1978 Xs650SE Barn Find

OE fuse box? It needs a cover. There should be no way for it to short. A replica fuse box is available from several vendors. A blade style box may make your life easier.
Yes, that is a very pretty motorcycle!
 
ElCamMan515 said:
I tried kick starting it in neutral, but it wouldn't grab. If I put it in 1st and pulled clutch in and went to kick start it, bike would want to roll.
Click to expand...
On these bikes the kicker engages the clutch/tranny.... which transfers to the engine. When you pull in (disengage) the clutch, you're not spinning the engine... it's been disengaged. The only way the kicker will work is with the tranny in neutral and the clutch engaged.
 
Last edited:
Jim- thanks for the info I had no idea.

I took the bike about 20 miles round trip today to get it inspected.. I was able to get into all gears but bike seemed like it lacked power. Rpms would stay between 4-5k in all gears and was hesitating when giving throttle, but then would start to pull. I hopefully can do a dead cylinder test and check for air leaks this weekend.

As I said before this is my first bike, but have been reading a lot on the forum to get me this far.

Thanks everyone,

Tim
 
ElCamMan515 said:
Jim- thanks for the info I had no idea.

I took the bike about 20 miles round trip today to get it inspected.. I was able to get into all gears but bike seemed like it lacked power. Rpms would stay between 4-5k in all gears and was hesitating when giving throttle, but then would start to pull. I hopefully can do a dead cylinder test and check for air leaks this weekend.

As I said before this is my first bike, but have been reading a lot on the forum to get me this far.

Thanks everyone,

Tim
Click to expand...
Sounds like Slide diaphragms to me.
 
I'm really not sure. It was an oddball assembly only used in that carb set so the aftermarket hasn't reproduced them much, if at all. If the diaphragm is indeed bad (is torn or has holes in it), you could get just a replacement diaphragm from JBM.

Take care if shopping eBay. The carb diagrams for the '78 Special are wrong. They show the BS34 carbs which didn't come along until 1980. Many of the sellers on eBay go by these diagrams so will list BS34 slide/diaphragm assemblies as fitting a '78. They won't.
 
I'll look up JBM thanks 5twins. When I rebuilt the carbs the diaphragms looked good, but the bike sat for at least 10 years so they could have micro cracks I didn't see.

Tim
 
ElCamMan515 said:
I'll look up JBM thanks 5twins. When I rebuilt the carbs the diaphragms looked good, but the bike sat for at least 10 years so they could have micro cracks I didn't see.

Tim
Click to expand...
I usually hold them up to a desk lamp in a dark garage, you'll all sorts of holes you couldn't see before. If slides for those aren't available it might be worth switching to the earlier style <77 BS38's. The outward appearance would be exactly the same but parts availability is better. Then there's always BS34's from 80< or aftermarket VM34's.
 
AS I usually do I wait a while after upstarting
Is the idle setting such that it remains low with a warm or cold engine was the choke in
Does the throttle cable allow for a snap back after blipping the throttle
That can be tested without a running engine .
And by hand on the idle arm on the left side ..not sticking or hanging.
It can get better after a while after the throttles has flexed a bit
Was the tank inspected so not rust is going down to carburetors.
If it has been sitting .That is a must .
I have had virtually no carburetor problems over 35 years .
I have seen diaphragms almost worn through
But since the bike ran lately I am at dirt or adjustment upstart
Cant rule out electrics since fuses are blown

But having said that taking out the throttles slides and inspect the membranes
And at the same time wipe clean in the bore makes sense since it is simple to do.
 
You can test the diaphragms to see if they're sealing and holding vacuum. Raise the slide with your finger and cover the oblong hole or slot at the top of the intake. Let the slide drop. If good and sealing (or no holes) the slide will drop very slowly (about 15 to 20 seconds).
 
Thanks for the input everyone. I ordered 2 diaphragms from JBM. I will see how well they ones that are in carbs now are sealing and if needed I'll have new ones to replace them with. I didn't have any issues today regarding the electrical system so hopefully that is fixed. I'll let everyone know my findings.

Tim
 
JBM has an addendum to their diaphram installation in regards to the slides turning - note it.
It might not be an issue with the bs34 slides that don't have a bevel at their bottom or the 38's if any of them don't have the bevel but my '78 bs38's terminate with a bevel and it needs to face rearwards. It so happens that some slides will turn within the new diaphram (surprise!) and the remedy is a spot of glue to hold them in place. I used a spot of gorilla glue on mine.....no problem.
 
Update:

Had a few moments between dropping kids off at school and going to work so I did some troubleshooting. I performed the diaphragm test and both moved slowly down and moved freely, I don't believe my diaphragms are bad. While bike was warming up to do a dead cylinder test I noticed the nut on the throttle cable bracket was loose. I tightened it back up and let bike warm up. I was wondering if a loose throttle bracket would cause the issue I experienced yesterday? I was not able to go for a ride as it is raining and had to head into work.

I was able to do a quick dead cylinder test, but right side is back-firing. What is the cause of this?

Below is a short video:
https://youtube.com/shorts/cz5vv0OxN78?feature=share

Thanks for everything everyone!

Tim
 
ElCamMan515 said:
right side is back-firing. What is the cause of this?
Click to expand...
Stock points? Back fire on one cylinder is usually breaker timing, check your gaps/timing & clean your points. Also make sure your advance unit is free and functional. A loose throttle cable could cause wandering/hanging idle. Let us know if that went away after tightening it.
 
Yes Sir
Best running XS 650 I have ever heard -- Only joking
A little minor plopping .. on a cold engine been sitting for 10 years.
If the tank is clean and a couple of longer runs
Fresh gas Gone through we can consider the Points inspection.
# 39 Mr R Pyles above
Besides cleaning them ..
Nothing major yet.
Wont hurt to check the bolts on the exhaust.
And if you have a strobe light a quick check of the ignition timing.
I would be surprised if it is off
Is it easy starting ??
If you like you can upload a blipping of the throttle we can see if the timing is about right
On the response.
Stay cool and give the right blinker a kick upwards ( Joking again )
 

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