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XR 650L NOT Starting After Top End Rebuild- HELP Please

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Hey Guys and Gals-

 

So I could really use some help here. I have a 1991 XR 650L that I bought a few months ago. Was running, but was smoking a bit, so I took the top end off to replace the piston rings  and valve seals. Took it apart, no problem. Took the engine to some great local guys here in Philly to re-hone the cylinder, replace the valve seals, check the valves, lap the seats, and clean the whole thing. Got it back, put the engine back together and bike would not run! It has spark, but it seemed like it was firing only on the exhaust stroke, which I know is ridiculous. It would turn and turn, but it would not catch. So I figured I put the cam, cam gear, or something back together incorrectly. It sounded like it was firing on only the exhaust stroke. I assumed timing was the culprit. 

 

So I took it back apart, and reassembled it to spec following the XR Manual I have (Haynes I think). Anyway, put the engine at TDC, put the cam in with the lobes pointed down so all the valves are closed, then put the cam gear on the cam with the "OUT" side facing out and with the two horizontal lines facing horizontal, and the one vertical line in facing vertically. Everything to spec it seems according the my manual and my common sense. 

 

So today, I put it all back together and its still wont start. Its doing the same thing. 

 

It has fuel, it has spark, the carb has not been touched. The spark plug will spark when its taken out and grounded. I even traded my friends CDI with mine and his bike still started up and mine would not, so its not CDI. 

 

I did not touch the lower end of the bike aside from taking the right side cover off. Nothing at the bottom has been touched, only the top. 

 

The only thing I can figure is that I left the Cam Plunger out of the top end, or it has pushed down in the head and I didnt see it. Regardless, would that keep the bike from starting? What does the auto decomp plunger do? I thought the plunger was only to keep the cam from rotating backwards in the event of a backfire. 

 

Here's to hoping Thumper Talk can help. 

 

Any advice appreciated. 

 

Thanks. 

 

Memphis Stout

Edited by Memphis Stout

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Yes, i believe you are both right- that it fires at every TDC with a waster spark. Not sure about the gas smell. 

 

While looking at the parts diagram, Im pretty sure that I dont have a Cam plunger installed on the bike. Dont remember if I took one off or not, but Im sure I didnt put one back in. It could be that its stuck in and I have not noticed it. I am running a stock cam. Could that keep the bike from starting? 

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If the spring and plunger that run in conjunction with the decomp mechanism on the cam aren't in the head the bike won't start or run...

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If the spring and plunger that run in conjunction with the decomp mechanism on the cam aren't in the head the bike won't start or run...

Wont run???or just wont turn over because of compression?

   my auto decomp didnt work, figured it was removed, i used the manual one, all good.

  when I removed the clutch cover, I found the plunger and spring laying in the bottom of the engine!

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Wont run???or just wont turn over because of compression?

   my auto decomp didnt work, figured it was removed, i used the manual one, all good.

  when I removed the clutch cover, I found the plunger and spring laying in the bottom of the engine!

I can only go on what I know or have experienced first hand. If you have the auto decompression system on the actual cam and

you neglect to install the spring and plunger the bike will not start or run..Been through it with my current bike,,seen examples of it

here before. In all instances putting the spring and plunger in or removing the entire mechanism from the cam fixed the issue..

Conclusion..That's what the problem is or was and that is the fix..On a 650L you plainly can't just remove the entire mechanism

from the cam as they have no kickstarter nor no hand operated decomp lever..600s it's not a problem as they have a kickstarter and

manual decomp lever..

 

Yes the engine will turn over if they are missing,,It simply will not fire or start.,Maybe I should say,,The 600 will turn over as you have

the manual decomp lever on the bars to ease compression,,What a 650L does I'm not sure as I don't own one or haven't seen anyone say..

Then again if the 650L had some massive compression piston in it it may not turn over at all with the battery system..variables come into play.

Edited by Horri

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Well if you know that parts are missing, you need to replace them.

Have you checked the valve lash?

If you see that it's sparking on the exhaust stroke, can you see if it's firing on the compression stroke too?

Have you tried starting fluid? Is the air filter clean?

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Thanks you Horri and Heart_of_darkeness! 

 

I have ordered the part and am waiting with bated breath. 

 

I hope my next post will be a video of my bike running!!

 

Stay tuned!

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Gentlemen-

 

YOU WERE RIGHT!

 

I bought the plunger and spring and put them both in and the bike started up immediately!!!

 

Thanks again for your help. I hope this post helps others who have trouble starting their XR after a rebuild. 

 

DONT FORGET THE PLUNGER!

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 I have a 1991 XR 650L that I bought a few months ago. Any advice appreciated. 

 

Thanks. 

 

Memphis Stout

1993 was the first year for the XR 650L   as far as I know  ( I have one so i see the cut off dates all the time when ordering parts )

 

If I am correct   wonder what you have ??

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So if it was running before, what happened to the original plunger? Just lost during the engine work?

I didn't know it existed, so I must not have noticed it when I took the engine apart. Apparently either guys who did my head work, or myself lost it. Regardless it was only $15 at Bikebandit and a lot of frustration, but at least she's running again!

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1993 was the first year for the XR 650L   as far as I know  ( I have one so i see the cut off dates all the time when ordering parts )

 

If I am correct   wonder what you have ??

Good Eye @Zimman! I have a 1994 XR650L, not a  1991. I just bought a 1991 Pickuptruck, so I must have that year on my mind. 

 

Thanks. 

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