# newer trimmer/pole saw engines smaller?



## wa5ngp (Aug 14, 2010)

I've got an old school ryobi 767rj. I'm looking at buying something similar for when this one is just worn out. This 767rj is 31cc. Looking at the new stuff it seems like the only way to get one that large is to go commercial grade.

Have the engines been downsized over the years? Less power now or are they doing some kind of loop charging to get the power back?

For the moment it looks like the best bet is to keep babying this one along.


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## 30yearTech (Sep 14, 2006)

Ryobi units sorry to say are low end. They used displacement to deliver power. 

You can purchase a much smaller displacement engine on a premium unit that will have more power and performance than a larger displacement less efficient units. 

Most older Ryobi units were reed valve engines, new ported engines do deliver better power/performance with smaller displacement. 

There are also EPA regulations that may affect the displacement of 2 cycle engines of certain designs.


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## wa5ngp (Aug 14, 2010)

tks for the answer. it motivated me to do some googling and study of the various 2 cycle implementations.

Don't worry you didn't hurt my feelings about Ryobi and low end stuff, I am aware. 

I wonder if after using the engine for a long while under heavy load as an extended pole chain saw (after burning a tankful of gas) that the reed valves get so hot that they stop working effectively. Then if the engine dies its impossible to restart until its allowed to cool down. 

I would think that a rotary valve (probably more expensive) would not suffer from this problem.


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## finaprint (Jan 29, 2006)

At high loads like that when they die pretty quick after loaded for a while they are simply too rich to start again. The die coastdown loads the cylinder up with the full rich mix you were last running. 4 stroke mowers do it all the time, often a much better hot start if you slow down to idle for a minute before you kill it, the idle eats the excess fuel. 

All types of induction 2 strokes (PP, RV) can do that. Not the reeds.


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## wa5ngp (Aug 14, 2010)

TKS for updating that old posting of mine. I'll keep that in mind. The problem was that it was stalling when it had been running hard so cool down would take a long time. Maybe it was time for a rest anyway.

In the meantime, I decided to splurge and spent $600 for an echo pas266 with weed eater and pole pruner. Runs great of course, but then of course its new. Amazing to be able to set it down and the idle keeps going even after a hard run.

I'm disappointed to see so much small plastic stuff on something so expensive and getting a string trimmer with a catalytic converter was a surprise too.

I will tinker with that old ryobi, it was actually one of the better early versions that they made. Not sure who made them, I see similar ones by craftsman. perhaps oem was Poulan before they got so bad.


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## 30yearTech (Sep 14, 2006)

wa5ngp said:


> catalytic converter was a surprise too. I will tinker with that old ryobi, it was actually one of the better early versions that they made. Not sure who made them, I see similar ones by craftsman. perhaps oem was Poulan before they got so bad.


2 cycle engines because of design are inherently "dirty" engines, the catalytic converter helps burn off the raw fuel in the exhaust from the scavenging process. The old Ryobi units were actually made by company called IDC (inertia dynamics corp.), I don't know if they are still around.

When an engine stalls during use, the engine does not "load up" with a rich mix, keep in mind when the engine dies unless it was due to flooding, the inertia from the run down also exhausts any fuel that is drawn in, there is no excess build up of fuel.


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## finaprint (Jan 29, 2006)

I respectfully disagree. If that were true then you could never flood a motor, the exhaust sweep would simply pump it all out yet it clearly doesn't. Not talking about clear flooding like a needle stuck open, rather a light or mild short term rich condition with nothing wrong with carb at all. As well if you hot stop at rpm and it won't start, it often starts up easier by pulling air filter assembly to then be leaner. Same with pulling a plug and then whirling engine over with plug out, it clears cylinder out and starts back up easier then. Not talking about a stall, but that can show it too, a normal hot stop on a full fuel tank can do it. Letting engine die while letting off throttle will add to it, the closed throttle runs decel vacuum up way high and cylinder then overpulls fuel to richen too. On a 4 stroke mower the engine slowing down lets the throttle close too as the airblade settles back to close the throttle plate, same thing happens. Inertia only clears the cylinder on a coastdown if the throttle is held full open yet that is usually not the case. Why emissions commonly go way up (excess HC) on decel and engine makers go through fits doing different things to control it. Where decel solenoids and valves and the like came from. The highest vacuum to pull fuel out of carb is at decel, the higher the rpm the worse it is.

