Flathead Limited Modified Spark Plug

G

GAKARTER

Member
Any feedback on using the NGK 6431 BU8H gapless spark plug for a limited modified flathead. Anyone having any performance issues with it, such as fouling too easy on methanol, etc. It certainly provides good valve clearance due to minimal protrusion into the combustion chamber area.
 
Yes they are a good plug. Make sure you shim the plug up in the head so its flush, otherwise you will bend a valve. Another thing to remember is on the cold nites it will be better to change to hotter plug, or its hard to start. JMO
 
Underground Motorsports said:
Yes they are a good plug. Make sure you shim the plug up in the head so its flush, otherwise you will bend a valve. Another thing to remember is on the cold nites it will be better to change to hotter plug, or its hard to start. JMO
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Appreciate the feedback and comments. How cold would it need to be before going to a hotter plug and what is the part number of the same style hotter plug. Thanks
 
I have used the BU8H in open and limited flatheads for very cold ice racing. Starting them with some gas or small squirt of starting fluid has worked well for me.
 
For us, when it got around 30-40 they were hard to start so we switch to an Autolight 292(electrode) plug. Or you could do as Freeze said use some starter fluid to start. I haven't shopped for them in awhile but I don't think there is a Bu7h, but I belive a autolite 2852(non electrode) plug is a little bit hotter than the Bu8h. The problem with gapless plugs is they have a tendency to foul easier(but can also clear them selves out imo). We had a several 292's left over from running stockers so thats why we used them. We also didn't want to be on the grid and it not start for a points race is why we didn't chance it with starting fluid. good luck
 
Underground Motorsports said:
For us, when it got around 30-40 they were hard to start so we switch to an Autolight 292(electrode) plug. Or you could do as Freeze said use some starter fluid to start. I haven't shopped for them in awhile but I don't think there is a Bu7h, but I belive a autolite 2852(non electrode) plug is a little bit hotter than the Bu8h. The problem with gapless plugs is they have a tendency to foul easier(but can also clear them selves out imo). We had a several 292's left over from running stockers so thats why we used them. We also didn't want to be on the grid and it not start for a points race is why we didn't chance it with starting fluid. good luck
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Thats what I've been hearing on the gapless plugs. The 292 is what I've always run with no real problems. May just stay with it.
 
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