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I don't get it, please see if you can help

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Well first I’d like to say hello to all the forum members. I’ve read just about every thread regarding Honda XR80s, and so far I’ve found some very helpful information, but I’m still unable to keep my bike running. However at least it’s running now thanks to this place and a little hard work.

I have a 1990 XR80r which I’ve switched out the head due to spark plug thread problems and bad oil seals. I used my old valves and springs with the 88 head I found and used the seals in the 88 head. So far no smoke and plenty of pep for this old thing it’s just that after riding hard for 10 minutes, it starts to slowly lose power and eventually dies after 3 minutes of noticing the power loss. I’ve also completely cleaned the air filter, cleaned the two main jets, cleaned bowl and float, cleaned gas tank and the filter that inside the tank, adjusted the needle from the middle stock position to the lowest then back to the highest setting with the ending result the same, the bike dies after about 5 to 10 minutes fun fast. And adjust idle and air intake to the stock postion 2 and 1 3/4 plus 3 3 1/2 etc. etc. etc. :thumbsup::devil:

After it dies I’ve checked the plug and it’s covered in carbon with a slight bit of gas. I think the gas is just from me push starting the thing after it dies on me. The last thing I checked was the spark coming from the plug after it ran for those 10 minutes and not much of any spark was left except for just a little hint of spark, is this a fouled plug or something else causing the low spark? To get it to spark I only use my arm to crank the engine over so I may not be getting enough kick to it. Now here’s the other thing if I through in a brand new plug tomorrow morning she’ll run great for 10 min only if I push start it, and then the whole process starts over again, (10min then dead).

I not sure what’s next electrical?

Maybe just buying a new carburetor like this one?

Hondatrailbikes

Please everyone just throw in your best because I think I’m about to give up and my nephew will cry for days, just a little taste of speed he's foaming at the mouth.

I currently have a wonderful Yamaha TTR 125, so my nephew is very eager to join me on the trails

Thanks again,

Karl :awww:

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I wouldn't rush out and buy a new carb unless you are sure that is your problem (or have money to burn.)

Problems like this can be attributed to electrical breakdown. When electrical components get hot they can tend to cause an open or partial "open circuit." When they cool back down things are back to normal. You will need a service manual for the resistance specs and an ohm meter to check the electrical components out before and after they heat up.

One question is did it have this problem before you changed the head? This may help narrow down but not rule out the possibility that this is even your problem.

Another easy thing that you might try is, starting with a new spark plug kick the engine over (not by hand) and observe the spark. Is it nice and "hot?" Good blue spark?

After it dies out have another new plug ready (to rule out a fouled plug) and re-check the spark. Still the same, or is it weak and yellow looking? This easy check will help rule out the previously mentioned problem.

Check your compression with a compression gage. A cheap gage can be had for around 20 bucks from your local discount auto supply store. Just make sure it has an adapter down your size plug hole. Check it cold and again hot when the engine dies. Just screw it in, twist the throttle wide open and give it at least 3 good kicks. If there is a big difference in pressure between cold and hot this could be your problem. BTW did you recheck your valve clearances after you ran the bike a few times? If not the valves that you installed could have seated, and have so little lash that when hot they may not even be closing completely.

This quick check is a long shot, but I have had it happen to me a number of times in my years of working on bikes and small engines. If your bike has a small hose coming of the gas cap this most likely won't apply to you.

If not try loosening (or removing) the gas cap while your engine heats up.

I have seen the vent hole in a gas cap plug, creating a vacuum which causes the exact same problem that you are having. The first time it happened to me it took a bunch of time to figure out what was going on.

Good luck and hope this helps.....Karl

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Karlznet I will try all those suggestions except for the compression test since I don't have that tool right now. And yes the same problem was happening before but I thought it was due to the bad oil seals and fouling out plugs. When I first traded for the bike it would run ok but smoke like a Bar B Q pit with lots of wet wood. With this new head I can tell that the bike is ready to go but 10 minutes is all it can stand right now.

The weekends are just about the only time Im able to play with this thing so please don't think Im a one time poster. I'll definitely be back with some more questions, like from a poor mans perspective can you clean or mod something to work as a honda xr80 coil from different bikes. That probably will get some :devil: but all I have is a Haynes manual I got from Half Price Books.

Also is Ebay my best shot for a coil because some of them look extremely expensive on a few other sites I've visited.

CRFThumper Hmmm....a coil sounds like a great diagnosis

I hope to post some success later, and will check the board often at work.

Thanks

Karl :thumbsup:

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This might sound funny...but a pinched fuel line...or too thin a line that when gets hot is getting sucked closed could also do it...My friend had put on a new afttermarket carb...he had it routed wrong with too sharp of a bend on some softer line made it suck the line closed and no more gas to float bowl...just a small thing to look at...probably electrical...but doesn't hurt to check...

Good luck!

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Well it was definitely the coil. Got a new one from a local shop for 30 bucks and I rigged my old condenser to the new coil. So far it doesnt die after 10 minutes. Now it kinda bogs after about 10 minutes so Im going to replace the condenser and play with the carburetor tomorrow. Eventually I'll get a carb kit or just replace the whole carburetor. Thanks to you guys for helping out.

Oh and :thumbsup:

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