Muckroot

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In another thread on this site XSJohn mentioned something that would lower cylinder temps by 20+ degrees.
Lowering the R/S hotter cylinder temperature will reduce the cylinder temperatures like 20+ degrees

I am REALLY interested in finding out exactly what John was talking about here, so I did some digging.
XSJohn's comments are in blue for clarity.

the cylinders cannot be controlled by oil temperatures or coolers.......only by directing more air over the cylinders and lowering the right cylinder temperature
This is a start, but there has to more information.

went through all this on 650rider till I was blue in the face
Found these posts, which thicken the plot considerably:
http://www.650rider.com/index.php?name=Forums&file=viewtopic&t=3075&highlight=one side hotter
"OK, xsjohn, you've got me curious enough to get serious.

For those who haven't been following the issue, John checked his cylinder temps with an infrared thermometer and found that the right gets hotter than the left by about 50* F. Every time others (myself included) have checked, they've gotten the same result. Ignition system isn't a factor--happens with points, OEM TCI, and Boyer. Happens with OEM and aftermarket exhausts. Happens with OEM and aftermarket cams. Happens with BS38's, BS34's, and VM roundslides. Happens with both stock and ported heads.

John's theory is that it's causing (caused by?) a power imbalance between cylinders that can be corrected by pouring more fuel to the right. What puzzles me is that I've neither seen nor heard reports of a higher incidence of piston holing/detonation, failure, valve burn, or premature wear on the right than on the left.

So--John's agreed to look into testing his theory on a dyno, and since I instigated him to do it it's only fair that I put some time and money behind the research too. Combustion temperature is what signifies, so in a few weeks there'll be a pair of probes hanging in my headers and a Westach double-needle EGT gauge in the instrument cluster. I think the cause is probably reduced right side heat dissipation due to the hot closed clutch cover, but we'll have some hard data to digest pretty soon.

John, we'll run this down if it harelips every cat in the country."


"Dang Griz you didn't have to do that but I truly appreciate you looking at it....dumping more fuel to the right is a bit of a stretch.....a bit of fuel is more accurate......Would be interesting to see it the exhaust temps are higher also.......

put 100 miles on it yesterday 60 degrees or higher and could not find any temp discrepencies anywhere.....measured plugs.....heads.....cylinders......and intakes.....at least 5 times......I feel its ready for the dyno when it warms up enought to survive the trip.........."



From a different post:
http://650rider.com/index.php?name=Forums&file=viewtopic&t=2416
"I always step in Dog Doo when I mention this…….With one carb there will be no balancing the heat with the right hotter cylinder.....I would be darn sure this was not occurring……..With 25 degrees higher temps on the right using the same carb for both would be a mess with no way of reconciliation ….No body believes this but that sure isn’t from lack of my warning…..I know people are doing it but have they checked….In the summer when temps are very marginal the right would be a furnace……Not for me…"

"From what I have found if you have a hot cylinder and both carbs are set the same once you warm it up completely to operating temps in essence the hot cylinder runs leaner than the cooler cylinder which in turn becomes a richer cylinder......Richen both cylinders the same and the hotter cylinder becomes happy but the cooler cylinder becomes to rich.......Having two carbs sure makes it easier to tend to each cylinder independently giving each cylinder what it needs when it is at operating temperature.........Sure has smoothed mine out and hopefully make it last longer.......More useable power also......I have kits for the BS34 and others will be coming soon.........."


John again mentions his carb needle kits here:
mitigations for temp reduction were carb needles R/L

So, Near as I can figure XSJohn, and a few other people who bothered to test cylinder temps found that after a good hard ride the right side cylinder was hotter than the left by anywhere from 25-50 degrees Fahrenheit. One person speculates that this is due to the clutch cover being filled with hot oil and therefor not wicking away as much cylinder heat as the left side alternator cover. Apparently the carbs used did not affect the temp discrepancy, nor did the type of exhaust, aftermarket or otherwise.

As best I can tell John's solution to this was to ever so slightly richen the right side carburetor so that when the engine reached operating temps the right side would not run as lean, and therefore would not get so much hotter than the left. This, in his experience, resulted in smoother running, more even power, and and overall happier engine.

Now,
-Does it make sense from a mechanical and physical standpoint? yes.
-Does this sound like a bunch of ghost stories to upsell one man's carb needle kit? Maybe.
-is it worth enriching the right side carb a wee bit to see if it results in more consistent emissions/temps from each cylinder? yes, absolutely.

