83 XR200R - idle problem

[MY83XR200R]

Have completed full resto and is now also a road legal bike once again but have one very annoying problem - can't get bike to idle. Motor was rebuilt with first oversize rebore and 10:1 compression piston fitted. Carb is standard Keihin PD28A-A which has a 138 main jet. Bike runs great on the road but will not respond as it should to idle fuel mixture adjustment which should be set at approx 2 1/2 turns out from fully seated. The only way I can get it to run half reasonable is 1/4 out from fully seated. Once the engine is hot from riding and I come to a stop engine will run on and then revs slowly drop and the fluctuate and eventually stall. Carb has been stripped and checked by a mechanic but he couldn't find anything wrong with it. Have checked for air leaks between carb, manifold and head but all is well sealed. Any help with this problem would be most appreciated thanks.

[antideaf]

sounds to me like there is fuel bypass somewhere i have run into issues where the needle on the slide from many years of offroading has misshaped the hole where it tucks into  to control the fuel mixture. It does not take much wear to throw the mixture out of whack.. If you installed new jets cleaned the carb and have no leaks thats what i would lean towards. Having to lean the mixture screw to compensate for the extra fuel is what i see from your description. hope this helps.

[MY83XR200R]

Hi antideaf - thanks for your response, most appreciated - will get a new jet and try what you suggest as the carb kit we got had the wrong size jet so we used the original one which could be worn as you have suggested - will let you know how I get on. Cheers Pete

[HomerDodd]

Clogged pilot jet (or partially clogged) and/or lean pilot. Go up one or two sizes. Put in a new spark plug, ride it and kill it. Remove the plug and "read" it. White on the tip and insulator is a lean condition (not good; can seize the engine over prolonged use). Black soot is too rich (not as bad as lean, but fouls plugs and loses a bit of power). A question: when it is idling, does it hunt or surge trying to find a higher idle? Does it pop out the exhaust when snapping the throttle open and letting go quickly? If so, these are lean situations. Must be corrected. Rich is more forgiving, but still should be fixed. Here is a rich/lean symptom link:

http://www.randakksblog.com/lean-vs-rich/

[MY83XR200R]

Thanks antideaf a new needle set has fixed the problem bike runs real sweet now due to go for a big road ride round the hills tomorrow so really looking forward to it.

By the way if anyone can help with another problem I have which is sourcing new tank decals which are resistant to the gas that leaches through the fuel tank as the ones I bought are no good as they are bubbling up badly?

[antideaf]

those tanks are very bad for "off gassing" the plastic will never allow for decals to adhere properly. the best you can do it polish off the oxidisation and have a shiny plastic tank!. I have an 81 xr200r with the same problem.

[MY83XR200R]

Thanks for your reply the tank was highly polished at the time the decals were applied but I also suspect it's partly due to the quality of the replica ones I bought.

[-82xr-]

I sealed my tank from the inside. Look up "blue lightning" gas tank sealer on the internet. It worked great. No problems with the decals now.

[MY83XR200R]

Thanks 82xr will look it up

[MY83XR200R]

Hey 82xr not much info on their website about application process for that product, can you give me a heads up please?

[-82xr-]

[MY83XR200R]

Awesome thanks 82xr most appreciated. Was 1 pint enough to do your tank? Just been for a sweet ride round the hills early this morning first decent ride I have had the opportunity to go on the xr just loves the tight corners on the road it just drops in without any effort i'm stoked 

[-82xr-]

Yes 1 pint will be plenty. It just coats the inside of the tank with a very thin film of sealant. As it says in the instructions most of the sealer will be drained out.

By the way your your xr is killer. I love seeing these things restored. Good job on getting it licensed.

Edited January 15, 2017 by -82xr-

[MY83XR200R]

Thanks 82xr will get the sealer ordered and thanks for your comments - have just done a garage listing of it with a few more pics and a bit of history to go with it.

[antideaf]

wow thats actually pretty cool, did not think you could do that! thanks 82xr

[HomerDodd]

I sealed my tank from the inside. Look up "blue lightning" gas tank sealer on the internet. It worked great. No problems with the decals now.

 

I have not looked it up yet, but does it work on plastic tanks, too? Seems like most of the older plastic tanks "out gas" and cause decals to lift.

[-82xr-]

Yes my tank is plastic so it works on plastic.

[Old School Al]

Thanks antideaf a new needle set has fixed the problem bike runs real sweet now due to go for a big road ride round the hills tomorrow so really looking forward to it.

By the way if anyone can help with another problem I have which is sourcing new tank decals which are resistant to the gas that leaches through the fuel tank as the ones I bought are no good as they are bubbling up badly?

 

 

What brand was the carb kit that you used..................Keyster possibly?  

 

Also, I'm not clear from your description exactly which parts you replaced to cure the idle problem........."new needle set"?  Slide needle and needle jet?

 

Nice looking early XR.................! ?

 

Old School Al

[MY83XR200R]

The orginal carb kit that was supplied to my son had the wrong jet and needle set supplied as our carb is a PD28A-A which has a 138 main jet. With the naked eye I couldn't see anything wrong with the original needle set but under high magnification you could see signs of wear. The original part numbers were of no use when I ordered a new needle set which included the main needle, bush and circlip so I measured the small diameter with digital vernier callipers and was supplied an exact match. See the photo of the orginal needle set and the one supplied in the carb kit which clearly shows a major difference in the small diameter.

[Old School Al]

📎Carb needle set PD28A-A.JPGThe orginal carb kit that was supplied to my son had the wrong jet and needle set supplied as our carb is a PD28A-A which has a 138 main jet. With the naked eye I couldn't see anything wrong with the original needle set but under high magnification you could see signs of wear. The original part numbers were of no use when I ordered a new needle set which included the main needle, bush and circlip so I measured the small diameter with digital vernier callipers and was supplied an exact match. See the photo of the orginal needle set and the one supplied in the carb kit which clearly shows a major difference in the small diameter.

 

 

What brand was the carb kit............??

 

That's pretty common for parts like jets and slide needles to be wrong as one kit covers many models.  That not a "bushing" ........ that's the needle jet (needs to be correct also).   The needle jet and the slide needle work together to control fuel flow.  Both wear which leads to more fuel flow and rich conditions such as you had.

 

Old School Al