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03 Xr80 idle issues

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Just rebuilt a 2003 Xr80 as a first clutch bike for my son. Went thru the entire motor and split the cases. Glad I did as there were a lot of big metal shavings in the bottom end. When I got the bike it was smoking a lot. Ended up being a blown exhaust stem seal. As well as worn rings. Prior owner had shimmed the cam up instead of replacing the stretched timing chain. Of course the journals were ruined. I went back with a new OEM head, cam, rockers, timing chain, cam sprocket, both valves and springs, piston and rings. Basically have a new engine. After getting everything put together and timed, first start went well. But after just a minute or so it started ideling down and dying. I checked the float height and made sure the pilot circuit was clean. Third clip down on the needle and air screw at 1 1/4 turns out. Found no leaks on the intake boot. Bike idles fine at around 1600 to 1800 rpm. Any lower and it is like its flooding out. Plug looks great. Not fouling or flooded. Never have I had this much prob getting a good o'l xr running smooth. I've built several of them. All jets are stock size. Any help would be greatly appreciated.

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"Any lower and it seems like it is flooding out.

I checked the float height and made sure the

pilot circuit was clean"

By pilot circuit, do you mean the air bleed

and fuel feed passages to and beyond the

idle mixture screw? Or just that you inspected

the low speed jet in the fuel bowl area?

Has the bike always had an air cleaner?

Is the inlet / air cleaner side of the throat

clean ? Does the engine respond to turning

the Idle Mixture Screw?

I am proposing that the fixed Idle Air Jet is

obstructed. Instead of an air/ fuel mixture

at idle, only fuel is drawn by manifold vac.

Turning the idle mixture screw has no effect

because the air feed to the IMS is blocked

upstream.

Or not.

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Yes meaning the entire starting circuit has been cleaned from the pilot/air screw circuit to the actual pilot jet through to the air jets on the air boot side of the carb.

Then last night I put a brand new (Chinese) carb that a friend had ordered for a xr80 prior that he had left on the shelve. It is a exact match to the stock carb on the bike. Intake is 18mm and the same 48mm between mounting studs. Same size jets. Still same prob. Done a compression test on it and I'm only getting around 60psi. Could this be the prob?? Not enough compression when it idles down to keep it running?i didn't mike the bore when I rebuilt it. I did check the end gap on the rings and they were in spec. Really aggregated with this one.

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Sorry Al.. Hadnt been on here untill today to see your post.. I have them both set on .003 Thou...

The prob ended up being the valves were not seating good...The valves that were in there only had about 5 hours on them so I didnt replae them.. They were pristine... But ended up being the new head seats were not matching to the seat of the old valves... I tried lapping them and got them to hold water without leaking, but im still very low on compression... I shouldve got new valves while I was at it.. They would have matched the new head.. OEM Valves I mean.... Would you just keep lapping to get them to match, or go ahead and put OEM valves back in there with the new head? I have done some lapping.. so I dont know whether I screwed myself or not... What do you think al?

 

How much valve lash do you have........?

 

Old School Al

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