Who is converting Toro trimmers?
 

Hello,
I got around to stripping down my new Toro 25cc powerhead that I got off Ebay. It looks a lot like Echo/Koritz engines. Trimming the flange will be a pice of cake, since it is heavily vented. Very nice two ring engine. The timing is retarded like many Weedeater fleatherlite. Exhust 65 degrees,Tranfers 51degrees,Intake 60 degrees. It looks like the ignition timing is retarded also. I am attaching some pictures of the raw engine. Don't be afraid to jump in with you two cents.

Thanks, Dave

RE: Who is converting Toro trimmers?
 

Dave,

I have been looking at the Toro conversion done here...

http://www.scottellingson.com/store_007.htm

He quoted me $155 plus shipping. I sure would be interested your results !

CJ

RE: Who is converting Toro trimmers?
 

That Toro looks a lot like a Kawasaki 26.3 cc engine that I have converted.The intake on your looks a lot like the intake on mine, and the casting on the front of your crankcase looks a lot like mine before I cut my crankcase. I found that the heat dam from a Stihl 25cc engine would work on the Kawasaki. I used the stock muffler but I modified it a little bit. There is a picture of my Kawasaki in this thread.

http://www.rcuniverse.com/forum/m_25...tm.htm#2525185

RE: Who is converting Toro trimmers?
 

Hi,
I have a new Makita 24.5cc from a RC250 trimmer, a new Toro 25.4cc trimmer, a used Mantix 21cc cultivator and all of them look like they came from the same designer. They all have the same basic design. I think that Koiritz makes them all. Does your Kawasaki have a two or three magnet flywheel? When the engine is at top dead center (TDC) where are the magnets positioned. With most o0f my American engines, the two magnets are centered under the two poles of the coil. This is true with Homelite 25,33 Ryobi 31,26 Echo 44cc which is a three magnet wheel. The trailing magnet is uncovered on the Echo 44cc saw engine. With the Japanese engines the magnets are centered on some and others lead or trail. I need to rig a degree wheelsetup so that I can use my timing light. These differences in timing are probably emissions related.

Dave

RE: Who is converting Toro trimmers?
 

I was wondering how suitable these are and looked here. Thanks for posting the pictures. I see some good points, the muffler bolts on instead of springs or wire, like you said trimming should be relatively easy, it has a rear bearing, a plus, and it looks like a built in mount for RC. All in all these look like they are better suited than most. I also like the way the flywheel is backwards like a Weedeater brand. Your pictures helped me, thanks again.

RE: Who is converting Toro trimmers?
 

Hi all, I am Scott Ellingson. I have converted many engines. Over 50 of different sizes and models. For a 25cc the Toro is the closest I have come to a G26. Actually if done right it will be as good or a little better. Zenoah claims 8900 on an APC 16x8. My test Toro is up to just over 8600 on that prop with a gallon of fuel ran through it. The engines I convert are a little different than the one you have. Mine have the rubber hoses running to the transfer ports. I like them because it allows me to mill out the transfer ports, then weld shut the covers and reinstall them. I then mill out the exahust and intake to a much larger size for better flow. The one thing i still want to try is moving the flywheel a few degrees to advance the timing a little. It will make it harder to hand start but should pick up power.
If you want a good quality 25cc to convert the Toro is it. I have done Poulan 25, Homelite 25, amd Mac 28cc's. The toro woops butt[:@] on all of them.

RE: Who is converting Toro trimmers?
 

Hello,
Here are some more pictures of the Toro 25cc witj out hoses on the transfer area. Also a modified manifold to accomadate a 11mm carb without a pulse hose.

Dave

RE: Who is converting Toro trimmers?
 

Hi, it is going to be hard to keep up with all that is going on here now, I know that none of us are going to puposely ignore any one. I just received the 8mm x 1 taps I ordered so now I can make a couple of prop hubs. I have an engine like you describe, designed with a 2 bbl carburetor and an engine like Dave Wallace's, designed with a single bbl carburetor. I kind of like these carbs, IF they will perform. No one has mentioned the original carbs that I have seen. I will "open ports" also if needed. I have mine cleaned up, the back plate mounts made, and when I get the hubs machined, I am going to test them against each other, with no porting and the original carbs for a baseline(s) of operation for these Toros. It is good to hear the report on RPMs that you are getting and I agree they are well made engines. They are nice and light also as you say. It looks like they have a forged conn rod besides the dual reasonably sized front and rear bearings. The 2 bbl version also has a 3/8" spark plug (3/8 x 24 threads, I think, they are fine threads, but I really didn't think to check until now. Normally you find a 7/16" thread on trimmer spark plugs. Oh yes, the reason I want to run them with the original carbs is because I ran them as a trimmer powerhead, as received, and the throttle response was excellent, nice and lively, but of course there was no load. The Toro carbs I discussed are not like a Walbro or a ZAMA and in fact are somewhat like the rotary barrel RC engine carbs. The idle adjustment that is more important to us than a weedeater user is accomplished by a mechanical limit stop of the rotation of the rotary barrel, cylinder, or whatever it is actually called. The single barreled carb is somewhat simpler, simply by having only one bore through the carb that the rotary part opens and closes like a RC carb. The bore on the single bbl does seem small and could be restrictive. The 2 bores of the 2 bbl carb also seem small. In spite of this I will try them and might work on them if necessary because I figure if they won't work as is, there is not much of a gamble in possibly ruining them. I have already figured how to lighten the spring return so a servo would not have to fight a fairly strong return spring. Some carbs are a challenge in figuring out a linkage for them that will be good and reliable. They all seem to be different in some way so expect to put on your thinking cap for this part of any conversion. So, has anyone tried a converted engine with the original Toro carb and what were the results? A new carb and the cost for it to get the most performance out of any engine is likely to be the same for these Toros as with most other engines I suspect. You at least need to have a 2 needle carb for RC. Most trimmers I see now have a single needle carb.)

