What are these spark plugs telling me?

[Technicallyabu]

The picture in your first post show plugs that look identical to mine.  I just took them out this weekend to fog the cylinders.  I think they look fine.  My engine agrees with me since it runs great.

[powbmps]

On 10/3/2016 at 3:40 PM, Technicallyabu said:

The picture in your first post show plugs that look identical to mine.  I just took them out this weekend to fog the cylinders.  I think they look fine.  My engine agrees with me since it runs great.

Unfortunately they are not looking like the first picture any more.  Per Edelbrock's suggestion, I am trying a new set of metering rods in the carb.  Stock is on the left at .068"x.047".  On the right are the new rods at .065"x.037".  Interesting stuff .  We'll see how it goes.

 

 

[powbmps]

What the......??  Went for a ski this morning with the new metering rods.  Now 7 & 8 look like this.  1-6 still look brand new, with just a slight discoloration on the side electrodes.  Compression is still good.

[MadMan]

2 hours ago, powbmps said:

What the......??  Went for a ski this morning with the new metering rods.  Now 7 & 8 look like this.  1-6 still look brand new, with just a slight discoloration on the side electrodes.  Compression is still good.

It looks like raw gas is running to the rear cylinders.

Have you looked down the carb, with the engine running, to see if gas is dribbling out of the secondary (rear) booster venturi? With the engine idling, none should be coming out.

[powbmps]

2 hours ago, MadMan said:

It looks like raw gas is running to the rear cylinders.

Have you looked down the carb, with the engine running, to see if gas is dribbling out of the secondary (rear) booster venturi? With the engine idling, none should be coming out.

I've checked before, but I will look again tomorrow.  Carb is new, so it shouldn't be an issue.  The metering rods seem to have richened up 7 and 8, but not 1-6.  It's driving me nuts.  The guy I was skiing with said it felt like it was misfiring when he was pulling me.  Not sure what exactly he means, but I didn't notice anything too crazy when I was driving (other than the ever-present bog).  I'm still suspicious of the Sierra coil I have (it has never been within the specifications in the Mercruiser info), so I am going back to the original Mercury coil tomorrow.  Even though it is 21 years old, it's still within spec.  Re-checked engine compression when I got home, and all cylinders were in the 155 to 165 range.  Rechecked all my plug wires as well to be sure they were good.  No issues there.  I believe the only thing left is the distributor (cap, rotor and sensor have already been replaced).

Sorry if I'm just rambling....

[Steve B.]

Sure sounds like you are gettin' a little too much fuel in a couple of spots. I didn't read all the posts. You did get the correct plugs, or the "hottest" plug you could get ?

You mentioned the word "bog" too. First thing I would do would be to dial back fuel. Jets, metering block, etc.

Also, whats the chance you have crappy gas?

Steve B.

 

[powbmps]

On 10/7/2016 at 3:30 PM, Steve B. said:

Sure sounds like you are gettin' a little too much fuel in a couple of spots. I didn't read all the posts. You did get the correct plugs, or the "hottest" plug you could get ?

You mentioned the word "bog" too. First thing I would do would be to dial back fuel. Jets, metering block, etc.

Also, whats the chance you have crappy gas?

Steve B.

 

The problem is that plugs 1-6 are bone white, so the Edelbrock tech guys are thinking it's running lean.  Just 7 and 8 are black.  Plugs are new AC MR43LTS, gapped at .045.   Gas should be good.  I buy 93 from the gas station 5 gallons at a time.  

Went out Saturday and it backfired through the carb (just once) when I was going full throttle.  It was ~42 when it happened, so I backed down to mid 30's and it didn't happen again.

[MadMan]

23 minutes ago, powbmps said:

The problem is that plugs 1-6 are bone white.  Just 7 and 8 are black.

