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Discussion Starter #1
First two pictures are from the TW with the 68mm piston and it runs great. To me it looks a little on the lean side but since it runs so well I am not concerned.

P4110031.JPG P4110032.JPG


Next two pictures are from The Parts Bike with the 70mm piston. It runs OK but wide open throttle it misses and just doesn't seem to do as well overall as the other TW does. To me it looks a little on the rich side, but again, not horribly so. Just a very slight amount.

P4110029.JPG P4110030.JPG

Comments, insights, opinions sought. What do you think?
 

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I'm confused at what I thought I knew.

Hard to tell in the pictures from here. I'm actually reading them opposite than what you are, but not entirely. 1st plug confuses me a bunch.

Has the plug been in the 68mm for a while or was it a new plug to start?

The 2nd plug or 70mm to me looks like it's running lean. Again confusing as it looks lean on one side and closer to normal on the other.
 
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Discussion Starter #4 (Edited)
Air filter has been cleaned on both bikes. First plug has 20K or 30k miles on it. I put it in a long time ago. Second plug about 2,000 miles, maybe 3,000 but not very many.

As I write this, maybe the plugs look the same mixture wise and it is only the mileage the makes them look different.

The miss could be something electrical and not related to mixture at all. I have new high speed jets on order.
 

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I'm with Admiral, did you maybe switch the pics and the captions?

Also, without knowing if the cylinders have two different compression ratios it's hard to tell much. Neither of these plugs looks too far off optimum. If your parts bike is running rich enough to bog at WOT in 5th I'd think it would be much more obvious. Most likely it's running a bit lean. How much increase in displacement does the 70mm create? If it's more than just a few cc, I'd suspect the carb just isn't quite big enough.
 

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Discussion Starter #6
Compression ratio supposedly identical. 10.25

Stock is 67mm = 196cc
Over 68mm = 202 cc
Over 70mm = 214 cc

Small increases.

Pics and captions correct.
 

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I'll add having seen an extremely lean plug, it looked much much whiter than either of these. Same for a rich plug, really really black with soot baked on.

If these were my plugs, I wouldn't be concerned thinking each is close enough to normal.
 

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Discussion Starter #8
I'll add having seen an extremely lean plug, it looked much much whiter than either of these. Same for a rich plug, really really black with soot baked on.

If these were my plugs, I wouldn't be concerned thinking each is close enough to normal.
I agree. I guess I better start looking for an electrical problem.
 

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The first plug is about past its sell by date - the colour is ok - just the build up of junk could become a problem

The second plug is also "ok" - colour wise - like Admiral I was wondering about the one sided burn pattern

Have you considered Iridium plugs ?
 

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Oh, I know it snowed back east, but it's way too early to be bringing these mid-winter topics up so early in the fall!:p


Gee-dang-it, now I'm gonna go look at my plugs! Power of suggestion elime!:D
 

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Were these pictures all made after a power run and then immediately shut off?

Were the plugs cleaned before the power run test procedure? Hopefully if cleaned, no wire brush was used as it stains/colors the inner insulator and reading can be tainted.

And do you have any representative plug examples before the piston changes for comparison?

I do not think you have an electrical issue on T2. I have ridden that bike (like I stole it) on many of our trips, and I never encountered the high speed miss/stumble you now have since the 70mm piston replacement. It only makes sense to me that any new stumble is not from a coincidental electrical issue, but due to changes in the compression/air/fuel area.

I also do not feel your use of a 20K mile plug for a reading will be valid. You need a better starting point plug.

Regarding the one side of an insulator being colored and the other side being light, it is my opinion this is more of a function of the direction of the flame kernel as it applies to the position in the combustion chamber (think plug indexing). However my caveat is that this is just a guess on my part.

And lastly I agree with the others regarding the lean interpretation being somewhat different than you see it.

The point is Tony, I'm not convinced these plugs are giving an accurate account of what is going on (certainly not on T1). My reasoning is that T1 plug looks worse, yet you say the engine runs better. I think you need to get a more controlled baseline.

 

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Discussion Starter #12
Personally, I would not leave a spark plug in these engines for 20,000 to 30,000 miles. Just changed mine out last week, with less than 1,000 on it.
.
I put a new plug in the engine when I got it about 30K miles ago and I don't remember ever changing it for a new one. I may have -- that is why I say maybe it was only 20K miles on this plug. Still, it starts easily and runs fine and never misses a beat.
 

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Discussion Starter #13
Were these pictures all made after a power run and then immediately shut off?

Were the plugs cleaned before the power run test procedure? Hopefully if cleaned, no wire brush was used as it stains/colors the inner insulator and reading can be tainted.

And do you have any representative plug examples before the piston changes for comparison?

I do not think you have an electrical issue on T2. I have ridden that bike (like I stole it) on many of our trips, and I never encountered the high speed miss/stumble you now have since the 70mm piston replacement. It only makes sense to me that any new stumble is not from a coincidental electrical issue, but due to changes in the compression/air/fuel area.

I also do not feel your use of a 20K mile plug for a reading will be valid. You need a better starting point plug.

Regarding the one side of an insulator being colored and the other side being light, it is my opinion this is more of a function of the direction of the flame kernel as it applies to the position in the combustion chamber (think plug indexing). However my caveat is that this is just a guess on my part.

And lastly I agree with the others regarding the lean interruption being somewhat different than you see it.

The point is Tony, I'm not convinced these plugs are giving an accurate account of what is going on (certainly not on T1). My reasoning is that T1 plug looks worse, yet you say the engine runs better. I think you need to get a more controlled baseline.




