Motor won't run after a valve job

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

Ok so I checked everything once I got it back from the mechanic and it's still not running. The guy that put the valves in is a car mechanic, he's also worked on motorcycles in the past, but I'm beginning to think he may have done something wrong.

The bike has good compression on both cylinders now (it used to have zero on the right side) the battery's good, there is a spark on both sides, and there is fuel in the carbs. (I'm even spraying carb cleaner straight in there)

When I kick it, it will backfire at times but this happens noticebly after I finish the kick. In other words I kick it and then it backfires seemingly on it's own. Does this mean that the timing is set way off?

I would really apreciate if someone could tell how to check/set the timing because I have no clue. In the service manual it says to get the engine running and use a timing light.

kingwj

Here you go. You need a test light or ohmeter. The attached files should help you out.

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

Thanks a lot for the instructions, it looks pretty easy. This is definitely much better then the service manual. I'll try to do it tomorrow.

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

Ok I tried to do it but I still can't get this damn thing to work.

The ohm reader should read zero resistance at the point that it fires right? But when it reads zero resistance on the F mark fully retarded, it will read zero way to the right of T on full advance. It should read at the far left mark. But there's no way to get it to read at F when retarded and the far left mark when it's fully advanced. Maybe there's a typo in the directions, it says when the weights are squished inward its retarded but when they are opened up it's advanced, is that right?

Ohh and when I crank it with the starter, there is a spark between the gap of the right cylinder points, but not on the left. What does this mean?

kingwj

You are only worried about where the points open, that is where the mark should be over the F. Make sure you are turning the engine anticlockwise to time. The points opening breaks the circuit and causes the magnetic field in the coil to collapse and generate the spark. When the points close power again flows to the coil creating the field until the points open again. There fact you have sparking on the right points leads me to think a condensor is bad. Switch the points leads and see if the spark switches to the other set of points. You shouldn't see sparking as this will wear the points quickly.

The ignition advances as the motor spins up and centrifigal force opens the weights. I would suggest you only check this using a timing light as advance up to a point is related to RPM and you might be getting a bad reading manually spreading the advance. You have checked to make sure the cam is timed to the crank? Also is the right point firing when the cam is at the power position? If you are off 180 degrees just switch the plug wires or leads from the points.

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

Ok the points open 180 degrees off from where they are supposed to. I also noticed that when the advance weights are opened up, the timing is retarded not advanced. Can you tell me what direction the advace is supposed to be spinning? Theres a little arrow showing how its supposed to spin but its rotating in the opposite direction.

I tried to switch the wires from the points (gray and orange), but still doesnt fire.

The mechanic told me that he put everything back just like it was. He marked the crank and rotor, but obviously something is wrong.

I really don't want to have to take the motor out again. Is there anything else I can try? Can you think of something that could be the cause of all this? You mentioned that the cam might not be timed to the crank, how can I check this?

kingwj

The point cam and advance turn the same as the engine. Are you getting spark at the plugs? An easy way to check cam timing is to remove the valve adjuster covers from a cylinder. Rotate the engine slowly and watch the rocker arms. The exhaust will close and the intake will begin to open. This is overlap and occurs at TDC so the mark should be on the T (or real close to it ) at that point. It is also the beginning of the power stroke for the other cylinder. I set my timing by moving the crank to the mark and then rotating the point plate until the points open

Cam timing at this site, tells you how to check with the engine in place:

Cam timing

grizld1

The ignition fires when the points open. When this happens your meter should go to infinite resistance, not zero. Be sure the point leads are disconnected when you try for a reading with the meter. Note that when the ignition is in the advanced mode (weights thrown out against the tabs by centrigugal force), the disc which is moved by the weights is pulled clockwise, opposite to the counterclockwise rotation of the advance unit body, and moves the point cam rod with it, opening the points sooner. A good way to hold the ignition in the advanced position is to hang a 10 mm. boxend from the point cam nut and hang a heavier wrench from the end of it, overriding the return springs. If things won't dial in at all, be sure the advance unit disc is correctly installed, with the marks lined up with the matching marks on the backing plate and the arrow visible.

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

It got really cold really fast here in Chicago. (one day it's around 50 the next day it's low 20s) I'm going to have to put off working on it till it warms up a bit. The mechanic's a good guy he didn't take any money until I get it running, but he's been really busy working on cars, so I can see how he could have messed something up. I did order the parts myself from Mikesxs, so I know everything should work fine.

The thing is that the points do open 180 degrees from where they are supposed to, the meter reads infinite. When the weights are pulled out, it retards timing instead of advancing it. I looked at pictures of the advance from before and it doesn't look like it's been put in wrong. For some reason my battery doesnt want to hold more then 13 volts (it's brand new, but I had it sitting for over 2 months without charging), but I figure it should still have enough to get it going but so far no luck even with the points wires crossed.

kclark316 · New Member Joined: Sep 20, 2005 Posts: 1 Location: mass

your govoner rod could be upside down or 180 degrees off Very Happy

What Happened to 650rider.com?

Yamaha xs650