Do carbs change spark plug recommendation?

[patssle]

Through searching, it seems almost everybody recommends the BP7ES for a 3.0L. But with CIS.

Does that still stand for a car with carbs instead? Or is there a good reason to change?

Thanks!

[snbush67]

No reason to change types at all, those are good plugs. Just check them a few times while dialing in your carbs to make sure you are getting a good burn.

[KTL]

Plugs are kind of a preference thing. Look around and some will recommend a 6 heat range for the NGK's and some even a 5.

(look at last sentence in green) Weber Carb Parts

I have Bosch 5's in my 3.0L with Weber and it runs OK. I use the 5s because that's what I got with the car. Runs a little rich (insulator is a darkish tan) but no fouling. I have some 6s and 7s that I plan to test and see how it behaves.

[JohnJL]

Same setup, I ended up with NGK BPR7s.

[T77911S]

it comes down to a fouling issue. i use 5's in my 2.7. with carbs, you might want a little hotter, (than 5 that is), but run as cold a plug as you can get away with.

its mainly got to do with the idle circuit or mixture. at cruising speeds, the mixture leans out enough to run cold plugs, but due to richer idles, the plugs need to be hotter.
i ran a set of 4's just for a test. normal driving they were black, but after a long hiway trip, they were fine. it was just the around town idling that made them black, but they never fouled.
you will also want a hotter plug (again, hotter than 5) for starting. no, the plugs arent hot when the engine is cold, but you want them clean from the previous run and you dont want them to foul at startup.

[john walker's workshop]

NGK, hot is smaller #. bosch is larger. basically. setting up a carbed engine is a fine line between getting it running the best and not fouling plugs. denso irridium plugs are fairly awesome for resisting fouling.

[jmcn3rd]

Does anyone know the equivalent Bosch plug to a NGK BPR5 plug?

[KTL]

Yep JW is right as usual. Forgot to follow up by saying the heat ranges of different brand plugs don't follow the same convention/trend of how the number relates to the "hotness" of the plug.

Here's a good reference for plug heat ranges and it's also a good source for plug interchange information.

Sparkplugs.com - Spark Plug 411

Also on the left sidebar, toward the very bottom of the page, of that sparkplugs.com site is a manufacturer's numbering system list for NGK, Champion, Denso, Autolite, Shiatfire, and Bosch

[Neel]

^ Bookmarked that site!! Great information!!
Thanks, Kevin

[BKC]

My 3.0 with Zeniths, which I just bought two months ago, is a basket case.

100 miles after purchase, severe fouling caused the car to start missing. Pulled the plugs (NGK 5 gapped to .05) out and cleaned them up. Car ran fine for 50 miles or so and fouled out again. Replaced with NGK 7 which I gapped slightly smaller. Ran 200 miles and they were toast. Just replaced those with NGK 5 gapped back to .05".

It seems to have all the appropriate vents and jets. Maybe I'll try the idle mixture if that's a legitimate culprit. Just hope I can figure it out before it damages the motor.