Topic: Plug chop for dummies?

[SamP]

So I've been wrestling with getting the jetting on my carbs fine tuned, and I keep coming across the phrase "plug chop." Well, never done one before, so Google to the rescue. All the plug chop videos and how-tos I come across involve actually cutting away threads from the plugs after running a new set of plugs under specific riding conditions. Except for this forum. I keep seeing members posting entire, unmolested plugs that have been ridden on, however briefly.
Well, I tried the cutting method with my cb550 with two different mains - 95s and 100s. After a warm up, plug swap, quick uphill ride with the throttle fully open into 5th (pretty much redlining in each gear), killswitch, coast to stop and swapping the new plug back out, riding home, and cutting it open, I find the ceramic at the base of the threads is still completely white, without the faintest haze of smoke or chocolate or brown. Is this an indicator that my mains are too lean, or do I need to ride uphill for more than 7-10 seconds at WOT to really register a color? Or are we not supposed to cut our plugs open at all on these bikes? Kind of confused because I'm not getting the expected results, and I'm fairly certain my jetting is on the rich side.
I'm on a 77 cb550k, stock airbox, foam filter, cleaned and oiled, pd46 carbs, 95/100 mains (not at the same time), 42 idles, clip on center position, mixture screws at 2 turns out, mac 4into1 exhaust. Bike is synched, dynamic timing is set, ethanol free gas.
If there's a how-to plug chop for our SOHC4s, I'd appreciate a link. The search function wasn't that helpful and I didn't see it in the FAQ under carbs/plugs.
Thanks everyone.

[flybox1]

I'll ride at least 3 miles at WOT when doing a plug chop.  Only 3rd or 4th gear (depending on traffic flow)
I have a 5 mile stretch I try to complete, but at about 3 miles there is a turnout for me coast to.
Your time at WOT is too short for any significant deposits to form.  Your lean reading means nothing, yet.
No need to cut the plugs open to see how the base looks.  Just look down inside.
Be sure and use some copper thread paste.  Might prevent cross-threading of plug holes in the soft/hot material.

[riffman12]

I don't know how you folks find enough open road to WOT for 3 miles. I feel like I would either be arrested or run into a mini van going 20mph under the speed limit

[flybox1]

As I stated above, 3rd or 4th gear is fine.   Your plugs don't care what gear you are in.
Its about throttle position, not speed.

[SamP]

Thanks Fly. If I'm in 3rd or 4th, I tend to need to keep it just under WOT to keep from redlining. How do I keep throttle open as wide and long as necessary, without staying in the red?

[flybox1]

I would bet not many of us ride for extended periods at or near redline, so exact mixture tuning is really not essential.
Keep it just under for your chop and you'll get a enough of a mixture picture to know what to do with your main.

[Deltarider]

I'll ride at least 3 miles at WOT when doing a plug chop.

Not necessary. One minute or even less should be enough ofcourse. 

[SamP]

Weather was amazing, so I tried my hand at a plug chop, cb style. Bike was synced on last ride. Warmed up the engine, rode out about 15 miles. Changed the plug in number 1, then rode hard in 3rd and 4th for about 3-4 miles. Pulled over and swapped plug back out, then rode home normal.
Here's a pic of the plug. Does it still look on the lean side to you? Oil temp was at ~220 when I got home, and I'm running 20w50.

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[flybox1]

Yes, that is still lean.  Go up to 105 mains and repeat.
13 thru 16 is what you're looking for.   Yours looks to be in the 20-22 range

[brewsky]

With all the additives, ethanol, nitrogen, cleaners, and who knows what else is in todays gas....I am much less trusting of plug chops giving the correct picture.

Note the comment about gas in the attached write-up from Jets r Us.

http://jetsrus.com/FAQs/FAQ_spark_plugs.htm

Years ago, I would have said that was way too lean, but not too sure now.

I would venture a guess that the example pics shown in the various plug chop articles were taken back in the leaded gas days?

To know for sure, a dyno or on board sensor setup is best.

If you have access to a local shop with a dyno, see if they will just do a pull for afr reading only (no tune). Should be a reasonable price.

[SamP]

Went ahead and ordered 105s. Realized that my bike's factory spec is 38 slow jets, 90 main. PO had changed the slows, but not the mains. Looking at others' mods on here makes me think the 105/42 combo will be ideal. Thanks flybox.

As for the gas, I'm able to get ethanol free locally, and have pretty much only run it through the engine. Not sure how it compares to gases from the 70s, but I think I'm running closer by using it. Will keep that in mind for future reference though, thanks.

