Hi Rich, I will try saving the photos and looking at them in my Camera software just for the fun of it and to see if it will work. Several posts back I give the diameter of a drill bit that I used as a gage to check the diameter and match up the port sizes and this drill bit is quite a bit larger than the original ports were. The original ports are susprisingly small and I don't think it is to prevent the rings from snaging the ports in this case.

Rich, I checked and printed the photos you supplied. I now see what you were talking about. How it works is different than I thought. It looks to me like the "lead Air" term they are using, as we might see it, is to finish purging the exhaust gases from the previous exhaust stroke and to prevent any of the incoming air/fuel charge from exiting the exhaust port before it closes. I would have thought that the emission design part of this engine would have had more to do with the burnt gases and now I wonder, Did this idea really work as they expected? Because of how these engines are designed, the Reeds are probably of no use to us?, but it is midnight, time to forget it and sleep. Maybe the rest of you will check these photos and come up with something.

Hi Rollmyown,
A lot of good info has been presented in the last few posts on the 2bbl Toro. The top carb barrel and the reeds act like the air injection pumps used for auto emmissions in the 1970's. They lower the combustion temp and NOX output. Later they went to the EGR exhust gas recirulation valve to do this.Many of the Homelite 25 and 30cc trimmers have the port above the exhust into the muffler. Maybe it is a California model.

Dave

Hi Dave, I have no doubt that California requirements have everything to do with the design of the two bbl Toro. Maybe it was also an attempt to get a 2 cycle engine to meet emission specifications and not have to go to a more expensive 4 cycle design. Some/many? of the manufacturers of small 2 cycle engines either have or are working on 4 cycle designs. Subaru and Tecumseh come to mind. Honda has one also as you know, but these 4 cycles are heavy.

The 2 bbl Toro might not have made the grade to meet stricter requirements?, and maybe that is why they are surplus? All that is of no real interest for us now. We only need to figure out if it is worth using or eliminating the Reeds? I am close to just following what Scott does and be done with it. I got 8200 RPM which is OK but this Toro could very well do that with the Reeds eliminated. I am going to do another 2 bbl like Scott does next.

Hi Rollmyown,
I think thats a good idea. It will make an interseting comparison.

Dave

You got 8200 on with the reed valves in place? That is very good. What prop did you use?

Hi Scott, I got 8200 RPMs with my 16x8 M/A classic propeller, which is the one I used for the other tests. This was with the modified Toro 2 bbl intake and a WT 324 carb sitting on top. The installation is the same height as with a Toro 2 bbl carb sitting on it. It is a bit of work to make the transitional 1/4" thick plate match the modified Toro intake and the 5/8" throttle plate bore of the Walbro. I might get aroungd to trying a bit larger Walbro. (I cut 1/4" from the top of the Toro intake, of course.) The reason I wanted to try this is because of the relatively small size of the main intake port of the 2 bbl engine, as you well know. Making a carb spacer for the 1 bbl engine is easy compared to the 2 bbl engine as you have also no doubt found out. It did seem to run pretty well, but I haven't run it since.

this reply to my post is to add photos to the thread because we have discussed the differences between a 1 bbl carb and a 2 bbl carb Toro engine but have not supplied side by side photos. The exhaust ports are identical on both engines. The 2 bbl engine which you can identify by the Reed inlet tubes also shown in the photo has a very different intake port than the 1 bbl Toro.

I just spent most of the day messing with the single and two barrel versions, with some interesting results.
First, the single barrel:

Exhaust timing duration- 130
Intake timing duration- 130

Completely stock-
Easy hand starts
7300 on APC 16x10
2000 idle

APC 16x8-
7300 (?)
2000 idle

MA 13x6
9200
2200 idle

Echo GT carb block and WA-167 carb-
Starting ok
7400 on APC 16x8
2200 idle
Poor transition

Stock + widen exhaust port
No change

Stock+ exhaust to 140
No change

Stock+ .005 cylinder gasket replaced original .020 (exhaust back to 130)
7500 (16x8)
6200 on Pro Zinger 20x6 (!)
Starts excellent
1800 idle

Two barrel:

Completely stock-
Easy hand starts
7600 on APC 16x8
1900 idle
Great transition

This engine seems to be (port) timed to make power around 7000. My plans include trying to find the bottleneck...



I checked the ignition timing, as the magnet position indicated it should be firing about 30 degrees after TDC!

WE HAVE AN AUTO ADVANCE MAGNETO!
Apparently, the coil picks up the impulse very early, like 330 degrees early.
It then delays the spark, depending on engine speed. Awesome!
Here's what I got:
At 2000 RPM, it fires at 20 BTDC.
As RPM increases the timing advances smoothly and proportionally, to 30 BTDC at 7400!!!

