XS650 Oddity

[Mickster]

Picked up an XS650 out of a pasture that has been there for 5 years. Been working/tinkering and got it running. Now not sure what I got.

The frame number 2F0 25xxxx shows it's a 1979 XSF. The motor number 4M4 01xxxx shows it's an 80 or 81 motor. I'm thinking 80 by the low number.

So, is it possible this came from the factory like this, or did some previous owner swap out the motor somewhere in it's almost 30 year life.

 

[Jim]

Numbers always matched from the factory.

 

[650Skull]

2F0-250*** is a 79 Special II. Spoke wheels, 19" front/16" rear, (the rims are alloy and one model only), Side Hinged seat, metal side-covers.



If the bike still has alloy rims they are rare.

Engine 4M4 is an 81SH...........

79 Bikes had BS38 Carbs, (Alloy Tops),but there were BS38's used from 70 -79 and the carbs set up changed every 2 years, and Points ignition.......

81 engines had BS34 Carbs, (Chrome tops), and Factory electronic ignition, (TCI),

Gonna need to identify the ignition system and carbs for diagnostic/repairs.......Some pics will help us help you.

 

[Mickster]

Yep, it has spoke wheels and aluminum rims, 19" disc front/16" drum rear, side hinged seat and metal side-covers. The carbs are VM38's with aluminum tops. It has electronic ignition, not sure what kind, and a green coil like what Mike's sells. Some kind of fatter exhaust headers.

So it seems somebody changed out the motor and put some of the 1979 stuff on it?

Or is it possible the factory put the 1979 frame numbers on, put in a 1980 motor, shipped it to the U.S. in 1980 and a dealer sold it as a new 1979? That just seems too weird doesn't it? I'm gonna go with somebody changed out the motor.

 

[Superjet]

Take the left side cam cover off and take a pic. That will confirm what you have for electronic ignition. Nothing = stock TCI, something maybe a genuine pamco or fake or something else (Boyer).

 

[YamadudeXS650C]

Nice bike for a "pasture find" !!

 

[gggGary]

The carbs are VM38's with aluminum tops.

Good looking bike!
Those are BS38's if the set from 79, a good year for stock carbs IF they've been rejetted for the exhaust.
Find and fix the problem that wad of electric tape is hiding on the RH spark plug boot.

 

[Mickster]

Here's a pic of the electronic ignition. Don't know what it is.

Also a pic of when I drug it out of the pasture where it had been a scarecrow for 5 years. Still had the 2012 plate on it.

When I took the carbs apart for cleaning, after the 3rd time, I made notes. The pilot jet is 27.5, main is 145, needle clip is in the lowest notch. Bike starts great, runs OK but after tons of fiddling is still running rich. I probably need new carbs, a professional rebuild, or somebody who knows what they're doing.

 

[5twins]

That oil sight glass on the right engine side cover came along in 1981. You have a Pamco ignition (or the recent knock-off).

You have a '78-'79 set of BS38s (same carb set used for both years) and the jetting is screwed up, not right for your mods. The 27.5 pilot is stock. That should be increased to a 30 or 32.5, what ever works best. The 145 mains are probably a touch too big. 140s or 142.5s would probably work better and be all you need. The needles are set at their richest position and that's no good. That's why it runs rich. Set the needles at slot #2 (from the top). That is one step leaner than the stock #3 (middle) position but will be required for the larger mains. Mix screws should dial in around the stock spec of 2.25 turns out, probably somewhere in the 2 to 2.5 turns out range.

 

[Jim]

I probably need new carbs, a professional rebuild, or somebody who knows what they're doing.

Or you could learn to tune them yourself.
The Carb Guide is an excellent resource.

 

[MaxPete]

That looks like a PAMCO ignition Mickster - it is good system which should perform very well for years to come. One thing to check is behind the RH side cam cover...

• a mechanical fly-weight system with cute little springs = the original ignition advancer;
• a plain aluminium rotor = there is a little blue electronics box somewhere else on the bike (it is called an e-advancer);

Either of the above will work fine - BUT - the original mechanical ignition advance system must be free of corrosion or schmutz to work properly and the mechanical advancer shaft that passes INSIDE of the camshaft should be cleaned and lubricated to ensure that it can do its job as well.