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[Duanob]

It all seems counter intuative to restrict the exhaust and then have the engine run lean. Do you have any baffle at all in the muffler? Have you tried changing the needle jet clip position? 

That's really the only difference between the older 550 K and F models, one comes with a 4 x 4 and the other 4 into 1. The F model lowers the needle by 2 clip positions to lean the mix for a more restrictive exhaust. Just sayin'

[SamP]

I installed the mac 4into1 as shipped, not sure if they come with baffles or not, but I did not put one on myself. I thought this system was less restrictive than stock, hence the formula I've seen posted around calls for main jet increases when going from stock to 4into1. I did lower the needle clip one position when I was rebuilding previously, so if anything that's helped keep it a little less lean.

[SamP]

Installed 105 mains. Synched, warmed up, them drove out about 5 miles. Swapped out my #4 plug with a fresh one, then rode back and swapped it out with the old one. Here's a pic of the chopped plug. I realized that I had put fuel stabilizer in my tank because I didn't foresee such a mild winter, which is probably why the plug is white. Does this mess up the reading too much, or can I trust it? Oil temps were at ~220 still, and I feel like I rode harder with higher rpms as well.
Thoughts? Should I test again in the spring with fresh gas? Up to 108s or 110s?
Thanks for your time.

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[flybox1]

Fuel stabilizer and air temps will have little effect on plug color in that short distance you rode.
Go to 110's and retest WOT
Please outline your 'chop' in detail from the point you install the clean dry plug.
You/we really need to be sure you are at WOT when you kill the engine.

[SamP]

Fuel stabilizer and air temps will have little effect on plug color in that short distance you rode.
Go to 110's and retest WOT
Please outline your 'chop' in detail from the point you install the clean dry plug.
You/we really need to be sure you are at WOT when you kill the engine.

I'll be honest, I was probably closer to 3/4 throttle through most of the run. I made it into 4th, but my RPMs kept going into the red, even in 4th I was hitting 70 MPH easily. What's more if that my tach cable kept giving me inconsistent readings - it would say ~4500 per minute, but then it would jump to 10k and stay in the red before bouncing back down. It was honestly probably closer to redline most of the time, so I had to back off the throttle to prevent overheating. My area is really hilly, so it's really tough to find a good stretch of road that is long enough and fast enough without rising and dipping too much.
Just so I'm clear - in a previous post you mentioned that it didn't need to be WOT the entire ride, just fast and under load, for 4-5 miles. Yet it's still important to kill the engine at wide open and coast to a stop, even though the deposits are almost entirely from the past few miles? Just not clear on what's more important and how to achieve it.
Last few issues - the engine dying when letting off the throttle and pulling in the clutch has returned, but not as much. I think it's because my idle jets are too small relatively speaking, and my engine starves suddenly - should I bump my idle now, or should I wait? I know all changes in jetting should be done individually, but I jumped from 42s and 95s to 42s and 105s, soon to be 110s. Seems like it's next on the list.
Thanks again for all your input.

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[flybox1]

Under load, at or just under redline.
(I shoot for 7500-8000 (my redline is at 8500) and hold it there for the test, and then kill it)
Not a lot of my riding is done at this rpm, so my plug chops were done with the thought to 'get it (main jet) close' to the right mixture.  For my setup, 110's were it.

Once your plug starts showing good color with main jet changes, your 1/2 to 2/3 throttle position plug chops will be the one you really should drill down on, as this is the upper end of (assumed) your most used throttle range.  This will dial in your needle clip/shim position.   I dont feel doing a chop here with just one plug is sufficient.  I chose to do all four each time to make sure there were no differences between cylinders.  I would vac sync and re-test if there was. 
You DO get pilot jet overlap here, so IIWY, id lean towards going back to a 40 pilots, and tune the needle clip position(richer) to compensate for it.

[flatlander]

sam from your description i'm not sure if you're technique is right?
after starting off from standstill, you should be in the same gear (3 or 4), at a constant throttle opening for about 10 seconds before killing the engine.
if you keep varying engine speed and gear over 5 miles you don't get an indicative plugchop. to determine main jet size what you want is a reading at a certain throttle opening, near WOT.
if your tach is shot then you could just hold it at a constant opening between 2/3 and WOT.