Perhaps I misspoke in a way, the mix is not so much 'richer' as in running rich, rather temporarily rich due to the hot engine boiling any after run coastdown fuel or fuel in carb to make the chamber richer in effect at that time. It happens on literally every older piece of equipment I have (I run them until they are pretty much dead, a mower often lasting 10+ years) and the issue shows during the heat of summer. The engines are NOT flooding and run normally and perfectly at least until you kill it. Then if you do not start it back up pretty much right then it becomes harder in a minute or so (time element of hot soaking) and only cooling it way down lets it go back to starting easily again. It's what is known in cars as a 'hot soak', a phenomenon known about for 75+ years. The fuel if close to engine hot parts boils to force vapor into intake to artificially richen it for a bit. Fuel commonly boils in bowls at 100+ degree temps, put clear fuel lines on and you see that all day long, the lines bubble like no tomorrow. 

The two things there combine to make motor harder to start, on a 2 stroke you start back up with throttle wide open and easier then. On the mower I generally yank the airfilter real quick, up and running instantly then when it wouldn't start. The problem is worse on older equipment, older engines being b-tchier about things just like us old people. Often you can clearly see it was rich, the first few puffs of exhaust are the black smoke of too rich, then motor cleans out in a second and runs perfect. The piece of equipment will idle perfectly all day long, again, nothing wrong with the carb. 

Most modern MPFI cars now have the throttles cut off the injectors if you hold them further open to start easier in hot temps for the same reason. Pumping air only and no fuel at all, then a pretty hot engine starts right up. Even though no fuel being pumped then the intakes used now have much more volume and commonly a low point in many that fuel drops out into, then the heat of hot engine percolates that to create vapors to make hot engine harder to start in the same fashion. Powerful electronic ignitions now used minimize that quite a bit too.


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## 30yearTech (Sep 14, 2006)

finaprint said:


> I respectfully disagree. If that were true then you could never flood a motor, the exhaust sweep would simply pump it all out yet it clearly doesn't.


We will just have to agree to disagree. 

First off I am not referring to anything but small engines. The rundown DOES exhaust any fuel that is drawn in and will not make it excessively rich enough to be hard to restart, *unless the reason for the stall was excess fuel*. 

If you have to remove an air filter or clear out any excess fuel, to restart an engine, there is an issue with the engine. A properly set up engine, in good mechanical condition, will not experience this type of issue.

*Yes you can most definitely flood a motor,* if you restrict the air intake to draw in more fuel and less air, an improperly set up or adjusted carburetor, a dirty air filter, incorrectly adjusted float or fulcrum arm etc. can flood and stall an engine. This will result in a rich condition that run down will not clear and result in a hard restart, unless the fuel is cleared.

Stalling an engine from an excessive load will not result in a *flooded* engine. 

An engine that stalls for any other reason, well obviously has some type of issue and that specific problem would need to be addressed. 

Most hard hot restarts can be for any number of reasons. They are often due to a compression issue or a lean issue (unless there is an actual flooding issue with the carburetor) Boiling fuel causing a vapor lock is a lean condition not a rich condition, and not often associated with small engines that have not been modified. 

http://www4.briggsandstratton.com/m...on_Troubleshooting_Detail_Reference_Guide.pdf


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## finaprint (Jan 29, 2006)

'Vapor lock' commonly misunderstood by many, you can easily be super rich there just like lean. If fuel boils in a bowl it commonly percolates fuel up and out the carb discharge point from the bubbles lifting it out. 

I was talking about work overload stalls, the engine runs fine right up to the second it chokes but then starts but puffing black smoke for the first 10-20 revolutions until it clears out to run fine. Starts easier if done right then, let it sit a minute and it gets worse and harder. You won't be fixing carb as nothing is wrong with it. The equipment then runs fine the rest of the day. Seen it multiple times and multiple pieces of equipment both 2 stroke and 4. Could be compression tied to the issue somewhat but in no way is the piece of equipment bad enough to need mechanical work on it, that would be way wasteful of money, it has years left to go yet.


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## 30yearTech (Sep 14, 2006)

finaprint said:


> 'Vapor lock' commonly misunderstood by many, you can easily be super rich there just like lean. If fuel boils in a bowl it commonly percolates fuel up and out the carb discharge point from the bubbles lifting it out.
> 
> I was talking about work overload stalls, the engine runs fine right up to the second it chokes but then starts but puffing black smoke for the first 10-20 revolutions until it clears out to run fine. Starts easier if done right then, let it sit a minute and it gets worse and harder. You won't be fixing carb as nothing is wrong with it. The equipment then runs fine the rest of the day. Seen it multiple times and multiple pieces of equipment both 2 stroke and 4. Could be compression tied to the issue somewhat but in no way is the piece of equipment bad enough to need mechanical work on it, that would be way wasteful of money, it has years left to go yet.


