I'm going to break down and ask for help as this is driving me nuts...

Issue started months ago after chasing a high idle issue since I purchased the bike used. One day it started up normal and was idling when it slowly died. On restart I found I had to give it a little throttle but the idle was really rough and required throttle to keep running. I tried this many more times when it was cold and everytime it would idle fine for around 30 seconds but then die. If I gave it a little gas to keep it running it would sputter and make a popping noise from the exhaust.

Based on the previous inconsistant idle issue, a low compression reading and characteristics of a poorly sealing valve, I tore it down for a topend. Upon investigation the head gasket was shot.

Machine work included:
-New 101mm Wiseco piston (stock compression) and cylinder bore/hone
-Head decked (to deal with any possible warpage from the bad head a gasket)
-Valve and seat face/grind
-New valve stem seals

Everything went back together well and with the RH valve lash adjusted way out got a compression of just under 150psi (harbor freight gauge so give or take +/- 20psi )

Started her up just now and she came to life with a nice idle so I kicked her back to 1/2 choke and went for my helmet. By the time I was ready to pull it off the stand it was starting to run rough and then required throttle to keep her running. She caughed and popped while I cussed and kicked tools...

This leaves two directions in my mind, electrical or auto decompressor, but I wanted to throw it to the experts to see if anyone has experienced this before or could point out the obvious.

2000 XR650L 23,000 original miles on the stock engine (prior to rebuild)
Stock carb w/ "Daves mod" and 160/58 1-1/2 turn out

Thanks,
Kell

A 58 pilot jet is pretty big, 55 is the norm, and 52 is stock. Whats your altitude ? I'd guess that with a 58 pj and the choke on, she's loading up.

zx12r, on 22 January 2012 - 01:33 PM, said:

Swapped back to 155/55. I'm only a couple of hundred feet above sea level so I would think at 40-50F I should be in the ballpark. Since the bike is unrideable I would think that something other then jetting has to be at fault.

It really seems like the popping out of the exhaust would be caused by a valve not being closed, maybe caused by the auto-decomp. However I don't see why it would run fine for the first 30-40 seconds...

Thanks,
Kell

If it`s popping out the exhaust while idling............it could be your valve timing is off.......or a valve is open from too tigh an adjustment,,auto decomp problem..bent/burnt valve..etc..



B

brianhare, on 22 January 2012 - 03:36 PM, said:

valve timings good with the cam lobes down on the "T" mark.

Freshly ground valves & seats (by a engine shop) with valve lash set at .004" on intakes and .005" on exhaust. When the engine was disassemlbed the timing was good so their should never have been contact between the piston and valves to bend a valve stem.

Has anyone seen failures from their auto-decomps? I'm tempted to remove it and and plug the oil passage but still don't see how it would run well at first.

k5kell, on 22 January 2012 - 03:20 PM, said:

If that little plastic retainer that holds the needle in the throttle valve comes loose, it will cause all kinds of odd problems, it needs to be turned till it snaps into place. Good Luck

zx12r, on 22 January 2012 - 03:55 PM, said:

I'm not sure what piece you are refering too. Are you talking about the retainer for the main jet needle in the throttle slide? So I may possibly have the main jet needle not secured to the slide and it could be causing way to much fuel?

If you could clarify it would be appreciated.

Well......there is a possibility the CDI is the problem,,,i wrote a thread on repairing them..it is "pinned" on the front page of this forum...

Other things to try,,,,,,,check flow from the fuel petcock....pull the carb and run a wire and compressed air through all the small ports...

Try smacking the CDI as i posted in the CDI thread first,,see if it runs better,,kinda sounds like it`s losing fire..

B

k5kell, on 22 January 2012 - 04:17 PM, said:

Yup........he means the piece inside the slide that holds the needle down and into place..

Did you try turning the fuel screw out some,to see what happens???????




B

brianhare, on 22 January 2012 - 04:18 PM, said:

When the carb was apart I carb cleaned all the ports/jets and then blew compressed air through them. Fuel supply through the petcocks looking good as well.

I did try tapping the CDI per the sticky but it didn't run any better. I did however grab the old sparkplug and tested for spark right after it got warm enough to run poorly and it looked like a good blue spark on every crank so I'm thinking electrical may be good as well.

brianhare, on 22 January 2012 - 04:30 PM, said:

Yeah I went between all the way in and 3-1/2" out with no noticeable changes.

Since it does smell like unburned fuel I will tear into the carb again to see if the needle retainer popped out. Might take awhile since I believe the carb will need to come out to get the top of the carb off. I'll post what I find.

Thanks all.

k5kell, on 22 January 2012 - 04:17 PM, said:

Yes, that little retainer has caused strange problems . Its part# 7 in this diagram.

http://www.cyclecent...=1997&fveh=4327

zx12r, on 22 January 2012 - 07:28 PM, said:

It was clicked in and looking good. I gave the carb another clean, and double checked that I could seee light through the main and pilots.

I ran out of time tonight but tomorrow after work I'm going to back the RH exhaust lash way out and see if it runs on one exhaust valve. Just idle to 1/4 throttle I figure should be okay. That should help figure out if the auto-decomp is causing the issue.

Backed the RH exhaust valve way out and ran it with the same results. I'm thinking that would rule out the auto-decomp. Now I'm out of ideas, damn...

Any thoughts?

I think it's the carb. Too rich. As soon as the engine starts getting some heat built up the mixture is too rich.

If it's too rich taking off the airbox cover may help diagnose it.

Just throwing a bunch of things out there. Maybe the exhaust valve seat is coming loose when the head heats up. Vacuum leak somewhere. Coil, pulse generator, resister in spark plug cap- check with a ohm meter. Loose, dirty connections, CDI. On the side of the CV carb there is a vacuum operated anti popping valve (forget whats its called) it has a diaphragm, make sure its not stuck, no holes.

If you can give us a detailed description of what you do when starting and exactly what the bike does, maybe it will ring a bell with someone out here. Can you rev it up during the 30 seconds its running? If your reving it up, will it stay running? How long before it will start back up? Good luck.

zx12r, on 24 January 2012 - 11:15 AM, said:

I checked the diaphram the other day and it looked normal. I fired it up and as soon as I gave it any throttle it would run poorly. It will rev but it sounds so rough and doesn't clean up.

In the process of checking spark I managed to break the plug wire today. I did measure the coil for resistance across the + & - after breaking it and it was around .6-.8 ohm (my manual mentions the range is .19-.23). Will a broken spark plug wire effect this reading or is it simply an internal resistance of the coil? I would think if it did effect this reading and it was broken I would get an infinite resistance.

I'm going to get a coil and see if that solves the issue since I need a new one anyhow.

On the bright side I got my KTM 300 starter working so I'm still batting .500!

Kell

air check valve in carb, that little bugger has been the bain of many an owners life.
worth a try, at least take a look at yours, run a small led light like a key chain lightaround it and look for light coming through, the smallest pin hole will cause problems.

thumpharder, on 24 January 2012 - 09:24 PM, said:

Air check valve? I'm not sure what you mean. Could you provide more details so I can look into it?