Super Jet 1995 701 stock compression? 145 to 150 is this low?

[storch]

I am getting 145 to 150 with new tester on an original motor?
Just bought a 1989 Kaw 650 sx with pipe and someothere mods, runs a bit stronger than the SJ, compression reads 180lbs, is the SJ in need of a fresh top end? it runs a bit soft on power out of the hole or out of turns.

 

[Vumad]

150 is stock. the SX probably has a milled head.

 

[storch]

Not happy with the responsiveness on low end especialy.
My need a little more fuel screw adjusting.

should i do a fresh top end and head work before shoping for a pipe?
winter project, done for the season

 

[Vumad]

Why would you put a fresh top end on a motor with good compression? My understanding is a pipe is the best bang for you buck for power, but I can't see milling a head costing too much.

 

[motozachl]

On my brothers ski the compression is 150 BUT has an AM head....shouldn't it be higher?

 

[Vumad]

On my brothers ski the compression is 150 BUT has an AM head....shouldn't it be higher?

aftermaket head does not mean high compression. depends on the size of the domes. aftermarket heads provide better cooling. It may have replaceable domes and he's running a larger dome (same as stock) and the head was only added to improve cooling. he needs to find out what cc domes he has and the expected compression for those domes.

 

[Vumad]

Not happy with the responsiveness on low end especialy.
My need a little more fuel screw adjusting.

should i do a fresh top end and head work before shoping for a pipe?
winter project, done for the season

compression isn't responsible for low end power. It's responsible for overall power. low hit on bottom end is going to be most likely related to carb tuning, pipe set up, prop pitch, timinig or porting (most likely carb). higher compression would only improve the bottom end because it increases overall power. if your bottom end sucks, dont try to compensate with more power. Fix the tuning issue.

 

[gabe_k]

Same ski, same motor.. Compression is 148/150 and rips pretty hard. I've got a protec pipe, 46mm carb, 9/17 prop.

Plan on switching to a b pipe this winter and some porting..

Your motor should run strong.. Keep on tuning that carb

 

[storch]

How sensitive is the low and high fuel screws, originaly I had to go way out on both like 3 to 4 turns to eliminate flat spots and dieing out on take off, would not hardly run with screws in the normal 1 turn out range.

Only mod is a Blowsion flame arrestor that was on it when purchased, though this may have leaned it out needing larger pilot and main, hopefully Im not sucking air thru main seals, idles steady

I had the carb tested and jetted up and now runs a bit better in the 1 to 1.5 turn out range.

It has a new Solas impeller that was recomended by impros, I belive it is the Concord 12/18

Still seems sluggish mostly when carving tight turns and giving it throttle, mid and up seems good.

Just thought that at 17 years old a fresh top end may be needed.