71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

[bigblue16.5]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Not to beat a dead horse, but did you try hooking your fuel line directly to the fuel pump bypassing that one way valve(I NOT TALKING ABOUT THE BULB), the valve is bolted to the engine. This is the easiest test and free. I may be a noob to outboards but not engines in general. I don't think this is a carb issue. This one way valve is what the fuel line slips onto on the engine. I think I am supposed to have a part on the fuel line from the tank that locks onto this valve by rotating it. I probably should have told you that my engine is a Mercury 500 with super thunderbolt on the block, haven't checked the year but I think it is a 72. It is hard to beleive that two seperate conditions could cause the exact same problem on engines that are very similar models and years.

PLEASE PLEASE PLEASE I begging, try this before you spend any more money or time on the engine. Its FREE and only takes seconds. If you want I can post the pictures of everything. I feel for you, there is nothing worse than missing out on good boating weather. Good luck.

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Thanks guys,

i will get back on it later,

i took the carbs off and inspected them last night, all seems good there, the pins and seats look like new and moved freely, and the floats, well, they float, is there more to it than that?

still the same problem...

I will try a direct fuel line from the tank to the fuel pump later.

if that doesn't work then i'll have to go to war on the electric system, when i figure out how!

thanks

phil

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

OK,

here's what i've tried today:

I took out the spark plug of each cylinder one at a time, earthed it and cranked, all seem to be firing ok.

I by passed the anti syphon valve that connects the fuel to the engine and hooked the line straight up to the fuel pump, now it doesn't start at all?

it had a brief moment where it gave a hint of firing but that pretty much coincided with the moment when fuel started to pour out of the choke air intake?

Is it possible the fuel pump can pump too much fuel into the engine and kill it?

thanks in advance.

Phil

 

[Fuzzytbay]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Its virtually impossible to flood those motors. Sounds electrical to me still

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Well, it would seem the fuel systems ok then??

I'll have a go at Moody Blues test on the switch box tomorrow and let you know how i go?

I guess i will have to trace all the wiring and check all the wires again, give them a continuity test perhaps, i'm just learning electrics so i'm not sure exactly if that's the term but basically make sure each bit does what it's supposed too!!

After that i hope to find a method to check all the components too...

maybe that will throw some light on the problem?

Hurricane Bill's just arrived in Wales so it's a good time to put some hours in on the boat at the workshop, big push this week, a result would be nice!

thanks for input everyone...

 

[bigblue16.5]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

My Bad.:redface: I'm an idiot I know. I should have told you that my engine won't start without the anit-siphon valve unless you pump the gas lever really fast and aggresively.

This is probably one of the reasons, other than having gas pour all over you when you take the hose off, that the valve is there. It will sputter a litter and then start. When I do this I don't even have to hit the choke button at all.

I thought I was flooding the engine at first too, but it was just the opposite. I don't think gas flooding out of the carb air intake means that gas is actually getting in and flooding the engine. I have yet to flood my engine, not for lack of trying, but I have found that imposible means more that likely with anything mechanical.

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

ok, this is it what is happening now, normally it would rev a lot higher than this when it does start but on this occassion it was only moderate revving that occured?

i know, i did turn it over a bit too long but i just wanted it to go for the video

http://www.youtube.com/watch?v=FwEhSdpQ3f8

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

I tried Moody Blues suggestion of doing a check on the switch box and both readings of red and white terminals came back with approx 12.4v

so it would seem the switch box is ok then?

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

I'm thinking now more and more that i might have done something as basic as wired up the starting switches wrong or something?

I don't have a key switch, it was missing when i picked up the engine and i wanted some nice switches on the dash of my boat

This is what i'm following for my engine, serial number 3052172
http://www.maxrules.com/oldmercs/Wiring/1966ona/31.jpg


here's what i have, i was advised to do it this way by an auto electric place. it's actually quite easy to follow if you write it down:

My ignition switch - On or Off switch - With Red from Battery (A) joined to White (F) looping out to choke, Opposite Yellow (B) to Starter

My Choke Switch - Momentary on - 2 x white, Tach and Loop in from ignition (F) opposite Grey to choke.

