Spark Plug Recommendations - Stock 77D

[cjv2001]

Im a noob with spark plugs and just threw some random ones in there when I got the bike don't know about heat to different numbers or anything really. What plugs would you recommend with stock coils and wires? Do I need to modify them in any way?

Thanks in advance.

 

[Niels B]

Have good luck with E3.46 plugs on a 1978 standard, found them to work well here where it’s pretty darn hot in the summer.

 

[Its been a long time]

With stock ignition system, leads and caps it's NGK BP7ES. Not to be confused with commonly offered BPR7ES which are resistor plugs.

In some parts it seems the NGK plugs are getting harder to find. In that case I can recommend Denso W22EP-U. I am using the Denso plugs.

 

[zrx1100]

if you are a purist, i have four brand new NGK BP7ES that I can sell you. I don;t need them as I removed the caps with resistors and now using the BPR7ES or equivalent. My recommendation would be to save yourself trouble and replace the plug caps with zero resistance onces along with fresh spark plug wires and buy BPR7ES.

 

[rideitfast]

I've run Denso plugs in my bikes and have for decades. Got in the habit back in the two stroke days when I found their Iridium plugs worked really well with no fouling. I have the IW22 plugs in my 650.

 

[5twins]

On NGK plugs, the lower the number, the hotter the plug. The 650 calls for 7's. 6's would be hotter and 8's would be colder. Make sure you're not running 6's now as they may be too hot and damage the engine. The colder 8's probably wouldn't hurt anything but would most likely burn darker and be more prone to fouling. The "P" in the BP7ES plug number indicates it has a projected tip. This supposedly gives a better "burn", so avoid the plain "B" type (B7ES).

 

[zrx1100]

For reference, in case you want to switch to the commonly available resistor plugs, I am using NGK LBF8309 caps with BPR7ES and iridium BPR7EIX
plugs. LBF8309 does not have a resistor

 

[cjv2001]

Thanks for the replies everyone. As of now I've got some Denso W22EP-U out for delivery today. @zrx1100 in the next few months I'll get some new coils and wires, as well as the non-resistant caps thanks for sending that chart. I just pulled my plugs and I was running BPR7ES, with what looks to be resistor caps whoops lol.

@5twins that's also good to know, and in other posts I saw stock gap is about .028-.031, and mine are .038 right now, plenty too wide! I understand that upgraded ignition, coils could widen that gap and be okay from what i've read. I will most likely just get coils from Mike's but let me know if there are any others you would recommend.

 

[5twins]

With stock points coils, I'd stick to around .028" on the plug gaps. Even with upgraded coils and an electronic ignition, I still only go about .032" at most. Yes, find some non-resistor caps. Seems NGK discontinued them too, along with the non-resistor BP7ES plugs, lol. These are the ones I used to get .....

 

[cjv2001]

Put the new plugs in, I am guessing since i was running resistor plugs and caps it may have been running a bit hot? so I was able to run a bit of a richer mixture like that. New plugs caused me to stall out at stop lights. Turned the BS38 air screw and put the mixture a bit more lean so we will see what happens.

 

[5twins]

Too much resistance in the line can cause a weak spark. I would think that might run richer, not leaner. If you have the original BS38 carbs then they have no "air" screw, they have a true "mixture" screw. It helps to know which type of screw you're dealing with because they work opposite to one another. Turning an "air" screw in cuts air flow and richens the mix. Turning a true "mixture" screw in cuts fuel flow and leans the mix. And you just don't go setting them anywhere, there is a recommended setting for each carb set. You start there and fine tune the screw for fastest, smoothest idle. You should find that within a half turn either way from the recommended setting. If it takes more than that then that usually indicates a jet change is needed.

 

[Jim]

Too much resistance in the line can cause a weak spark. I would think that might run richer, not leaner. If you have the original BS38 carbs then they have no "air" screw, they have a true "mixture" screw. It helps to know which type of screw you're dealing with because they work opposite to one another. Turning an "air" screw in cuts air flow and richens the mix. Turning a true "mixture" screw in cuts fuel flow and leans the mix. And you just don't go setting them anywhere, there is a recommended setting for each carb set. You start there and fine tune the screw for fastest, smoothest idle. You should find that within a half turn either way from the recommended setting. If it takes more than that then that usually indicates a jet change is needed.

And as a rule of thumb...

How do you know which one you have?
An "air/fuel" mix screw will be between the slide and the air filter. Like a VM carb
A "fuel/air" mix screw will be between the slide and the intake manifold. Like our BS carbs.
And as stated above, turning in an air mix screw will richen and turning in a fuel mix will lean.

Another dead giveaway is the size.
An air mix screw will be a fat little bugger, and blunt on the end.

A fuel mix will be more like a skinny little needle point....................

 

[Grimly]

Put the new plugs in, I am guessing since i was running resistor plugs and caps it may have been running a bit hot? so I was able to run a bit of a richer mixture like that. New plugs caused me to stall out at stop lights. Turned the BS38 air screw and put the mixture a bit more lean so we will see what happens.

If you have a weak spark, you have to introduce more fuel for a bang, so it's running richer (caused by the throttle control), but not richer in a good way.
Sort out the spark and only run one resistance per lead (in the plug OR in the cap) and it will put you on the road to sorting out the mixture within its proper set of parameters.

As an aside, NGK plug caps are getting harder to find, grab them where you can, and watch out for fakes.

 

[zrx1100]

I had some time on a dyno today and did a test of Iridiums vs regular NGKs: https://www.xs650.com/threads/spark...dgKK9w_aem_ltHIB8_hR6p8cOdeBzLjyQ#post-875150