Lean sneeze warning

[Cricket Too]

Just wanted to ask a quick question about troubleshooting the lean sneeze my 2000 200hp Johnson has developed.

I was going to start by looking for an air leak along the fuel lines. This is made a little easier by the fact that there are twin engines on the boat and the other one has no lean sneeze. So at least I know I don't have a problem from my tank to where it branches off to the two separate water separators.

It occured to me that there is a fuel restriction warning on the newer style system check gauges, and I know it works on mine. So I was wondering if I had enough of an air leak in a fuel line before the OMS pump, would it set off the fuel restriction warning horn??

If this is possible, then I could maybe narrow my search down a little, as I would only have to check from the output of the pump to the carbs, and also inevitably my carbs. I gotta get this taken care of, the fall bass run is on and I don't want to smoke an engine while I'm out there.

So is it possible for an air leak before the OMS pump to set off the fuel restriction warning?

Thanks, Mike.

 

[Cricket Too]

Re: Lean sneeze warning

Wow! Did I stump everyone or have the experts just not gotten to this yet.

My fuel restriction warning hasn't gone off, just wondering if an air leak would set it off.

Any comments?

 

[Dhadley]

Re: Lean sneeze warning

An air leak shouldn't set it off. To set of the restriction alarm the fuel delivery has to be restricted forward of the pump to the point that the pump sucks so hard it closes the vacuume switch. The pump will suck air all day long and not work hard at all.

When the motor "sneezes" it's seeing an air leak, or too lean a mix, from the carb back including the intake / front half and lines attached. Basically the flow path that is directly related to the suction action of the piston.

If there is a air leak in the line forward of the pump it will result in bubbles and those bubbles will be, for the most part, disperssed in the float bowls. I guess it's possible to get so much air that the fuel level wouldn't be right but then the motor wouldn't run right at higher rpm.

I'd look for an air leak around and lines or gaslets from the carbs back. Look at the side plates on the carb bodies. Look at the sync-n-link. Remember there are 4 carb assemblies and related linkages. There's a link betweem the two top carb assemblies (each a 2 bbl assembly) and an 1 barrel under each 2 barrel on each side. That linkage under the top assembly can be a bear to get right.

The butterflys have to be completely shut on every throat. If someone has tried to set the idle up by using that screw in the throttle arm, you'll have to reset everything according to the manual.

 

[Cricket Too]

Re: Lean sneeze warning

Hey thanks for the response and info Dhadley. It's good to know that I shouldn't waste any time on anything forward of the carbs, seeing as how this thing runs perfect at high RPM, no drop at all at WOT RPM.

I'm just confused on one thing though. You say that there should be 4 carb assemblies, 2, 2 barrels on top and then a 1 barrel under each. But this engine has 6 carbs on it. Is this a different model, and if so is there anything in particluar I should look at on a 6 carb model?

Thanks, Mike.

 

[Dhadley]

Re: Lean sneeze warning

Trust me, you have 4 carb assemblies. The key word here is assembly. There are 2, 2 throat throttle bodies. One on each side. One throttle body feeds cylinders 1 & 3 and the other feeds 2 & 4. On each dual throat throttle body are two carb bodies. Below each dual throat throttle body is a single throat throttle body. Each of the 2 single throat throttle bodies has a carb body.

Each carb assembly is made up of a throttle body and a carb body. 2 dual throat assemblies and 2 single throat assemblies. Or 2, 2 barrel assemblies and 2 single barrel assemblies. IE - 4 carb assemblies.

Now that you're really confused -- the front half of the block is what they call an "X" front half. The carb assemblies on the starboard side feed the port cylinders and the port carbs feed the starboard cylinders.

Look at the cylinders. The top starboard spark plug is slightly higher than the top port plug. That's why the top starboard cylinder is #1. The top port cylinder is #2.

Look at the carbs. The top port carb is slightly higher than the top starboard carb. The top port carb feeds the top starboard cylinder.

Easy, huh?

 

[wilde1j]

Re: Lean sneeze warning

Dale, I think his motor is a V6, not a V4, therefore 6 carbs.

 

[Cricket Too]

Re: Lean sneeze warning

Correct wilde1, whew I thought I was losing it for a minute. Yup this is a 200hp. That's why I was confused about the 4 assembly thing.

Is there any known trouble spots on the carbs for this year V6 (2000)? They have the plastic bowls on them, so I was thinking of checking around them. I've heard they warp. They are original from 2000 and I don't think they have ever been rebuilt. I have owned it since 2003.

Thanks, Mike.

P.S. wilde1...I used to live in Salisbury. Went to SSU. Used to drive down and fish and surf in O.C.. Awesome place.

 

[brokeboater]

Re: Lean sneeze warning

i have a 99 200. carb assemblies he is referring to are the plate assemblies the carb bolts on. the top 2 carb plates on each side are one assembly. bottom carbs are single plate. take a look at it close and you will see what he is talking about. between the middle and bottom carb is also the linkage that can be difficult.

just went thru the lean sneeze thing with my motor. had a piece of trash in one of the carbs causing mine. cleaned carbs and idle circuits. you need a factory manual to show how to do the proper reassembly (sync and linK)

 

[Dhadley]

Re: Lean sneeze warning

Dont confuse carb bodys with carb assemblies. A V6 looper has 4 carb assemblies. 2, 2 barrel assemblies and 2 single barrel assemblies.

