1978 XS650 Special Project

That was a very bad product they were selling back then.

Bad isn't the word I'd have chosen.... :wink2:

I found pics in my camera of the machining angle and mine is pretty much perpendicular with the face.
To avoid any distortion from the camera, I tried to take the photo as far away as I could, then zoom in and then cropped. This gives a better representation of the angles than if you take a photo just a foot or two away.
You can see how the casting is off though as stated before. I'll post this also to the other thread.

Machining angle is correct for New MikesXS Front Guide

Original (top) and MikesXS (bottom). You can see the casting was done wrong for the bosses even though it was machined at the correct angle.


Original (left) and MikesXS (Right) Note the A0147 in the casting between the 2 threaded holes..
On the lower right, you can see the plastic that FULLY de-laminated off the original. I caught it in time before the chain dissentigrated the plastic.
You can do it that way. I think that's the way gggGary likes to do it. I like to check/adjust it as the engine sits there idling. I also like to do it on a warmed up motor. If you set it on a cold motor, it may end up too tight once hot and with the parts all expanded due to the heat. Most of the tensioner parts are the same on the type D and type E assemblies. The exception is the longer type E plunger of course, but the adjuster screw may differ in length as well. This was due to the 1mm thicker rubber/metal damper washer used on the latter type E assemblies. So, measure the length of your adjuster screws and whichever one you use, pair it with the correct damper washer (60mm long screw + 2mm thick copper damper washer or 59mm long screw with the 3mm thick rubber/metal damper washer). If you mismatch the parts, you'll get one of these scenarios and adjustment will be more difficult and confusing .....

View attachment 258343

One of these is what you want ......

View attachment 258344

I've revised my thinking on the head nut torque values, keeping them in the 28-30 lb. range now. I have tried up to 35 lbs in the past but I could feel it was really putting a strain on the studs. I do feel 25 lbs isn't enough. Also, this is on lubed fasteners, so you're actually applying more torque than on a dry fastener. So, for yours, I would remove the fasteners one at a time, lube them (I use anti-seize), then reinstall and bring up to around 25 lb. Once they're all done, go back and bring them up to 28 lbs. There's also the two bolts under the spark plugs. These are part of the head bolt fastening pattern so need to be checked when torquing the head. They are smaller so the torque spec for them is less (14 to 16 lbs I think). Again, if you installed them dry, remove them, lube them, then reinstall and torque. And lastly, there's the small M6 bolt at the rear between the carbs. Once the engine is installed, it's difficult to get a torque wrench on that one so you may just need to check and tighten it (if need be) by "feel" with a wrench. Just make it the normal tightness you would use for any other M6 bolt on the bike.

Just double checking this post because I THINK it looks like the 60mm screw * copper damper washer (original to my 78) is Shorter than the updated one correct? here is a pic of the 2 side by side. The LEFT one is the one I"m putting in. The left one is LONGER because it has to fit both the locking nut, copper washer (shown on the left) plus enough room for the acorn nut. Correct? It looks like the amount of spring compression is consistant between the two.

I'm swaping these as I'm working to pull the carb apart and change the jetting to richen things up today.
So, This is stock specs for '78 according to my research
Main 135
Pilot 25 (edit: it is 27.5)
Needle 3 (center slot)

What was in the carb as I just pulled apart
502 Needle
Main 135
Pilot 27.5
Needle 3 (center slot)

What I am setting up right now to test
Main 140 (2 richer)
Pilot 30 (1 richer)
Needle 2 (2nd from top) to lean out

Cleaning up that needle too cause I never pulled it out the first time I rebuilt carbs.

Last edited:
Measure the length of the cam chain adjuster screw you're going to use and pair it with the appropriate damper washer (60mm long screw w/ 2mm thick copper washer or 59mm long screw w/ 3mm thick rubber/metal washer) .....


