Problem starting a 1074 Pioneer, compression?

[redbrass_ca]

Dear Members,

I am looking for some coaching on a problem experience with my old pioneer 1074. The saw was very reliable until a month ago. The saw fails to start because the fuels is not drawn to the carburator. The intake fuel line ( which is clear) is full of air. The gas tank filter has been replace. The carburator ( Walbro Wa)has been cleaned and overhauled. When the saw is primed it start for a short spell. If a pressurized seringe full of mix gas is applied to the intake port of the carb if can be started for a short while also. The carburator diaphragm is new. If I draw gas from the gas tank using a seringe it fills readily. It appears there is insufficent vacuum created by the piston to draw the gas. I did a compression test on the saw and it is low ( about 105 PSI). The compression on a new saw should be in the range of 150 PSI . Can the compression of the saw affect the vacuum considerably? Can this vacuum be measured?

As chainsaw age, they loose compression overtime from wear and tear. How much compression can they loose before failing to operate? Could you loose 20 % of you compression without adverse effect besides power loss?

Any insight would be most welcome

Thierry G. Papion
Halifax Nova Scotia

 

[Woodie]

Not much of a wrench myself, but I'm thinking 105 lbs. is about the point where a saw would fail to run...how old are the ring(s)?

 

[cuttinscott]

The 1074 has a auto decompression valve so your 105lb reading is incorrect. I would recheck fuel lines and carb

http://www.acresinternet.com/cscc.n...6cb8b65e3260962688256b00001a7609?OpenDocument

Scott

 

[redbrass_ca]

Thanks for the quick replies.

I forgot to add that when I took the compression test, I removed the linkage that depress the compression release valve so I could get an accurate reading. Hence the 105 PSI reading is what is created without the pressure release valve open.

Thanks T. Papion