Older Jiffy Model 30 Compression Numbers

[sr73087]

I did a compression test for the heck of it today on my old jiffy model 30 and got 120 psi. Is that normal for most augers?

[hankthecrank]

I would say those are pretty good numbers, if tuned right should be a strong runner.

[dkfry]

I looked in my service manual PDF file and saw no mention of compression psi. Maybe it is there I am just blind but I looked 3 times. You are not going to have high compression on most 2-strokes. I would say your 120psi number is fine especially if it was taken dry. Just so it runs good and has good power.

Just for a comparison the compression psi for the older Homelite 25cc and 30cc engines were 90psi.

[hamms]

The model 30 is like 85cc...

[dkfry]

Two stroke outboard motors are a lot larger than 85cc and most have a compression ratio between 6:1 - 7:1. To convert the ratio over to an approximate PSI number you multiply by 14.7. So a 7:1 CR would equal approx 103psi.

[toofuss]

thats more than my old 50hp johnson outboard has and I was told mine was exeptionallly good for its age. i think mine was 110 and 108

[Rebelss]

Rule of thumb is anything over 100 is good. You're dandy. 

[Dags Bait Maine]

I did a compression test for the heck of it today on my old jiffy model 30 and got 120 psi. Is that normal for most augers?

I would be very Happy with that much compression, especially in an older motor.....~Marcel