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Why dont it start good n' Idle smooth?

thudpucker

thudpucker

Regular Contributor
:pIm a fair hand at engines.
All my life I've wondered what is the cause of that intermittent miss and stagger, the Spitting out the exhaust, the back spitting out the Carb?

I have put so many engines together with new rings, gaskets, carb cleaned, good points, new plugs and all that stuff.

I dont think I ever got a Two stroke to Idle well. Perfect I mean. They all worked good, unless it was something I ran down and fixed.

What causes misses?
What do some of you guys know that you'll share with us. :cool:
 
Thanks,
I've often wondered about a Cheap (quick n' dirty) EGT gauge or indicator.
If its too lean the temp should be cooler, and too Rich it should be a little hotter, for Idle settings.
As the RPM's go up, the Reverse is true. Lean is hotter than Rich.

I wonder also whats in the future of that kind of indicator with this new Alcahol laced fuel.
 
thudpucker said:
Thanks,
I've often wondered about a Cheap (quick n' dirty) EGT gauge or indicator.
If its too lean the temp should be cooler, and too Rich it should be a little hotter, for Idle settings.
As the RPM's go up, the Reverse is true. Lean is hotter than Rich.
.
Click to expand...

I have wondered the same. Why not use a IR heat gun pointed at the spark plugs for the fine tune tweaking as a way to get the low speed fuel flow as close as possible between carbs? I thought the temp would go up as the engine ran lean, and down for rich???
 
Nope, temps are not that sensitive. You will not be able to detect such a small variation.

My 2 cents.

Poor idle is also caused by not having the throttle butterflies ABSOLUTELY closed when at idle.
It will spit and pop back a bit on the carb that has the butterfly cracked open a bit.
You can often see the mist spitting back out, and you can definitely see a piece of paper towel getting wet,
and the towel blowing back away from the open carb throat. It looks a bit like when you have a bad reed.

The butterflies must be closed at idle, and then work on a lean sneeze mixture problem as described by racerone above.
 
There's usually a mark on the cam that slides against the carburetor throttle roller which opens the throttle butterfly. The throttle butterfly should just start to open when that cam mark is dead center with the roller, not before or after. If opening too soon, as stated above..... the popping and spitting back begins.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.
When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

--------------------------------------------------
(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle valve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, waiting for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustments, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
 
I copied that. Stuck it into my OMC manual.
Mr Reeves seems to know what he's doing eh?

All my life, I've never ever had an outboard (mostly Johnson's or Evinrude's) that would Idle over long periods without the occasional burble or three burbles from time to time.
Fishing in places with some distances between them, I set out on a 9 mile straight run at full throttle.
I noticed the same thing on that run. Just the occasional burble which seemed to cause the other cylinder to fail and it'd stumble for a half second before going back to being a good boy.
Half a dozen times in 9 miles.
Nothing to worry about, but I sure am curious what the OMC engineers know about things like that.
 
You have a screw on type water/fuel seperator installed? Small (very small) BB type debris sort of welded to a spark plug electrode?
 
Joe if understood that, you are saying I might have trouble with the Fuel filter.
This question was almost rhetorical, as I have three OMC's and a Mariner. The question was pretty General.
All of my engines do the burble and most others that I've been in for long periods of time.

I noticed all the B&S engines on my Farm stuff wont hardly idle at all, but at high speed they don't have the burbles like the outboards do. Must be some technical difference eh?

Yes I clean the filters. I never have found any debris in there. No water either.
You make me think though.

I could install a water filter and an inline filter as an assembly on the interior of the Transom. Then using the normal connectors, plumb that to the engine on a short line, and plug the tanks into the input side of that assembly with the normal connectors.

One time I bought gas from a station that was going out of business. My old 35 Hp Evinrude suffered from that. There was water in there and it chipped my crank at the middle bearing. (took me two days to row back)

Fouled plugs are rare in these stock OMC's. It happens more often in my Mariner. I put new plugs in occasionally. I've never had an occasion where changing plugs made anything better, except on engines that have been sitting in the Barn for a long time.

Racing motor cycles did develop the Bridged plugs. The English riders call that "Feathered".

This is a topic that will keep you sharp, now that its too cold to go out fishing.
 
Can you define exactly what you're experiencing at high rpms. I can not visulize just what you mean by burble.

I've been in this line since 1960, that is strictly with Evinrude and Johnson outboards, and my experience having been that if the engine is in the condition it should be in, it runs smooth and true regardless of any time period at a certain throttle setting. However, on the other hand, I have never had reason to hold one at full throttle for a nine mile run.

Nevertheless, to encounter a scenario whereas all engines would encounter the identical problem under the same set of circumstances is quite strange. That statement led me away from the engine(s) into the rigging itself.

Pertaining to a "filter"..... If the only filter is the one on the engine itself, that really won't do the job seperating and containing water from the fuel. That calls for the screw on type water/fuel seperator assembly (looks like an automotive oil filter). I'm still not sure what type filter you're speaking of, that is what type you're using.

The small bb's I mentioned are usually caused by a very slight entry of water to the combustion chamber (not enough to completely shut a cylinder down), normally via a slightly defective head gasket but I've encountered this due to water entry from elsewhere. My thought was that perhaps water may also exist elsewhere in the fuel supply IF the mentioned BB scenario existed.

Also, at the moment, are we speaking of any one particular engine or just two cycle engines in general? If a particular engine, what engine (year, make, hp), and what spark plugs are you using?
 
Buble is a small interuption to the flow.
We'll assume my old 35 Hp Johnson, about a 1960 model.
In Alaska, salt water, I'd go out of Seward, toward the glacier. Then I'd idle while trolling.
So the start was 9 miles, but then some times it was as much as 30 miles back.

So at high rpm the engine is running fine and suddenly the engine would miss a time or two and then settle down again.
That miss, at that speed is more like a giggeling sound. the Engine colw moves back and forth, the boat feels the shudder, but all is well in the next second.
My theory is a miss on one cylinder would destroy the vacuam to the next Cylinder so it would misfire.
But what causes that first miss?
At 3500 Rpm that might be as many as 10 misfires in a row, but just as suddenly everything starts working good again.

That same thing happens at Idle while trolling. It'll miss two or three times in a row, then be OK for a long time.
My 6 Hp and all of my 9.5 and 9.9's did it too. Those are all Johnson or Evinrudes.
 
I can't imagine what would cause something that identical and intermitent on so many engines. I going to stand back along the sidelines and see if any other members might have a theory.
 
Way back in the 50's some sales guy left a pamphlet with Dad on Plugs. I read it, talking about plug failures, misfires caused by Carbon build up, resistance to ground, hot combustion chambers causing a loss of grounding for the plug. That was before Carbon trace plug wires and they had plenty to say about the sins of metal wires.

My own feeling is the fault is in the plug not firing because of some electrical anomaly.
Fuel and Air are pretty solid and continuous. In other words you wont have an intermittent space with no fuel or air. That flow, once started is pretty much a solid and continuous event. No sudden stops in the flow for a 1/4 second or so.

Electricity is susceptible to intermittent loss's all throughout the circuit.

Years ago I put new wires on one of my old engines. It got better immediately. Thinking about that event, I made up my mind to go back and insulate every place where the wires were clamped down to the block. I never did it though. That's one place to pick on because everything is being made cheaper these days and the insulation might be the culprit.
Dirt at the Points would be another.

With the new Electronic ignitions, its possible the problem dissapeared. None of my older motors have that.
 
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