somewhat low compression and squish?

[1980mcneil]

So my bike probably Has less than 40 hours on it since I replated it and did a top end. My compression is at 120 which is within spec. That test is being done with an automotive compression tester which might yield lower results by five psi or so. With that said plenty of people have use the same or similar compression tester and their bike is in the 160s on a fairly fresh motor.

The reason I’m Diving into this is partially bored and partially necessity. I just woods ride and I want my bike to idle. It doesn’t have to idle for 10 minutes. But although it runs great starts on the first kick when warmed up and has plenty of power, it doesn’t wanna idle well.  For the tight trails riding I’m doing it’s annoying that sometimes the bike won’t even idle for five or 10 seconds. If the idle is too low like it is now the bike sometimes just wants to die. If I turn up the idle too much more it wants to surge and get into a high idle.

I started reading about squishing one night and I thought to myself maybe the lower compression and an improper squish just isn’t allowing the bike to run as efficiently as it needs to to have a strong idle.

That leads me to the squish test. First of all is there a better way to do this then using a piece of Solder?  I’m just not confident with the readings I’m getting. It looks like I’m in the .185 range. It’s hard to measure where the actual tip of the Sauter is. But let’s say that’s accurate and I could get it down to the .15 range taking off 30 or 35,000.  With that much give me the extra 40 psi I’m looking for on the compression test?

[1980mcneil]

One final question. If I’m stuck at this compression till after the riding season, not having any head work done till winter. Should I use a hotter plug or anything to help with idle?  I think the carb is dialed in as far as on the throttle. But I still don’t get the light brown color on the top of the spark plug.

[Powermax]

I’d recommend checking the operation and function of your Accu-products decompression Valve.  I’ve had issues in the past with decompression valves being the cause of lower compression numbers.  Maybe try pulling it out and replacing it with well sealed pipe plug and try your compression test again.  Maybe not your issue, but worth trying to eliminate the decompression valve as a potential source of your problem.

[sandblaster]

Before we go down a long and dark hole, I'm wondering...
What year is your engine? pre 89?
When you rebuilt it, What piston did you use?

Here is  better way to measure your squish.
That part starts at about 4 minutes.

https://www.youtube.com/watch?v=eTjceU2M7kw

[1980mcneil]

So I did replace the piston rings.  I was getting a little blow-by in the same spot on both sides.

I want to get rid of my Accu-products Dcomp anyways.  Gonna get the electric start this winter so I don't need a weak spot.  I've removed it before for cleaning. I dont think it is leaking though.  No soot in the threads and not through the clean valve after cleaning and not using the valve for a rid and checking it again.  No blow-by on the valve.

but I've always suspected that the style or any pressure release would have to lend itself to at least slightly less compression since the chamber is larger for part of the stroke.

I admittedly have a BS car compression tester.  before replacing the rings I was getting 120psi and after replacing, only 125.  I later read that possibly a car Comp tester is inadequate for testing a dirt bike.  There is not enough turnover speed and volume to fill the larger 1/4 hose that is used. 

The new rings felt harder to kick over after a heat cycle.  But my bike never seems hard to kick like people talk about. I can pretty much sit down and kick it.  I am 240lbs though.  Might be different if i was 170lbs like "MX ridier".  I don't even bother using the compression release on the trails.  Could be my compression is just fine now.  My buddy has a "dirt bike" comp tester.  So that is the next step I guess.

If you know about the Accu-producks style valve.  Could I send my cylinder in to get the "sleeve" pulled out and plugged on the cylinder wall and outside of the cylinder, or just plug the wall with an aluminum plug and re nickasil the cylinder?

Say I am only getting 125PSI comp test.  I'll figure it out over the winter, but should I try going to a 7 heat range to get rid of my sooty plugs?  I run non ethanol 100 octane fuel.  Or should I just not bother?
as a side note, besides the plug I had to (and failed too) scrape a layer of buildup off the piston.  Never got it all off... 
I've only ever fouled 1 plug and I did have the carb way to rich. but would running a 7 help keep the plug or even the piston cleaner? If either of those are even a concern?  Would I still be okay to open it up on the straights with adequate jetting and 100 octane race fuel. (BTW I run 32:1 Castor)

to answer your question I have a Wisco 2 ring stock size piston and Millennium coated the cylinder about 20 rides ago.  3 hour ride average mostly low speed 1st 2nd gear trails, with occasional higher speed roads.

I will say a lot of this is pure curiosity, tinkering, fun, and dialing it in.  Other than my idle at times the bike runs like a champ.  Even if it's not putting out every HP possible, Its way more powerful than my buddies yz250. It starts cold on 2-3 kicks, and warm (i can get quick or lazy sometimes, but if i try) starts on 1 solid kick.

So My issues are nothing like some peoples.  I just like learning, researching and absorbing info on things I'm interested in.  Looking forward to your responses.  Thanks for your time.

[1980mcneil]

Before we go down a long and dark hole, I'm wondering...
What year is your engine? pre 89?
When you rebuilt it, What piston did you use?

Here is  better way to measure your squish.
That part starts at about 4 minutes.

https://www.youtube.com/watch?v=eTjceU2M7kw

It's a 2004.  Supposedly a very low hour bike.  The limited specs I could check on the crank with the cylinder off showed it was still tight.  it was 2017 but I think I checked side to side slop and connecting rod slop.  I sent off a stock size weisco piston to millennium coating they matched it and did mild port work for "bottom end".  Before this year I had less than 10 outings on the new top end.  2-3 hours max each time.  This year I probably have another 30-40hrs on it.  replaced the rings 2 rides ago.  A little blow by and lots of caked soot on the top of the piston.  I cleaned up the sides of the piston where the blow by left soot and scrapped the top of the piston with a plastic scrapper and various solvents.  Got rid of some of the build up on the outside, but deposited remained on the center.