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02 xr50 power issues

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I bought a 2002 xr50 a few months ago. Cleaned it up, painted the frame, got new plastics and put it back together.

I cleaned the carb, drained the gas, put fresh gas in, new sparkplug, and put in a new air filter.

The bike fires right up and idles, but it sounds a little high. There is almost no throttle response when i twist the throttle though, and no power. No carb adjustments seem to make any difference.

I've pulled the carb a couple of times now and cleaned for good measure, but no change.

I'm stuck on what to try next.

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Try a valve adjustment first (intake - .002" and exhaust - .003"), and then a compression test. Since the bike is 12 years old, might be time for a complete top end and head rebuild

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does it die when you open the throttle or does it just lack power? does it smoke? are the gaskets on both sides of the intake fresh?

It doesn't die when i open the throttle. Just sort of slowly winds up. It is smoking a bit. I didn't replace any gaskets.

The bike was running fine before i started all this.

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if you didn't open the engine, there is really not much that can be wrong, backtrack and check everything you touched when you took out\reinstalled the engine.

check Your wiring and see if everything is ok.

check Your valves and adjust them if necessary, valves out of spec can cause all sorts of trouble.

check and replace Your intake gaskets, if you are sucking air somewhere you shouldn't, you will lose Power.

 

smoking indicates worn piston\rings\cylinder, is it a Heavy smoke or does it go away when the engine gets warm?

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I am going to chime in with Norway regarding the smoke.  Valves generally get tight and result in a hard starting and difficult idle.  Those still need to be checked just to make sure.

 

However, the smoke and slow to build RPMs sounds like a compression issue.  it may not need a new piston, but it is sounding like the rings are worn.  And since you will already be in there, you might just want to replace the piston was well.  You just want to make sure that it only needs a piston kit and not an over bore.  To do this you need to measure the cylinder and see if its shape has become ovaled.  Meaning, instead of a constant width from top to bottom, it gets slightly wider in the middle of the cylinder compared to smaller at the top and bottom.  If you measure that the middle is wider than the top and botton, it will need to be bored the next size up.

 

If you do this, get the piston first, ensuring it is larger than what you are measuring now, and take it to the machine shop with the cylinder.  it is better the cut the cylinder to the piston rather than bore it out and hope the piston fits properly.

 

Norway also talked about wiring.  If you took the carb off, make sure the grounding wire is attached to the frame.  It connects at the same point where the air box connects at the top of the frame.  If it is loose it can cause some issues.

 

Also ensure the choke is off after warmed up.  I was killing myself wondering why the bike wasn't running right one day and finally my 7 year old son pointed out his choke was still on. :banghead:

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Thanks for the help guys and sorry with the slow response. I only tinker with it on the weekends and haven't had much time.

 

I pulled the carb for what is probably the fifth or sixth time and cleaned it, replaced fuel lines for the same result of poor running.

 

I ordered a brand new carb and installed it this weekend and it runs in exactly the same way. Starts up on the first kick and idles fine. Still no throttle response. I open it up full throttle and it sort of slowly winds up but not to a full throttle type rev. It's got zero power. It does smoke.

 

Again since it was running fine before i was messing with the carb i figured that's about all i could screw up.

 

The ground issue is a possible since i painted the frame. I thought i cleaned up the contacts but maybe not good enough.

 

If not that, i am at the end of my mechanical abilites. I think i'll go ahead and take it to the shop.

 

And yes the choke is off :) in fact if i put the choke on it dies...

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Top end kits are actually not that bad.  I put another one in our bikes this past weekend.  Just remember to put oil in it.  I forgot to do that after the rebuild and ran it.  It probably fried the piston and rings and will require another set.

 

If you have a manual, it can be done with basic tools and little effort.  There is a great 4 part series on youtube about doing a top end.  That helps also.

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Compression is good.

 

I brought the bike to a mechanic. He said the smoke was from it running too rich. Spark plug was soaked.

 

When he drains the fuel out of the bowl via the drain, it runs normally. Then after a minute it runs like crap again.

 

Adjusting the settings on the carb doesn't seem to have any effect.

 

Any ideas why it would be running so rich or what to do?

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Did you adjust the new carb properly?  Idle screw, fuel screw?  And when the plug was pulled, was it wet with gas, or oil.  How did the end of the plug smell?  

 

Did you ever adjust the valves before doing of the carb work?  .002 intake and .003 exhaust.  Those need to be set right before trying to many other diagnostic tests as they can throw everything off.  Try adjusting those first and see if it does the same things.

 

Was the new carb adjusted properly?  Idle screw and fuel screw.  fuel screw should be about 2 turns out.  If you still get the same issue, try going two and a half to see if it improves.

 

If plug was wet with gas, then on most bikes it would be a float issue.  and that may still be the issue if the bowl was drained a little and it ran correctly.  its a little harder to adjust a 70 carb because the tab that holds the float needle is plastic and may or may not hold its post when you put it back together.  Check out a video or article on the subject before trying it.  You need to have a good idea of what and why you are doing it.  Trust me, it will help.

 

Let us know how that goes and report back.

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Problem has been resolved. Since the carb was the most likely culprit, I bought a new one in order to make sure everything was perfect. Unfortunately I was cheap and bought an ebay el junko carb. I assumed it was fine, but it wasnt. The local bike shop put a legit carb on it and now it runs fine.

Thanks for all the help here and let this be a lesson. Spend the extra couple bucks and buy the right parts and save yourself a whole bunch of trouble.

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