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Proper Cam timing of 86XR600

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Just wondered if someone could explain what I am missing on timing my friends 86 XR600,have been going by manual and still pops under power and starts hard,bike does have a thumper cam I am told as he bought it with a new piston in it and the cam also it had both exhaust valves bent when we tried to start the bike so we swapped the head and got it running but unable to make it run right so any help is appreciated thanks guys:banghead:

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They're real easy to time... Just pull the cap off the stator cover, and line up the "T" mark on the flywheel with the little cut in the top of the hole under the cap. Then, line up the cam sprocket so the two marks on it are flat with the top of the head. The lobes on the cam will either be up or down, and it doesn't really matter which way they are, there's no half round off, it fires the plug every round like a two stroke since the pickup is on the crankshaft and not the cam. I usually do it with the lobes down just to make it easier to put the cover on the head with the rockers, you're not fighting the valve springs like that.

As for popping under load and just not running right, it sounds just like what I'm fighting with my '86 right now. I've posted a thread about it and got some very good info. I'm leaning hard towards weak spark, and suspect that the stator is at fault. I'll try to change it soon and see, a guy here is sending a stock one for me to try. Mine always stars with one kick hot or cold, and idles all day long though. It's only under load or higher speeds that I have a problem. Here's that thread:

http://www.thumpertalk.com/forum/showthread.php?t=882822

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I would probably have to say that the valves are bad or not sealing properly. The seats might be worn or some other mechanical black magic. But, your valves are probably out of spec. Try adjusting them.

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Thanks for the info guys gonna work on it tonight with him and see what happens,that is how we adjusted the cam the first time but when it started popping under load he was second guessing himself so he tore it back apart to double check,now I know it is correct so we can move on and look at other issues,will keep you posted if I find out the breaking up under load issue

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Ok we rechecked the cam timing lined up ok with t mark and cam gear so that is ok,swapped the CDI and Coil from my bike no change,removed carbs and disassembled,cleaned and re-installed them also no change,gonna try my carbs next bike seems lean plug does not get wet,still pops and misses under load and won't start now without pullstarting,if carbs don't do it he wants to pull top end apart again and inspect the valves since he bought the bike with 2 bent exhaust valves,still scratching my head on this one

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Check for weak spark and if you find it, check resistance on the stator windings and pulse generator. The following is for '88-90 XR600s, but it will give you idea if the resistance readings are in the right ballpark.

5a8f5ed5.gif

If spark is strong and you're still having the current problems, then it's realted to either fuel, air, or compression. Will it fire on starting fluid? If so, then it's definitely fuel.

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Is the cam chain tight on the top gear? If you try to pull on the chain, up and down, there should be little to no slop.

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I would tend to agree with it probably being the stator. It sounds just like what mine is doing, with the only difference being mine will start and idle fine, it's only under load that it acts up, and it gets worse as it gets hotter.

I should get the stator in soon that Scott sent for me to try. If it turns out that mine doesn't need a stator, I'll have two good ones then, and will be happy to pass it along to you to try... :banana:

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Timing chain tension seems to be ok,had to take loose at cam to roll around and set the timing,will check out the stator also,the lights on the bike don't work and most of the electrical connectors have a brown burnt look to them that makes me suspicous of the electrical system on this bike

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The wire from the lighting coils on the stator should run directly to the voltage regulator on the bike, a little box under the seat with some cooling fins on it. I've got a wiring diagram I saved when I was working on mine the other day, it's on my laptop though, I'll have to post it later.

Nevermind, found it on this one... :banana:

xr600r_1985.jpg

If you click the link it's a little bigger, text is easier to read...

http://i447.photobucket.com/albums/qq197/keithluneau/xr600r_1985.jpg

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Well I checked stator resistance and its ok,cleaned the flywheel and stator area,removed cylinder head and rechecked the valves which look great seats and stems are good,swapped out the carbs for my set and bike runs the same,seams lean but idles ok once started but is very difficult to start. Is there a chance that the larger cam can cause this not sure what it is he was only told it was a thumper cam when he bought the bike but that guy wasn't the one that built the motor,seems like the larger cam would need more fuel so the carbs can't keep up without some changes to them,just trying to help my friend out before he lights this bike on fire or sells it :banana:,told him its not worth much without fixing it

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Just an update,swapped out the thumper cam for stock and bike seems to run better and start better but issue is still there,does have some improvement though still frustrated with this one:foul:,really leaning toward a carb issue even though we swapped them out with another set that set hasn't been used in some time either,bike never seems to foul plug so suspect it is no an ignition fault but is lean condition which would explain the hard start issue it has,still trying to keep friend form swapping or selling off and fixing the issue:smirk:,sorry to hear your bike hasn't been fixed yet Keith was hoping that did it for you with the stator your bike seems to be acting similar to this bike and was hoping your fix would solve the mystery with this bike also,does anyone know if you can still get carb kits for these old dual carb bikes anymore? Thanks for everyones input and suggestions:thumbsup:

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Another update and problem solved,switched out the pulse generator and no change so I swapped out the CDI box and ignition coil together and problem solved,starts better when cold and no longer breaks up when under power acts like a different bike

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Ha, I was just coming back to the forums to update my situation. No matter what I changed, nothing fixed it, only thing I hadn't tried was the CDI box. So I bought a new one, put it on this evening. Started first kick and runs like a new bike! :thumbsup:

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I was wondering how your bike was coming along Keith,good to hear yours is fixed also,I am going to re-install old CDI box to confirm it was that or the coil that fixed it he was to busy riding it until he broke his foot from starting it guess he should have boots on:lol:,still does start hard though but gas drips when you try to start so now I think it is a carb issue yet but it runs way better then before:thumbsup:thanks for all the help guys

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Yeah, mine will drip a little from the overflows when I'm rocking it around starting it. If I ride it slow through the trail by my house which has a lot of hills and bumps, I'll notice some gas on top of the motor. (no drain hoses) I need to check the float levels, but I did before and they were spot on. Maybe it's normal for them to leak a few drops as the gas sloshes around in the bowls. Mine does start with one kick cold, and will idle until you're tired of hearing it run... I do have an issue though, with it coughing when coming back down to idle when riding it. Nothing major though.

One other thing to note... I had went up to 125 main jets, from the 122 stock. I have a Uni Filter in the stock box with no snorkle, and a Jardine 2" pipe. The bike was running a little weak and smoking black. I put the 122s back in and it woke it right back up. Plug looks good to, so I'm leaving them. :thumbsup:

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Just wanted to say one more thing... I just went out and reset my air screw, set it a touch on the rich side, and the spitting and coughing while coming back down to idle completely disappeared, the bike is running like a dream now! :thumbsup:

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