help with my xr500r

[tredog500r]

I recently purchased a nearly immaculate '81 XR500R. When I picked it up, I test rode it and the only thing that was obvious was a small bit of oil leaking from the head cover. When I got it home and rode it for a longer time, the leak was more substantial. It also was idling erratically. I checked the valve clearance and it was right. I also tested the CDI and the coil. They both checked out. Now the more that I have run it, I have started to see a small amount of oil appearing where the head gasket is. Would a small leak in the head gasket cause the erratic idling? It runs strong beyond idle. I have also set the fuel mix screw to factory and that didn't change much. I have already ordered a new head gasket, would valve seals and exhaust gaskets also be in order. Thanks Tredog500r

[DGXR]

If the oil leak at the head gasket is small, it should not affect the idle quality so much. Exhaust gaskets might not be necessary, check the condition of the existing ones, and replace them if in doubt. If you're replacing the head gasket, throw in new valve seals while the head is off. And get an old worn out flathead screwdriver and scrape any carbon off the piston crown and combustion chamber (head/valve area), being careful not to gouge anything. You might replace the plug wire too, if it's old it could be causing a misfire. Hope this helps, good luck

[Horri]

My 82 XL500-R(Same engine basically) has a blown head gasket and a blown base gasket and the idling isn't affected at all. Its a bit difficult to start but once running runs like a scalded cat..I'll get round to fixing it sometime. but as is with engines it gets hard to build up the enthusiasm when it still goes well.

[tredog500r]

Thanks for the replies. I am now wondering if a carb rebuild might help. I took the carb apart and thoroughly cleaned and inspected it, but I didn't check the float level and the float bowl seal was hard to get back in the groove. Could this be causing the erratic idling? Thanks again for any help.

[Horri]

I don't know but shouldn't think so..I forgot to mention my 500 has a Flatslide Mikuni..carb on it..think its a 38mm.It was on the bike when I got it and it's forever leaking gas if you happen to leave the fuel turned on and its not running..no probs when it is..I also read a lot about float levels here and to be honest in 30 years of messing about on Honda four strokes I have never ever had to bother adjusting something like that to make a bike run properly..Now someones probably going to come along and say well maybe thats why the carbs leaking..I've checked it isn't but the needle jet may well be jamming open due to old age...I expect you've done the absolutely most basic thing and changed the plug..Its amazing how something as minor as that can occasionally cause a problem.

If you want to get a carb kit for it by all means do..25 odd years is a pretty good run from that one .Poor thing won't know whats happened with the new bits attached..A new babys born.;and really just because my Gaskets are blown and so is possibly yours doesn't mean your bike would have the same non-reaction as far as idle goes.They are all different..Like women.

[tredog500r]

Yes I actually did change the plug almost immediately. I think I will just change the head gasket, and readjust the valve clearances and decomp. I have read that if the decomp isn't adjusted right that it can cause a bike to run erratically. I just want it to run as good as it looks. thanks again for any help. As I said I'm still learning and new to working on these myself. Also I inherited an '82 500r that I'm probably just going to use for parts. I thought of trading coils to see if that makes a dif.

[Horri]

Does your bike have a decompressor actuated by the Kickstart and also one you can use by pulling a lever on the handlebars.I took the cable to the one thats operated via the Kickstart off my 82 XL as I'd rather just have the one..less things to concern yourself with adjustment wise.The handlebar one either works when you pull it in or it doesn't,,theirs no real half measures and it's kinda obvious if its adjusted ok if you use it and then try kicking the bike over without it.Replacing the Head gaskets probably an idea...just one of those things in my case that I can't be bothered fixing if the bike still goes ok albeit hard to start..Cost/Time/effort and all that.

[michael hasek]

You should do a leak down test on it before tearing it down to see if the rings and valves are sealing good . More than likely it's the carb causing your problem. the decomp cable is any easy adjustment to make . once the kick startarm is returned there should be a little bit of slack at the lever where it goes in the head.

[Beyond The Pale]

Check for a air leak between the carb and the engine. With the engine idling spray carb cleaner or even WD-40. If you hit a leak the idle will change a lot.

If you didn't remove the jets and clean all the passageways there could be varnish or crud in them. Carbs need to be spotless. I wouldn't go with a rebuild kit unless the the gaskets are leaking, the float needle is shot, or a jet is beyond hope. At least I don't get a rebuild kit unless one of those conditions is met.

If the valve cover is leaking try snugging down the cover bolts. The the head gasket is leaking, it has to be replaced to fix it. Get a manual before you start on something more major like the cylinder head.

[tredog500r]

Thanks for all the ideas guys. I will probably remove the auto decomp cable since I do also have the manual decomp. As for the leak test, I plan on doing that before I tear anything apart. Like I said before, the bike runs great beyond idle and if the small oil leaks are more than likely not causing the idle problem, I would rather tear down the bike this winter for that job. I just want it to run right so I can get a few miles on it before winter. Also, I did purchase a shop manual so I'm not going in totally clueless. Thanks again.

[eric318]

I recently purchased a nearly immaculate '81 XR500R. When I picked it up, I test rode it and the only thing that was obvious was a small bit of oil leaking from the head cover. When I got it home and rode it for a longer time, the leak was more substantial. It also was idling erratically. I checked the valve clearance and it was right. I also tested the CDI and the coil. They both checked out. Now the more that I have run it, I have started to see a small amount of oil appearing where the head gasket is. Would a small leak in the head gasket cause the erratic idling? It runs strong beyond idle. I have also set the fuel mix screw to factory and that didn't change much. I have already ordered a new head gasket, would valve seals and exhaust gaskets also be in order. Thanks Tredog500r

I also have a 1981 XR500R (had it from new back then). Also had idle problems. This was a combination of busted valve seals, overflowing in the carb and blocked idle jet.

I recently acquired another 1981 XR500R, fitted with a Whitebros aluminium swingarm, a Ohlins shock, Simons fork and a bespoke header exhaust... Will restore this one soon and fit a few more racing bits (oversize Wiseco HC piston, Megacycles camshaft, Supertrapp spark arrester, oil cooler, 38mm carb, etc.)

Would love to hear more about your bike.

[a242volvo]

My 82 XL500-R(Same engine basically) has a blown head gasket and a blown base gasket and the idling isn't affected at all. Its a bit difficult to start but once running runs like a scalded cat..I'll get round to fixing it sometime. but as is with engines it gets hard to build up the enthusiasm when it still goes well.

I dont know man, I would replace your head and base gaskets. you will end up eroding the head with nice channels if you dont. (much more $expensive$ of a fix)

[eric318]

Tredog,

rereading this thread here are 3 thoughts:

- There is often a tiny amount of oil seeping from the large screen that serves as an axis to the rockers. There are above and on both sides of the spark plug. It is nothing more than a dirty annoyance.

- Idle problem are likely caused by a faulty carb. Full rebuild sounds in order.

- Removing the automatic decompressor cable is a poor idea. You will struggle to start the bike and get hurt.

[Horri]

{Quote}- Removing the automatic decompressor cable is a poor idea. You will struggle to start the bike and get hurt. Talk about dredging up history. You still have the one on the Handlebars. It's far easier to use that for lining up TDC for the kick than have the Kickstart actuated one messing around with things. Still, some of us have it and some don't so I guess use whatever.