[SamP]

sam from your description i'm not sure if you're technique is right?
after starting off from standstill, you should be in the same gear (3 or 4), at a constant throttle opening for about 10 seconds before killing the engine.
if you keep varying engine speed and gear over 5 miles you don't get an indicative plugchop. to determine main jet size what you want is a reading at a certain throttle opening, near WOT.
if your tach is shot then you could just hold it at a constant opening between 2/3 and WOT.

I tried this twice and that's what's prompted this post. I did the 10 uphill run, killed the engine and coasted to a stop. Swapped my test plug out, took it home and cut it and was getting absolutely no deposits. Plug still looked brand new.
Flybox posted that on these carbs we need to be running for a few miles at or near WOT.
I realize it could just be that my jets are entirely too lean, but I was getting absolutely nothing on my plugs.

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[flybox1]

The longer you run at a specific throttle position, the more accurate your deposits will be.
1mi minimum.  10 seconds is nowhere near long enough for a good sample to form, but you should see some color if the jet is right.  Because they were still white, I suggested 110's

[alacrity]

At a certain point, your forward motating speed actually DOES matter, because (depending on your intake/airbox setup), it will effect how the clean air is getting into the engine.

IF you have a stock box and that little inlet under your seat and you have an inner fender and side covers and you are sitting still with your legs tucked in, then you can presume very nearly the same available air at 40 or 80mph... I would guess.

IF you have modified stuff... like running pods for example, or if you have removed the side covers or are tunning different ones, or if you took off that top snorkel thing on the airbox or ANYTHING... then you have introduced a variable that will be an issue when looking for plug chop results at different speeds.  You might have the "right" mains for 40 mph and the wrong ones at 80 or vice versa... etc.

[jonda500]

I don't know how you folks find enough open road to WOT for 3 miles. I feel like I would either be arrested or run into a mini van going 20mph under the speed limit

^ This is exactly how I feel about WOT plug chops- I have never found a road where I can safely hold WOT for even one minute without risking over reving or breaking the speed limit and I really value my licence!!

If my bike had a problem at WOT, I would try riding it after removing the air filter & air box lid and see what the effect is- if it runs worse then I know it's lean at WOT, if it runs better then I know it's rich at WOT.
John 

[seanbarney41]

I don't know how you folks find enough open road to WOT for 3 miles. I feel like I would either be arrested or run into a mini van going 20mph under the speed limit

^ This is exactly how I feel about WOT plug chops- I have never found a road where I can safely hold WOT for even one minute without risking over reving or breaking the speed limit and I really value my licence!!

If my bike had a problem at WOT, I would try riding it after removing the air filter & air box lid and see what the effect is- if it runs worse then I know it's lean at WOT, if it runs better then I know it's rich at WOT.
John 

+1, are you guys dragging the brakes or something else you are not telling us?  For a main jet plug chop I will just do a dragstrip run on a safe stretch of road....run it through gears 1-3 or 4 at full throttle, as much as I have room for.  I am fortunate my shop is on a nearly unused stretch of road.  I think readings are easier to see and changes show up faster on used, but cleaned, plugs.
     I honestly think the use of plug chops for tuning should be discouraged here on the forum.  It is WAYYY unsafe.  And so many of those attempting to tune for pods etc. are inexperienced riders.

[flatlander]

yes. what's wrong with going to a dyno and actually measure a/f ratio? over here it doesn't cost that much, unless prices in the US are exorbitant... ?

[SamP]

FWIW I've also been getting quite a bit of spitting back through the carb bodies, almost exclusively when I crack the throttle. I know this is indicative of a lean condition, which is why I think Flybox is right with increasing jet size. Not quite sure I understand why the slow jets should go DOWN, but I'll piece that together once WOT and 1/2-3/4 throttle is dialed in.
Possibly unrelated, but it's also a bear to start. Starts on first kick when warmed up, but it takes like 15 minutes before it's sufficiently warmed up to get to that point - as well as to where cracking the throttle doesn't bog it down and it stalls out.
Immediately after this last test I ran, it sounded like I was getting some clatter at the valves/tappets. Need to check that before I run any more tests. 110s on order, will update when the weather and time allow.
Would also love some more input on how else I can determine proper jetting that doesn't require hauling ass at redline down windy, hilly roads for a few miles. 
And while I've got everyone's attention for a second, a quick question about vac synching - I have been synching so that the draw at idle is even across all 4 (or as close to even as I can get it). However, when I blip the throttle or hold down the throttle, I can't help but notice that the pull is stronger for certain carbs, namely 2 and 3, then 4, then 1. Vacuum is not even once the throttle is open, but it evens out once the throttle is closed again. Is this normal?