Spark plug reading

jseng1 said:
Yes it is unleaded pump gas. Thats all we have here in Calif. You just have to have a few miles on them for the color to show.

Spark plug reading


The "leaness of the light plug" with the speckles shown in the previous thread looks like it could do some damage.
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270 mains, pump gas.
75 miles to a Roadster tank full.
You gettin 50 miles?

Everyone still trying to apply the rules used with LEADED FUEL.
 
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Nope that right hand plug in the orginal pic is not too lean on modern gas, the right hand is slightly rich but not to the point it will foul. Ride it.
 
htown16 said:
I'd just ride the thing if it is running good. The rich one doesn't look like it's in danger of fouling and the lean one doesn't look like it's in danger of detonating.
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When you read a plug, you look right down inside at the porcelain just before where it meets the metal. There should always be a about a 3mm black ring there where the carbon has not burned off. If you use a hot plug for tuning, you should stay safe. The carbon in a hot plug burns off at a lower combustion temperature. Plugs of different heat ranges conduct heat at different rates. Cold plugs conduct heat quicker. A hoe plug burns the carbon off quicker, so the balck ring disappears at a lower combustion temperature. But if you do most of your riding using less than one-half throttle, the plug readngs might not be a reliable indicator of combustion conditions.
With a race bike, I only use plug readings for getting the main jets right, everything else is about getting the best acceleration. If you do a plug chop, it might be important to cut the motor dead after a long hard blast - don't let the motor idle before you read the plugs.

If you use a mix of metric and number drills, you should be able to remove half a thou of an inch from within your needle jets. I make my own, but I use methanol - not petrol. Petrol is much more critical.
 
concours said:
Running lean burning a piston is a very misunderstood phenomenon.
Was that pickup hauling a camper?
Racing, or working very hard is the only way the elevated combustion temperatures can overcome the pistons ability to transfer the heat away.
At Part throttle cruise, LOOOOONG before an engine "burns a piston", that engine will run VERY POORLY, and be way down on power output.

Ethanol mixed fuel doesn't burn pistons, it has less heat value per volume.
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Yes. Pickup mostly hauls a camper, 9,000 # gross. On long mountain grades it'll be WOT for 10-15 minutes at a time running 2900 RPM 0" vacuum (think I-80 eastbound from Ogden UT to the continental divide. Oil temp will climb to 250 F on hot days, water temp about 210. Ethanol causes it to run lean, altitude saves the day except Imperial Valley, California is at and Death Valley is below sea-level. Climbing out of Death Valley has one of those WOT, 30-minute grades. Oil consumption and down on power started before that but I'm sure it didn't help. I've ridden my Norton over that route but I'm no where near WOT on the grades. I did put an oil cooler on it though.
 
Thomasa said:
Yes. Pickup mostly hauls a camper, 9,000 # gross. On long mountain grades it'll be WOT for 10-15 minutes at a time running 2900 RPM 0" vacuum (think I-80 eastbound from Ogden UT to the continental divide. Oil temp will climb to 250 F on hot days, water temp about 210. Ethanol causes it to run lean, altitude saves the day except Imperial Valley, California is at and Death Valley is below sea-level. Climbing out of Death Valley has one of those WOT, 30-minute grades. Oil consumption and down on power started before that but I'm sure it didn't help. I've ridden my Norton over that route but I'm no where near WOT on the grades. I did put an oil cooler on it though.
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Oil cooler on mine as well, for the summer months.
What six banger?
 
Danno said:
Doesn't the drive side always run a bit hotter than the timing side?
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I put a pair of temperature gauges with under plug sensors on my bike and ran them for the first time last weekend. Left side hit 200C, right side more like 190C.

Close enough to assume what you suggest is true.

Might be an idea to jet the left a little richer, but so far I just tried a washer under the jet clip.

And you still have the question, should I make one richer or the other one leaner?
 
SteveA: where does one get the under-plug sensor setup? Is it a thermououple?
Concours: Six banger is a 62 Chev 261 truck engine; bigger bore version of the 235 started in 1942 or so. Crude but effective.
 
I agree with that comment about it being unlikely to burn a piston or a valve when you are not using full throttle. That is the reason my main jets are always slightly too rich. I run as lean as I can everywhere except at full throttle. With 6D Mikuni needles, I feed the throttle on, as I would do with a two stroke. Full throttle is reached when I am well into the straights. So getting maximum power there is not so important. Getting maximum acceleration does not depend on using full throttle - it is a balancing act. If the fast guys are going to pass, they need to do it at the ends of the straights, as they approach the next corner, and most of them have plenty of go there anyway.
 
I'd agree, those look pretty close to perfect. Hard to get that light brown with modern gas. No pepper specs that would indicate detonation.
 
When I install a carburetor single or twin I go to the motor side of the slide and use a .040 gauge wire to set the idle screw. It should start with a slightly high idle. This saves me tons of time especially with twin carbs.
 
mean gene said:
A while back I installed new 34mmm Amal premiers on a 750. Originally I had problems starting and lean mid. So changed needle and got a immediate improvement. Goes down the road great accelerates without any hesitation. Starts 1-2 kicks if I do my part.. So today I came down the street about 30mph, hit the kill switch. Pulled the plugs and this is what I saw! Both carbs are set up the same. They were synchronized with vacuum gages. Do you think the cause is Boyer ignition or they are not synchronized in the mid range? Thanks

View attachment 99701
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If I had plugs which looked l like that, I would look to see if the rich carb was touching the frame.
 
seattle##gs said:
When I install a carburetor single or twin I go to the motor side of the slide and use a .040 gauge wire to set the idle screw. It should start with a slightly high idle. This saves me tons of time especially with twin carbs.
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The motor should idle perfectly with throttle fully closed. The slides need to hit bottom together. If you wind them fully open, then let them drop, you should hear a single click when they hit bottom. When I set the idle, I lean-off with the screw until the motor misses, then back-off until the motor idles perfectly - usually about half a turn. When I start my bike, I put it on the rollers and open the enrichers, fire it up with the throttles closed. When the idle rate starts to slow, I close the enrichers. Some guys tend to grab a handful of throttle and try to start the motor - I do not do that. While the motor is idling, I look into the oil tank to see if the oil is circulating and returning.
 

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