The stock carb is amazing too. Although there are no means to adjust mixture, it did well with 13x6 thru 20x6 props!

More to come...


Joe Petro

Hi Joe, Welcome to "Tinkering with Toros". Dave Wallace and myself have been talking about modifying the timing on a Toro. Last week I used a timing light on one, but I wasn't running it, I was spinning it with a Sullivan 24 volt starter, in the basement, and I really couldn't tell what was going on. I actually have two timing lights and they were not responding the same, so I gave up. I suppose you were running yours for your test? From emailing this subject with Dave and from a couple of things he mentioned and looking at how the engine is set up, I was wondering how it runs in the first place. If they have something extra built into the magneto, that would explain a lot. I have had a suspicion about that possibility since last year when I used an ohmmeter to compare a few Magnetos and could not tell much, I would have thought they were junk, but the engines for them run. I was getting ready to test run the 2 bbl engine with the Walbro and conversion plate on it tomorrow with the flywheel advanced a bit more than the width of the keyway and now you have me thinking this over. Now I am also wondering if a search on Magneto design will turn up anything.

One other thing..
It always starts on the second flip, never the first.
This may indicate a CDI unit with logic.


Joe Petro

Actually most of the newer magnetos on trimmers and saws change the timing. A poulan 46cc does the same. If you look at Walbro.com it will explain that all thier magnetos retard timing at idle and advance up to 15 deg or so at high rpm. That is why I do not understand why people are so concerned with electronic ignition like C&H. The magneto does the same thing and is more bulletproof than C&H ignition will ever be. Weight savings is minimal because a mag requires no battery or extra ignition box.

Joe. I noticed the same thing about 2 flips to start them. Never just one.

I will post some pics of my latest 1bbl model engine. I have a great intake for them now that runs remote pulse and turns the carb. I stopped porting on the 2bbls for a little while. One engine I sold lost compression so I want to get it back and make sure the chrome didn't peel due to the porting. It is a possibility. Hopfully it is just a cracked ring or somthing.

I also did a compression check on the 1bbl Toro. I got from 145-160 PSI on the 6 I tested. Very high. All the Poulan 46cc engines I have checked are around 125. Also some Poulan 25cc's were 125.

Removing the magneto also changes and upsets the dynamic balance. I will look up and attempt to post the engineering analysis for use as reference material. Electronic ignition adds complexity with a net weight saving of only 6 to 8oz.

Stihl also retards the timing for starting on some engines.


Bill

I gave up on messing with the timing on a Toro. If you can get 8k+ on essentially new, not broken in, engines, what more can we realistically ask for? As far as removing the flywheel and using a CDI unit to save weight, I agree wholeheartily with what you and Bills are saying. The engine is designed with the flywheel for more reasons than the ignition and its built in fan to cool itself in the original plastic housing as a trimmer, chainsaw, or whatever. The dynamic balance of the engine as Bills put it is an important part of it. The single cylinder flywheel is also an absorber of the harmonics produced by the power pulses of the engine firing. I am trying to say this in a way so every reader can get some idea of the actual complexities of the total design of engines that appear on the surface to be simpler than they are. I am not an engine engineer but I have enough interest to have researched the subject some. The torque output of a piston being driven by the burning and expansion of the air/fuel mixture is not linear, it has a rise and fall curve to it. Multi-cylinder car engine cylinders can balance each other out as far as some of this is concerned. A single cylinder "gasser" has a huge flywheel, compared to the Damper/Harmonic balancer on a multi-cylinder auto engine because there are no other cylinders to help out with balancing. With our single cylinder "gasser" conversions we can get away with "trimming" the flywheels and then we add some "flywheel mass" back to the engine by using a prop hub and the propeller itself. Removing the flywheel and turning the "harmonics" loose can possibly result in shortened crankshaft life and even breakage from what I have read, so I have no intention of removing a flywheel. If an ignition system could be designed to use the flywheel magnets, I would consider that a possibility to improve performance, but I strongly suspect that many others would not look past the weight of the flywheel. Does my reasoning make sense to you two, Scott and Bills?

rollmyown,

Makes good sense. Most of the time when weight is discussed the weight of the battery and coil and ignition box added back is omitted. As stated we will be in the minority. Having a magneto flywheel is not considered cool. Although I have two ignition units on the shelf my engines have magneto ignition.

