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

[Phil303]

I'm piecing together an old 71 Merc 800 thunderbolt, i've got it all the way up to getting it on the boat and wired it up as below, i'm just struggling with the last bit which is making it run!

It has an electric start.
I have an ignition switch.
I have a choke Switch.
I have an a push button start on the dash.
I have a kill switch too..

it will not start at all unless the throttle lever is fully lifted.

With throttle fully lifted it will fire, Roar like a tiger! but then dies straight away?? It fires as i'm pressing the start button, i take my finger off it and it roars for maybe 3 seconds and then just stops totally?

is it likely i have wired it wrong at the switches? they all seem to work fine and i followed a wiring diagram so can't have gone too wrong?

I don't think it's fuel as even if i pump the fuel bulb when it's starting it still does the same.

Is there some other electrical connection i've missed? or is it likely to be something like a carb set up issue?

any suggestions greatly appreciated!

I've got so close yet can't go out! and it's perfect boating weather

thanks in advance!

Phil

 

[CharlieB]

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

Most two strokes need additional fuel to start cold, and a little more than just the idle mixture to stay alive long enough to warm up a bit before settling down to a normal idle.

Set the fast idle lever about 2/3 the way up, more is OK but when the motor starts drop the lever to maintain about 2000 RPM.

Many outboard ignition switches have the choke built into the key switch, push the key switch IN to choke, hold it in while turning the starter. In your case with separate push buttons for choke and start then you will hold the choke while pressing the start, once fired release both.

Once the motor fires immediately release the choke but be ready to momentarily push it in again just for a heartbeat if the engine speed begins to falter.

Once the engine has warmed enough to maintain a steady fast idle speed then you can begin to slow the fast idle down to the normal idle speed.

This is all dependent on CLEAN carbs, adjusted to the letter as spelled out in the factor service manual.

 

[Phil303]

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

Hi CharlieB,

Thanks for that one, i have tried starting the engine with the fast idle lever up and down, the only time it starts up at all is when the lever is right up full power, but it doesn't seem to matter whether i drop it immediately or even keep it up there? it starts and then stops about 3 seconds after?

I don't think it's a cold start issue as it will do this repeatedly, i've had it start 20 times in a row, roar up towards max rpm and then die again within 3 seconds.

The confusing thing to me is that it's not even a case of it slowly spluttering to a death it just totally stops.

I will go through the carb setup on the manual. I am reluctant to do this though as when it came off the last boat it was running good, this was about 5 years ago though?

thanks

Phil

 

[CharlieB]

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

If you are pumping the primer bulb prior to every start then the fuel pump could be suspect.

If it absolutely will not continue to run then I'd also suspect the idle mixture and carb cleanlyness not allowing fuel flow thru the idle circuit.

Keep 'bumping' the choke and see if the motor continues to run, if so then you know that there is little to no fuel thru the idle circuit.

Initial idle mixture screws should be 1 1/2 turns out from very lightly seated.

 

[buddybarnhill]

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

alright not an expert here but sounds to me like you may have stopped up carbs and if its roaring to max rpms mabe your throttle cable is stuck you just need to do a good look around mabe go back over the wiring make sure you didnt get hypno eyes and wire something wrong hope this helps and let me clear up one thing when you start your engine in the water it should be level and the choke/key combo the way it works is while you have your switch off you hold it in for 5 seconds release choke turn key on which shots gass into carbs then turn motor over do not hold choke in while holding choke in it willl burn up your fuel pump learned from experience this happend to me

 

[Phil303]

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

Thanks guys,

After further investigation there's some fuel coming out of the front of the carbs? also after it has started and died, someone suggested i took out the plugs to have a look, they were wet with fuel.

So, i think chances are it's bunged up carbs or a sticky something?

will get eh book out and try and get a look at the carbs tomorrow...

thanks

Phil

 

[coolguy147]

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

ok well if u have fuel leaking out of the holes on the top of carbs the float bowl. well u have to take the tops off and adjust the the needle height. now this happened to me cause i didnt have thema adjusted. adfter adjusting pull a vacum on it with the fuel hose and see if leaks if so then needle and seat may need replaced

put the wet plugs on ur palm and wipe all the gas off see if helps. choke if cold

 

[Phil303]

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

Ok, things are getting trickier... really confused now...

