Restarted project again

Pork Chop

XS400 Junkie
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Alrighty, I've had enough of not finishing my bike project so I dusted off the old bike and got out the tools. I need some help with trying to get this bike back on the street. The pig just doesn't want to run. It is an '81 xs250 with xs400 barrels and pistons. Stock xs250 bottom end, head & thoroughly cleaned bs32 carbs. Compression has been brought under control with a thick copper cylinder base gasket. Valves have been reseated. I've gone up 2 sizes in pilot and mains jets. Charged battery & fresh 95ron fuel. Yesterday it wouldn't idle, blip the throttle would get back fires & flames out the mufflers but I had to stop working on it. So today I thought mixture was too rich at 2.5 turns out so I tried mixture set at 2 then 1.5 turns out but no joy. Enrichener makes no difference. Kick starting can give small pffftts out carbs or nasty kick-backs from time to time. Spark plugs are new and when checked after yesterday's activities they were a bit dark and sooty. This is budget build & I've done all the work myself (excluding vapour blasting). Can anyone shed some light on what might be wrong. Cheers.

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I would try the stock jetting first with a clean set of plugs. What is the compression in the motor? Kickback/puffs out of the carbs is a sign of a timing issue. Also maybe a valve not seating well.
 
Thanks Chris, I have been reading back over my original build thread and there is some sound advise there that I did not follow that as I was kind of hoping for the best. I'll do some proper testing this weekend and update when I have more info.

Cheers.
 
Calling ignition timing gurus - I need your help.

Based on the first picture I think my timing has too much advance. Am I correct?

The second picture is of the rotor position at LF. Should I rotate the ignition to the blue line so that it lines up with the rotor?

Does the rotor position possibly indicate that I have missed a tooth on the cam sprocket or that the 2.5mm cylinder base gasket has pulled the cam out of whack just a bit?

Am I about to screw this up royally?

Cheers.

left fire timing.jpg

rotor position at LF.jpg
 
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The dot on the rotor is the side you use for the firing point. Yes you can move the pickup so the marks align. The TCI box will do all the advancement during running. As for the chain, I have never lowered the compression on one of these before so you may need to do more research on this.
 
Hey Chris thanks heaps mate,

Your help has been invaluable to me and my looooooooong term build project. I will check the position of the dot on the rotor - hopefully I just took the photo with it 180 degrees out.

Also, is it possible for the rotor to wear out to the point that the spark wont jump the gap to the pickup? Is there a maximum gap?

cheers.
 
There is no "spark" that jumps from the rotor and pickup coil. It's a magnetic trigger for the TCI box. It won't wear out. There is a test for the amount of ohms in the pickup tho in the manual. This is the dot I was talking about.
 

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Thanks again Chris. I checked the rotor and all good with the position of the dot - I just had it in the wrong position when I took the photo. I rotated the pickup to and it made kick starting much more pleasant with no kickbacks.
So on to the next problem. With mixture set at 3.5 turns out with enrichener on it will idle for a while but dies as soon as I give any throttle. Test at 1.5 turns out and no start. Set at 3.5 to 4.5 turns out and same result. Needle clip is in middle position. I guessing that it is running lean and will test with bigger pilot jets tomorrow but any suggestions on things I should try/check would be appreciated.

Cheers.
 
Hi pork chop, are your emulsion tubes or whatever they called clean? And the rest of the carb passages etc, maybe it got gunked up from sitting. It sounds like its not getting juice when you give it some throttle so something could be blocked up maybe. I think mine was doing something similar and it was the emulsion tubes had crap in all the little holes and just werent doing theyre job.

I would tear down the carbs and give them a good clean (if you didnt already). Btw I have a good contact over here who can get any jet size you want for around $6 a jet, and carb rebuild kits if you need.
 
Compression test the motor. What do the plugs look like after the idle? Carbs synced with manometer?
 
Thanks guys. I'll give the carbs a clean & do some testing and update. I've got some larger pilot jets so I'll try those too.

Hey Greasey that is the price I pay for jets so we probably buy from the same place.

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