1975 Yamaha RD350(LC) Preservation-mod Hellride
- Thread starter irk miller
- Start date
Good point. I have the perfect shelf already hung. Just need to set the offerings.
It's back in business. Only ate through the plastic coating over the magnets in the rotor, so I cleaned it off the stator and turned the inside of the rotor on the lathe to remove the frayed plastic. Then I coated everything in shellac.
200 mile plug check
CarbsAndCylinders
Careful With That Axe Eugene
I'm waiting to see the comments on this plug because everything that I thought I knew about plug reading appears to be incorrect.
The biggest problem with reading plugs is understanding what it's all about. First thing to keep in mind is that plugs get hotter under load. Sounds obvious but what we are reading is really how hot the plug got. At low load a plug tip might be around 200-300 degrees C and at full load it might reach anything from say 600-1200 degrees. Plugs are designed to self clean between 850 and 100 degrees.
What does that mean and why doe is matter?
Two implications: First if the plug chop is not done when the plug is at peak operating temperature, what we think we are reading is misleading. A plug should look "rich" at low load because the plug isn't hot enough to burn off the deposits. We also can't tell if the plug itself is getting too hot, if we don't chop it at load.
The flip side of that is that if we mess with jets to make the plugs look clean at low to moderate load they will be too lean when we blast up a long hill at full throttle. Oops.
The other thing about plug temperatures is that we want the plug to be hot enough to clean itself, but not so hot that it glows or melts.
So the first thing we want to do is to run the bike flat out with clean new plugs under load for a minute or more if possible. Then we cut the ignition and coast to a halt. And we do that somewhere safe of course.
Then we look at the plug to see if there are signs of detonation in the form of specs of aluminum. And we look at the side electrode or ground strap as it's also known to see how far the clean burn heat signature is on that. We want to see it clean to just around the bend so to speak. If the plug shows signs of overheating it tells us we have, too little fuel, too much advance, too hot rated spark plug or perhaps we have an exhaust with too little pressure bleed.
So we start safe and make sure the plug isn't too hot before we start changing everything at once. For peak power a plug chop doesn't tell us much except that the plug is at the right temperature unless we already know that we have close to the right jets in to begin with. A dyno is best because it tells us what the mixture is, but it really tells us what jets make the most power for our particular motor given a set of air conditions. Some motors need to be slightly richer than perfect to make most power and all make power at A:F ratio closer to 12:1. 14.7 may sound familiar and it's the theoretically perfect mixture but for power we need more fuel and for economy we need less - maybe up to 15 or close to 16:1.
For that particular spark plug I don't know if it was a plug chop or just a couple of hundred miles of break in so it's hard to draw too many conclusions. It shows no sign of overheating and the insulator is fairly clean but we can't see the mixture ring so we can guess that it is fine for the conditions it was run at. If that was a mix of mainly low load riding without sustained high load high RPM running, it may very well be too lean once it runs flat out.
If the mix of riding is how it will be ridden in the future it is probably fine. And safe is always better than bleeding edge.
If that was a clean plug and the chop was done under load, then it looks a little cool and might benefit from a smaller main jet, but the key to that is how it performs. What really matters is how well the bike works. The old trick used to be to run up a slight hill between two known points and check the top speed and the time to accelerate. Change jets and repeat and see which set give the best WOT acceleration and highest top speed. That assumes you have somewhere that you can do that safely and without getting locked up by the local LEOs. Then look at the plugs and see what they look like just as a reference.
And let's not forget that there are two variables in Air to Fuel ratios. We talked about fuel but cannot forget air. Hot days with low relative air density have less oxygen to burn and cool dense air has more, so if the jetting is perfect on a hot summer day it may well be lean on a cool fall morning or evening when the traffic is light and we feel the need to see what she can do.
If you take a bike for a dyno run, the power readings are adjusted or corrected for air conditions. That's appropriate but we need to remember what those conditions were for the future. With dyno availability, the best way to get jetting close to perfect across the board is on the nearest dyno. Plug chops have their place but you can find out more in an afternoon on the dyno than in days of risky hard running on the street.
What does that mean and why doe is matter?
Two implications: First if the plug chop is not done when the plug is at peak operating temperature, what we think we are reading is misleading. A plug should look "rich" at low load because the plug isn't hot enough to burn off the deposits. We also can't tell if the plug itself is getting too hot, if we don't chop it at load.
