xr70 has no desire to start

I have a 2000 XR70R that was rebuilt 9 months ago.  I had an aftermark* carb and air cleaner on it for 4 months, they have been removed and NEW OEM carb and NEW OEM air cleaner assembly have been installed as well as new throttle cable to match.  New spark plug and new gas.  There is plenty of spark but it doesnt even come close to firing.  The bowl fills with fuel, however the plug doesnt seem wet when I check it.  I ran a wirebrush bristle thru the NEW jets and all are clear.  **Bike was running on aftermarket carb & aircleaner, however not very good, this is why I wanted to return to factory setup.**  I AM STUMPED!!  Any ideas?

Thanks

 

 

 

Check compression. Use a compression tester or press thumb firmly over spark plug hole and see if it blows your thumb off.

Bad gas maybe?

Kill switch?  It has happened before.  Also check to ensure it is grounded where the 10mm bolt holds on the air cleaner.  it is easy to let that fall away and not hook it back up.  Should be a green wire with a flat round connector.

Kill switch?  It has happened before.  Also check to ensure it is grounded where the 10mm bolt holds on the air cleaner.  it is easy to let that fall away and not hook it back up.  Should be a green wire with a flat round connector.

He says it has spark, ruling out a electrical issue basically.

Yep.  Just blew past that one in the post.

 

Okay, how about too lean on the fuel air mix.  Screw it in all the way until it barely gets tight, and then back it out two turns.  If I remember right, that should be the recessed screw that does not have the visible spring.  

 

Actually, let's back up and get some other info.

 

1. when you say it ran bad with the aftermarket parts, can you describe that.  It may not be a carb issue

2. when you bought it, what was the condition then?  clean, dirty, beat, etc  Were you the one who rebuilt it, or was it a prior owner

3. how easy is it to kick over?  You could have a worn piston and lost compression (assuming somene you bought it from said it had a rebuild when it might not have)

4. If you did the rebuild, how did it run after the work?  When did you start to notice it was running poorly?

Yep.  Just blew past that one in the post.

 

Okay, how about too lean on the fuel air mix.  Screw it in all the way until it barely gets tight, and then back it out two turns.  If I remember right, that should be the recessed screw that does not have the visible spring.  

 

Actually, let's back up and get some other info.

 

1. when you say it ran bad with the aftermarket parts, can you describe that.  It may not be a carb issue

2. when you bought it, what was the condition then?  clean, dirty, beat, etc  Were you the one who rebuilt it, or was it a prior owner

3. how easy is it to kick over?  You could have a worn piston and lost compression (assuming somene you bought it from said it had a rebuild when it might not have)

4. If you did the rebuild, how did it run after the work?  When did you start to notice it was running poorly?

 

1. the bike ran, seemed like it didnt have as much power, had some smoking issues out of the pipe.(blackish/grey), didnt like to start with kick start(usually had to bump start it)

2. I bought it from a MX racer(not his race bike) and it ran great then.  My 2 sons rode it for a few years,  did routine maintenance nothing drastic.  then changed carb and cleaner to aftermarket and started going down hill after that.(coincidence....not sure).  I had a guy who owns a bike shop rebuild it, he also rebuilt my KTM 200sx(top end /bottom end) wich runs like a beast, he knows his stuff.  Im trying to fix this myself to save some money as i am looking to sell the xr70 and pick up an RM 125.(for my youngest son)(i want it fixed right so if I cant do it, it goes back to Eric).

3. Kicks fairly easy but does push finger when in i put it in plug socket. 

4. race shop owner did rebuild. started running poorly after i switched to aftermarket carb and air cleaner.

thanks for your time

Try a valve adjustment with .002" for the intake and .003" for the exhaust side, just make sure the piston is at TDC before adjusting.

When it started running poorly after the carb and filter change, what did that involve?  Hard to start?  Backfiring? lack of power at mid throttle?  lack of power at full throttle?  Was it cutting out at throttle?  Did it idle rough?  The details will help.

 

Valves can be an issue that create a lot of frustration.  I would have assumed they were adjusted as part of the top end, but you never know what amount of work someone will do.  And, in the time between the rebuild and now, they could have tightened up on you.  definitely give those a check.

 

Did you pull the end cap off the exhaust and clean it.  My lads dumped the bike once and got a little mud in there that caused some blockage.  That didn't keep ours from starting, but it was a little tougher to start and down on power until they told me about the mud puddle crash and i cleaned the backfire screen.

 

you said the bowl is getting gas, but is it enough?  you can bend the little tab on the float a little to adjust the level in the bowl.  it is suppose to be set at the factory, but I have messed with mine a little to get it set correctly.  

When it started running poorly after the carb and filter change, what did that involve? Hard to start? Backfiring? lack of power at mid throttle? lack of power at full throttle? Was it cutting out at throttle? Did it idle rough? The details will help.

Valves can be an issue that create a lot of frustration. I would have assumed they were adjusted as part of the top end, but you never know what amount of work someone will do. And, in the time between the rebuild and now, they could have tightened up on you. definitely give those a check.

Did you pull the end cap off the exhaust and clean it. My lads dumped the bike once and got a little mud in there that caused some blockage. That didn't keep ours from starting, but it was a little tougher to start and down on power until they told me about the mud puddle crash and i cleaned the backfire screen.

you said the bowl is getting gas, but is it enough? you can bend the little tab on the float a little to adjust the level in the bowl. it is suppose to be set at the factory, but I have messed with mine a little to get it set correctly.

It was harder to start and would bog down at full throttle. Plug was black when I took it out. This is why I decided to go back to factory equipment. Some backfiring but not a lot.

well it lives....the spark arrester was clogged solid, stalls out if i put it back in. it smokes a bit (white), and the breather tube is getting gas(?) in it, but at least its running again.

Sweet.  Now you can tune it to run better with the problem discovered and fixed.  

 

The aftermarket carb may have been putting too much gas in the cylinder and not burning it all.  That rich condition is what most likely caused the excess build up.  So, you can either rejet the aftermarket carb and try it again, and also tune the fuel/air mixture, or stick with stock and tune that set up.  Either way, you should be able to get things running well and get it on the market.  You can just say it comes with an aftermarket carb and airfilter and let the new owner deal with it.

 

I guess its time to start checking out Craigslist for average XR70 prices.  

Yes. Hoping to get $500 for it. And thanks again for all the insight and knowledge.

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