1984 70HP Acceleration Bug

[joe7670]

Need some advise on a fuel issue. This is a new boat and motor to me.

Friday - Took it out and after running it for a while the motor stalled. Repetitive pressing of the choke and trying allowed it to work. Primer bulb was sucked up.

Saturday - Cleaned tank throughly and found some silicone in there that would have kept fuel from flowing. Replaced lines and bulb anyways. Fuel/Water separator filter is new.

Took boat back out and it ran great, trolled for a good while... Got back into bay and tried to gun it full throttle and it stalled. Took a little while to start with excesive choking. Bulb was not sucked up this time. Ran rough and after about 2-3 minutes it seemed smooth out.

Took off again ran 1/4, 1/2 and upto 3/4 throttle just fine. When I tried to go past 3/4 it stalled again. Same spiel, took a while to start up and then ran it at 1/4 throttle in to dock to avoid getting stranded.

Ideas where to look first? Checked the fuel filter piece on the motor and it looks ok.

 

[CharlieB]

Re: 1984 70HP Acceleration Bug

When you replaced the hoses did you also replace the fuel line connector to the engine? With a FACTORY fitting?

Sometimes these fittings do not seal perfectly under fuel pump vacuum, they hold pressure from the primer fine, but any air sucking in may cause the motor to run low on fuel at WOT.

Test by replace a section of hose between the fuel pump and carbs for a temporary inspection, look for any air bubbles flowing through the hose while underway.

Remember to replace with REAL hose once finished with your testing/repairs.

 

[joe7670]

Re: 1984 70HP Acceleration Bug

That was the only piece I didn't replace thinking that there is no issue with that.

Will try the test and replacing as needed and will report back.

 

[joe7670]

Re: 1984 70HP Acceleration Bug

OK. I'm really confused now. I swapped the plug into the motor for the fuel.
I have 3 tanks. 1 aluminum tank, 1 red 12gallon tank and one on my kicker that holds 1 gallon.
Boat is a 17' boat.

So I get out there and run on the aluminum tank with all the new lines, bulb and connector. Run for a while and the motor dies on me. Now the bulb is not getting sucked up as it was before. Seems to do it more when i'm on the ocean side, but has done it in the bay.

So I think, maybe it's the tank??? Plug into the 1 gallon tank and it runs great for a bit and then craps out again.

Plug into the 12 gallon portable tank, similar issue.

Usually when it dies I need to choke the crap out of it to keep it running for a little bit until it smooths out.

Seems like it's starving for fuel. When it's getting fuel it runs great.

My thoughts are:
1. Fuel pump? How is this checked and would it work intermitently?
2. Possibility that as the boat bobs through the waves and the fuel splashes aroung in the tank it's getting air? I doubt this one, but a thought.

Any ideas on what I should try next?

 

[CharlieB]

Re: 1984 70HP Acceleration Bug

Have you pulled a fuel sample from each of the tanks to look for any beads of water rolling around in the bottom.

Tanks sweat inside as the outside air cools, the sweat rolls down the inside same as on your favorite iced drink, but once under the fuel it NEVER gets out, it just lays there and keeps growing until one day it gets deep enough to get picked up by the fuel pickup tube.

Once in the carb the surface tension will not allow the bead os water to pass thru the jet until you drain it or artificially raise the vacuum on the fuel port by placing your hand over the carb inlet, choking it hard.

Clean out one of your smaller tanks and retest with known clean fuel, if it is a water issue then the clean tank should run fine.

Then clean all tanks and install a water separating filter to reduce the possibility of future occurance. Change the new filter annually.

 

[joe7670]

Re: 1984 70HP Acceleration Bug

My main tank was empied, vacumed and refilled. It also has a water separator on it as well.

 

[CharlieB]

Re: 1984 70HP Acceleration Bug

It is entirely possible that you have two issues, with the first being the fuel supply problem and the second one hasn't been diagnosed yet.

Running fine up to 3/4 throttle for a period of time and NOT developing the problem till WOT indicates that the fuel AND ignition systems are both fine at these load levels.

WOT increases demand for fuel flow AND increases voltage demand from the ignition system. The increased load on the ignition system is caused by the additional air/fuel mix in the cyl, when under compression causes more resistance for the spark to jump across, if the spark plugs are too fouled, then the spark will take the path of least resistance and short out, very effectively killing the cyl and the engine dies.

