Bosch Spark SUPER 4 plugs any good?

Hi, i have a problem with cylinders 1 and 2 there is spark on all 4 pots but 1 & 2 cylinder is not a hot as 3 & 4 (did the water spray test on the headers) i want to change the plugs,

also all 4 pots have dark carbon like color.. i don't know what it exactly means.. to rich mixture?
carbs has recently been cleaned (church of clean TY 2 1/2 turns out on the mixture screws.. anyways i have some BOSCH Super 4 (FR78X) sparks plugs i would like to try out since the old once that came with the bike was also a (Bosch Super) will it be a bad idea? has anybody tried it? the obvious difference i notice is the FR78X has same threads but slightly smaller size head?

or should i just buy new NGK BP7ES ? is this correct? whats the difference between the two plugs?

Many thanks! this site all of you guys & girls are the best! i won't bother fixing this old bike without you guys

Amiel

 

NGK BP7ES.

The plugs you have now are in the wrong heat range, and I am fairly certain that is why you see the carbon deposits on them. I can't even seem to find what you have as being appropriate for the XJ on any cross-refrence table. Part of the issue is that it's a resistor plug, where you need a non-resistor plug (if the plug caps are original), and the electrode gap on that plug is 1.1 mm, where the gap for your ignition system should be 0.7 mm.

In short, get the correct plug.

 

Ok.. tried the new set of NGK BP7ES today sooooo much better almost like there is no need for addition carb tuning

thank you k-moe

 

I put bosch in a Honda Accord. Month later took it in as it was running like crap. Mechanic put NGK back in and it ran great. Lesson leather.

 

Did he use the correct plug? Who makes the plug doesn't matter much. Whether the plug is right for the engine does.

I've got, on hand, plugs made by Champion, Autolite, Bosch, and NGK. Some are the OEM plugs; others are not, but all meet the OEM specification for the engines that they are fitted to. I have had occsional trouble with individual plugs (from each of those manufacturers), but a new replacement from the same manufacturer has always fixed the problem.

 

Sounds like an upstream issue. I had a 64 olds in high school and it ran like crap. Mechanic changed plugs and ran good for about a month. Took back, he changed plugs and "tuned carb". Ran great for about a month. Got new mechanic. Carb floats were full of gas and causing it to run rich. Then came the fun of finding floats for a 30 year old Rochester 4GC without the internet.

Like Kmoe said, doesn't matter who made it as long as its the right plug.

 

I too thought as long as it is the proper plug, brand wouldn't matter. However, my 1995 Accord ran for another 100,000 with the NGK, never had it back in the shop, no issues. I had put the Bosch plugs in myself, my mechanic specialized in Honda autos ( not Honda dealer) and said Honda autos are finicky about plugs and only use NGK like the OEM.