gs 650 wont run, timing issues?

[rcklobster]

So I recently picked up an 82 GS 650 and have been troubleshooting it.

Here is what is going on:

I have a spark on all cylinders. The carbs have been cleaned and inspected and everything looks fine. The bike cranks over and pops and backfires out of both the intake and exhaust. So I suppose it has to be the valvetrain.

Someone has had the rocker covers off before, so I expect that is where the problem is.
I took the cams off and retimed them as the service manual says. I aligned the crank to the "T" 1-4 mark on the spark advance governor. I aligned the exhaust cam "1" mark horizontally to the outside of the top of the cylinder head. This is all looking at the motor from the right side. (Same side as the signal generator) Next I aligned the intake cam "3" (i think it was 3) mark to the 20th rivet down from the timing mark on the exhaust. The tensioner is functioning properly.

It didn't solve the problem.

Any ideas? Specifically, did I have the crank misaligned? Is it possible that the cam sprockets are misaligned on the cams? And finally, the notches on the cam ends are on the right side of the motor, the same side as the signal generator, they are not backwards are they?

Any help would be greatly appreciated.
Thank you!

[Nessism]

Did you clean the carbs by tearing them down all the way, soaking the parts, and replacing all the O-rings? Did you replace the intake boot O-rings? Did you adjust the valves? Did you service the air filter and make sure the airbox is sealed against the carbs? Is the bike stock or modified, and if modified with intake/exhaust mods, was the carb jetting compensated accordingly?

Please check my signature for some good info appropriate for new GS owners.

Good luck

[MisterCinders]

Your description of the cam timing sounds right. Did you check and adjust the valve clearances?

When you tried to start it, did you inspect the plugs? Are they wet?

Have you checked compression?

Even if your timing is right, if your valve clearances are too tight, you could have stuck/burnt valves. That will blow your compression, removing a critical element.

Also, did you check your ignition timing? Getting spark is good, but not if it comes too early or late.

HTH

[rcklobster]

Thanks guys!

The carbs were completely tore down and thoroughly cleaned. The airbox was off at the time. Would that prevent the bike from starting? The plugs are new and were wet after a few minutes of cranking. The bike is completely stock. I have a compression tester so I will test compression and that should tell me if there is a valve problem. I will also double check my timing again just to be safe. Does anyone know what cylinder the bike is actually timed off of? If I knew that I could watch the cams and be able to verify that they were correctly aligned.

[Steve]

Which 650 do you have?

I don't remember which is which, but one of them uses 20 pins between the cams, the other uses either 19 or 21.

Make sure you are looking at the right spec.

having the airbox off will allow it to start, but you won't go much higher than that.

.

[MisterCinders]

Definitely put the airbox back on. Even if you manage to start it without the airbox, you won't be able to diagnose anything from how it runs with that much (i.e., waaay too much) air flow.

[rcklobster]

Alright I'll definitely put the air box back on. Maybe that will cure it? If the compression is fine it should start cause it's getting fuel and ignition. The bike is a 82 gs 650g by the way.

[hjfisk]

Have you got your plug wires in the correct position?, 1-4 fire together and2-3 fire together Haven't got 2 crossed have you plus you need the air box

[tom203]

Put your bike year/model in your signature, so you won't have to remind us that it's a 82 650 G in later posts. 20 pins is correct between 1 and 3 for shaft engines. Was the cam timing far off when you first looked? Like hjfisk said, doublecheck plug wire positions - left coil fires 1 and 4 - it's real easy to misconnect as you tear into things. Did you bench sync the carbs? the throttle plates will appear almost completely closed when these are in the ballpark.

[rcklobster]

I will also check the plug wires. Yeah, the carbs have been synced. If I can't get it running correctly I will take and post some pictures of the cams and chain. I am over 99% sure they are correct but who knows? Anyway, I'll check the compression and plug wires, and reinstall the airbox. If that doesn't fix it, and the timing is verified, then it pretty much has to be a valve problem I would think.

[Steve]

If you feel you have more work to do that might involve removing the carbs, you can do one small modification that will allow the bike to run without the airbox.

fold a shop rag in half, drape it over the carb intakes. Secrure it to the mouths of #1 and #4 with hose clamps or zip-ties, making sure it's also reasonably snug over #2 and #3. This is not good enough for jetting checks, but will allow you to go for a test ride around the block.

.

[Suzuki_Don]

Cam Timing Can Be 180 Degrees Off

If the sprockets have been removed from the camshafts and replaced in the incorrect position then the cam timing on that camshaft will be 180 degrees out. When the cam timing has been done correctly with the "T" mark lined up and #1 on exhaust sprocket facing to the front of the engine and 20 links between #2 and #3 then the two notches on the end of the cams should be facing each other.




As per above pic.

[rcklobster]

Thanks guys! I got it figured out. The sprockets were boogered up. I got it back together and it started right up. Now the carbs just need tuned and the idle set. I do have a little smoke. Out the exhaust. Either 3 or 4. Hopefully it isn't hurt... might be rings. Can't be too bad but because she runs well. Thanks again for the help!

[IanW]

Hi Guys,

I have exactly the same problem as this. If you look at the picture below, on the left hand side the timing mark on the exhaust sprocket is aligned nicely with the gasket face on the head. However, as you can see under it, the slots on the cam ends are not well aligned. My buddy thinks we should rather set the valve timing as shown on the right, where the cam ends are better aligned and the arrow on the sprocket can go hang.
We tried it my way, and the bike won't start, even without carbs on starting fluid.
Next weekend we'll do it my buddy's way, but before we do can anyone tell me if my buddy is right?
Thanks,
Ian
cams.jpg

[IanW]

Well, just to close off this thread with the final answer, the arrow on the cam sprocket is the mark to go with, even if the marks on the ends of the shafts themselves look misaligned. As usual, the manual was correct. It did run with the cams aligned such that the marks on the end of the camshafts looked correct, but very rough. Moving the cam chain back one tooth so that the sprocket marks aligned made the bike run perfectly.
My problem turned out to be coil 1/4 firing when 2/3 should have been. Even though I checked the wiring over and over again, I still don't know why. Nor particularly care now that I have a running bike!