Spark Plug Heat Range

Ive been running a BPR7ES for about a year now and my running temps never exceed 300 on an M1 15 Sha Gila kit, today I switched to a 6 like the manual says and I topped my temp at 310.

Whatcha running and why? Im trying to figure out if the 10 degree cushion is worth the slightly darker plug.

Re: Spark Plug Heat Range

I run a B6HS in my V1 polini race bike, usually. If the temp is over 90° at the track, I run a 7.

Ideally, for max performance, you should run the hottest plug you can, without scorching it. According to Graham Bell's two stroke bible.

Re: Spark Plug Heat Range

Yeah I used to think that but I've talked to a bunch of really good tuners and they all say go as cold as you can without fouling.

The hotter the plug the faster the charge lights off but that can mean detonation if you are under a heavy load or running hot. The plug heat range shouldn't make your CHT change unless it's kicking off detonation. The people I've talked to say you want as much margin as you can get, but I've found a 7 or 8 is about right, if you do a 9 it might read a false rich and a 6 might read a false lean. I keep 6 around for stock bikes with low compression. And occasionally I'll run a 8 on bikes that run hot, but almost all my bikes run 7.

Either way that's pretty cool for that m1 kit, you are running the MF head, right? I'd try bumping up timing. I always forget the 'p' plug but that's a great idea on that head since the plug is a little shrouded. I would keep pushing the timing up until you see the temps start to pick up, then check the piston crown after about 200 miles for excessive carbon buildup.

Re: Spark Plug Heat Range

> Graham Motzing Wrote:

> -------------------------------------------------------

> Yeah I used to think that but I've talked to a bunch of really good

> tuners and they all say go as cold as you can without fouling.

>

> The hotter the plug the faster the charge lights off but that can mean

> detonation if you are under a heavy load or running hot. The plug heat

> range shouldn't make your CHT change unless it's kicking off detonation.

> The people I've talked to say you want as much margin as you can get,

> but I've found a 7 or 8 is about right, if you do a 9 it might read a

> false rich and a 6 might read a false lean. I keep 6 around for stock

> bikes with low compression. And occasionally I'll run a 8 on bikes that

> run hot, but almost all my bikes run 7.

>

> Either way that's pretty cool for that m1 kit, you are running the MF

> head, right? I'd try bumping up timing. I always forget the 'p' plug but

> that's a great idea on that head since the plug is a little shrouded. I

> would keep pushing the timing up until you see the temps start to pick

> up, then check the piston crown after about 200 miles for excessive

> carbon buildup.

yeah that's the head Im running, I think I talked to you about it before.

Im gonna go back up to the 7, and advance the timing a bit. See if I can get it close to about 350 full blast.

I read somewhere on here about someone running an 8 and down jetting to even out, it just sounded dangerous. I couldnt imagine running it like that for two long and it working out, especially if you get a false rich and down jet too much.

Re: Spark Plug Heat Range

Starting point for selecting heat range is to run the COLDEST plug you can that does not low speed foul for best performance. You should be banging that heat down the pipe and not trying to run hot plugs which will take on a glow when you are heat soaked and punishing the engine.

Read the plugs you are running, then will give you a goodly idea where you are for the way you ride.

BasicPlugReading1.jpg

Re: Spark Plug Heat Range

For sure Rebel, I used that image to get to the 7, I still need to go back and test again.

Im waiting on a new Polini carb to get that low end crispy, Im sure the Super Rich low end on a Sha doesnt help pin point the issue.

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