At this point I'm skeptical, but there is certainly enough information to prompt further investigation. XSJohn and some other people mentioned Dyno'ing a 650 with the carbs adjusted as John implies to verify his theory, although I couldn't find any mention of this ever actually happening.
I think the best way to verify the validity of John's "right side hotter" theory is to measure engine temps after various rides, both aggressive and relaxed, and see if the temp discrepancy is present. If it is, the next step would be to enrich the right side carb, although by what amount I am not sure. the easiest way I can think of is to adjust the mixture clip on the needle, although this won't enrich the cylinder mixture across the full spectrum of carb function (idle to wide open). However, I believe it would be enough to test John's "hotter because leaner" theory because a majority of riding is done in the range directly affected by the needle. cylinder temp data should again be collected after a variety of rides. We can then compare the data from the "balanced carb" rides to the data from the "right carb richer" rides and see if the cylinder temps were affected. Finally, emissions data would be helpful during both tests to see if the "balanced carb" bike's right cylinder does run leaner at operating temps, and if the "right carb richer" bike's cylinders run at the same mixture at operating temps.

If John is correct, and the right cylinder runs 25-50 degrees hotter than the left, and enriching the right carb fixes this temp discrepancy then we can all rather easily extend the longevity (and to a lesser degree performance) of our bikes. Please expand the information on this topic by linking to John's old posts or to posts others have made regarding a temperature discrepancy between the two cylinders of the XS650.

Lastly, a shameless plug; I upload all the progress I've made on my 1975 XS650B hardtail project to instagram (Muckroute). Give it a look if you're bored, or if you think you'd enjoy the self teachings of an amateur mechanic building his first motorcycle.
 
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grizld1

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I ran the question past Michael Morse once, and he mentioned that race tuners for Brit twins often "stagger jetted" the mains with a richer jet on the primary side. It stands to reason that the right cylinder of the XS650 would run warmer for the same reason: the primary side case cover is sealed, and the drive side is not, so that there's less cooling at one cylinder base than at the other. John's solution was well thought out. Since he was tuning for street use in the cruising range, not for full-throttle racing, he fabricated richer needles for the right side. My personal take was and is that the temperature difference wasn't great enough to worry about. Still, in every dead XS650 motor I found with a holed piston, the ventilated item was on the right, except for one. Note that all of those motors except the one with the holed left piston also had breaker point ignition that had been dialed in to the "F" mark at full retard and was advancing well past 40*, and one had stock jetting and no mufflers as well.
 

LA_Rider

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I ran the question past Michael Morse once, and he mentioned that race tuners for Brit twins often "stagger jetted" the mains with a richer jet on the primary side. It stands to reason that the right cylinder of the XS650 would run warmer for the same reason: the primary side case cover is sealed, and the drive side is not, so that there's less cooling at one cylinder base than at the other. John's solution was well thought out. Since he was tuning for street use in the cruising range, not for full-throttle racing, he fabricated richer needles for the right side. My personal take was and is that the temperature difference wasn't great enough to worry about. Still, in every dead XS650 motor I found with a holed piston, the ventilated item was on the right, except for one. Note that all of those motors except the one with the holed left piston also had breaker point ignition that had been dialed in to the "F" mark at full retard and was advancing well past 40*, and one had stock jetting and no mufflers as well.
I realize that this is a really old thread, but from what I've read, if accurate, a pair of temperature sensors, one on each cylinder, attached to a simple microcontroller (perhaps even an Arduino?) programmed with requisite code could be used to sense the temperature situation, sending commands to servos afixed to the carbs to adjust the fuel flow, with feedback from the temp sensors closing the loop. Basically an ECU for the XS650 engine. Its just a thought.

Any Opinions?

LA_Rider
 

RustiePyles

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I realize that this is a really old thread, but from what I've read, if accurate, a pair of temperature sensors, one on each cylinder, attached to a simple microcontroller (perhaps even an Arduino?) programmed with requisite code could be used to sense the temperature situation, sending commands to servos afixed to the carbs to adjust the fuel flow, with feedback from the temp sensors closing the loop. Basically an ECU for the XS650 engine. Its just a thought.

Any Opinions?