From your video, it looks like you've matched up the parts correctly because the plunger is coming out just flush with the end of the screw. I've tried both the copper washer and the later style rubber/metal one and found no difference in the way they operate or the noise level. However, if I have a 59mm screw available, I do like to use the rubber/metal washer. I figure it's probably a little softer than the copper one so should pad the plunger better when it contacts the back of the housing.

The stock pilot jet size for the '78-'79 carb set was a 27.5.
I stand corrected on the pilot jet. I thought I used that table to take my notes but looks like I looked it up wrong. I edited my post above.
So, I took a 20 mile ride and it was 47F out. It pulled and did not bog. It however was sputtering/misfiring (some) near idle throttle and some decel.
Overall it was a good ride.
It also was cutting out at idle when I got back to the house. I thought it was the idle mixture and was prepared to do some adjusting tomorrow but then I just looked at the pics of the plugs I took at the end of the ride.
Yup, Left plug I must have dropped or something and the gap was nearly un measurable. Before posting, I reset the gap and idled it in the garage a little and seemed to be ok, but I'll take a ride Sunday to see.

Oh, on the cam chain tensioner, One issue with the swap. The tensioner sticks out more, so now it made it much harder to pull the carb. Before, only the Nut got in the way of easily pulling the carb. Now, the tensioner main threaded part gets in the way. So I pulled it back out replaced carb and then put it back in, reset the tension then till I can get some suggestions.
ught it was the idle mixture and was prepared to do some adjusting tomorrow but then I just looked at the pics of the plugs I took at the end of the ride.
Yup, Left plug I must have dropped or something and the gap was nearly un measurable. Before posting, I reset the gap and idled it in the garage a little and seemed to be ok, but I'll take a ride Sunday to see.
It is those little "gotcha" s that make things interesting.
Your jetting sounds good. It's what most of the '78-'79 carb sets like for your basic minor mods (pods and pipes). However, some are happier with another step up on the pilots, to a 32.5. But tune your mix screws first. If they're set too lean, you'll get that popping on decel. The factory spec is 2.25 turns out, but that's really just a suggested starting point. You should fine tune them from there to find the best setting. What you're looking for is the "sweet spot", about a half turn range on the screw where the cylinder you're tuning runs fastest and smoothest. Go past this ideal setting range in either direction and the speed should begin to drop off and the cylinder will begin to run rougher and stumble. You should be able to hear this and tune it "by ear" just by kneeling next to the cylinder and carb you're adjusting. So, start with the screw set to the factory recommended spec then open it ¼ turn at a time, waiting a few seconds between turns to let the change have an effect. I like to set mine at the rich end of the "sweet spot" range, as rich as I can get it before the idle speed begins to drop off and stumble. I find this helps alleviate the popping on decel. If you need to go much past 3 turns out to find the "sweet spot", I'd say you need the 32.5 pilots.
thx 5twins.
Previously I was at 3 & 3 3/4 turns (right being 3 3/4). I reset the rigth float to be a little lower (higher fuel level) so with new jets I ended up today at
L 2 1/8 and R 2 1/2
Of course, with the spark gap wrong, I'll have to re do the idle mixture and sync again.
I'll do it by ear first and see how it goes instead of using the colortune. I'm used to the colortune in the 4 cyclinder XJ650 cause w/ 4, its much harder to tell how that one cyclinder is doing with the other 3 unless your WAY out of tune. I may also have not warmed the bike up enough when I colortuned it. so I'll let it warm up more, maybe even take a ride in the neighborhood first.
Yes, float level is very important. If it's off, adjusting the screws may have little to no affect.
Still cold here in the high 40's.
Set the spark gap on the BP7ES plugs to 27/28, cleaned them off and then tried to sound tune the idle. Not sure how well I did but ended up at 2 1/2 & 2 5/8 turns out. Still think low end is a TAD lean but after warming up, it was sounding really good on the road and at stop lights. Did a short 25 mile ride.
Seems as if this bike likes 4K RPM.
Thx everyone for the suggestions.