low compression=?

scottorious · Post by **scottorious** » Mon Mar 28, 2011 9:48 am

So my aero tested out to be 50 psi compression. Much lower than what it should be, but that scooter still runs essentially fine. Starts easy and runs up to 38 pretty easy. With compression that low would I still be seing the scooter run that well or is my compression gauge lying to me.

bakaracer · Post by **bakaracer** » Mon Mar 28, 2011 12:02 pm

how many times did you crank it?

Trafficjamz · Post by **Trafficjamz** » Mon Mar 28, 2011 12:31 pm

scottorious wrote:So my aero tested out to be 50 psi compression. Much lower than what it should be, but that scooter still runs essentially fine. Starts easy and runs up to 38 pretty easy. With compression that low would I still be seing the scooter run that well or is my compression gauge lying to me.

Your gauge is lying to you.

50 psi would never run .......especially all the way to 38 mph.

Bear45-70 · Post by **Bear45-70** » Mon Mar 28, 2011 5:31 pm

Compression test is done with the throttle wide open and preferably with a warm engine. However, I agree with TJ, they won't run at 50 PSI. I have a 60 PSI Aero motor and it will not run, it won't even pop.

scottorious · Post by **scottorious** » Mon Mar 28, 2011 10:24 pm

I did it with the throttle wide open and i cranked it quite a bit and ran multiple tests. Tomorrow I am going to check all the connections on the guage to see if anything was loose.

eliteguy50 · Post by **eliteguy50** » Tue Mar 29, 2011 12:11 pm

scottorious wrote:I did it with the throttle wide open and i cranked it quite a bit and ran multiple tests. Tomorrow I am going to check all the connections on the guage to see if anything was loose.

Try a dry test and a wet test to see if your gauge reads different. I've had scooter engines that run at 60 psi but they would only get to about 2/3 of top speed.

Trafficjamz · Post by **Trafficjamz** » Tue Mar 29, 2011 12:31 pm

bakaracer wrote:how many times did you crank it?

How many times should you crank it?

killerpancake · Post by **killerpancake** » Tue Mar 29, 2011 1:54 pm

i always crank until the psi stops climbing, then i go a few cranks more.

bakaracer · Post by **bakaracer** » Tue Mar 29, 2011 7:28 pm

Trafficjamz wrote:
bakaracer wrote:how many times did you crank it?
How many times should you crank it?

yeah crank till the needle stops. thats usually around 7-10 kicks

Wheelman-111 · Post by **Wheelman-111** » Tue Mar 29, 2011 8:11 pm

Greetings:

Small-bore engines are exquisitely sensitive to the volume of the compression gauge and its hoses and adaptors.

My $10 HF gauge came with an adaptor that when installed caused the readings to go down 30 PSI.
(I eventually discovered I could connect the hose directly to the spark plug threads)
I'm not sure how comparable readings from different gauges can be.

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