think? My guess is there is something out of adjustment, maybe the waves knocked something loose or stuck? Could the motor have gotten wet? It dried out for 2 days, new plugs - still nothing."

"Doug, most likely a fuel rela

"Doug, most likely a fuel related problem (somewhere in the system).

Start with the easy stuff. Hitting the waves could have stirred up some "crud" in the fuel tank.

Check the pick-up in the tank (it usually has fine mesh which may be partially blocked). Then check the fuel filter (ok it's new, but might have sucked up something from the tank and blocked).

Check to make sure that the tank vent is open (could have got jarred), and if the fuel tank is built in, check for an anti-syphon valve (which only lets gas flow from the tank, not back into it) - again something that may have stuck on you.

I wouldn't suspect that the engine got wet and caused the problem, but you never know.

The items I have suggested are the easy stuff to check out first. If all seems ok you can try pumping the fuel bulb the next time you are out - if that helps it could assist in diagnosing the problem if nothing above was the issue..."

"Graham, I will check those fu

"Graham, I will check those fuel related items today. By the way what is that knob for on the "MerControl" box for? It spins around both directions and does not have much resistance - could it be an adjustment for something that I screwed up?
Thanks again!"

"Here's the status: I dis

"Here's the status: I discovered that the knob on the MerControl is for connecting a tach - right now it's just a plug/grommet that spins - so, I didn't screw anything up there. I drained out the fuel line (rubber hose and bulb), checked all the pick ups (clean) checked the cap vents (OK and working) checked all the plugs (new ones - nothing fouled) checked all the screws around the carb/throttle (nothing loose) then realized that I had bought gasoline that has 10% ethanol - OH $h*t! the previous owner warned me not to use that because it absorbs moisture, I didn't listen to him. So, I put 1/2 a bottle of Heet into a 6 gal can (one bottle treats 10gal) shook up the can - then fired her up ... wouldn't ya know it might be the gasoline. I will launch her tonight and keep you all posted. I have to travel 20 miles out of my area to get the untreated gasoline - so I guess I'll be buying a couple of 10gallon storage containers for that special gas."

"Doug, the new E10 (ethano

"Doug, the new E10 (ethanol fuel) is probably what we are going to be stuck with. Anyhow, it can initally cause a number of issues with outboards.

It does "suck up" water and then separates in the tank, leaving a slurry mixture in the bottom and sub-standard gas above (well below 86 octane).

It also works like carb cleaner as well - dissolving all kinds of crud in gas lines/carbs etc.

So keep an eye on any filters/separators etc that you have in your fuel system and make sure they "stay" clean.

We are probably going to have to get used to using this fuel, just takes some extra care and it will work fine...

Merc, Yamaha, Suzuki and Honda (OMC never contributed) all suggest running "stablizer" in the tank "at all times" if using E10 fuel...."

"Graham,
Here's the resul

"Graham,
Here's the results: I dumped the premium E10 fuel at the local hazardous waste site. I bought non-reformulated gas - mixed up a tank and took it out for a cruise - it idles perfectly - purrs like a kitten. Now my problem is that I cannot get full throttle performance - I have the control arm all the way down and the boat is traveling about 1/2 of it's full speed. I ordered a service manual on CD from ebay, should be here any day now. I checked all the linkages for the throttle - nothing looks loose missing or misaligned (no extra parts or screws laying in the engine compartment), but I'm not sure what I'm looking for either. My naive guess is carb adjustment or the throttle cable adjustment. Neither have been messed around with by me. The only thing I messed up on appears to be bad gasoline. Any ideas or suggestions would be greatly appreciated. I have an appointment for service on Tuesday. Hopefully I'll have this problem resolved before then."

"Doug, I would suspect that th

"Doug, I would suspect that the carb needs a good cleaning. I would concentrate particularly on the high speed jets. Your manual will give you all the instructions you need to clean these.

It is fairly common for these to foul/gum up. The carb kinda works in 2 stages. The low speed jet handles the idle etc, and the the high speed takes over when you open it up. These are actually quite small openings, so the least little bit of blockage and you lose many rpms.

The bit of E10 that you had in the system could have easily disolved enough gum and varnish to put a good clog in the jets. However, easy to remove and clean with some carb cleaner or laquer thinners."

"Graham, you are a wealth of i

"Graham, you are a wealth of information. Please have patience with me. Do I have to take the carb apart? without the manual, I'm not sure what I am doing. Am I just removing a cover ? Do I squirt some carb cleaner in there then? I'm no mechanic, but I can follow diagrams and instructions well, just not confident about disassembling a carb without knowing what I am looking for. Would you recommend giving it a try before that appointment?"

"Doug, a carb can not be prope

"Doug, a carb can not be properly cleaned unless it is removed and completely disassembled. Just too many tiny passages etc that need to be cleaned.

And not something you want to even try without a manual. It's not a super hard job, but definately a "instruction led, step by step".

My advice, let them have a look - will most probably recommend a cleaning - if their rates are reasonable, let them do it - you would be looking at (for sure) a couple of hours yourself, plus a kit (about 30 bucks), some cleaner and then trying to fill in some of the gaps that the manual doesn't completely explain.

A clean (and possibly rebuilt) carb that is looked after annually, with very little maintenance requires no regular service.

I have 86, 87 and 91 Mercs, none have ever had a carb cleaned or rebuilt (although I have a rebuild kit for each incase that day comes). And it takes me less than an hour annually to prepare these motors for storage, and recover them in the spring. A little bit of care goes a long way...

So unless it is really something you want to do yourself, weigh their "cost" compared to your "cost"...."

"Graham, I got the boat back f

"Graham, I got the boat back from a shop that would accept it. BTW, 8 calls, 3 said outright no - don't want the job, 2 did not return my messages, 3 accepted appointments, 1 mistakenly thought it was newer and 1 of the last 2 just fixed it. Turns out my simple hosing it down with Gummout cleaner did a good job. The problem was a stud/bolt that came loose that affixes the choke. With the stud off - laying in the bottom of the motor case the choke was in th open position. At WOT it died. I just took it out last night and it ran perfectly again! $180 for the diagnostics and repair - $100 for dynometer. The technician said my engine has much better compression that he had expected and it doesn't need anything else
Now for my test run ... after using up one tank of gas (an original metal Mercury container - I switched to my plastic Quicksilver tank. It died every couple of minutes -starved of fuel - my vent on that Quicksilver tank is not working. With the vent open, I cracked open the whole cover and released a lot of pressure - that was another problem resolved! I thought it was working before, but I guess the valve on the cover no longer works ... I'll see if I can buy another cover otherwise I'll stick with just refueling the metal one. Thanks so much for your help and suggestions!!"

"Glad it worked out for you Do

"Glad it worked out for you Doug.

Now lets see, new 80 horse (6 to 8 grand for a basic model that you need a computer to work on and is expensive to repair)

- 280 bucks for good working motor -

sounds like a deal to me "