Bill

It makes perfect sense to me also. These engines are not DA 50's designed from the start to be run on CDI ignition. Just look at any ad for a CDI ignition engine. They give the weight and a picture of the engine. It almost never includes the ignition unit in the pic or in the weight. They just show a sleek engine with no mag, flywheel or anything. They have everyone thinking that an engine with magneto ignition is not worth putting on a plane. Most people do not know a magneto is able to retard and advance the timing as much as a CDI setup. Plus I hate waiting for batteries to charge. The last thing I want is another battery to go dead. Also from what I have been reading. Magneto ignition with a resistor plug causes far less raido interference than a CDI setup. I know the Futaba 127DF has trouble with CDI ignition and interference. Magneto ignition keeps everything up front on the engine where it belongs, away from the radio gear. Plus how many times have you heard of a magneto going bad. Not often. Look here on RCU and you will find tons of posts about CDI ignition problems. Simpler is always more reliable. My computer screws up constantly. My calculator never does

Incidentally a Stihl blower engine has a magneto without fins that is only 3 1/2� diameter.

Bill

Hi Bill, I think that 3.5 inches in diameter is close for a lot of 2 cycle engines. That is what a Toro is and my McCulloch engines are. After all, Walbro and Phelon make a lot of these as suppliers. While we are on the subject of a flywheel helping to smooth out the non-linear power pulses of a single cylinder engine, I happen to remember where you can actually see the power pulses of an engine. I have seen this at an airport and most recently on Wings on HBO, where they have shown a big Radial engine idling. Ever notice that the blades of the prop on a big recip seem to play with the Sunlight? If you look closely, at the slow idling speed, you can actually see the varying acceleration of the propeller tips as the cylinders fire. I had noticed this many many years ago and then later after I had learned how an engine ran, I became more observant. It is noticeable with the big recips and their 3 or 4 bladed props and about the only place to see them now is on Wings. I bet the mechanics on these engines noticed it and just took it for granted. Another thing I remembered was in an RC magazine about a year ago where a big twin gasser sheared the engine hub off behind the prop at full throttle on a ground run up. No one was in front of the engine and the prop stuck a blade in the ground breaking one blade of the Polycarbonite prop off. I would suspect a harmonic problem of some kind here. This was a 30" prop as I remember. I have propped full scale airplanes a few times and I make it a point to respect all props.

Many years ago while testing props I observed quite by mistake that the tail feathers shake differently at idle depending on the prop location relative to top dead center.

At some prop locations the tail feathers shake like a streetwalker looking for her next job. Rotate the prop 90 degrees and she looks like church lady all prim and proper. Didn’t understand at the time but rotating the prop simply changed the dynamic balance.

Bill

Hi Bill
Now that you mention this, I saw this happen yesterday while running a Mac 32cc, I just converted and was testing. The first thing you think of is if you machined the flywheel off center or something. When I increased the RPMs a bit the prop tracked true, but I could still see what you described along with the prop tips reacting to the load and RPm of the engine. I will have to try a different position. I more or less have it lined up with the magnet and counterweight for ease of propping, but maybe that is not the best position.
John

Hey. I had a guy who bought a 25cc Toro from me. He put C&H fixed timing ignition on it. He set it at 30 deg I think and gained 500 rpm on an APC 16x8. He is up to 8950. He only lost about 5oz in weight and the hand starting suffered but he did get more power.

Hi Scott,
What version was it, a 1bbl or a 2bbl? Did you ever figure out what caused the loss of copression on one of your motors? It sounds like the stock mag timing can gain from a slight advance, right?

Dave

It was a 2bbl model. I did the usual enlarging of the intake and exahust and cut the transfer ports deeper. I think the 2bbl has more potential than the 1bbl because of the larger transfer ports. I didn't get the bad engine back yet. I hope it wasn't chrome peel or that will put a halt to the 2bbl engine for me. Hopefully it was a ring that broke. I could have cracked it putting it together. My fingers are crossed
I do think we could get a little more out of these engines by rotating the flywheel a little bit clockwise. Just enlarge the groove for the key and putting some locktite sleeve retainer on when putting it together. Just a few degrees to advance the timing some more. It can't hurt and using the standard mag it will still retard the timing at low RPM. I want to try it as soon as I get time. It seems like when I think I have a chance to do it 2 more engines sell. It is hard to keep up but there is going to be alot of Toro weedeaters flying around the country

Re post 137
My Futaba 127DF is 8 inches from my firewall. Both batteries are between the receiver and firewall...Rubber boot on the spark plug, no shield on the wire....NO interference....CDI is no worse than a mag, if the circuit is INSIDE the mount

Hi Ralph,
I havn't figured out how to put the CDI inside those flat plate mounts that I have been using.

Dave

Let me know if you figure it out