poulan/weedeater 25cc timing changes
03-31-2007, 06:29 PM
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poulan/weedeater 25cc timing changes
I remember reading about someone increasing the intake and exhaust timing on Poulan/Weedeater 25cc engines for an increase in power, but I could not find it again when I did a search. Whoever posted the info, could you post it again and go into more detail on how to do the modifications?
04-02-2007, 01:55 PM
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RE: poulan/weedeater 25cc timing changes
http://www.rcuniverse.com/forum/m_1267448/tm.htm
theres some stuff on that thread about port timing...long thread happy hunting
theres some stuff on that thread about port timing...long thread happy hunting
04-02-2007, 04:12 PM
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RE: poulan/weedeater 25cc timing changes
Typhoon pilot,
The concept is simple, raise the exhust and transfer ports to advance timing and increase duration. On a piston ported intake engines, you can trim the piston skirt on the intake side or lower the intake port to increase duration. On a reed valve, such as Ryobi, bend the reed limit stop out to increase flow. Be careful not to let the limiter come to close to the crankpin and con rod. I am attaching a 360 degree timing wheel that you can printout. Instructions for using it are on the CH Ignition website. Some stock engines have more advanced port timing them others. Homelite's and Ryobi's are examples of trimmers like this. Toros, Echos and weedeater trimmers have less port duration. A good starting point is 150 degrees exhust, 110 degrees transfer and 140 degrees intake duration. Most chain saws already have these port timings or slightly greater. Be care not to widen porte too much or the rings will catch on the port edges. Pinning the rings allow wider ports. Always place some sort of guard over any area that isn't ment to be modified. When you slip and you will, you will be thankful that you did. Practice on a junk engine, such as one that was run without oil.
Dave
The concept is simple, raise the exhust and transfer ports to advance timing and increase duration. On a piston ported intake engines, you can trim the piston skirt on the intake side or lower the intake port to increase duration. On a reed valve, such as Ryobi, bend the reed limit stop out to increase flow. Be careful not to let the limiter come to close to the crankpin and con rod. I am attaching a 360 degree timing wheel that you can printout. Instructions for using it are on the CH Ignition website. Some stock engines have more advanced port timing them others. Homelite's and Ryobi's are examples of trimmers like this. Toros, Echos and weedeater trimmers have less port duration. A good starting point is 150 degrees exhust, 110 degrees transfer and 140 degrees intake duration. Most chain saws already have these port timings or slightly greater. Be care not to widen porte too much or the rings will catch on the port edges. Pinning the rings allow wider ports. Always place some sort of guard over any area that isn't ment to be modified. When you slip and you will, you will be thankful that you did. Practice on a junk engine, such as one that was run without oil.
Dave
04-16-2007, 08:47 PM
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RE: poulan/weedeater 25cc timing changes
I posted the changes for the weedeater some time ago, I modified the exahust port timing from 135 degrees to 145 degrees and the intake from 115 I think to 125 degrees, measure your base timing and let me know what your numbers are, I didn't fool around with the transfer ports, it works great as it turned out.
AERO NUT.
AERO NUT.
04-17-2007, 12:08 PM
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RE: poulan/weedeater 25cc timing changes
Thanks Aero Nut. Still breaking them in as weedeaters right now. I have to finish up a couple of other projects first anyway.
Typhoon pilot
Typhoon pilot