I bottled it at the point where i had to unscrew everything to get the carbs off so i took it to a workshop, shame on me i know!

They've come back to me saying the fuel leak at the front of the carbs was fixed for 10 mins and then the needle stopped working again so it needs a new carb kit or something?

even when it was working though, the engine would still fire up, roar to max rpm and then stop dead still within 3 seconds?
the workshop said it could be the distributor, looks like screws have been tampered with? and carb set up too?

i'm wondering if i'm sitting on the edge of a money pit?

it must be fixable?

i have the blueband 66 to 72 manual but it's super basic and not really helping me here?
The manual states a possible air leak in the fuel system would make it start then stop immediately, is it possible the 35 year old fuel lines going hard would lose their airtight seal? is that common or likely to be a problem?

thanks

Phil

 

[coolguy147]

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

uhh ya u should replace 35 year old fuel line whether or not there good. ya replace the fuel line all up in the motor. and while at it u might as well go and take the carbs off and clean then one at a time. i believe u can take the carbs off all at once

 

[Phil303]

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

thanks coolguy147,

Ok, i'll replace all the old fuel lines in all the engine and see how i go,
i'll also set about cleaning the carbs again and getting a carb kit for it.
if i do all that then i don't see what else it could be?

does firing, instantly revving to max rpm and dying within 3 seconds sound like a timing issue?

from what i can gather:
it's getting spark otherwise it wouldn't fire at all?
and then it's getting stopped by too much fuel or the spark's stopping as the plugs always end up wet?
would bad timing stop it sparking and cause it to die so quick?

i know zero about timing... now, but i'm keen to learn

thanks

phil

 

[buddybarnhill]

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

if it has jumped time it wouldnt fire at all it would just turn over so no i dont think its a timing issue

 

[coolguy147]

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

ya it would probably just make one loud back fire like gunshot if it was off timing.

ya it sounds like its running out of fuel to me. im really sure

so u already cleaned the carbs?

again i still would make sure ur priming it cause my merc500 dual carbs instead of three takes a little while to prime up. cause it has two carbs. so u pump one thing and keep pumping make sure u have enough gas in the tank rightly mixed. and keep priming till u cant no more. merc r really cold natured.

one test u can do to check ur needle and seat is turn the part with the needle and seat u can disconect if please from the carb u can turn upside down and with ur mouth make sure to wipe up any fuel and pull a suction and it should creat a pretty good vacum. if it doesnt hold then check clean or replace needle and seat if needed

 

[bigblue16.5]

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

This is my first outboard so I dont know any of the tech terms for anything. I just got my first large boat and had this exact same problem yesterday and missed a fishing trip because of it. It was the the one way valve that the gas tank hose slips onto on the engine. It might have been sticky. I was just about to pull the carb off like everyone else is saying to do when I noticed there were to of them. Yes I am a noob. That seemed like way to much work. Then I realized that that valve explains everything. The engine will only start when the gas lever is all the way on and when primed hard and choked because that is the only time there is enough of a vacuum to open that valve at all. To check I hooked the gas tank hose directly to what I think is the fuel pump or at least the next conection after the valve. The hoses were different sized so I put a couple of zip ties on really tight just to test. Worked great engine pured like a jacked up dog(spark timing issue quickly fixed). Engine starts with a bump of the key on the lowest gas setting. Hope that helps. Old timers be gentle this is my first outboard:redface:.

 

[Phil303]

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

Hi All,

thanks again for your suggestions... i'm still not there though

I followed the book and started at the beginning

Fuel - i have good fuel, i have a new fuel line on it as the old one was really hard and badly sealing. I have new fuel lines on the engine too with good seals and clips on.
I have had the fuel pump off, all is ok there.
I can Pump fuel through freely and easily to the carbs now, the bulb goes hard, stays hard and there's plenty of fuel there.

