Low compression numbers

[darringer]

My gauge also has the check valve at the base of the gauge. The hose measures 21". Compression taken on my ice cold 99 cr250 is 210psi. I don't think it would be any higher with a gauge that has a smaller hose. If I can find someone that has one, I will test with both and report the findings.

 

[holeshot]

Checking the snap-on site shows that their $216 tester has six check valves.

A trip to Autozone revealed that all the compression testers that they sell have check valves at the base of the hose (looks like the air valve on your tire). The top-of-the line $40 unit even has a spare check valve.

The cheapo POS Harbor Freight unit that I bought does not have this one essential feature.

Lampooned by my own cheapness. :(

So everyone is correct. If you're naive enough to buy a $10 tester, then hose length probably will make a difference.
If you spend a little more to get one with a check valve at the hose inlet, then hose length should make no difference.

 

[reelrazor]

Even with the check valve at the bottom of the hose, it DOES make a difference. Each stroke has to overcome the previous stroke's pressure to defeat the check valve. This gets proportionally higher and higher as the pressure rises. i.e. the piston is higher up it's stroke when it does overcome the stored pressure. This means it is displacing even LESS volume each time, while trying to raise the pressure in an already largish volume.

Basically, yes, you CAN achieve the same pressure reading with a long hose, but it will take waaaaay more kicks/strokes than a short hosed(small volume) unit. You will hit a point where the needle is rising but at a rate that seems like it has peaked and you will notice that the needle peaks and then settles some before 'storing' a reading.

Ever filled a portable air can? You know how it takes more time to get the last 20psi in it than it does to get it up to 100psi from 0?

Same effect.

After talking about this last night here I spent some time at my shop testing this very concept today, plugging my echo guage into every hose available in my bike/sled shop and the next door auto shop, with hoses from cheap units and hoses from that $216 snap on kit. My echo guage has a check valve on the guage head and one on the plug end of each of its' hoses. I used a 440rotax powervalved sled engine(twin-220cc per hole) with no exhaust pipe and carbs removed. With the stubbiest of hoses(an inch of hose between hose end connectors) I saw 185psi in two pulls. With a 25" hose w/o a check valve on the hose I gave up at 136psi after 15 pulls. With an 18" check valved hose I achieved 185psi after 9 pulls. Each pull on the sled starter rope equaled 6-7 crank revolutions.

 

[holeshot]

.

Basically, yes, you CAN achieve the same pressure reading with a long hose, but it will take waaaaay more kicks/strokes than a short hosed(small volume) unit..

I agree. I meant that the end result should be about the same (as long as it has a check valve at it's base). A longer hose will make you sweat more.

:eek:

 

[JasonWho]

What's a check valve?

 

[reelrazor]

What's a check valve?

Allows fluid flow in one direction only. Like the shrader valve in your tires/tubes(yeah yeah I know, you CAN let the air out of tires, but you are manually defeating the check valve and/or running over ****).

 

[russ2400]

hey, what type of pre-mix do you use? and did you say you didn't de-glaze the cylinder wall?

 

[holeshot]

Took the $10 Harbor Freight tester back and purchased a proper tester from Autozone (long hose with a "shraeder" type check valve at the bottom of the hose) for $25.

This tester came up with a reading of 180 psi (65 psi higher).

Lesson learned: Never test your motorcycle with something that costs less than two pannidos at Jack-In-The-Box.

:joke:

 

[JasonWho]

Hello. Thank you very much for the information. I am glad you got it all straightened out. I was leary of some of their stuff, so I guess that proves it on at least one item.