I have no misunderstanding about what I know from over 45 years of experience, but if it works for you then that is what is good for you.


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## finaprint (Jan 29, 2006)

About the same length of time here, but with engines of all ilk, I raced plenty of 2 and 4 stroke motorcycle and modded them as well and lots of drag racing and engine building, we specialized in American Motors engines but also ran 700+ inch BBC prostockers at over 200 mph.

Food for thought.................if the equipment has a hand throttle and you release it and then kill it, the closed throttle then bumps decel vacuum way up and you pull more fuel in on the slowdown. If say 4 stroke and you kill ignition to coastdown, the engine then is not combusting and then there is much less exhaust sweep, most of it being by the big bang that ignites to have big pressure seeking a way out. At that time the exhaust valve being smaller than the intake will not flow as much past it to 'clear the cylinder out' with simple pressure wave pulsing. As well there are always frictional losses that leave some fluid droplets behind and more so with 2 strokes being they are loop charged. There are often remainders of fuel left in the crankcases, another reason why they are 'dirty' engines. Many multicylinder 2 stroke bikes looped one crankcase to the next with check valves to pump those remainders out, it made for cleaner more reliable starts and less emissions. Crankcase pumping that pressurizes say chain oil tank does the same. 

Fuel pumped into an engine needs to burn, if not it tries to stack up. Much or most will sweep through but not all. I've changed literally hundreds of wetted plugs out from that. Modern MPFI in cars is worse as it injects whether the engine is started or not. Simply whirling starter around to flip the motor over can foul plugs if you don't get it running in 3-4 tries. Why the injectors turned off thing was created. 

With all that going on it's a wonder even new ones manage to start at all. I personally see little difference in any engine other than size, the only thing that changes is the way they treat air, smaller ones are more 'air active' than larger, making the bigger ones less efficient. It being a physics thing. 

Luck to you and yours................I always love your posts.


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## 30yearTech (Sep 14, 2006)

finaprint said:


> Food for thought.................if the equipment has a hand throttle and you release it and then kill it, the closed throttle then bumps decel vacuum way up and you pull more fuel in on the slowdown.


 That would be true if the throttle plate was positioned where the choke plate is, but with the throttle plate virtually closed, there will be minimal if any additional fuel drawn through the main jet from the carburetor, in this type of scenario. In fact if the high vacuum from the deceleration of closing the throttle did in fact draw excess fuel, the engine would die on it's own rather then continue to run at an idle speed. It wouldn't matter if you shut it down or not, every time the throttle plate is closed on a running engine intake vacuum increases.



finaprint said:


> If say 4 stroke and you kill ignition to coastdown, the engine then is not combusting and then there is much less exhaust sweep, most of it being by the big bang that ignites to have big pressure seeking a way out. At that time the exhaust valve being smaller than the intake will not flow as much past it to 'clear the cylinder out' with simple pressure wave pulsing.


 Fuel from run down tends to accumulate in the exhaust not the cylinder, hence the need for after fire solenoids to help prevent the after fire bang that occurs when a hot engine is shut down.




finaprint said:


> Fuel pumped into an engine needs to burn, if not it tries to stack up. Much or most will sweep through but not all. I've changed literally hundreds of wetted plugs out from that. Modern MPFI in cars is worse as it injects whether the engine is started or not. Simply whirling starter around to flip the motor over can foul plugs if you don't get it running in 3-4 tries. Why the injectors turned off thing was created.
> With all that going on it's a wonder even new ones manage to start at all. I personally see little difference in any engine other than size, the only thing that changes is the way they treat air, smaller ones are more 'air active' than larger, making the bigger ones less efficient. It being a physics thing. .


 We digress. 
Once again, I am only referring to small engines, the type used on outdoor power equipment, not motorcycles, racing karts, or automobiles. While the basic principle of operation is the same for these engines, there is a world of difference in them. There are a few fuel injected engines available now in some outdoor power applications, but the engine the OP was asking about is a carbureted engine. I am not offering any explanations to anything other then what was being discussed in the original post.

I see that I am not going to get you to see from my perspective, so like I previously stated, we just have to agree to disagree on this.


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