The flip side of that is that if we mess with jets to make the plugs look clean at low to moderate load they will be too lean when we blast up a long hill at full throttle. Oops.
The other thing about plug temperatures is that we want the plug to be hot enough to clean itself, but not so hot that it glows or melts.
So the first thing we want to do is to run the bike flat out with clean new plugs under load for a minute or more if possible. Then we cut the ignition and coast to a halt. And we do that somewhere safe of course.
Then we look at the plug to see if there are signs of detonation in the form of specs of aluminum. And we look at the side electrode or ground strap as it's also known to see how far the clean burn heat signature is on that. We want to see it clean to just around the bend so to speak. If the plug shows signs of overheating it tells us we have, too little fuel, too much advance, too hot rated spark plug or perhaps we have an exhaust with too little pressure bleed.
So we start safe and make sure the plug isn't too hot before we start changing everything at once. For peak power a plug chop doesn't tell us much except that the plug is at the right temperature unless we already know that we have close to the right jets in to begin with. A dyno is best because it tells us what the mixture is, but it really tells us what jets make the most power for our particular motor given a set of air conditions. Some motors need to be slightly richer than perfect to make most power and all make power at A:F ratio closer to 12:1. 14.7 may sound familiar and it's the theoretically perfect mixture but for power we need more fuel and for economy we need less - maybe up to 15 or close to 16:1.
For that particular spark plug I don't know if it was a plug chop or just a couple of hundred miles of break in so it's hard to draw too many conclusions. It shows no sign of overheating and the insulator is fairly clean but we can't see the mixture ring so we can guess that it is fine for the conditions it was run at. If that was a mix of mainly low load riding without sustained high load high RPM running, it may very well be too lean once it runs flat out.
If the mix of riding is how it will be ridden in the future it is probably fine. And safe is always better than bleeding edge.
If that was a clean plug and the chop was done under load, then it looks a little cool and might benefit from a smaller main jet, but the key to that is how it performs. What really matters is how well the bike works. The old trick used to be to run up a slight hill between two known points and check the top speed and the time to accelerate. Change jets and repeat and see which set give the best WOT acceleration and highest top speed. That assumes you have somewhere that you can do that safely and without getting locked up by the local LEOs. Then look at the plugs and see what they look like just as a reference.
And let's not forget that there are two variables in Air to Fuel ratios. We talked about fuel but cannot forget air. Hot days with low relative air density have less oxygen to burn and cool dense air has more, so if the jetting is perfect on a hot summer day it may well be lean on a cool fall morning or evening when the traffic is light and we feel the need to see what she can do.
If you take a bike for a dyno run, the power readings are adjusted or corrected for air conditions. That's appropriate but we need to remember what those conditions were for the future. With dyno availability, the best way to get jetting close to perfect across the board is on the nearest dyno. Plug chops have their place but you can find out more in an afternoon on the dyno than in days of risky hard running on the street.
Here's what I think I know:
I'm not bothered by this plug. It's certainly rich, but from a performance standpoint, the bike has great power and smooth delivery. No flat spots or bog.
The insulator is really good on top, a bit dark but not bad. The base of the insulator fades to dark and the inside of the metal cup is pretty dark, as well. I have also been running the high side of fuel/oil mix (32:1). I don't want to take any unnecessary risks with this engine, so I'd rather be on the heavy side with oil. The crank is a combo TZ/RD crank that I don't think will be easy to replace or repair cheaply, so I want to make it last. I imagine that contributes to the color of the plug, as well.
Thanks for the write-up, Teazer. Really glad to have that in this thread. I am pretty happy with how the bike performs. I'm not bothered by the plugs, as they are. I'm running oil @ 32:1 and I'm intentionally on the richer side. I'm currently seeking dyno time.
I have dyno time scheduled for tomorrow, but I am rescheduling due to a school event conflict. I was able to get a weigh in and the RD weighs in at a spritely 279 lbs wet, with a full tank of gas. I feel extremely happy with that number. I had hoped to be under 300 lbs.
HollywoodMX
Coast to Coast
Looks pretty darn good to me. If anything a tad lean. I can't see the detail but with that plug and a white ring around the electrode is perfect in my books.