You provided an important clue in that it requires a LOT of choking to restart and runs rough for a while till it smoothes out. Fouled out plugs can ignite and overly rich mixture and given enough TLC can burn reasonably clean enough to run up to a limited load, pushed beyond their limit they will foul out again.

Inspect your spark plugs. If surface gapped, look at the shiny black carbon on the once pristine white porcelain between the electrode and housing, if it will clean off with a scotch brite pad they may be usable. When in doubt, replace them. Or screw in a new set of standard electrode NGK B7HS gapped at .032 and retest.

 

[joe7670]

Re: 1984 70HP Acceleration Bug

After further testing i do indead have multiple issues.

The spark mention is ver likely as I found that one of my coils was leaking the black stuff.

Also at last run after replacing the fuel pump, my impeler looks like it started malfunctioning cause the motor stopped pumping water. Overheated a little bit, but luckaly we caught it very quickly.

A while later tried it again and it pumped very weak.

So before any further testing, water pump kit is on order, coils are on order and the plugs are too.

We will see where it goes later this week.

 

[kenmyfam]

Re: 1984 70HP Acceleration Bug

Right thing to do. Make sure it cools correctly before trying to diagnose anything further.

 

[joe7670]

Re: 1984 70HP Acceleration Bug

OK. Update.

After replacing the fuel pump, impeler and water pump housing, coils due to seeing one leaking here are the results. Also after switching to only a portable fuel tank cause my aluminum tank developed a leak.

While running on a new plastic red fuel tank, the boat ran great, but after a while of running the primer bulb got sucked up. Lines are new, primer bulb is new(bulb is factory johnson brand). Only things which are not new are 1. the johnson fitting that plugs the fuel line to the tank and 2. the water separator housing.

I have items in this sequence. Red fuel tank with johnson fitting, line going to fuel/water separator filter, line from there to primer bulb (which is laying horisontally, followed by fuel line running to the motor and connected into the motor using johnson plug. Lines inside the housing to the fuel pump and to the carbs is all new.

I'm guessing it's the johnson plug into the red tank which is the culprite, but wonding if i'm missing something. I wouldn't think the bulb would get sucked up due to carb clog would it? Also read some threads about putting the primer bulb vertically, any idea if this could be it or the correct position for that matter?

One of these days I'll get this thing straight!

 

[CharlieB]

Re: 1984 70HP Acceleration Bug

A flattened primer bulb indicates a restriction between the bulb and the fuel in the tank.

First thing I would suspect is that new filter, pull it off and pour it into a clear container to see how much water it has picked up from your other tanks.

With a new tank and fresh fuel you may bypass the filter and retest.

 

[kenmyfam]

Re: 1984 70HP Acceleration Bug

Are you sure the tank you are using is properly vented ??

 

[joe7670]

Re: 1984 70HP Acceleration Bug

Venting was a pinhole on the cap.

I've already gone to Bass Pro and picked up a moller 12 gallon with screw vent in cap. Good point on the water separator filter. I will do the filter check and I guess replace it just in case.

Will report back.

 

[kenmyfam]

Re: 1984 70HP Acceleration Bug

Venting was a pinhole on the cap.

I've already gone to Bass Pro and picked up a moller 12 gallon with screw vent in cap. Good point on the water separator filter. I will do the filter check and I guess replace it just in case.

Will report back.

Vent hole may well be present but is it actually doing it's job ??

 

[joe7670]

Re: 1984 70HP Acceleration Bug

Another update.

Removed water fuel separator and it was about half and half.

Put it back on the pumped with the primer bulb and it came back about 1/8 water 7/8 gas.

So I'm going to deam the gas that's left contaminated. Of course in my inexperience and trying to save $ I transfered the fuel from the old aluminum tank to the new tank which considering it may have been contaminated carried that issue with it.

On the clogging side, I found some silicon pieces in the water separator which were from a seal that it looks was made on the old tank using that orange gasket maker. Thanks to my father in law for "rigging" it as he was the prior owner.

So i am quite confident that later this week with a new tank, fuel, filter and just for kicks plug into the tank I may resolve this fuel issue.

Will report back later once installed and tested. Maybe I will get the boat running well by lobster season!

 

[joe7670]

Re: 1984 70HP Acceleration Bug

Success!!!!
After replacing water fuel separator filter, installing new tank, fresh gas all went perfect.

Motor ran great and had no fuel issues.

Now I got a small issue where some times at full speed the tell tale stops shooting water. Will start a new thread for this though.