Intermittent "cough" during startup.

[DunbarLtd]

Hello all, I am working on 1988 85hp.


I've been enjoying the summer and fall out here in the west (USA) with minimal issues. Although, I still have some Im chasing down.

#1. I still experience a "cough" when cranking. It sounds like a big HISS or PSSHHH for just a second and then the motor stops cranking instantly. Cold or warm doesnt matter. It is completely random as well. Sometimes it cranks perfect and fires right up (only after warm). Starting cold it seems to cough more. Choke or no choke. Even if I give it gas by pushing in button on throttle handle. I always make sure to squeeze the primer bulb. It stays firm.

#2. Not sure if the cough is related but I have pretty good shaking of the motor when going maybe 5mph. It rattles the glass on my bayliner. I have it set to idle around 3.3mph at about 700rpm i believe. At that speed it shakes but its gets worse until maybe 10ph or so.

Ive checked static timing and it is 28btdc

I have all 3 carbs air screw set to 1 turn out.

Carb bowl floats are brass and do float as ive tested in gas. They are set to parallel. I installed a repair kit with new needles and tested to make sure they dont leak.

I have replaced all fuel lines and fuel pump diaphragm.

Also replaced base gasket and stopped exhaust oil leak.

Also replaced all 3 coils with new wires. This fix did not fix the issues.

Compression is around 130psi on all 3.

Ive done a link and sync many times.
Ive sprayed starting fluid everywhere around the intake and the motor will still shake and idle does not change up or down.

I get to 4400-4500 rpm full power and I had it going 35mph last week. So it seems to have worked itself out for some odd reason where I had a previous issue with wot speeds.

So now I would like to figure out why it is coughing and shaking.

I do notice (by sound) it seems to have a slight miss as well when in gear at idle speed.

I have been out by myself every trip so I cant really use the timing light while in gear.

Any help is appreciated. Thanks.

- Mark

 

[racerone]

Open low speed mixture screws 1/4 turn each.----Test run.-----Repeat if need be.

 

[pnwboat]

That's pretty much normal. As long as it doesn't backfire, you should be good to go.

You can also check the drain back reeds and passages to make sure the intake passages aren't loading up with fuel. At low speeds, the fuel flow isn't moving that fast, so the fuel/air mixture has a tendency to puddle up in certain areas. The drain back system is supposed to get rid of the fuel that has puddled up and route it to the intake where it is burned. The drain back reeds are part of the kind of dogbone shaped cover on the side of the motor. There are some vacuum lines that run to the covers. Make sure the check valve or reed plate (depends on what year as to whether you have check valve or reeds) is working and hose is intact. Make sure the gasket is OK too.
See Picture below.

 

[DunbarLtd]

Ive cleaned and checked the recirculation system twice now. Reeds looked great. Minimal carbon buildup. Even replaced the hose.

Why does it chuff or cough randomly though? Itll start first crank and then next time i start it, chuff or cough or whatever you call it. Im trying to understand what actually causes it. Does it mean lean or rich or what? I just dont get it. How it can start perfectly fine and for no obvious reason have an issue on the very next startup after a run and shutdown? Doesnt matter if I shutdown for 1 minute or an hour. Its still quite random and completely confusing.

 

[DunbarLtd]

Open low speed mixture screws 1/4 turn each.----Test run.-----Repeat if need be.

Thanks. I assume I adjust all at the same time?

 

[jerryjerry05]

The one turn out from lightly seated might not be open
enough for your motor????
One customer needed his 84/85hp 3 carbs open almost
3 full turns out???
Sometimes: Different carbs need to be set at different levels???
Start at 1 turn and adjust from there.
Turn 1/8th turn on the top carb and let it run for 15 seconds.
Then again 1/8th turn, wait 15 and repeat.
as soon as it coughs and stutters turn the air screw in 1/2turn
and then repeat on the other 2 carbs.
As long as you don't go under the 1 turn out you shouldn't hurt
anything.

 

[The Force power]

I do notice (by sound) it seems to have a slight miss as well when in gear at idle speed.

I have been out by myself every trip so I cant really use the timing light while in gear.

- Mark

To add to the advice already given;
- Tie the boat to the dock and check the actual RPMs in gear
(it may running too low at idle)
- Check all wiring connectors on the terminal-strip
(they may look good but the wire can be broken under the shrink-wrap causing intermitted contact)
-Check if all cylinders fire consistently if not;
NO FIRE OR INTERMITTENT ON ONE CYLINDER:

1. Check stator and trigger resistance, trigger wire sets read approximately 50 ohms between the wire sets (DVA-4V or more), stator reads 680-800 ohms (factory) and 200- 300 (CDI/RAPAIR) DVA 180V or more from blue to yellow.
2. If readings are good, disconnect kill wire from one pack. If the dead cylinder starts firing, the problem is likely the blocking diode in the other pack.

 

[racerone]

The ---" lean sneeze " ---in outboards is not well understood.

 

[The Force power]

The ---" lean sneeze " ---in outboards is not well understood.

Yes, it still can throw me for a loop

 

[racerone]

You could start learning by searching for -----LEL gasoline-----Using google.

 

[topgun3690]

I googled it.....Lower Explosive Limit.....and Upper Explosive Limit......one would think gas would burn at all times, but not so. Interesting info. My engine "coughs" sometimes too, but only on the first start...after that, no problem.

 

[racerone]

That is why when an engine is " flooded " there is too much fuel in the air mix.----Even though there is spark it simply will not ignite.------

 

[The Force power]

Temperature, pressure, and the concentration of the oxidizer also influences flammability limits. Higher temperature or pressure, as well as higher concentration of the oxidizer (primarily oxygen in air), results in lower LFL and higher UFL, hence the gas mixture will be easier to explode. The effect of pressure is very small at pressures below 10 millibar and difficult to predict, since it has only been studied in internal combustion engines with a turbocharger.

1Millbar = 0.0145038 psi
1 bar = 14.5 psi X 10 = 145 psi (lets say; average head pressure)
Another reason why good head pressure is important. lol

 

[racerone]

Force power-----Do you understand why these 2 strokes sneeze when set too lean on idle mixture ?

 

[The Force power]

Force power-----Do you understand why these 2 strokes sneeze when set too lean on idle mixture ?

thank you

 

[racerone]

Would it have anything to do with the fact that at the bottom of the piston stroke the crankcase is open to the exhaust housing ?

 

[The Force power]

Would it have anything to do with the fact that at the bottom of the piston stroke the crankcase is open to the exhaust housing ?

I don't know and I'm not sure to what this is referenced ?

 

[DunbarLtd]

Well plenty of interesting ideas here. I will start with mixture and go from there.

Also, Im assuming if this were a timing issue I would not have WOT power and it would be tough to start all of the time?

 

[jerryjerry05]

Testing while tied to the dock is about the same as testing in your
yard.
You can do the tests on the trailer but problems need to be addressed in the water and in gear moving.
The rpm's on the trailer or in N 11-1200 in gear 750-800

 

[foodfisher]

That is why when an engine is " flooded " there is too much fuel in the air mix.----Even though there is spark it simply will not ignite.------

Well plenty of interesting ideas here. I will start with mixture and go from there.

Also, Im assuming if this were a timing issue I would not have WOT power and it would be tough to start all of the time?

Check plastic connector at top of timing tower for crack/break.