Starting Issues 1978 Mercury 800

[Sean Leonard]

I recently purchased a well used 1978 Mercury 800 80hp outboard and I am working on getting it running. The previous owner could not tell me the last time it ran. I have replaced a good portion of the wiring and now I am getting spark. Now the issue is fuel. I tried priming and starting but it wouldn't fire.

First I checked the hoses starting at the fuel tack and working towards the carbs. All check out fine and were moving fuel along when the primer bulb was sqeezed.

Next I tried using starter fluid (I know this is a huge debate but it's already done so I can't undo it). The motor fired right up then died. A few more attempts and it was running fine. I let it warm up and then set it to idle.

After a few more minutes I turned the motor off and tried to start it again without the use of starting fluid. It still wouldn't start.

I plan to remove and clean the carbs as the motor has been sitting for an unknown time and I don't know what the previous owner did prior to taking the motor out of service.

What I can't seem to figure out is why this motor will not start by priming. Once it's running the fuel pump seems to be working fine.

Any suggestions would be welcomed.

 

[GA_Boater]

Re: Starting Issues 1978 Mercury 800

Cleaning the carbs is a good start. Old fuel could be gummied up and causing the floats to stick and plugging jets.. My old Merc took a lot of bulb squeezing to get her going at first too. Same as you the PO had no idea how long it sat. Also don't forget about the impeller, it prob needs changing as well just for well being.

 

[impatico]

Re: Starting Issues 1978 Mercury 800

if the needle in the float bowl is dirty and doesn't seat properly when you prime it you will force fuel past the needle and flood it and it will be hard to start

rip the carbs apart and yes impeller change I wouldn't even check it first just change as they are too cheap

 

[Faztbullet]

Re: Starting Issues 1978 Mercury 800

That engine has carbs that have a enrichment/choke built in the carb body, when you hit "choke" the plunger pulls up the linkage and closes a internal air passage on the idle circuit causing a overrich mixture. Do a complete carb rebuild with NEW parts and clean and blow all passage with a compressed air source and replace the fuel pump diaphram. Also replace the plastic venturis as these will warp and cause bogging issues..

 

[79camaro]

Re: Starting Issues 1978 Mercury 800

I have a 78 Mercury 900, these motors are GAS hungry. Instead of starter fluid, fill a spray bottle of gas mixture. I've stater fluid the hell out of mine though, and even if people here say not to, these older outboards can totally handle it.

I'd try cleaning the carbs, they are super easy to take out. The choke on these motors are also a big issue. Make sure the starter is the right one. Again these motors LOVE gas, so make sure it's thirst is quenched with plenty of gas.

 

[79camaro]

Re: Starting Issues 1978 Mercury 800

After further thought it sounds like it just might be a timing issue, have you checked the timing? You can easily do it with a timing light.

 

[Faztbullet]

Re: Starting Issues 1978 Mercury 800

nd even if people here say not to, these older outboards can totally handle it.

Totally BAD advise... starting fluid washes ALL the rod bearings and labyrinth seals of reside oil thru resulting in basically a dry start.

 

[Sean Leonard]

Re: Starting Issues 1978 Mercury 800

I didn't want to get the starting fluid debate going. I only used it as a troubleshooting tool. I do not plan to use it everytime to start the motor.

To update my above post, I pulled the carbs this weekend and I am just waiting for the rebuild kit to arrive along with the fuel pump diaphragm and water pump impeller.

Thanks to everyone for their input.

 

[79camaro]

Re: Starting Issues 1978 Mercury 800

Yeah people get real touchy here regarding starting fluid, I am just throwing my 2 cents in. I have a 30 year old motor that I've used starter fluid on, and my mechanic who owns his own performance outboard shop said it's fine. A lot of the newer starting fluids even have lube in them. If you want to be cautious you can always fill up a spray bottle with your gas/oil mixture and use that instead.

 

[Chris1956]

Re: Starting Issues 1978 Mercury 800

Do the choke plates on the carbs close when the push-to-choke button is activated?

