Bike will not start - running out of ideas...

[stange_dk]

Dear XS650 friends,

New poster here. I have a 1975 XS650B that refuses to start so I am looking for some help/ideas to where I could be doing something wrong.

The bike:

- VM34s with the correct needle
- Bigger header pipes with torque peak inserts and shorty mufflers
- Boyer Bransden electronic ignition (blue box)
- NGK BP7ES plugs, new. Big blue spark.
- aftermarket regulator/rectifier unit
- minimized wiring, no starter motor, flasher relay, etc.
- Cleaned up ports (not polished)
- New piston rings, +.25

The head and cylinder have been tightened down to torque specs. Checked that the cam dot is aligned with pistons at TDC. Set valves. Fresh gas in the tank.

The story:
Las season it began running poorly, killing plugs, running one one cyl. and smoking out of the right pipe. Turns out that compression was low and pouring some oil into the cylinder helped this. So I pulled the motor and put new rings in, put it back together as per the manual and popped it back in.

And now it will not start.

I can get a puff or two if I give it starter spray directly into the carbs but else: nothing. I tried pulling the VMs off and put the old BS carbs on (that it ran fine with back in the day) and still nothing. Put another Boyer unit on. The same.

Any ideas to what I am doing wrong?

Thanks a lot from a frustrated XS650 rider in Copenhagen

 

[retiredgentleman]

Is the Boyer Bransden timing set correctly? My knowledge of them is very weak, but I do remember that the timing must be set at full advance first.

Do you have good compression?

 

[Paulrxs650]

Hi, welcome and thanks for the detailed overview.

The only thing (I assume) that has been touched is the engine. So I would start there. It sounds like your timing is off. Check the timing is correct with the Boyer by making sure that the left hand (sitting on the bike) cylinder is on its compression stroke at the full advance mark. Then adjust the Boyer pick up plate so the white dot aligns through the hole.
You can also check that youare getting a spark from the Boyer unit. With a plug out and grounded against the engine, get the two wires from the Boyer that go to the pick up. With the ignition on strike them together and you'll see a spark (hopefully) at the plug.

Boyers are quite picky on having a fully charged battery too. Make sure your battery is putting out at least 11.5v the test above will determine whether or not it's sparking.

 

[CDNTX650]

The timing mark on your cam should line up with horizontal plane of the rocker box sealing surface with the rotor mark on T...thats how you have it forsure?

 

[stange_dk]

Hi all,

Thanks a lot for the quick replies.

I *think* that I set the Boyer right, but Paul's comment about the compression stroke makes me think.. Because I just lined it up with the timing hole - I didn't check that the left hand cyl. was on compression.

Gentleman: The compression was significantly better so I didnt pull out the tester, but will do that.

CDN: The timing notch in the cam is vertical (pointing up) when the pistons are at TDC. That's how it is described here: http://www.650motorcycles.com/CamTiming.html

One thing I forgot to mention: I swapped the bottom end on the '75 for a '77 bottom end because big bearings on the '75 crank were tired. Would this affect how things line up?

 

[Paulrxs650]

Hi, definately check the timing is set off the left cylinder on its compression stoke.

 

[stange_dk]

Thanks for the advice, I'll check tomorrow at the workshop and let you know!

 

[Scrambled]

I would go over your all your electrical connections and components seeing as how you minimized your wiring . . lots of reasons for your bike to refuse to start .

 

[CDNTX650]

Okay strange...notch up dot on horizontal plane. Good to go

 

[crescendo]

It could be the problem of fuel pump not pumping the right amount of fuel to engine to start. Or it could be the problem of kick start energy. May be the kick is not producing the right amount of electricity to start the engine.

 

[Paulrxs650]

Hi, there's no fuel pump on these bikes, they are gravity fed.
The Boyer unit requires a battery to maintain the necessary amount charge, so a normal kick will produce a spark.

 

[westonboege]

Sounds like ignition timing to me.... i would adjust the ignition timing a little advance and retard until it starts.

Also for the cam timing... the bottom end doesnt care which revolution it is on right? You just need the pistons at tdc and make sure the cam is set at the correct marks right? Ive had 3 or 4 top ends apart and never had any troubles. Just clarifying for my own head..haha...

 

[Paulrxs650]

Left hand cylinder (sitting on the bike) at the top of its compression stroke is TDC

 

[scabber]

Welcome to the site not much to add Paul and others advice should get you going. Sounds like you have a real nice bike a picture would be nice. Report back and let us know you make out.

 

[stange_dk]

Hi all, thanks for the advice!

I went through the wiring and there was actually one wire I hadn't connected but it was for the charging system... However, it should all be good now.

Also, I checked the valves to see that the left cyl. was on compression stroke when timing the engine. It also looks good. Put in a brand new battery and checkked that it's at 12,5 V.

So, I tried to kick it and still there's a good spark.

But it still does not fire at all. Not even a cough :/

I guess I'll play around with the timing tonight and see what happens. It's just weird since it normally fires up even on one cylinder!

Again, any suggestions are welcome... and I'll see if I can snap a photo of the bike tonight

 

[retiredgentleman]

What is the condition of the carbs inside? Are they clean, and are the float levels set correctly? Are the valve clearances set correctly?

I would again try spraying some starter fluid or gasoline into the carbs and try starting.

Do those carbs have a choke lever and are you using it? You need a rich mixture to fire up the engine.

 

[stange_dk]

Carbs have been cleaned and checked.

Checked valve timing and adjusted ignition again and tried to start it. I got a few coughs our of the right cylinder only.

Got the compression tester out and checked comp: not good. 51 psi on the left and 36 on the right.

I then poured some oil into the barrels and tested again: 54 psi on both... When I turn the crank slowly with a wrench I can hear a hissing sound. Kinda like opening a bottle of carbonated water.

So, it seems to be pistons, right?

 

[nj1639]

Either the rings, valves or the cam timing is off.
Swapped out the lower end so the cam chain was disconnected.....may be off a tooth or so, possibly need a bore on the jugs and a new set of pistons and rings.

 

[retiredgentleman]

I asked you if the compression was good in post #2!

You've had the top end, and the bottom end, apart once. Well, its time to do it a second time, but this time take it slow and do it right. Re-building an engine requires careful attention to detail.....................you made some mistakes on the first go around.

Take it apart slowly and read the Yamaha Servive Manual to find out what went wrong.

 

[jayel]

180 out on the timing?