This is a 2004 ds 90. It slowly lost top end accel. over a couple of weeks then quit running at more than an idle. I put in a new plug, removed and completely cleaned the carb and jets, replaced the electric choke(107.00dallar bust) and still the same prob. I then removed the back section of the tailpipe, just in case the exuast was restricted, no luck. Took off the jug, checked rings, end gap etc.. Cly. was in near new condition as was the piston and head. removed all of the exuast, sameo sameo, starts and idles, no top end. Pulled the reed box ,all ok there. The one odd thing is at idle speed it seems that that air/gas mixture blows OUT the carb a bit, enough to lightly coat your thumb if you hold it close to the opening. I'm at wit's end and have run outta things to pull off and check. It's gettin expensive on the beer tab, sitting here and trying to figure it out!! ANY ideas or suggestions would be greatly apperciated. Have a Merry Christmas.. Jeff K

 

Happy Holidays to you also jeff.
I know alot of ppl have big trouble with the eletric choke carbs. Most opt to buy a different carb.
I consider the slight blowback normal.
I realize the piston/cyl looked good, but I think i'd do a compression test just to see what it is.

 

Thanks for the reply, I ran a comp test Sun. and came up with a staggering 80.(3 differnt times) What should it be as per factory specs? I've looked online and can't find an awnser. Also should I buy a new cyl/piston/ ring set or bore and replace piston/ring only. Power was not an issue when it was running. Thanks again, Jeff K.

 

Most compression readings are from 100-120 depending on brand.
You would take the cylinder to a shop for a new bore/piston. No reason to buy a new one.

 

thanks for the help. I will redo the cly/piston and see what happens. Have a great new year. Jeff

 

Hey guys, I would only bore the cylinder if it has deep gouges or groves. Since your compression is low and you said the ring clearance is good I would do a light hone and replace the rings with the standard set. In my opinion it is a little overkill to bore to the next size piston and costly if this doesn't fix your problem.