 

[Sean Leonard]

Re: Starting Issues 1978 Mercury 800

Okay, I rebuilt the carbs using the mercury carb rebuil kit. All new jets (the kit didn't include the main jet and the vent jet but I bought them), new floats & hinges, new inlet needle. I set the floats according to the manual (11/16"). I cleaned all of the passage ways including the enrichment valve. While I was at it I replaced the fuel lines, fuel pump diaphragm and the water pump impeller for good measure. I removed the tell tale nozzle and it was packed with dirt & mud so I cleaned it and the hose as well.

We tried starting it up today and it wouldn't fire. I squirted a few shots of fuel in the carbs and it fired right up and kept running. It still will not start without a shot of fuel in the carbs.

Why am I having to squirt fuel each time to get it started?

What determines the throttle position during starting? It acts like it's starved for fuel. The butterflies don't seem to move much when I move the lever next to the throttle/gear selector. (BTW what is the lever called next to the throttle/gear selector?) How much should they open when this lever is fully opened?

Sorry for the long post, I am at a loss for ideas,

 

[Faztbullet]

Re: Starting Issues 1978 Mercury 800

Do the choke plates on the carbs close when the push-to-choke button is activated?

These carbs don't have choke plates.....

Why am I having to squirt fuel each time to get it started?

Checkthat when you hit choke that the solenoid is pulling the choke linkage fully closed on carbs,if not check linkage or shim solenoid up to increase stroke length.

What determines the throttle position during starting?/hat is the lever called next to the throttle/gear selector?

The warm up lever on control box controls how much throttle & spark advance during starting,at full up carbs should be about 1/4 open ,

 

[79camaro]

Re: Starting Issues 1978 Mercury 800

I had the EXACT same problem about a year ago after rebuilding a 78 mercury900. These motors are fuel hungry, you really can't flood them.

There are a few things imo that could be the issue.

1. The starter. After a lot of work this was one of our problems. The previous owners had put the wrong starter on it so it was underpowered and struggling to keep it going. We still have the starter on there but a little starting fluid or fuel sprays to the carbs starts it everytime.

2. The timing. I couldn't get the timing right. I took her to an outboard specialist and after that it worked like a charm.

 

[Sean Leonard]

Re: Starting Issues 1978 Mercury 800

The warm up lever on control box controls how much throttle & spark advance during starting,at full up carbs should be about 1/4 open ,

The butterflies are barely moving at all when the warm up lever is pushed all the way forward. Can this be adjusted?

 

[Sean Leonard]

Re: Starting Issues 1978 Mercury 800

I had the EXACT same problem about a year ago after rebuilding a 78 mercury900. These motors are fuel hungry, you really can't flood them.

There are a few things imo that could be the issue.

1. The starter. After a lot of work this was one of our problems. The previous owners had put the wrong starter on it so it was underpowered and struggling to keep it going. We still have the starter on there but a little starting fluid or fuel sprays to the carbs starts it everytime.

2. The timing. I couldn't get the timing right. I took her to an outboard specialist and after that it worked like a charm.

The starter has plenty of power. The timing however is going to be tough as the lines are on the timing decal but the words have been rubbed off or faded over time. So I can't tell what the marks are supposed to be.

 

[Faztbullet]

Re: Starting Issues 1978 Mercury 800

The butterflies are barely moving at all when the warm up lever is pushed all the way forward

Post a picture of your control box, if the old style 2 lever the cams are worn on box.....

 

[79camaro]

Re: Starting Issues 1978 Mercury 800

When using the priming bulb are you able to fill the bowls filling? You should be able to hear them filling and the bulb should get tight. Also make sure the motor is all the way in the water. You can also lean on the priming bulb when cranking it to force a little more fuel into it.

If the wamer isn't opening the carbs you have a linkage problem with the warmer linkage.

 

[duckhunter138]

Re: Starting Issues 1978 Mercury 800

Hey I beat myself up on a fuel issue for 2 weeks just like you. After replacing a lot of parts,again like you, I found out the jet screws werent adjusted right. Run them all the way in and turn them out 1 1/4 turns. Mine fired right up after i did this. Been running great ever since.