NOTE: do NOT attempt to bend any of the parts of the advancer mechanism. They are very hard and will break if you try to "persuade" them. Also - be gentle with those little coil springs - they need to be intact and they need to apply the same force for the system to function correctly.

Pete

 

[5twins]

Yes, the original advance assembly and the rod it mounts on are some of the most neglected parts on these bikes. Many have not been serviced (cleaned, greased) since the factory assembled them new.

 

[lakeview]

I really like your paint job. It came out of the field with very early direction lights; I see you have replaced them. Previous owner has blocked off a petcock, take heart that the last guy may have known what he was doing!.

 

[5twins]

Maybe for some things, but not about carb jetting, lol. It's not very often you run across someone who knows how to do it all. And these were a "budget" bike, many purchased by first time bike owners who simply didn't know much about bikes and their upkeep requirements, even less about how to properly modify them.

 

[Mickster]

Yeah, the inspiration for the paint job was Shamu.

I just checked and it has the weights/springs as the advance mechanism.

The previous owner or owners had some work done to it cause you can see the edges of new gaskets on the left and right engine covers. A new clutch I think and maybe some other stuff. The oversize exhaust has the reducers in it too.

The carb manual jimD54 turned me on to says when the throttle is wide open and then turned back a bit the revs pick up = too big a main jet. If the revs don't drop right away after shutting down the throttle (like when shifting) it's too small a pilot jet. If the exhaust pops when gearing down it's too small a pilot jet. My bike does all of those things.

I'm ordering the pilot and main jets from Mike's and will do exactly what 5twins said to do.

Another before pic just for fun.

 

[MaxPete]

and will do exactly what 5Twins said to do

Good. MANY people on the Forum have found that this is absolutely the right thing to do with respect to carb issues.

He knows his stuff....

 

[XSLeo]

Instead of getting Chinese knock offs from Mike's Why not get genuine Mikuni jets? Jets R Us or Niche cycle both sell the real deal.
The price is about the same.
Leo

 

[Mickster]

I did what 5Twins said.
The jets came in and are installed, needle position changed, carbs back on the bike, no other changes. Mike's didn't have a 32.5 jet, but I did get the140 and 142.5 main. But here's where we're at so far.
Pilot jet was 27.5 is now 30.
Main was 145 is now 140.
Needle was in the 5th groove is now in the second (from top).

Using the kicker, it fires right up. Runs for several seconds pretty good, then the idle starts to drop down and the bike stalls all on it's own. Fiddled with the pilot screws from 1 turn out to 3 turns out with no change. Fiddled with the idle speed adjustment and when upped caused the bike to stall even sooner.

When at idle giving it even the slightest amount of throttle the bike chokes and stalls. Can't get past even the smallest addition of more throttle which explains why the bike died even faster when the idle speed screw was upped.

The jets are probably right (I think?) but maybe the needle position needs to be in a lower grove?
What do you think?

 

[5twins]

Sounds like a fuel level problem. Have you carefully checked and verified float settings? Are the floats good and not leaking (taking on fuel)? Are the float needle and seat assemblies good (not leaking)?

 

[Mickster]

Thanks for the reply 5twins. The floats are at exactly 24mm and look good.

Here's an update. It still does the things as posted earlier with an addition. I've gotten the bike warmed up by running for short periods and kick starting it.
It goes like this. Bike is warmed up. Kickstarted with the enrichener on, bike starts and idles (not that great but idles), the moment I turn the enrichener off it stalls. It'll pop out the carbs every so often too.

With the enrichener on, I can snap or slowly twist the throttle and hold the revs at 3-4-5 grand no problem, shut off the enrichener while still holding the throttle and it just dies.

I've been reading the carb manual jimD54 said I should to the point of I got a freakin headache.

What should I do? Take the carbs apart again and check to make sure Mike's sent me the correct pilot jets? Lift the needle to the 4th or 5th slot? Put in the 142.5 main and leave the needle where it is?

Gentlemen, what would you do if this was the bike you were working on. Other than buy new carbs or look for the nearest dumpster of course.