 

[Cricket Too]

Re: Lean sneeze warning

OK I kind of understand now. I will take a closer look this weekend. These carbs have never been off, so is it more likely that I have something in the idle circuit causing this or that the linkage in between the middle and lower carbs is out of whack?

Also will a lean idle circuit, cause any lean running at any other RPM? I would tend to think it wouldn't, as you move to a different circuit, but I don't want to assume anything and run this thing lean at 4000 RPm when I'm cruising. I have no performance issue at all at high RPM, runs WOT at 5700 like it always did.

Thanks for explaining it all.

Mike

 

[Dhadley]

Re: Lean sneeze warning

The idle and mid range jets on your motor are air bleeds. That means the fuel mix in those circuits is controlled by adding or taking away air. "Conventional" carbs adjust the mix by adding or removing fuel as does the high speed circuit on your motor.

IE - to lean out the idle in a conventional carb you go smaller on the jets because they meter fuel. (Less fuel / more air = leaner) On your motor the jets meter air so to go leaner you go bigger. (More air / less fuel = leaner)

An air bleed jet is simply a controlled air leak. Those holes (jets) are open all the time, from idle to wot. There is nothing that moves to take them out of the circuit. As the rpms increase the influence of those air jets is still present but is overshadowded by the larger amount of fuel going thru the high speed circuit.

So, to answer you question - yes, the air bleeds allow air into the motor thru the entire rpm range.

Now, that being said, the source of your air leak can be present all the time. If it's from a slightly open butterfly at idle then obviously it's not a factor as the butterflys open and the rpm comes up. But, if your air leak is from a leaking side plate or a bad throttle body gasket or a carb body O ring or a reed gasket etc then the air is being sucked into the motor at all rpms.

As the rpms come up the motor will pull enough fuel to mask the signs but the mix may be leaner than it's designed to be. Obviously the correct thing to do is find and correct the source of the extra air. Remember, the one part that suffers the most from a lean mix is a piston.

We'd start by pulling the airbox and locate the cylinder(s) that are being affected. While the motor is idleing you should be able to locate a "puff" everytime it sneezes. At least that will narrow down your search.

This is where the discussion about the X front half comes in. If you figure out the motor is lean on #1 cylinder (top starboard cylinder), remember the #1 carb is on the opposite side of the front half (top port carb).

BTW -- never, ever run the motor under a load with the airbox cover off.

 

[h_lankford]

Re: Lean sneeze warning

"BTW -- never, ever run the motor under a load with the airbox cover off. "

just curious, why not?

thanks

 

[wilde1j]

Re: Lean sneeze warning

Leans the mix to all cylinders.

 

[Dhadley]

Re: Lean sneeze warning

Yep, it'll lean out and the pistons will revolt. We've seen as much as 12-15 numbers different on the high speed jets depending on the air box style. Those carbs are designed to have the air come in from behind and flow around the venturi rather than come straight in.

 

[Cricket Too]

Re: Lean sneeze warning

Great explanation Dhaldey, I will do my best to try and pinpoint the lean cylinder this weekend.

When you say "puff" do you mean I will feel a puff of air coming back through the carb as it sneezes? That's what I took it to mean.

Also do the two single barrel assemblies for the bottom two cylinders work in an X configuration also?

Thanks for the great explanation.

Mike

 

[Dhadley]

Re: Lean sneeze warning

Yes on both. When it sneezes there will be a puff of air somewhere. It may come thru the carb throat or from where ever it's leaking. You may feel it with your hand more than see it but sometimes you'll actually see it as it blows fuel out.

And yes the bottom carbs are across from the cylinders they feed. The front half of the block is the X configuration. If you notice #1 spark plug (top starboard) is slightly higher than #2 (top port). But the carb body in front of #1 cylinder is slightly lower than the top port carb body.

I stress the carb configuration only because when chasing a leak it's real easy to look at the wrong carb body or assembly.

The carbs on the port side feed the starboard cylinders. The carbs on the starboard side feed the port cylinders.

 

[billaranguren@yahoo.com]

Re: Lean sneeze warning

I have a 99 200hp, had the same problem early last December. It was getting a bit cold in NJ to work on the carbs outside, and it seemed like it was probably more than carbs because it I could not isolate it to one carb by partially blocking the carb throat to rich up the mixture. I didn't expect multiple carbs at one time. I also wanted to get back on the water fast for a few more weeks until the stripers left. Took it to the dealer and hung around while he did the diagnosis:

Pull off one spark plug wire while running, replace it and try another. The one or ones that seem to have no impact are the carbs that probably need the most attention. He rebuilt three carbs and I have not had a problem since. Before he did it, I had a 25 micron filter. Have since gone to a 10 micron. I think I was letting some crap into the carbs.

 

[billaranguren@yahoo.com]

Re: Lean sneeze warning

By the way - as far as the carbs are concenred, the last time I had the hood off, all six looked like cookie cutter copies of the others. 99 Johnson 200 hp.

It has been a couple years since I personally pulled a carb to work on it. And if I remember correctly, you can pull the carbs without screwing with the link/sync elements.