Carbs - The carbs have been stripped, serviced and rebuilt.

Tuning - I have checked the timing and throtlle pick up etc. all is good and as the book suggests.

Still it will not run, it starts, roars and dies.....

That must mean something electrical?
i noticed a couple of earths rotten and the two wires from the stator are in a fairly poor corroded state? is that likely to be the cause?

Electrics is my worst element!

how would i go about testing the stator with a multimeter to see if it's good and if the rest of the circuitry is working roperly?

the book goes a bit over my head there?

i need basics!

thanks in advance.


cheers

Phil

 

[Phil303]

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

i have now got a multimeter but the instructions say refer to the workshop for operating instructions and the workshop manual says refer to manufacturers manual??

 

[Fuzzytbay]

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

Check your wireing on the ignition, key, or the key itself. I had the exact same issue, diffrent motor, but the same problem. I'd turn the key, motor would fire, let the key back to run possition, the motor died. Turns out, I was grounding out one of the coils. I found my ignition switch was for a diffrent motor. It was wired correctly, but the internal connections were diffrent.

 

[jimg984]

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

sounds like you got the igination wire connected with the start wire you stated it would run as held the start button on

 

[Moody Blue]

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

Not sure what you are trying to do with the multimeter.

When I first read this thread I was convinced it was a fuel problem. After reading a second time and "reading between the lines" I would have to say that you have a bad trigger in the distributor. A classic sign is that the motor will not run unless the key is in the start position. Check this link, specifically Item 3).

Troubleshooting Mercury Battery CD Ignitions

******** This information is supplied as a service guide only and Outboardparts.com is not liable for any misunderstandings, errors or omissions regarding this information. The information has been obtained from actual unit analysis, parts manuals, and other sources. ********

Recommended Tools:
For DVA: Fluke Multimeter with CDI #511-9773 Peak Adapter, (or CD-77)
CDI #511-9701 Battery CD Tester
CDI #511-9710 Trigger Tester
CDI #511-9766 Spark Gap Tester
Jumper Wires
A Reliable Volt/Ohm Meter (it the CD-77 is used for the DVA)
CAUTION; DO NOT USE A MAINTENANCE FREE BATTERY WITH THESE TYPES OF IGNITIONS AS THEY TEND TO OVERCHARGE AND BLOW THE PACKS.> Typically 17 Volts +.

Note: A large portion of the problems with the battery CD units are caused by low battery voltage or bad ground connections or high battery voltage. Low Voltage symptoms are weak erratic firing of cylinders. Misfiring after a few minutes of running can be caused by excessive (Over 15.5 Volts DC) voltage at the pack. - WARNING : Check the voltage on the red (or purple) wire at the CD unit through the RPM range. At no time should the voltage exceed 15.5 Volts DC.


WARNING!! BATTERY REVERSAL WILL USUALLY DESTROY BATTERY CDs AND TRIGGERS.

1) Check all battery and ground connections.
2) Dead or no fire until you release the key switch:
Disconnect the mercury switch and reset, if the engine fires, replace the mercury switch. Check the voltage on the red and white ignition wires at the CD unit. If the voltage is less than 9 1/2 volts during cranking there is a problem in the battery s or the ignition switch box. These units require at least 9 1/2 volts to fire properly. On a 332-2986 switch box, check the voltage on the brown terminal (white/black for 332-47960 where the trigger is hooked up. It requires at least 9V at cranking. DVA check between the white and black wires (black and blue on 332-4796). You should read at least 2 1/2 volts at cranking. Connect a jumper wire directly from the battery POS (+) terminal to the red and white ignition wires (the red wire is not needed for the CDI units). CAUTION: DO NOT CONNECT THE JUMPER WIRE TO THE WHITE TRIGGER TERMINAL. Retest: ATTENTION: in order to kill the engine if it cranks, the jumper wire has to be disconnected and/or choke the engine. If the engine still fails to crank, recheck voltage as above. If low, replace the battery and retry. If there is still no fire, disconnect points wire (or trigger wires) and connect the Battery CD tester (511-9701), according to the instructions in the manual, and align the rotor with a spark plug wire. Connect a spark gap tester (511-9766) to all spark plug wires and turn the ignition switch on. If the CD unit fires to only one spark plug wire, check points wire (for breaks or shorts) or trigger. If ANY other spark plug fires besides the one the rotor is aligned with, the distributor cap and rotor should be replaced. The Battery CD tester will fire the system to approximately 3000 RPM. If the Battery CD tester is not used, see related drawings on the Schematic page (following). If the CD unit fails to fire with this hookup, it is usually bad. Following the instructions included with the Trigger Tester (511-9710) check the trigger to see if it is good or bad.


