Is this a lean sneeze or a misfire?

[sutor623]

 

[F_R]

Sounds like a lean sneeze to me.

 

[sutor623]

Thanks FR.

So I should start by richening up the idle fuel jets on the carbs?

I have the gas mixed at 50:1 AND the Vro hooked up to oil tank until I know I can trust it. Do you think this can also happen because there is too much oil in the mix which actually leans out the gas? I checked the DVA where the powerpack hooks into the ignition coils and it is at 130V at all four of them, just like in the CDI guide, so I don't think it is a misfire.

 

[sutor623]

On a sidenote, I have just dismantled the carbs, cleaned them up and re-installed.

 

[sutor623]

Anyone else notice how it blows out a puff of smoke from the exhaust relief when it kicks?

 

[F_R]

Did the sneezing start before or after you worked on the carburetors? In either case, double check the throttle butterflys linkage. The butterflys must be completely closed at idle speed. If not, it will sneeze.

The smoke puff is not something I would be concerned about.

 

[sutor623]

Did the sneezing start before or after you worked on the carburetors? In either case, double check the throttle butterflys linkage. The butterflys must be completely closed at idle speed. If not, it will sneeze.

The smoke puff is not something I would be concerned about.

Im not sure. When I acquired this motor it had been setting for 5 years. When I tried to start it up it was running very poorly and backfired once or twice. I didnt feel comfortable letting it run like that. So I rebuilt the entire fuel and cooling system.

The carb butterflys have been link and synced well so they are completely closed at idle. I am going to disconnect the VRO and run 50:1, de-carb the engine (which it looks like it really needs from what I can see through the spark plug holes) and change the spark plugs and I will check back in. I will also make sure the idle jets are set to factory spec.

The motor was smoking like heck when I ran it the first few times. I think just running it with gas/oil had already started breaking some of the carbon down.

 

[sutor623]

Update:

Engine is warming up properly and idling at 750 rpms while in the test tank in neutral.

Compression continues to be at #135 for all four cylinders.

I disconnected the VRO from its oil source (and am mixing 50:1), checked all the idle jets and checked the carb butterflys and am still having issues. I pulled the fuel pump apart once again just to make sure all was well in there. Plenty of fuel is making it to the system. I believe this to be an electrical issue.

So, the DVA from where the powerpack connects to the ignition coils in the CDI manual is supposed to be 130V or more. All of the DVA readings on these points are right at 128V or so, although I have seen it down to 120V on all cylinders, but I beleive this to be caused by idle slowing down.

Hooked a timing light up to the motor, and all of my cylinders are triggering properly. I marked TDC for each cylinder on the flywheel and the timing light is only firing the proper cylinder at the proper time. (When hooked to cylinder 1, only 1 is triggering at TDC etc.) Resistance is correct for all timer base connections. (It is very difficult to check DVA of these connectors due to the way they connect, but i believe the voltage is there to trigger the signal properly.)

The powerpack was replaced when the boat was put up (5 years ago) and has hardly any use on it. The blue wire was shorted to ground when it was mounted, so I do not want to completely rule it out as a culprit, although unlikely. Whatever mechanic that was troubleshooting this issue in the past obviously didn't figure it out entirely.

Battery is charging well, and voltage climbs as it should under increased load. I pulled the yellow wires from the stator off of the rectifier with no change. Mis is still present.

I went to a last resort and pulled plug wires from the motor while it was running. Nice blue spark arced from the plug wire to the plug. Motor stumbled to nearly a halt when I pulled the wires from cylinders 1,3 and 4. When I pulled wire from cylinder 2, there was no change. The spark was still there, just maybe not as dark blue as the other cylinders. I also noticed that the spark plug for this cylinder was cooler to the touch than the other three plugs. I swapped the spark plug, wire and coil (one component at a time) with a different cylinder and no change. So I know all the ignition coils, spark plug wires, and plugs are all okay.

I need to check the DVA of the brown wires from the stator, but with this style connector it is difficult to get a test probe to bare wire. Is there a way to make a pin adaptor of some sort to be able to check this? The stator is the original OEM stator as far as I can tell.

Bottom line: Something is preventing the spark on cylinder 2 from firing STRONG enough to actually fire the cylinder properly, although the wire is actually firing enough to engage the timing light. At this point I believe that I have narrowed it down to the stator and/or (possibly)powerpack.

What is most likely the culprit of one CYLINDER not firing properly as opposed to an entire bank? Any suggestions here guys?

 

[racerone]

There may be issues with carburetor for # 2 or the crankcase compression for # 2 cylinder.

 

[sutor623]

There may be issues with carburetor for # 2 or the crankcase compression for # 2 cylinder.

How would I know if it is crankcase compression? Can I use carb cleaner or something like that and spray around the crankcase or other gaskets to try and find a leak? What would cause such and issue and are we looking at powerhead dismantling to fix it?

The plug looked like it hadn't been firing the mixture well. It was the darkest of all 4 plugs. Wouldn't a crankcase leak cause it to run lean with a hot plug?

 

[sutor623]

Racer you were on point. I checked all of my electrical with a DVA meter and resistance, and everything seemed to check out.

I swapped the upper carbs and the bad firing cylinder FOLLOWED the carburetor. Obviously there is an issue in that carb. (Thank goodness I dont have to hunt a crankcase leak.) Here is my question. When looking at the motor, which carb goes to which cylinder? Do the carbs criss cross behind the motor or do the come directly across to the cylinder? I swapped the upper two carbs so Im wondering which one I need to pull. I am thinking that the highest carb goes to the highest cylinder. Is this picture correct?

 

[sutor623]

So that picture is correct.

Anyways, F_R you were on point about the lean sneeze. That is in fact what I was dealing with. The electrical system on this boat is in great shape. I checked all of the major components and they all checked out.

And Racer, you have helped me with numerous items on this motor so I thank you. Once I swapped the carbs and figured out that was the issue, I broke her back down and cleaned her up.

Finally, the motor seems to be running great!! Ill check back in when I get her in the water.