Ryobi 31cc Hop-up question
10-17-2005 | 04:19 PM
#1
Thread Starter
Senior Member
My Feedback: (1)
Joined: Aug 2005
Posts: 1,152
Likes: 0
Received 0 Likes
on
0 Posts
From: Eugene, Or
Ryobi 31cc Hop-up question
Ok I've been doing alot of reading today about prot timing and mods for assorted motors but not much comes up for the Ryobi byond the basic conversion and reed valves...
I know it's limited by it's weak conecting rod so I'm looking at mods to allow it to swing a bigger 2 or 3 bladed prop in the same PRM range.. Say 7000-8000rpm
If I were to remove the case to clyinder gasket to raise the compression I know it will also increase the intake timing and reduce the exhaust timing.
There isn't much you can do about the intake timing but would it be reasonable to open the exhaust port to compensate for the lost timing? or open it even more to make the increase in exhaust timing match the increase in intake timing?
What about the transfer port?
By doing all this wil I move the power band to high? or can I still make good in the 8k range with a larger prop?
I'm sure someone will say "put down the dremmel and walk away
"
I know it's limited by it's weak conecting rod so I'm looking at mods to allow it to swing a bigger 2 or 3 bladed prop in the same PRM range.. Say 7000-8000rpm
If I were to remove the case to clyinder gasket to raise the compression I know it will also increase the intake timing and reduce the exhaust timing.
There isn't much you can do about the intake timing but would it be reasonable to open the exhaust port to compensate for the lost timing? or open it even more to make the increase in exhaust timing match the increase in intake timing?
What about the transfer port?
By doing all this wil I move the power band to high? or can I still make good in the 8k range with a larger prop?
I'm sure someone will say "put down the dremmel and walk away
"
10-17-2005 | 07:52 PM
#2
Senior Member
My Feedback: (29)
Joined: Jan 2005
Posts: 1,402
Likes: 0
Received 0 Likes
on
0 Posts
From: San Antonio,
TX
RE: Ryobi 31cc Hop-up question
Hi sscherin,
The intake is a reed valve which is opened and closed by crankcase pressure, so lowering the cylinder won't effect intake timing. The exhust and tranfer ports will be slightly retarded. The stock timing is about 75 degrees before bottom dead center (BBDC) for the exhust and 58 degrees BBDC for the trasnsfers. This is the same as the stock Homelite 25/30cc engines which are great performers. The newer rods are beefier then thw ones used on the older engines. Many people have lowered the cylinder to get a boost in power successfully. A larger carb and free breathing exhust will help. Take it one step at a time, checking results as you go.
Dave
The intake is a reed valve which is opened and closed by crankcase pressure, so lowering the cylinder won't effect intake timing. The exhust and tranfer ports will be slightly retarded. The stock timing is about 75 degrees before bottom dead center (BBDC) for the exhust and 58 degrees BBDC for the trasnsfers. This is the same as the stock Homelite 25/30cc engines which are great performers. The newer rods are beefier then thw ones used on the older engines. Many people have lowered the cylinder to get a boost in power successfully. A larger carb and free breathing exhust will help. Take it one step at a time, checking results as you go.
Dave
10-25-2005 | 02:54 AM
#4
RE: Ryobi 31cc Hop-up question
Bend the stop on the reed out a bit. That way the reed will open more and allow more fuel in. BE CAREFUL and don't bend the stop out too much or it'll interfere with the connecting rod and crank pin.
Switch your carb. The stock carb is tiny. There is a bigger carb that fits the monting block perfectly. WT438? or a WT348? Can't remember--it's been awhile since I did that.
Get a new ring from Frank Bowman in Farmington, NM. Better seal and less compression blow-by. Makes a few hundred RPM difference.
Mix your oil at 32:1 or 40:1. Oil makes power. It also carries away the heat.
Switch to electronic igniton--lighter.
A little here and a little there---before ya know it--you got a screamer on your hands.
Switch your carb. The stock carb is tiny. There is a bigger carb that fits the monting block perfectly. WT438? or a WT348? Can't remember--it's been awhile since I did that.
Get a new ring from Frank Bowman in Farmington, NM. Better seal and less compression blow-by. Makes a few hundred RPM difference.
Mix your oil at 32:1 or 40:1. Oil makes power. It also carries away the heat.
Switch to electronic igniton--lighter.
A little here and a little there---before ya know it--you got a screamer on your hands.