CarbsAndCylinders
Careful With That Axe Eugene
Some people say that to properly read a plug you need to cut the threaded portion off and examine the base of the porcelain.
https://www.motortrend.com/how-to/spark-plug-reading-101-dont-leave-hp-table/
https://www.motortrend.com/how-to/spark-plug-reading-101-dont-leave-hp-table/
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We can see the base of the porcelain. I wasn't trying to play this off like an actual plug chop, but there's enough there to glean a general tune. The dyno will fill in the blanks. Really just focused on making it as good as it can be with a butt dyno and staying away from lean, so posting the plugs was more about not being too rich than anything.
CarbsAndCylinders
Careful With That Axe Eugene
I wasn't trying to be negative, it's just that I have spent too much time burning fingers, collecting lots of jets, needles etc. setting up my carbs and I never knew about removing the threaded portion and reading the base of the porcelain. I can get it in the ballpark but I guess the dyno is the final solution. Have you used an exhaust gas analyzer mounted on your bike?
It's easier to get a spark plug reader which is a loupe with a light in it.
No idea what Irk tried, but I found that watching an air:fuel gauge is a good way to ride into something stationary. They are all over the map. I tried a datalogger with TPS set up and that wasn't much better in terms of making out the Lambda at different throttle settings.
And the second issue is that you don't know what number we are aiming for. At idle it's probably 8-10:1, at cruise maybe 15:1 or more and full power 12.5-13.5 but what number is best for a particular situation? The answer is that the best number for power is the whatever gives the most power plus one jet size for safety, not the other way round. And at less than full throttle A:F just tells us a number and what matters is the responsiveness. the A:F at part throttle is a number or data point so as we make changes we can see what works best. The actual unumber is interesting but is only of use in giving us a starting point. For example if we see A:F of say 10:1 at WOT at high revs, we know it is probably rich, so our next attempts will be with smaller jets. It's indicative rather than definitive.
No idea what Irk tried, but I found that watching an air:fuel gauge is a good way to ride into something stationary. They are all over the map. I tried a datalogger with TPS set up and that wasn't much better in terms of making out the Lambda at different throttle settings.
And the second issue is that you don't know what number we are aiming for. At idle it's probably 8-10:1, at cruise maybe 15:1 or more and full power 12.5-13.5 but what number is best for a particular situation? The answer is that the best number for power is the whatever gives the most power plus one jet size for safety, not the other way round. And at less than full throttle A:F just tells us a number and what matters is the responsiveness. the A:F at part throttle is a number or data point so as we make changes we can see what works best. The actual unumber is interesting but is only of use in giving us a starting point. For example if we see A:F of say 10:1 at WOT at high revs, we know it is probably rich, so our next attempts will be with smaller jets. It's indicative rather than definitive.
TresCuatros
Active Member
If you collect enough AF ratio info as you tune, I could see it being help in setting a target for future mods.
I've been doing modest checks just to get what I think is a baseline and good performing tune, but with an eye on being conservative early. There's a WERA race team, P-1, less than two miles from my shop with a dyno. I'm just waiting on them to install their new compressor, which should be by the end of the month. We had planned to dyno today. My plan was to use the dyno to fine tune the engine vs obsessing over plug chops. I can get a good 10 pulls for $300. He normally charges $75+ per, but that includes all the flashing and tuning, which can jack the price. He's only racing and working on EFI stuff. Since I show up with carb bikes and do all the work, he doesn't charge me much.
CarbsAndCylinders
Careful With That Axe Eugene
This makes a lot of sense.
The CB front end was awful on this bike, so I made a swap.
Really just putting on the miles and making tweaks here and there. I just replaced both crank seals, as the left side sucked air. Machined a billet fuel cap and covered the seat foam with leather. Painted the fenders.
Small update:
I’ve been getting more weeping than I like from the glass tank and I’m honestly not wanting to risk trashing a fundamentally irreplaceable tank, so I sought out an RD400 stock tank to swap out. A friend hooked me up at Barber with a tank that had one decent size punch in the knee dent. Got it all fixed up and covered in base coat and ready for graphics.
I’ve been getting more weeping than I like from the glass tank and I’m honestly not wanting to risk trashing a fundamentally irreplaceable tank, so I sought out an RD400 stock tank to swap out. A friend hooked me up at Barber with a tank that had one decent size punch in the knee dent. Got it all fixed up and covered in base coat and ready for graphics.
