2 Black sparkplugs

[Niels45]

 

[Niels45]

Hello, I’m Niels from Holland. I’ve a Draco 23 with a mercruiser 3.0 140hp ‘80. Motor runs fine but when I checked the spark plugs, I saw the difference between them. Numbers 1-2 are oké, but nr 3-4 are black. Compression is fine, engine is rebuild, carb is rebuild, ignition is Delco electronic.(placed it myself last year). The spark is a bit weaker then the original point ignition, but it runs and starts a lot more stable.
How knows what the problem can be?

 

[Scott06]

They are all showing a bit rich.here is a article on plug reading http://wallaceracing.com/plug-reading-lm.html

i assume the correct jets for this engine are in the carb ? Id recheck the float level and verify fuel pressure is like 4-5 psi

what makes you think the delco ignition is weaker than the original points ? Delco is a very good system should have same or hotter spark than points

 

[alldodge]

What are the compression numbers?
Your running regular gas and not high octane, right?
What is the timing set at?

 

[Rick Stephens]

Might just be bad valve seals if the compression is good.

 

[Paintman1960]

Might just be bad valve seals if the compression is good.

OP stated a engine rebuild ..

 

[Rick Stephens]

OP stated a engine rebuild ..

I've seen cheap valve seals ride up after 2 minutes.

 

[Paintman1960]

I've seen cheap valve seals ride up after 2 minutes.

Yes, and thats not right either !
Cheap being the key Word here

 

[alldodge]

Could also be motor was not rebuilt correctly

 

[Niels45]

They are all showing a bit rich.here is a article on plug reading http://wallaceracing.com/plug-reading-lm.html

i assume the correct jets for this engine are in the carb ? Id recheck the float level and verify fuel pressure is like 4-5 psi

what makes you think the delco ignition is weaker than the original points ? Delco is a very good system should have same or hotter spark than points

Before the rebuild, the carb and jets were ok. Color of spark plugs was also fine, so I didn’t change the jets.

 

[Niels45]

What are the compression numbers?
Your running regular gas and not high octane, right?
What is the timing set at?

Compression I don’t know now, but a month ago it was good.
the timing is 6 btdc. at 700rpm. Intitial timing is 1 btdc.

 

[Niels45]

Could it be the adjustment of the fuel air mix screws? It a 4 barrel carb, and the right screw seems to be to far open. Is it correct that the right screw is for cylinder 3-4?
I also have a feeling that the engine needs an earlier timing. The curve of the delco unit seems to give less advance then the original points. What’s your idea about this.

 

[alldodge]

The idle screws only adjust idle. They have nothing to do with higher speed

 

[Scott06]

Could it be the adjustment of the fuel air mix screws? It a 4 barrel carb, and the right screw seems to be to far open. Is it correct that the right screw is for cylinder 3-4?
I also have a feeling that the engine needs an earlier timing. The curve of the delco unit seems to give less advance then the original points. What’s your idea about this.

I think you have a two bbl carb not 4 bbl as no manifold ofr 3.0 exists that takes a 4 bbl carb. If your idle mix is too rich this can cause them to foul like this. I think on a merc 3.0 there is only one opening for the carb so it will feed all cylinders. It sounds like may be you need to set your idle mixture if you havent. Usually 1.5 turns out from completely closed is a good starting point.

The delco may have less total advance than points you can measure with an advance timing light but I dont know what total advacne should be for a '80 3.0

 

[Niels45]

The idle screws only adjust idle. They have nothing to do with higher speed

Thanks for your answer, but I wrote the fuel/air mix screws.

 

[Niels45]

I think you have a two bbl carb not 4 bbl as no manifold ofr 3.0 exists that takes a 4 bbl carb. If your idle mix is too rich this can cause them to foul like this. I think on a merc 3.0 there is only one opening for the carb so it will feed all cylinders. It sounds like may be you need to set your idle mixture if you havent. Usually 1.5 turns out from completely closed is a good starting point.

The delco may have less total advance than points you can measure with an advance timing light but I dont know what total advacne should be for a '80 3.0

My carb has 2 holes which lead to the manifold. And also 2 air/fuel mix screws.

 

[Niels45]

I think you have a two bbl carb not 4 bbl as no manifold ofr 3.0 exists that takes a 4 bbl carb. If your idle mix is too rich this can cause them to foul like this. I think on a merc 3.0 there is only one opening for the carb so it will feed all cylinders. It sounds like may be you need to set your idle mixture if you havent. Usually 1.5 turns out from completely closed is a good starting point.

The delco may have less total advance than points you can measure with an advance timing light but I dont know what total advacne should be for a '80 3.0

It’s a 2 bbl, your wright. Both mixture screws I’ve set and know the problem is fixed. Thanks for the advice!!

 

[Scott06]

It’s a 2 bbl, your wright. Both mixture screws I’ve set and know the problem is fixed. Thanks for the advice!!

Good

 

[nola mike]

My carb has 2 holes which lead to the manifold. And also 2 air/fuel mix screws.

I haven't heard of a carb with off idle air /fuel mix screws

 

[Rick Stephens]

I haven't heard of a carb with off idle air /fuel mix screws

Me either. Would love to see pics of this fabulous carb that adjustment of made all better.