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512 BBi spark plugs

3455 Views 6 Replies 0 Participants Last post by  Drew Altemara
While I work on my

While I work on my still seems to be running rich, I removed the spark plugs. They are NGK BP6E S brand......slightly black, but not wet. They are gapped at about 0.8+mm. The manual calls for 0.6-0.7mm...but of course, they are referring the Champion plugs. The plugs were replaced 2 years ago, and they show no signs of rounding of the edges of the center electrode (not platinum).....which is of the normal "wide" kind.

The extenders show an Ohm reading of zero.

My questions are:

Should I replace the plugs, and if so, then what kind?....Platinum? The car is all stock, with no cats.

Should I just re-gap the present plugs to the 0.6-0.7mm.

Any thoughts?

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>>it still seems to be

>>it still seems to be running rich,>>

Beyond the static idle mixture setting, the mixture is controlled by the Aux. Press. Regulators by way of Control Pressure to the FD Head.

If you suspect rich running, then a Fuel Press. Test would be in order to determine if the control pressure is within spec & the same side to side.

Sounds like the easisest most direct thing to do is simply put in a new set of plugs gapped correctly and run them awhile. I don't really see a need for platinums, however I think the factory did run champion G's which were gold with a wide heat range.

I think with these cars getting older and the chances of one system problem or another increasing and plugs being the first thing to look at and replace when problems occur the cheaper plugs are probably the way to a sacrificial annode so to speak.
JRV: After adjusting, to a 0.

JRV: After adjusting, to a 0.9 CO, and 150 HC, I drove the car for about 200 miles......the engine was smoother, and did feel better. Re-checking reveiled a CO of 1.2 and HC of 500-700.

I plan on re-gapping the plugs to the 0.6-0.7mm, drive it a while and then re-check the HC/CO.

If no better, then I will have to check the pressures. Are there any adjustments if these are off.......or do I have to start replacing parts?

Here are my thoughts...

Here are my thoughts...based on your CO/HC readings. Although she is indeed running slightly rich, the high HC readings indicate that inefficient combustion is taking place.

Verify the condition of all ignition components...If OK, proceed to:

Before condeming any FI components, I would re-set the mixture, making sure that when you take an exhaust sampling, the plug (over the adjustment hole)is back in the fuel distributor (ensuring that you're not drawing in additional air into the engine.) Very important...! False air entering the motor can really skew the mixture readings.

If, after re-setting and re-checking the CO/HC, you still find high HC readings...I'd remove and test the injector spray patterns.

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>>Re-checking reveiled

>>Re-checking reveiled a CO of 1.2 and HC of 500-700. <<

1.2% CO cannot account for 500 ppm HC's.

1.2%CO is actually a lean reading, not rich, and should help engine run a little smoother because you're just above the lean miss threshold. You will need to account for the 500ppm with some other reason. I would suspect balance side to side, but it could be related to plug, wire, air leak, linkage slipped, dirty injector. Since you did see 150ppm at one point I sorta doubt injector issues.

I'd check Hg balance first to see if it changed.

Regards, JRV
JRV: I will hold off at this

JRV: I will hold off at this time on the gases....I will take your advice and verify the ignition is OK, first....besides, the GA is showing an "error"...will send it in to have it checked.

One of the extenders (black) showed an Ohm reading of 10K. The other 11 (all brown in color), showed an Ohm reading of zero (with the meter set at 10K ohms range. Interesting, in that the TR has "black" extenders with zero Ohm readings.

I ordered some new ones from Rutlands.

RE: Ignition. I plan on checking the idle and 5K RPM advance with a timing light. The distributor was supposedly rebuilt. I don't have a BBi ignition manual. The OM state 6 degrees at 1000 RPM and 29 degrees at 5,000RPM. Are these numbers correct? Does one turn the distributor base to adjust the idle advance?


BTW: Maybe you could post an ignition check technique in the tech section for us readers, since, BBi service manuals are not available.
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David Feinberg point


David Feinberg pointed out to me that the manual is a little confusing on advance. On a carburated Boxer the manual states 5 deg static (950rpm), 16 deg at 3200rpm and 37 deg at 5000 rpm. However the 5 deg and 16 deg is distributor advance which translates to 10 deg and 32 deg engine advance.

If you read the owners manual very carefully you can see this. I'm thinking that maybe the 6 could mean 12 deg engine advance. Anyhow, if you set it to the mark just to the left of the PM1-6 (TDC) at 1000rpm it should be right.

Yes, turn distributor base to adjust advance. Counter clockwise will advance, clockwise will retard timing. At least it did on my 512BB.

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