# 2 Cycle Compression



## ccrider966 (Jul 8, 2006)

I fix a lot of weedeaters, blowers, etc. Usually I just renew the fuel lines and replace the carb diaphram and clean the carb filter screen, and clean out all the passages. Sometimes I get one that will not start or run which I suspect is due to low compression. I have even shot some oil in the cylinder and sure enough it would run a little. I tried to measure the compression and I get from 55 to 65 psi on my gage on both those that run and those that do not. Are these typical readings after 5 or 6 pulls? I read somewhere that it takes 70 psi for an engine to run.
I have had this problem with a lot of Weedeater Featherlite Weeders. Some won't run even when gas is squirted in the carb. I don't understand how the gas gets from the carb into the cylinder, does it first go below the piston? Also what works the diaphram, is it vacuum or pressure and how does it get there?
I have really good luck with Craftsman Blowers which have a reed valve visible beneath the carb. Does that make them better and what does it do?
I think these points would be of general interest to this forum! Thanks!


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## jsouth (Jan 31, 2008)

My 2 cycle manual says no less than 90# of compression.I found some of the 2 cycle equipment doesn't run good on 90# of compression.I like it to be 120# or better.Hope this helps.

Jerry


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## Rentahusband (Aug 25, 2008)

I worked on an old Lawnboy snowthrower that had 65# of compression. I thought it was to low to mess with it. Another member on here tested a similar engine of his that ran fine. He also had 65#. I put a carb kit in and it ran fine. Apparently some of the older Tecumseh motors have a compression release.


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## 30yearTech (Sep 14, 2006)

These were probably reed valve engines. Engines that utilize reed valves can operate with lower compression then ported type setups.


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