XR70R Still Smoking After Rebuild

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XR70R Still Smoking After Rebuild

Postby 4Strokes » Thu Jun 02, 2016 9:45 pm

Topic: XR70 smokin like crazy, even after rebuild
Author: dswezey
Posted: 07/19/2004 07:42:18 AM

Have a '99 xr 70 that is smoking like crazy. I Made sure the oil if filled to the proper level. Put in new piston and rings and re-bored the cylinder. Adjusted the valves. Split the cases for its 5 year tune up and put in new crankshaft bearings while I was in there. Still smokes and runs like garbage. Could it be bad valves? What else should I look at?

Reply by xr-for-ever on 07/19/2004 08:57:33 AM
When you bored it out did you get a piston for the over-sized jug? and did you make sure that when you installed the rings that they were not lined up with each other, the split in the ring should be spread out around the piston.

Also does it just smoke at start up or does it smoke when you are riding it for a long time? If it is at start up only then your valve seals are bad but long term smoke comes from your pistons and rings.

Reply by dswezey on 07/19/2004 09:04:54 AM
It smokes like a bad diesel truck. I had my local Honda dealer re-bore the cylinder and order the new piston so I assumed it was a correct fit. I did make sure the rings were offset. I must have done something wrong with the top end rebuild. It's the only thing I can think of.

Reply by farmboy on 07/19/2004 10:03:19 AM
A neighbor had a similar problem and it was the muffler full of oil from before the rebuild. The bike had been ran a long time when it was in need of repair and coated the inside of the muffler with oil. He went through the top end (valve job, overbore, new piston)and it still smoked. He used kerosene to wash out the muffler and the smoking stopped.

Reply by xr-for-ever on 07/19/2004 1:43:34 PM
When you say it smokes like a diesel, is the smoke dark black or is it blue, if it is black then you need to rejet or raise the needle in the carb, I am getting the feeling from the smoking like a diesel that it is running to rich, run it wide open for about 100 yards and kill it, pull the plug and take a look at it, if it is black then you are running rich. Give it a try and see what it looks like.

Reply by dswezey on 07/20/2004 11:27:44 AM
Its a gray blue smoke. I ran it for about 5 minutes and tried to get it revved up but its sputtering at high RPM. When I was done there was actually spooge like you might find from a two stroke at the back end of the silencer.

I'll try cleaning out the pipe. That would be a nice easy fix.

Yes the plug is real sloppy. It running rich. Unfortunately getting jets for the stock XR carb is virtually impossible.

VERY IMPORTANT INFO I LEFT OUT BEFORE> This is the second top end in less than a year. The bike ran fine for years. Now I get a bad smoking problem with only 15 hours on the new top end.

Reply by xr-for-ever on 07/20/2004 2:58:20 PM
You can raise the needle a clip position or 2. Your local Honda dealer should have jets for it, it sounds like there is more wrong with it then just jetting, the smoke is puzzling, it sounds more like oil and water smoke then gas. I wish I could help out more but it has me puzzled. Let us know if you figure it out. Good luck.

Reply by dswezey on 07/22/2004 12:56:31 PM
Now I know why I couldn't figure out my problem.: (Finally had a gear head work buddy over for some beers and engine diagnostic fun.)

  1. I was using a micrometer that must have been damaged and when I was measuring the tolerances on the valves was way off. They were shot. Especially the exhaust valve. Time for some new tools.
  2. The Honda dealer made a mistake on the re-bore. They bored it out just a few mics larger to accommodate some damage after 5 years of neglect from the previous owner but forgot to order the larger piston and gave me a stock replacement. It was close enough to work but not for long as indicated by the ridiculous amount of grey smoke.
  3. I had two exhaust gaskets overlayed. One was crammed up against the cylinder head and was so crusted with carbon that I never new it was on. Put the second one over it which created an air leak and the problems associated with that.
  • My local dealer who is very good is providing a replacement piston at no charge.
  • Ordered all new valve stuff.
  • Popped out the extra exhaust gasket.
If that does not fix it than I'm busting out a hand grenade.

Reply by Honda Maniac on 07/22/2004 2:31:19 PM
lol... hope it works

Reply by xr-for-ever on 07/22/2004 7:24:14 PM
I do believe I had said something about the piston size before. Well I am glad to see you have narrowed down and hopefully you get it going soon. Let us know how she does when you get it back up and running.

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