electrics

B101 · Post by **B101** » Fri Jun 07, 2013 11:04 am

now that i am happy with the carbs being balanced i thought i would look at some new plugs. it had Bosch WR78X super 4plugs that had been in there for the last 12 years.
after doing many hours of research and reading up on forums i thought i would try the NGK BP6ES-11.

a guy down at BNT was kind enough to sell them to me for $3.80 each instead of $6.99 that supercheap were asking for. put them in and took it out for a test drive on the motor way, it went great and made a big diffrence at top end compaired to the old cruddy plugs. parked her up at home and had it sitting at 4000rpm for about 20 seconds then stopped the engine to see what the plugs would look like. Now i know that my plugs would be getting carbon built up at idle because of the bigger needles in my carbs but wanted to see what it was like when at higher rpm.

in the photo it goes in order from left - right 6-1, as you can see # 4,3,1 are not as burnt as 6,5,2.
now please tell me if im not correct here but isnt the front carb supplying 1,2,3 cylinders and the back carb supplies 4,5,6? does this mean that it isnt my carbs because if it was the back 3 or front 3 plugs would be rich or lean? instead of them being all mixed up?
if this is correct then could i be right in thinking that my HT leads might also be a little old??

i noticed when i was checking the timing that when i put the light on the number 1 HT lead that the timeing light was rather weak so i dicided to put it on #2 HT lead and sure enough the light flash was a lot brighter. Does this mean that it was getting a weak spark because of the HT lead? or is there a test i can do from the dizzy cap to test the current that the coil is preducing?

hope this all makes sence

and if it doesnt then im sure someone on here will put me straight.

cheer,
Brian

nzniggles · Post by **nzniggles** » Fri Jun 07, 2013 2:54 pm

Sounds like some leads might be a good idea. Done a compression check?

Jabo · Post by **Jabo** » Fri Jun 07, 2013 5:56 pm

Ahhh dirty old number 4 cylinder my nemisis. I had a similar problem when I converted the 280 to twin carbs. It turned out to be a whole lot of things but mainly check for vacuum leaks and I may be wrong here but I think number 4 is the last in the firing order so if you have weak spark it will suffer the most. These are just things I noticed on mine don't take it for gospel just thought I'd share

B101 · Post by **B101** » Fri Jun 07, 2013 11:42 pm

Ok so I got some new top gun leads from BNT and put them on but for some reason it isnt running as good as it did with the old champion HT leads. . . Checking the plugs after letting her sit at 4000rmp for 20-30 seconds shows that the plugs had alot more carbon buildup on them compared to when I had old HT leads on.

Has any one used these Top Gun HT leads befor?

B101 · Post by **B101** » Fri Jun 07, 2013 11:44 pm

nzniggles wrote:Sounds like some leads might be a good idea. Done a compression check?

Compression is good, all around 200psi

B101 · Post by **B101** » Fri Jun 07, 2013 11:46 pm

Jabo wrote:Ahhh dirty old number 4 cylinder my nemisis. I had a similar problem when I converted the 280 to twin carbs. It turned out to be a whole lot of things but mainly check for vacuum leaks and I may be wrong here but I think number 4 is the last in the firing order so if you have weak spark it will suffer the most. These are just things I noticed on mine don't take it for gospel just thought I'd share

I have checked for leaks and can't seem to find any. My vacuum gauge it telling me that there isn't any leaks.

ZMAD · Post by **ZMAD** » Sat Jun 08, 2013 5:45 pm

Leads come in many types. Straight copper wire with no resistance, Silicon with resistance and Silicon with extra resistance for noise suppression. Something like that anyway. Some spark plugs also have a resistor. Usually have an R on end of code. A good multimeter can be used to measure old and new leads as well as plugs. If old leads measure OK and have no damage they probably OK. About that no. 4 plug. The engine stops randomly at any point so doesn't always fire at no. 1 first, so that's that theory gone. I have the same thing happen with my plugs, the carbon causes a weak spark then a misfire. I tried running a hotter plug, same thing. I have new dizzy caps for sale. Check that and rotor for wear and tracking (HT taking a short cut).

Baker93 · Post by **Baker93** » Sun Jun 09, 2013 11:49 am

Hi

Assuming all the normal tuning things are ok (spark, leads fuel etc tho fuel unlikely to be cause with twin carbs) you most likely have a mechanical fault with that cylinder. Try to measure the temp on that cylinder. Is it running cooler than the others ? You could also have damaged oil ring, valve stem seal etc.

Andy · Post by **Andy** » Sun Jun 09, 2013 1:12 pm

Jabo wrote: I may be wrong here but I think number 4 is the last in the firing order so if you have weak spark it will suffer the most.

Not so certain about that hypothesis, there is no start or end to the firing order it is a continuous loop and will start on whichever cylinder is first up when starting. The firing order as written has a beginning and end but that is because we dont write in circles.