CONTINUOUSWAVE

While cleaning [the carburetors on a 1990 Johnson 200-HP outboard engine], I took note of the orifice sizes. The orifices are size 42 on the top and size 46 on the bottom. However, one carburetor had a size 36 orifice inserted at the top. [Eventually clarified as follows: the size 36 orifice was in a location where all the other carburetors had size 46. See follow up post far below that clarifies this--jimh]

What effect would [one carburetor having an orifice of size 36 at the top while the other carburetors have an orifice size 42] have on the [running characteristics] of the engine?

Would [the effect of that one orifice size being different] be noticeable?

[This particular 1990 Johnson 200-HP engine has had a history of] not being able to accelerate to more than 5,000 to 5,200-RPM without the alarm chirping.

I'm not sure if [the sensor that was causing the alarm] was the fuel restriction sensor or the oil [motion] sensor.

Iceboy149 wrote:I'm not sure if [the sensor that was causing the alarm] was the fuel restriction sensor or the oil restriction sensor.

Re the aural alert sounding at 5,000-RPM on your c.1990 OMC V6 engine:

On a c.1990 OMC V6 engine, there is typically a vacuum sensor in the fuel line that senses the suction pressure. I do not see any mechanism by which one carburetor's air bleed orifice size being different would affect the fuel line suction pressure. In order for the fuel line suction pressure to increase, there must be a restriction that is UPSTREAM of the sensor. The carburetor is DOWNSTREAM from the sensor, so it cannot affect the suction pressure. This rules out the the carburetor as having a role in the alarm.

On a c.1990 OMC V6 engine there is a sensor in the OMS (Oil Mixing System) pump (sometimes called the VRO or variable ratio oiling pump). This sensor detects the oil pressure pulse rate and compares it to the tachometer pulse rate. If the two pulse rates are not in the proper ratio, it sounds an aural alert. I do not see any connection between the carburetor and these pulse rates. This rules out the carburetor as having a role in the alarm.

As for which sensor is signalling an alarm, there is no way to deduce this with a c.1990 OMC engine because the engine pre-dates the use of the System Check tachometer. You have to distinguish the condition being signalled by the alarm based on the circumstances.

The most likely inference is the alarm is from increased fuel line suction pressure, as the flow rate demanded by the engine at full throttle will be the highest flow rate and thus most likely to cause the greatest suction on the fuel hose. The remedy is to check the fuel system for obstructions, such as a fuel hose that has collapsed, improper size fuel hose inside diameter, improper fuel fittings, and clogged fuel filters.

Iceboy149 wrote:The orifices are size 42 on the top and size 46 on the bottom. However, one carburetor had a size 36 orifice inserted at the top.

Re carburetors on a c.2000 OMC V6 engine:

There are two dual-throat carburetors and two single-throat carburetors on the engine, for a total of six carburetor throats. Each carburetor throat has three orifices:

--idle speed air bleed orifice;
--intermediate air bleed orifice;
--high speed fuel orifice.

In your narrative you only mention each carburetor having two orifices, and you describe them by their vertical orientation of top and bottom. I infer you must be trying to describe the idle speed and intermediate speed air bleed orifices, as they are located near each other and could be described by terms like "top" and "bottom." Those are air bleed orifices. They affect the fuel-air mixing ratio at idle and intermediate speeds. These orifices meter air into the carburetor, which is why they are open to the air and you can see them.

The high speed fuel orifice is generally not visible, as it is located beneath an O-ring and sealing screw, in order to maintain the fuel system integrity.

In the service manual for a c.1990 OMC 200-HP V6 engine, I do not see the orifice sizes called out or specified.

You can find the orifice size by examining the parts breakdown for your engine. See the website

http://shop2.evinrude.com

Select your engine model year and model number. You will see that the orifice sizes for a 200-HP engine vary depending on the model designation. The size #46 orifice stays constant across many models. The other orifice size varies between size #42 and #36, depending on the particular model of 200-HP engine.

It could be that OMC determined that one orifice on one throat of a carburetor for a particular cylinder would be a slightly different size than the others due to its location on the engine.

Or it could be an error.

Consult with an experienced OMC mechanic to distinguish which case this might be.

The effect of one carburetor having a different size orifice in an air bleed jet would be to affect the fuel-air mixture at the speed range for that orifice on that carburetor for the cylinder that the carburetor feeds.