My Starter Button - Momentary Push on - Inline on Yellow (B) to starter

My Kill Switch - Momentary on - 2 x black to Battery and Tach (D) opposite a Tan (E) which dissapears in the harness i think?


Have i done something major wrong that would be making it misbehave like this?

or is it something totally different once again?

thanks in advance for your help... i'm close to running out of ideas now...

any suggestions greatly appreciated...

Phil

 

[bigblue16.5]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

On the vid, sounds like she is starving for gas. I can't tell in the video if you are, but try pumping the bulb and the gas lever on the remote. I just removed the remote and put it near the engine while I was working on it. Makes this alot easier, that is if you can do this.

Just checking, but is the vent on the gas tank open and unobstructed, beleive me, I've done it and the video sounds familiar:redface:.

If you were flooding it I doubt it would even sputter that much.

As for the electrical, I haven't messed with mine, but my 500 looks similar to your 800. I will try to get some good clear close-ups of all the wires and terminals tomarrow if I have time. Beyond this, I am running out of ideas.

If this is going to cost a lot more money you might want to try craigslist. Out here in the great northwest, USA, 2 strokes come cheap. Because of economic reasons and being banned from lots of lakes for pollution reasons, they are being sold off in mass.

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

thanks big blue, i have done the pumping the fuel bulb and gas lever and it doesn't help, vent's open, tanks full, fuel lines and filters all clean.

it seems to have fuel to make it start but then something suddenly stops?

either the fuel or the spark..

driving me crazy!

thanks

phil

 

[bigblue16.5]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Sorry, haven't had the time to get the pics or even touch my boat.

In the video, what I think is the switch box(the thing with all the terminals and wires hooked up to it at the front of the engine) is loose and tilting forward. I was wondering, isn't that thing suppose to be grounded to the frame directly by bolting it down tightly(a bolt on either side on mine)? Even if the bolts are in loosely and there is metal to metal contact, are you sure you are getting a good enough ground? If you have good contact while the engine is off, the vibration of the engine could make this ground iffy and intermittent at best as it rattles around.

How strong are these little fuel pumps on these things? It looks like your tank might be on the ground in the video. Would it help to move the take closer to the level of the engine? You can probably hear me scraping the bottom of the idea barrel from your house. Look on the bight side, at least there isn't a computer to deal with

 

[coolguy147]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

have u tried to keep it choked while u started it up hold warm up lever all the way up then after 5 mississippi's or when the it dies out or revs up then unchoke it i guess?


try choking it longer

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Hi all,

It's been a while since my last posts as i've been away for a while, the boat took a back seat over the winter for more pressing things, but, now i'm back with second wind to try and crack this beast once and for all..

I have checked the tank, lines, bulb, hoses, pump, all the fuel feed system, and it is all good..

The carbs have been off, cleaned, tuned, replaced, so that's all good...

the set-up, synchronization, pick up has all been done by the book... on more than one occassion to double and triple check!

now we're still get the same problem as the very beginning, the engine will start, roar to max rpm and then cut out...

the only logical and unexplored avenue is the electrical side.. i'm steering more towards the distributor side of things at the moment as everything else seems to work fine,?

We're generating a strong spark no worries. as the engine starts and the rpm picks up it seems the spark timing runs great as it picks up towards max rpm (remember it will only start and fire at all at WOT) then as it climbs the rpm to the top it suddenly seems to get the timing of the spark all wrong and the engine just stops, it doesn't even belch and burp it's way to finish, it's quite a definite cut out, this all happens within a couple of seconds so it's difficult to determine at which point the spark is either stopping being generated or the timing of when to spark goes all to ****?

Could the distributor be to blame?

I was told there is a sensor in there could be duff?

there is a small 1 cent size chip out of the cap on the rim at the same place as the sensor on the disc above the rotor arm, could it simply by the chip? the sensor? or something else? do the symptoms sound like any of these could be the cause?

elsewhere i noticed some pretty rotten wiring coming from under the flywheel, is it possible wire corrosion could be a cause?

