Does right cylinder run hotter than left on these bikes?

XS650D

XS650D

XS650 Junkie
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I have spent countless hrs trying to tune my xs650 and have it running pretty good.
I noticed that if I pull my plugs the right cylinder plug is always a lighter grey colour on the
electrode tip than the left which is light brown or beige ,regardless of what I do, fuel screws,sync
screw, valves ect ect its always this way.I tried to adjust sync so that right cylinder runs richer
and plugs look the same BUT then the performance suffers.Is there away around this or is it an inherited
trait of the engine design , am I missing something in my tuning? Both cylinders give matching compression
numbers,cheaked valves many times .Should I tune for best performance OR balance carbs for plug color and heat range in the cylinders.Thx
 
There could be a difference right to left, can't think of a reason why. I remember that the two cylinder, two stroke, snowmobile engines that we had in the 70's used two different heat range plugs because of the huge cooling blower on the one side.

Scott
 
A looonnngggg time ago, there was this same question. One answer was that the Alternater makes a lot of heat that side. The left side. Why the RT side? Leaner burn? Advanced timing?
 
TwoMany,thx for the attachment,thats interesting info.Based on that I think I will reset my SYNC back to
spec for performance and even pull and tweak the jetting slightly on the right carb needle. I think thats a superior remedy.
Couple things I noticed maybe worth mentioning is there is a lot more rattle and engine noise on the right side
of the engine, very noticeable when cruising down the road, any one else notice this.The left side is very quiet (with everything both sides properly set).
Also I picked up 2 complete after market carb kits at Yamaha (sitting on the shelf for years and they sold me for cost to get rid off) that fit the 76 thru 79 model years. Some parts like mains are bigger 135,s. Pilot jets 127.5 (No needles) Complete choke assembly, all gaskets,Needle and seat assembly and all internal springs.I think this kit is more suited to the 78/79 but was able to use most of its worth it.
The part numbers on each part i.e.:needles, mains,pilots,fuel screw needles ect ect are the same as stock BUT
there fuel metering is slightly different that the stock Yamaha products.I have noticed this on pretty much every part.
They all seem to run slightly Richer than a Genuine Yamaha part (same size) Noticed it first on the Fuel/Air Screw or needle,definately richer.Visually looks the same
in every way but obviously different.I may try running the aftermarket stuff on the hotter side and stock stuff on the left.That just might be the ticket.Thx for listening to me ramble on!
 
Azman, you got it backward. The primary (right) side runs a little hotter because it's sealed. The alternator side runs cooler. Michael Morse pointed out to me that Brit bikes ran hotter on the primary side too, enough that some race tuners stagger jetted them. D, If you want to obsess over correcting a normal condition of the engine, by all means have at it.
 
XS650D, xsjohn(RIP) did extensive research on this and resolved it with/by altering the profile of the right needle. Threads can be found on the old 650Rider site. Search xsjohn needles and infrared temps. As far as getting a set (if you desire) you could post a WTB ad in the classified.

+1 on grizld1's post. It is the nature of the beast.
 
For years I've been wanting some sort of night vision, IR imaging. Wanna see my nighttime varmints, both 4-leg and 2.

This thread pushed me over the edge.

Just ordered a SEEK imager for my stoopidphone.

SEEK thermal XR.jpg SEEK thermal image.jpg

Will figure the thing out, then see what kinda images I get on my XS...
 
XS650D......................You can't use the sync control to change the mixture in cylinders. The sync controls the amount of fuel/air in a cylinder, which should always be equal in both. Use the mixture screw to fine tune the mixture (dead cylinder method works well).

Regardless, I would not be concerned about the plugs being a slightly different colour.
Its like chasing ghosts, this perceived difference in temperature of the two cylinders. If it does exist, IMHO, for practical purposes, it does not affect the everyday operation of the bike.
 
It was more pronounced on the later models with the more E.P.A. mandated (leaner) carbs. It shouldn't be much of an issue with your '77 carbs.
 
Yeah I may be obsessing a little!! Im running out of things to look at I guess.
Goin a leave it an just ride the dam thing. Ill be into a new rear tire an brake pads soon enough
and can play with that! Final question for the day, will bike run leaner or richer when really hot weather?
 
just a note; the Yamaha Royal Star venture; a liquid cooled V4 fueled by 4 mikuni down draft carbs, comes stock with 3 different size main jets in the 4 carbs.
"Stock jet sizes: pilots are #15, and mains are #122.5 for cylinders 1 and 2, #117.5 for cylinder 3, and #120 for cylinder 4. The staggered main jetting is a little strange. No one has a real good explanation for it, especially being a water cooled engine. But that's what they did."

Cylinder Numbering:

Front left = #2 Front right = #4

Rear left = #1 Rear right = #3

Primary is on the left...........
When an XS holes a piston. (lean) my informal surveys and dead bike experience says it is very likely to be the RH piston.
 
Interesting.....hard to imagine that the heat from the primary drive side can transfer that effectively all the way up to the head and affect the combustion process.

I do know that many 3-cylinder ring-dings (2-strokes) have richer jetting for the middle cylinder to help prevent piston distress.
 
weekendrider said:
XS650D, xsjohn(RIP) did extensive research on this and resolved it with/by altering the profile of the right needle. Threads can be found on the old 650Rider site. Search xsjohn needles and infrared temps. As far as getting a set (if you desire) you could post a WTB ad in the classified.

+1 on grizld1's post. It is the nature of the beast.
Click to expand...

With Johns needles and all else being equal, Autolite 65 in the left cylinder, 64 in the right.
Plug caps would have to be changed to accept the solid, unscrewable plug top of the 65 or grind the plug top of the 65 to fit the plug cap. XSJohn (RIP) recommendation.
 
+1, Gary. Every time I've seen a holed piston in an XS650 motor it's been on the right side. I'll add that all but one of those messes occurred on machines with breaker point ignition, and most showed ATU defects.
 
OK - here is another question on temperatures:

- I just installed an of DogBunnys dipstick-thermometer combo units in my '76 Stamdard. The thermometer read about 205-210 deg. F after a 6 mile ride on freeway and city streets.

Is that a value that you would expect?
 
Max you are at the low end of reported temps. IIRC they ranged from 205 - 230 kinda. There are a couple of threads from several years ago. I have experienced higher oil temps. Alarmingly high but the bike never seemed to suffer and is still rideable.
 
Hmmm - ok, thanks.

I had always thought that Lucille was pretty cool - but it's great to have confirmation.

Pete
 

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