3) Engine cranks and fires as long as starter is engaged:
This problem usually indicates a bad trigger.


4) Check the ignition coil.
An open, cracked or poorly grounded coil can burn out a battery CD.


5) Check the DVA voltage on the primary input wire to the coil.
Using the fluke meter with the peak reading voltage adapter (5111-9773), or CD 77. The reading should be approximately 100 volts or more for OEM CD's, and 200+ for CDI electronics units.


6) Inline engines with internal exhaust plate:
If the engine speeds up when you remove one spark plug wire, the internal exhaust plate is more than likely warped. The following tests can be performed on the bench or on the engine. NOTE: Disconnect the trigger mechanism prior to testing.


Essentially the starter motor is keeping the motor running. Once the starter is disengaged the faulty trigger is unable to provide spark to keep the motor running. The rev to high RPM is "normal" if you have the fast idle lever pushed forward. Once the key returns to the RUN position the ignition is disabled and the motor dies within a couple seconds. There is a procedure on how to test the ignition system including the trigger. Do a search in this forum for "Battery CD Ignition Test".

Good luck

 

[Phil303]

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

Thanks again for your suggestions,

Just to clarify, when i press the start button the starter shoots up and spins the fly wheel, the engine then fires and roars up the rpm, as it's accelerating the starter disengages as i take my finger off the start button, then engine then carries on accelerating up to high rpm and then dies within 2 seconds.
So it is still firing momentarily after the starter is disengaged.

I was hoping to poke around with the multimeter to find a dodgey wire that might be stopping the engine continue running, i thought if there was some way it might not be getting the right power to it to continue running? hence my thoughts there might be a dodgey stator cable or lead to the distributor perhaps? these i wanted to test with the multimeter when i figure out how to use it, it looks fairly simple though, i watched a how too video on you tube.

The more i look and think about it though, the more i consider the fuel problem again, i think they serviced the carbs, i'm not sure if they replaced the guts of it though? perhaps a bad needle or seat or float would be causing it to flood and stop? i keep having the fuel on the spark plugs after its stopped in the back of my mind?

at first i thought it was stopping firing, but i've cranked it with the plugs out and earthed the plug, it keeps popping its spark across ok it would seem?

so perhaps it is a carb issue after all? i thought having it serviced by pro's would have solved it but perhaps not replacing and only servicing the guts of the carb was the wrong thing to do..

I'm worried it's a bit of everything!

i'll double check my wiring first and look at the carb again and let you know how i get on...

thanks for your help again, i will crack this beast!

phil

 

[Moody Blue]

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

Do the following test after the engine dies. Don't touch the ignition switch or anything once the motor quites. Actually you don't even need to start the motor, just turn the key to the RUN position.

Measure the voltage at these two terminal on the switchbox. You will need to set the multimeter to DC volts (--) and set the scale to 20V. Place the black meter lead on the motor cowling (GND) where the black battery cable attaches.

1) Place the red meter lead on the RED wire terminal of the switchbox (4 terminal side). Should measure 12V.
2) Place the red meter lead on the WHITE wire terminal of the switchbox (4 terminal side). Should measure 12V.

You may have to clean off the terminals if they are covered in the black waterproofing stuff that Merc used. You need clean metal to make the measurements.

If you don't measure 12V on BOTH terminals then you have an issue with the ignition switch arrangement.