On every hot-rodded, carbureted, engine I built, I've had to stagger jet the carb (different jetting front/rear or left/right) and/or weld "dams" to the floor of the intake manifold plenum.  This was to correct fuel distribution problems, some cylinders rich, some lean.  I've never had one as bad as you're experiencing though.  But you could try leaning out the rear jets 2 or 3 sizes while richening the fronts a couple sizes.

[powbmps]

Just now, MadMan said:

On every hot-rodded, carbureted, engine I built, I've had to stagger jet the carb (different jetting front/rear or left/right) and/or weld "dams" to the floor of the intake manifold plenum.  This was to correct fuel distribution problems, some cylinders rich, some lean.  I've never had one as bad as you're experiencing though.  But you could try leaning out the rear jets 2 or 3 sizes while richening the fronts a couple sizes.

By "rear jets", do you mean the secondary jets at the rear of the carb?  I'm not sure how that would affect the fuel delivery to specific cylinders (but I don't know squat). 

[MadMan]

39 minutes ago, powbmps said:

By "rear jets", do you mean the secondary jets at the rear of the carb?  I'm not sure how that would affect the fuel delivery to specific cylinders (but I don't know squat). 

Yes, the secondary jets, they are physically closest to the ports that feed cylinders 7 & 8. 

[powbmps]

10 minutes ago, MadMan said:

Yes, the secondary jets, they are physically closest to the ports that feed cylinders 7 & 8. 

Ahhh, I think I get it.  The stock configuration is .098 primary and .101 secondary.  Maybe I could switch them around and see if it makes a difference??

[MadMan]

12 minutes ago, powbmps said:

Ahhh, I think I get it.  The stock configuration is .098 primary and .101 secondary.  Maybe I could switch them around and see if it makes a difference??

I like this, maybe a no cost solution.

[powbmps]

1 hour ago, MadMan said:

Yes, the secondary jets, they are physically closest to the ports that feed cylinders 7 & 8. 

Hmmmm.  If this is the case, I may have found a contributing factor.  I just went to switch around the .101 secondary's with the .098 primary's and found that they accidentally installed .104 secondary jets????  Confirmed with Edelbrock that it should have not been shipped that way.

So for now I have the .104 in the primary and the .98 in the secondary.  Am I right in thinking this could richen it up down low, and lean it out up top (and maybe clean up 7 & 8 a bit)?  I have four .101 jets from the original Weber 9770 if I wanted to try those.  Maybe go with all four at .101? 

[MadMan]

11 minutes ago, powbmps said:

Hmmmm.  If this is the case, I may have found a contributing factor.  I just went to switch around the .101 secondary's with the .098 primary's and found that they accidentally installed .104 secondary jets????  Confirmed with Edelbrock that it should have not been shipped that way.

So for now I have the .104 in the primary and the .98 in the secondary.  Am I right in thinking this could richen it up down low, and lean it out up top (and maybe clean up 7 & 8 a bit)?  I have four .101 jets from the original Weber 9770 if I wanted to try those.  Maybe go with all four at .101? 

I'd try it the way you have it now, then depending on how it goes, try .101's in each corner (or maybe some other combo).

[powbmps]

Thanks MadMan.  After all the tinkering, the jet switch seems to have done the trick.  Went for a ski today (after two times out just driving around) and no bog/hesitation.  I'll check the plugs tomorrow to see how they are looking.  

Just in time to put it away for the winter .   

[MadMan]

17 hours ago, powbmps said:

 After all the tinkering, the jet switch seems to have done the trick.

That's rockin good news.

[Woodski]

@powbmps:  Glad to hear the jets solved the issue.  Yes, the larger mains will richen the mixture when secondaries are closed and smaller secondary jets may lean out (or keep approximately what you had) for the last 1/4 throttle approx. when the secondaries open up.  You would want to check a flow chart to see the exact effect.  If you do decide to tinker some more, and install the Weber jets, you might want to compare the needles (diameter) to see where they are different.

[powbmps]

It did just occur to me that the metering rods I am using was meant to go with the .098 jets.  Just ordered a couple sets of metering rods that will let me try some of the recommended combinations.