The answer that would apply most often is "no".

When the new jets arrives I will try them out. I also have a spare carb I can try and then see what happens. I also ordered the next leaner jet available and I already have the next richer jet so I will have the a jet on either side of the stock one to experiment with.
 

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Hi Tony,

In my uninformed opinion the first 2 look rich and the second 2 look OK.

I don't put too much stock in plug color.

For me, it's about how the engine runs: idles steady, accelerates from idle to full throttle in each gear with no hesitations or flat spots.

My TW ran fine with a plug that looked like this:



Way too rich, even for me, but the bike ran good. It did have an occasional miss at idle.

I have since changed the plug to an iridium...no more miss...but that may just be due to it being a new plug.

I also changed my main jet from a 130 to a 128...but that's another story.

Before you go too far chasing demons, check your ignition with a timing light.

jb
 
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Discussion Starter #15
Hi Tony,




Before you go too far chasing demons, check your ignition with a timing light.

jb
jb -- I swapped CDI with my other bike which runs great and nothing changed, so thankfully, 99% sure it is not the CDI.

BTW, nice looking plug! Tony
 

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Discussion Starter #16
I swapped in a #38 pilot jet (stock is #40) in the TW using the second spark plug. It says T2 on the picture somewhere. This bike has the 70mm piston and I feel it is not performing as well as it should.
P4130030.JPG

The idle mixture screw had to be reset to 3 1/2 turns out and the idle speed screw slightly adjusted. The butt dyno / placebo effect / wishful dreaming says the performance is better throughout the lower and mid rpm range but is about the same at the upper end. I looked at the spark plug after a 24 mile ride and it looks basically the same too.

P4140035.JPG P4140036.JPG

I am starting to wonder if the tachometer is accurate. The motor sounds like it is going fast but the the tach reads 8400rpm and I can't get it to go faster unless I am pointing down hill. My other TW I have held at 8800 rpm for many miles and it would easily go over 9300 rpm. (I was using restraint keeping it at 8800 rpm.) Something is wrong. I figure the 70mm piston bike should easily out perform a stock piston bike but it isn't, at least not yet.

I have two new high speed jets on order: #110 and #114 (stock). I already have a #116. When I get all three I will start experimenting some more. (I wanted a #112 jet but they are no longer made. I figure I can take a small file and ever so slightly enlarge the 110 jet should it look like it is necessary)
 

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In your first post with pictures I would be very satisfied with the plug color in the bottom right and would not change any carb settings other than a tiny twist one way or the other of the air/fuel mix screw we call the pilot jet. Some of my bikes also did a high RPM miss which I was able to clear up with just a Painful tweak once the bike was at full operating temperature. Maybe a Miss is not the right description but I did feel a sort of uneven surge at WOT.

GaryL
 
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Discussion Starter #18
In your first post with pictures I would be very satisfied with the plug color in the bottom right and would not change any carb settings other than a tiny twist one way or the other of the air/fuel mix screw we call the pilot jet. Some of my bikes also did a high RPM miss which I was able to clear up with just a Painful tweak once the bike was at full operating temperature. Maybe a Miss is not the right description but I did feel a sort of uneven surge at WOT.

GaryL
The bottom two pictures are different sides of the same spark plug -- I just wanted to make sure that was clear. It has been suggested I index the plugs and no doubt I will get around to it someday soon.

As I have posted before, I once had a terrible high speed WOT miss that was cured simply by replacing the old #114 jet with a new #114 jet. Same thing happened to BigD's TW. I think if you have a WOT high speed miss an easy first step, at least to eliminate it as a cause, is to replace the #114 jet with a new one no matter how good the old one looks.

I am pretty sure I already replaced this jet in this carburetor but just to make sure I am doing it again. Reports to follow.
 

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As I have posted before, I once had a terrible high speed WOT miss that was cured simply by replacing the old #114 jet with a new #114 jet. Same thing happened to BigD's TW. I think if you have a WOT high speed miss an easy first step, at least to eliminate it as a cause, is to replace the #114 jet with a new one no matter how good the old one looks.
Amen! I had tried a 116 before the new 114 was delivered to me. The 116 was just too big and still demonstrated the WOT issue. But as Tony had instructed in the 1st place, try replacing the 114 with a new one and it resolved my WOT issue.
 

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Hi Tony,

In my uninformed opinion the first 2 look rich and the second 2 look OK.

I don't put too much stock in plug color.

For me, it's about how the engine runs: idles steady, accelerates from idle to full throttle in each gear with no hesitations or flat spots.

My TW ran fine with a plug that looked like this:

Way too rich, even for me, but the bike ran good. It did have an occasional miss at idle.

I have since changed the plug to an iridium...no more miss...but that may just be due to it being a new plug.

I also changed my main jet from a 130 to a 128...but that's another story.

Before you go too far chasing demons, check your ignition with a timing light.

jb
Hey JB,

Got my carb apart, troubleshooting. Read your post here. I'm assuming your rich plug readings were with the #130 main jet installed, causing you to switch to the #128? I'm wondering if you've been happier with the #128? How has that change affected running/performance?

Asking because right now, I have the following setup:

#130 main jet (I have a #128 in hand)
Qty (3) 0.01" washer shims on main needle
Air/fuel adjuster bolt 2.5 turns out from bottom
OE exhaust
OE air box

Sorting out a non-start, pretty sure related to needle valve/float issue. Considering taking out 1 shim & switching to #128 main jet while it's all opened up again. Second guessing my current setup. Any advice appreciated.

Thanks,

-K-
 
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