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Plug chop, too lean I think?

Discussion in 'The Garage' started by Brassneck, May 4, 2016.

  1. Brassneck

    Brassneck XS650 Guru

    Hey All,

    '79 Special II, all stock engine.

    Earlier this year I de-restricted my exhaust a bit (punched 1/2" hole in the stock baffle) and have really enjoyed the improved "Oomph" in the motor...and the sound is perfect for me.

    However, the other day I was thinking that perhaps I ought to do a plug chop and make sure I'm not running too lean....as I haven't really done one since last summer and I was on the richer side of things at that time.

    Other notes: I get great performance throughout the power band (very snappy), no back-firing/popping--although I did enrich the idle mix screw 1/4 turn as it was a little lean at idle after the "baffle job", no hanging rpm's or really any issues with regard to throttle response...idles great, and starts up without any hiccups. BUT...it does feel a bit warmer than it use to...so I went out today, warmed up the bike (old plugs) then swapped out for new ones (BP7ES) and did two 1/2 mile passes at WOT plug chops.

    Here's the results, sorry if the pics aren't very clear (And no, I didn't cut them, but I think you can see down the porcelain):



    My thoughts: They look too lean, but perhaps a second or dozen pair of eyes could weigh in? Or maybe there's not enough mileage to tell and I should ride a bit longer?

    If too lean: Could I raise the needle a step or two, or would rejetting be the way only way to go?

  2. Punkskalar

    Punkskalar Hugh's HandBuilt

    When I plug chop, I use a dremel tool to cut the threads off so I can the base of the insulator - I've gotten far better feedback that way. Worth a look :thumbsup:

  3. Brassneck

    Brassneck XS650 Guru

    Good point, I was hoping to avoid cutting them with some initial thoughts. As they look pretty clean...definitely not a 1/4" of tanning that I can see... I'll cut them if need be...but my gut tells me they are going to be lean...

    Anyone else have thoughts based on these pics?
  4. Punkskalar

    Punkskalar Hugh's HandBuilt

    Spark Plugs are cheap, pistons aint' :D

    How long have you run them? THey look quite new, did you install them with an already warmed up engine, not using choke, etc?
  5. Brassneck

    Brassneck XS650 Guru

    Thanks Hugh...per my post, they are brand new:

    "...so I went out today, warmed up the bike (old plugs) then swapped out for new ones (BP7ES) and did two 1/2 mile passes at WOT plug chops."

    Yep, I'm not worried about the cost of plugs...I have a box of these, but again, if this is telling me it's too lean now, or if I didn't run it long enough, I would prefer to use them...not being frugal, just practical.
  6. Punkskalar

    Punkskalar Hugh's HandBuilt

    I would er on the side of lean, and that's what I get for skimming over a thread post, instead of reading it fully :doh: End of the day, let's go home :laugh:

  7. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    At WOT, you're talking main jets.
    I'd try a series of equal tests, on a series of mainjets, noting performance and comparing to the plugs.
    Then decide...
  8. Brassneck

    Brassneck XS650 Guru

    Ha ha...No worries, I get it. And thanks for the feedback. I may just cut them to get a better look...but let's see if anyone else chimes in.

    More importantly, I'm wondering if raising the needle a step or two will work or do I need to rejet. I don't have any issues with the powerband, but want to protect the pistons...

  9. Plugs don't color like they once did with todays fuel. If your carbs are set to factory base line jetting or bigger depending on your carbs and your not running straight pipes you should be ok. It takes longer then a couple of passes my opinion.
  10. Brassneck

    Brassneck XS650 Guru

    Thanks...that's good to know. Yep, factory jetting...not running straight pipes, stock pipes with a hole in the baffle...lol.

    I might play with the needle...but may just ride it a bit more and then see how it goes?
  11. A google search reading sparkplugs an expert opinion in the first thread a good read.
  12. Brassneck

    Brassneck XS650 Guru

    Yep, read it. :)

    I think I just need more time with these plugs to tell...other than the tips looking very gray, which tells me they are lean...
  13. What do the old plugs look like.
  14. Brassneck

    Brassneck XS650 Guru

    Here's a pic of the old plugs. Note: I didn't change these out after I had cleaned up my carbs and tuned them...they were running very rich for a long while....then getting leaner at the end after my "baffle job"

  15. You should be ok if they don't turn black after a day or two of riding.
  16. Brassneck

    Brassneck XS650 Guru

    What if they stay white...that's my bigger fear...rich isn't as worrisome to me. :)
  17. grizld1

    grizld1 Grumpy old man Top Contributor

    http://www.strappe.com/plugs.html. If your motor runs clean under full throttle, don't go larger than a single step up on the mains; carbon buildup in the head is not a good thing.
  18. Brassneck

    Brassneck XS650 Guru

    Thanks...good read.

    That's just it, bike runs awesome. Sounds good... no stumbles, loss in power...I am probably being paranoid. LOL.

    I took it for a casual spin (about 5 miles) and the plugs are looking way better. Tips are turning gray/brownish...the insulator is turning tanish down low...

    Maybe my mains are running a tad lean, but the pilot and mid-range seem to be good?

    Dunno...I'll ride some more tomorrow and post up pics.
  19. 5twins

    5twins XS650 Guru Top Contributor

    If you're concerned, try 137.5 mains. That's probably the only way you'll know for sure if they're better. When your jetting is very close, as yours seems to be, plug readings between one size off and the ideal jet size aren't going to change much. You will be deciding more based on how the bike preforms with that jet size. Yes, plug readings can easily indicate when you are really far off on the jetting but when close, not so much.

    Yes, a couple half mile passes with today's cleaner burning fuels isn't enough to color the plugs much, if at all. I don't think you need to be cutting them open either. You can see down in them well enough for our purposes. Your old plugs nicely illustrate what cold starts using the choke do - they blacken the plugs right up quick. It takes a bit of riding afterwards to burn them clean again, maybe as much as 15 or 20 miles. But just the centers will burn clean, that outer ring at the top of the plug's threads will stay black or very dark, never getting burned fully clean again. Here's some of mine after a fair amount of run time. The side electrode gets gray or tan, the porcelain stays pretty clean, but the outer ring stays dark or black. You can't see it in the pic but there is a ring of color down at the bottom of the porcelain .....


    Also, if you're going to be doing frequent plug reading, you may want to label them "L" and "R" with a Sharpie so you don't lose track of which you're looking at with both out.

    Some notes on your carb set - the stock 135 main is the largest ever put in a 650. I don't think you need worry about being dangerously lean with just your one mod. Still, one size up on the main could be better. But like I said, trying it is probably the only way you'll know. But you may need to go further than that. These 650 carbs seem to need more tinkering than many other bikes. Here's what happens many times - your larger main bleeds over into the upper midrange making it too rich. You lean (lower) the needle to compensate. That also leans the upper part of the idle circuit sometimes causing a stumble. You go up a pilot jet size to fix that.

    So, it looks like you may be on the verge of learning all about carb jetting, lol.
  20. Brassneck

    Brassneck XS650 Guru

    This is perfect...thanks 5T, I really appreciate the summary. I've got some jets coming, so I'll need to wait on that. Meantime, I'll ride it a bit and post back if anything looks off.

    Much appreciated everyone!

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