Pincushion Posted January 15, 2009 Report Posted January 15, 2009 I finished up with the rebuild last night. Stock jugs punched .020 over with some wiseco pro lites. I buttoned her up, filled the radiator and she fired up in 3 kicks. Idled fine and everything was good for the 10-15 seconds I ran it until I woke up my son and caught hell from the wife. Today I go out to fire it up and do a heat cycles and the fugger wont start. Compression feels low to me, but I'm used to my high compression YZ so its probably just me. A little history: Got this quad last summer. Stock internals, FMF fatties/silencers, TORS removed and K&N pods. Compression was low (120#), so I decided to rebuild. The stock pistons were in there too long as there was piston blowby and cylinder scuffs from the piston being sloppy in the bore. Today I did a compression test and both cylinders blew 130# (isn't that low for a fresh motor at 300' ASL?) and the bastard wont start. Jetting was 27.5PJ, 320 mains and stock needles in 3rd clip. I tried putting is some 40PJ (which is what was there when I got the quad) and no difference. Any ideas why it wont start after it fired right up last night? I've got a camp spot reserved at Florence tomorrow and I'm going to send this thing off a cliff soon. Any input will be appreciated! Quote
moneybags Posted January 15, 2009 Report Posted January 15, 2009 130 PSI sounds about right. Check to see if you are getting spark and go from their. Quote
tundish2800 Posted January 15, 2009 Report Posted January 15, 2009 put a little raw gas in the cylinders and kick it. If it has any spark it will hit. Quote
Mjv420 Posted January 15, 2009 Report Posted January 15, 2009 If your using a stock head or 22cc domes, 130psi sounds right. As far as it not firing back up, Check your plugs, Check your coil, Make sure the choke connection tube between the two carbs is in place. Quote
kawiking Posted January 15, 2009 Report Posted January 15, 2009 If your using a stock head or 22cc domes, 130psi sounds right. As far as it not firing back up, Check your plugs, Check your coil, Make sure the choke connection tube between the two carbs is in place. i agree.. i had 130 on my last 350 rebuild. im 300 above sea level.. .030 shaved head. with a light port job Quote
Pincushion Posted January 15, 2009 Author Report Posted January 15, 2009 Thanks for the replies folks! It fired right up with a shot of starting fluid. It looks like my choke and/or idle circuit needs some attention. These damn carbs are finicky!!!! The compression numbers worried me at first, but I realize I dont have good ring seal yet and with the stock head I wont be seeing any numbers too high. It just seemed odd that my WAY worn out pistons/jugs blew 120# and my fresh motor blew 130#. I'm still learning. And getting pissed off at the same time Thanks again! Quote
blowit Posted January 16, 2009 Report Posted January 16, 2009 Thanks for the replies folks! It fired right up with a shot of starting fluid. It looks like my choke and/or idle circuit needs some attention. These damn carbs are finicky!!!! The compression numbers worried me at first, but I realize I dont have good ring seal yet and with the stock head I wont be seeing any numbers too high. It just seemed odd that my WAY worn out pistons/jugs blew 120# and my fresh motor blew 130#. I'm still learning. And getting pissed off at the same time Thanks again! You are not going to get much higher comp than you have right now. You also have hinted on something I have explained for years and that is compression numbers do NOT always reflect an engine's condition and life left. I have literally tested a motor with 170psi pumping comp with the rings in several pieces and falling out of the piston. Regarding your starting problem, you need to make sure your carbs are balanced correctly and you may need to adjust the pilot screw to get it to start better. Try turning both all the way in and start there. Brandon Quote
Pincushion Posted January 16, 2009 Author Report Posted January 16, 2009 (edited) By pilot screw, do you mean air screws? And yes, I need to sync the carbs. I dont have much faith in the 'look and listen' method of syncing the slides. I'm sure that will get it in the ballpark, but I want it spot-on. This 350 motor is throwing me for a loop. I've been riding and wrenching on smokers for 15+ years. A single cylinder, mild compression 2 stoke 250 is a much different animal. My compression numbers will go from 260# fresh down to around 220 (15-17%) after approx 50-60hrs tun time. Compression readings seem a much more accurate and usable on a 250 single as a general gauge of engine compression. And I do agree that it should not be used solely as a tool to gauge engine life. It's a tool to gauge cylinder compression, which is just one aspect of overall engine health. Thanks for the reply! -Brandon Edited January 16, 2009 by Pincushion Quote
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