Engine won't start, backfiring

[STVR]

Hello,

I just wanted to say this forum is pretty great I gotten a lot of help here and well I need a little more. So here is the issue, I just rebuilt my entire motor (75 XS 650) bottom and top end. The motor is in the bike everything is looking good. Getting it started seems to be a major issue right now.

I'm assuming its my points or the timing. I set the points to what the manual recommends and the seems to be closing and opening when they are suppose to (they are new points) the contact plate is set to the middle in between retarding timing and advancing it. When I kick it over doesn't seem like it wants to start and I get major back firing.

I'm assuming that I need to set my timing correctly or at least get it in the ball park so the engine will start. If this is in fact the issue can some one point me in the right direction to correctly set the timing. I don't own a timing light.

Steve

 

[5twins]

If you're going to own a bike with points, you're going to have to get a timing light. In the mean time, this will walk you through static timing the engine. You can get it very close but the only way to really know if it's exactly right is to use a timing light .....

http://xs650temp.proboards.com/index.cgi?board=ID&action=display&thread=7984

 

[TwoJugs]

Make sure your condenser is hooked up right too.

 

[STVR]

Engine still wont start followed all of the tips and instructions that 5twins gave me but she just doesn't want to start. Condenser is new coils new, I'm getting fuel and getting spark, I've messed with the timing for 4 hours tonight. Gapped points,followed instructions on timing using the light bulb connected to the points method. I'm stumped.

 

[hmusket]

Have you tried switching plug wires? Maybe connected to wrong sides?

 

[STVR]

the wires that go to the points?

 

[hmusket]

I was just thinking switch wires at the plugs, left to right, right to left.

 

[5twins]

If that fixes it then you have assembled the advance rod incorrectly.

 

[STVR]

I actually thought about that already I never switched the plugs but I did notice that when I lined up the rotor with the F mark (making sure the right side tappets had play in them) the piston was at the bottom and correct me if I am wrong but that piston should be at the top as the right side is getting spark to ignite and create an explosion. So I took out the advance rod and put it in with the pins up I think I did put it in wrong. Still didn't start up I went home after that.

 

[STVR]

When I did the timing I basically found the high point of the cam, gapped the points. Then did the right side made sure I had play in the right side valves. Lined up the rotor with the F mark. Then loosened up the backing plate (the right side plate first, then turned the rotor 360 to do the left side) and moved it until the points commenced to separate, but when ever i moved the backing plate the points always stayed the same I never saw them start to separate. I did this like 5 times

 

[5twins]

You won't see the points start to open. That's why you need the test light. It should be out and come on just as the points start to open. That should happen somewhere between the 2 slash marks designated by the "F" mark. There is a 2 or 3 degree range there that is acceptable for your idle timing.

I don't think you're using the test light properly. Remove both plugs so you can turn the motor by hand easily. Hook the test light to the right set (upper) of points and turn the key on. Rotate the engine slowly by hand using a wrench on the alternator nut. The light should be out as you approach the "F" mark with the mark on the rotor. The light should come on when you get there. If the light comes on before you reach the "F", your timing is advanced, after, your timing is retarded. Don't worry about what the valves are doing. If you need to adjust the right points timing, move the whole backing plate.

Once you've set the right side, repeat the procedure with the test light hooked to the lower (left) set of points. To adjust their timing, only move the half plate they mount to, not the whole backing plate.

 

[TwoJugs]

Try some starting f;uid sprayed into the carbs. a quick check on the fuel supply. If you get a pop r wanna start then start looking into the carbs. If nothing at al after a few tries then you must have an ignition problem. As long as you have the cam timed right and decent compression the fluid will make the motor fire with any close spark.

 

[Goldy]

Sounds like you've done your best to eliminate an ignition timing issue. You've had the engine all apart, right?....are you sure you timed the cam correctly? A quick check will confirm this: your exhaust valve should be just closing and the intake valve just beginning to open at TDC on the cylinder that is NOT firing. You can also check the ignition timing by slowly rotating the crank with the sparkplugs removed and sitting on the cylinder head...just turn the engine slowly in the direction of rotation and listen for the snap of the spark when the rotor marks pass the stator mark....make sure the plug that fired is from the cylinder that is at the top of its compression stroke (valves not rocking).
Gotta be something fairly simple, don't lose heart!

 

[STVR]

Thanks a lot for all of the suggestions. Gonna try and try again