LA_Rider
A problem as old as the motorcycle it self, almost all carbureted motorcycles have a delta T of roughly 25-50F from side to side or front to back. The problem was largely solved with EFI. Which is basically what you're proposing with fuel metering servos on carbs, except attaching a servo to a carb and metering fuel flow across the RPM range is easier said than done. It would be easier to just harvest an EFI system off a wrecked 2 cylinder bike and install it on the XS. Use of servos would require the use of a throttle position sensor, a pair of servo controllers, logic, a means of servo driven jet metering. All that cost and complexity added to still only have 45HP. The same can be achieved by simply going up one jet size on the main on the hot cylinder or raising the needle one clip. And to top it all off your only increasing fuel flow and decreasing economy to cool a cylinder, not really gain any performance. Also not really sure how you would adjust fuel flow on a carb with a servo, you would have to find a way raise and lower the needle independently of the slide or find way to increase/decrease jet size without use of a valve. Using a servo to rotate the throttle shaft would manipulate air and fuel flow causing an imbalance between the cylinders.
 

grizld1

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Amen, RP! The reason for the temperature difference is known. The fact that it's not unique to the XS650 is known. That millions of air cooled engines have operated well for decades in spite of temperature differences between cylinders is a simple observation. Bottom line: That which is not a problem does not require a solution.
 

grizld1

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If anybody is still fretting over right cylinder heat, I suggest that they mount a pair of temp gauges with ring sensors that mount under the spark plug washers and ride both ways with a crosswind blowing. That little experiment demonstrated to my satisfaction that stagger jetting my carbies wasn't worth doing. The difference between the windward side and the leeward side will show greater than the straight-on difference between left and right.
 

RustiePyles

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If anybody is still fretting over right cylinder heat, I suggest that they mount a pair of temp gauges with ring sensors that mount under the spark plug washers and ride both ways with a crosswind blowing. That little experiment demonstrated to my satisfaction that stagger jetting my carbies wasn't worth doing. The difference between the windward side and the leeward side will show greater than the straight-on difference between left and right.
Where did you get ring probes?
 

Jim

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Amen, RP! The reason for the temperature difference is known. The fact that it's not unique to the XS650 is known. That millions of air cooled engines have operated well for decades in spite of temperature differences between cylinders is a simple observation. Bottom line: That which is not a problem does not require a solution.
Well said Dick. And to expand on what you said above about holed pistons.... if you're running lean enough to hole the right piston, the left is only about 25-50° away from doing the same.... in other words, you're way too lean to begin with.... and which one holes first is just splittin' hairs.
 

Jim

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https://www.aircraftspruce.com/catalog/inpages/mitchcht.php


1652815403800.png
 

gggGary

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got a set of plug ring probes with a dual gauge in the carb bins. Probably from a 503 Rotax, never was motivated enough to try em on an XS
The ultralight aircraft 2 stroke guys run em. Long perieds of WFO with increasing altitude makes them a must watch.
 

gggGary

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2 into 1 exhaust and holed pistons a popular combo. those 2 into 1 are pretty efficient. Installed by dummies that have no idea what rejetting means and gggGary ends up with another "used to run" barn find.
One I bought, the PO admitted the tale; installed a MAC ran fine around the area for several months then he headed to minneapolis, made it about 100 miles on the freeway before most of the engine oil exited via the RH cylinder.
When I asked if he jetted for the pipe I got a blank look. "Case closed"
 
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grizld1

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I've seen exactly one TCI bike with a ventilated piston. All other cases had breaker points systems. In some the advance curve had stretched due to wear and the points were timed to open at the idle marks, with advanced timing left to fall where it may--waaay before 40* BTDC. In a couple of others the advance governor had done a comealoose and the owner had tried to "ride through" the misfires. In some cases the ignition defects were been found on bikes that had exhaust and/or intake tampered with. A little ignorance goes a very long way.
 

dps650rider

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I'm retuning my BS38 carbs after putting in throttle shaft seals and replacing carb holders. Just on plug readings I believe i can see the difference in temps. With carbs set identically and synced and after setting float levels and verifying with a sight tube the left plug runs just a bit darker than the right. I ended up shimming the left jet needle with a 0.037 mm washer to make them look about the same.
 

dps650rider

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One more thing, I have had a couple engines in my bike and between them and used parts I have bought I have seen 3 right side rod small ends with some damage and 2 right pistons where 1 was siezed and the other was scuffed. IMO this is definitely worth addressing.
 

RustiePyles

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Watcha plannin' Fletch? I might have a few in my airplane stash. Want I should look?
nothing specific, but I like having an assortment of temps probes at work for getting baselines on automation equipment. I also think a ring probe or two would be handy for running bikes on the lift during tuning. I have an automotive O-scope that has probe receptacles.
 

gggGary

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Dug in the bins the other day and what I (could find :shootme: ) was two sets of 2 exhaust probes (EGT) with a dual needle gauge. hose clamp holds a 1/8"? probe into a small hole drilled in the exhaust. Still think there's a spark plug ring gauge set somewhere.
 
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