Iceboy149 wrote:Would [the effect of that one orifice size being different] be noticeable?

The effect of the orifice size would likely be most noticeable at the engine speed range the orifice is intended to affect. Since only one of six cylinders is affected by the odd sized orifice, the ability of a boat operator to detect this change in orifice size is unlikely. Detecting the complete loss of one cylinder on a six cylinder engine can be difficult for an operator to deduce simply from the running characteristics, so the notion that a slight change in orifice size on one throat for one speed range on one carburetor of a six-cylinder engine seems unlikely. However, that is not to say that further investigation into the size for the orifice that was intended by OMC should be abandoned. The odd size of one orifice might be something done intentionally to account for the peculiarities of that cylinder due to its location in the engine block.

A corollary but unasked question: what is the effect of different orifice size on engine running characteristics?

For the idle air bleed orifice, decreasing the size of the opening in the orifice will cause the fuel-air mixture to enrich. The engine idle speed running characteristics will be affected by this change in fuel-air mixing ratio.

Thanks Jim, very much appreciated, lots of good stuff in there. And yes, I know there's the high speed orifice in the bowl; I just mentioned the other two. I ordered a size 46 orifice last night.

Here's my next question: If you remember from an old post last month all six of my flywheel magnets became disengaged, three were shattered. After pouring through the manual I believe someone had put a 1994/95 225-HP engine stator on my 1990 200-HP after tracing the wire colors back to the schematic in the manual. The tolerances were so close that it dug into the underside of the flywheel and in my mind was probably the cause of the magnets becoming disengaged. Last weekend I installed a new timing base and new stator (that is, new to me and newer than 1990).

So with all six magnets off, I can see now the old reference marks where the old magnets used to be but does it matter if you're off by a slight bit with the epoxying of the new magnets?

Will that affect the timing at all?

Have you guys ever used the magnet retainers that I've come across on the internet or are they more of a sham?

The ignition spark timing will be affected by the physical position of the magnet in the flywheel relative to the physical position of the piston in the cylinder. However, if you follow the proper procedure for setting the ignition spark timing, you will compensate for any variation in the magnet position. See the service manual for details of how to perform the spark ignition timing procedure.

Older Johnson and Evinrudes had problems with the adhesive that held the magnets on. Problem shows up after the motor starts getting older. Many people have epoxied them back on.

D-

To expand my remarks about magnet physical position: all the magnets should be located in the magnet mounting slots in a uniform manner. If there is any slop in the fit of the magnets into the slots, the magnets should all be placed into the slots with the slack or slop oriented similarly. You cannot compensate for variation among the magnets in the slots.

A new size #46 orifice showed up. Flywheel magnets showed up. The epoxy packets are so old that I think [the epoxy packets are] past the point of no return. I will order new epoxy and do [the repair on the] flywheel [on December 6 and 7, 2018].

THERMOSTAT GASKETS (new topic)
I got Johnson-Evinrude gasket sealer for the thermostat gaskets like the manual says to do.

HEAD GASKETS (new topic)
Sierra told me the head gaskets were dry fit gaskets.

SEALANT USE (new topic)
Is your opinion [to use] sealant only on the thermostats [gaskets and] not [on the] head [gaskets]?

Does temperature do the rest?

Yes, dry fit on head gasket.

D-

Iceboy149 wrote:Does temperature do the rest?

What is "the rest" that you are describing? I am not certain what you are referring to.

Iceboy149 wrote:A new size #46 orifice showed up.

Were you able to determine that the one cylinder carburetor with air bleed orifice size #36 was a mistake and was improperly installed?

As I mentioned earlier, for that one cylinder to have a different size air bleed orifice might have been intentional so as to give that particular cylinder a different fuel-air mixing ratio at the engine speed range that is affected by that air bleed.

I was not able to determine if [the one odd-size #36 air bleed] was intentional.

I swapped it out because I had an old set of six carburetors from a 1994 200 Ocean Runner which had all-alike orifices.

By "the rest” I meant the block heating up and sealing the heads against the block without using sealant.

Shouldn't the new orifice be a size #42?

If the existing #36 was in a position that all other cylinders had a #46, then that does seem more like a mistake. But I thought your initial description was a #36 in one cylinder and #42's in the other five cylinders at that location.

Yes, I meant the 36 was in the 46 hole.

I only get to work on the engine at night after the infant and toddler get to bed, so I'm usually pretty tired. That led me to misspeak.