I don't want to start replacing bits for the sake of it as some things are pretty pricey in this department!

Anyone have an old 1971 merc 800 distributor in need of a good home?
how about the (stator i think it's called?) from under the flywheel? so i can replace this rotten wiring? i'm sure there's more rotten wiring in the harness too, replacement harness anyone...
replacement engine anyone....

i love boats.. and i hate them!!

 

[chum1]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

After reading through your problem it sounds like a fuel starvation issue.

If it runs at all the spark works, the compression is there and the fuel is being burned. Sounds like the fuel in the carb bowl is all that gets burned.

Did you remove the little finger screens on the inlet of the carbs? , they are behind the metal fuel elbows were the hoses connect.

They could be filled with a bunch of old hose fragments, mud, sludge or beer.

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Thanks chum1,
yep, the fuel lines including elbows, and the carbs have all been cleaned and checked by a merc mechanic, i understand on the face of it everything shouts fuel starvation but i'm 99% sure it's not that? i've done a lot of cleaning, checking and tweaking..

pretty well exhausted the fuel feed side of things i think... mentioning exhaust, is it possible for an ehxaust to be blocked to stop it? never thought or heard of that?

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Reading elsewhere on numerous other ignition problems, i quite commonly came across faulty stators, rectifiers and duff battery techniques...

I confess to using a fairly small car battery to start mine, not 'proper' technique i know but it does crank well..

My stator appears to have heavily corroded wires, (they are practically blue and falling to pieces inside), although even if it wasn't plugged in it would still run, just the battery wouldn't charge.... so i doubt this is my initial probem. just the next problem!

Lastly, i read if the rectifier/regulator (i'm assuming this is the same thing?) that the HT lead comes out of i think?, if this is corroded or cooked it can have "anything from no spark to a high speed miss", could failure of this part result in a case where as the rev's pick up the miss becomes so bad it won't spark at all and kills the engine....
likewise if it's as heavily corroded as the stator then could that explain it's poor attempts at starting?

can you hear the finger nails scraping the bottom of the barrel for ideas

 

[chum1]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

It acts like a very simple problem, the fact that you know the history of it and it ran good 5 years ago is a plus, it is probably an installation problem.

will it pump fuel with the starter only? are the little fuel pump valves by the diaphragm in correctly? does the fuel bulb pump rattle when dry from a broken piece of plastic valve?

If your thinking spark try seeing if it will start on three cyl's? Plug one of the spark plug holes with an old plug then ground your good plug after putting the boot on and see if it will make spark at the high rpm's. If it sparks from start to finish it probably isnt that.

try disconnecting your kill switch ground on motor and the mercury (tilt) kill switch

some of this you may have already done but troubleshooting involves systematically checking each area from start to finish for best results.

Phil

 

[Phil303]

Re: 71 Merc 800 Outboard Fires, starts, Roars and then dies instantly?

Well....

After a second mechanic's been to look at the engine i was told it had to be carburettor isuues, so i assumed wasted money mon the last one and stripped it back and cleaned it all up again, the new one told me the other guys must have done it wrong... etc... etc...
Well, sticking it all back together after a second clean, the same problem..

So, i trawled through the book and found a phrase saying something along the lines of a dodgey trigger mechanism can be very difficult to pinpoint and often produce erratic results including random shut downs.

Dizzy cap does have a small crack, so i whipped it off and cleaned her up, using some epoxy resin and glass on the crack on the outside of the cap, putting it back together, boom.... it ran!!! i got maybe 45 seconds out of it before it spluttered to a stop after an attempted idle... the whole tune up and the rest of restoration can go on now, progress at last!

i've researched everything there is to know about boats trying to solve this thing, i now know my engine intimately, i was so happy when it started and kept going..... it's taken me ages... but i got there!

thanks to everyone for their help along the way... lot's of useful info!