RE: Who is converting Toro trimmers?
 

Scott, I wonder if you have seen a single bbl Toro engine? They have a bigger and different intake port but the exhaust port seems to be about the same as the 2 bbl version. Since you have good results by porting, I will look closer at the ports of both. As far as trying to alter the timing a few degrees, we won't know if it is worth the effort without trying. Have you figured out how to do it with doing any damage to the basic engine? I have a suggestion you might consider. How about rounding out the mounting holes in the magneto coil and then make some bushings to fit with off center holes, which would give an excentric adjustment ability. (Like adjusting the camber on some cars front ends.) Of course, this will probably be a trial and error deal. A washer on top (maybe the bottom also) would then be needed to tighen it all down. One other point to add: Getting more power on the top end by changing the timing might negatively change the engines idling ability. What do you think? Be conservative at first? ( I like a good idle without the engine quiting because I have been in enough trees.)

RE: Who is converting Toro trimmers?
 

In my Hot Rod days we used an off set key to change the cam timing

RE: Who is converting Toro trimmers?
 

I actually have thought of changing the timing. I was actually going to remove the key on the flywheel and tighten it down in slightly different locations to try it. If I find a good result I will widen the key-way and use sleeve retainer on the flywheel. Only problem is it will never come off :) I have not had time to do many things with porting the Toro. I have got it to the point I am now and it should (after break in) put out the same as a G26 at less weight. 3lbs 7oz ready to fly. I have been to busy building engines I have sold to do much more. I make all my own parts so it takes allot of my extra time. This winter when thing slow down I am going to blueprint the engine and see where all the ports are timed. That will help to figure out the best combo for even more power. Reliability is just as important as power so I am not sure how much more can be squeezed out of the engine. I agree a reliable idle is a major concern. My test engine never dead sticks now. It has around 2 gallons through it and it runs from takeoff to landing perfectly. The biggest thing is tuning. Many people are not that good at tuning a gas engine. Much different than glow but once you figure it out it is easy. I am putting a 25 in a 110!QUOT! Sig Rascal right now. It will be a great combo. Our test engine is getting moved from an 18lb biplane to an 11lb 1/4 scale space walker. It will be a better plane for the engine. The biplane is a pile of crap. So warped up it takes 3/8 trim on the ailerons to keep it level. Like pulling a box through the air.
To answer your question about the single bbl toro engine, No I have not done one. I ordered 40 of the engines and all were the 2 bbl. I got lucky, I machined a 2bbl model for a guy a week ago. It looked the same but was cast different. There was far less aluminum around the intake and exhaust. Very little room to machine. That model is no good for conversion. At least it will not put out the same power.

RE: Who is converting Toro trimmers?
 

So your saying the 1 barrel version is the one to convert.

I've been looking for the 2 barrle version.

RE: Who is converting Toro trimmers?
 

I am sure not saying that. I have only done the 2bbl version. I like them because of the ablity to increase the size of the transfer ports. The results I have goten are very good. A good running, light, and powerful engine. I think either convert well. I would have to see some numbers on the 1bbl version to decide which is best. My conversions get 7800 to 8000 rpm on an APC 16x8 prop. They will pick up around 1000 rpm or more after break-in it complete. That will take 4-5 gallons of fuel on non synthetic oil. Synthetic is not good until break-in is complete.

RE: Who is converting Toro trimmers?
 

About my suggestion to change the timing, I was thinking about another magneto with slots. I looked at the Toro just now, my suggestion is not that good for this engine, it would take some engineering to change the timing and who knows if the time would be well spent. I tend to be satisfied with 7500 to 8000 RPMs out of 25cc. I just read your comments about the 2 bbl version with not much metal around the ports to enlarge them. I think this is what I have and I was wondering when I read you saying you enlarged the ports a lot. That is now cleared up. I haven't had a whole lot of time either up to now to work on these Toros. There must be several versions of these engines, maybe some we haven't seen yet. I took the rear cover off of the rear intake, you know the little rascal where the rear rubber tube connects, to be absolutely clear. There is a Reed valve in there. Is that familiar? I didn't check the front one yet, but I expect it will have one also. With these particular engines, lets call them the "2 bbl light castings", I would think the exhaust ports could be enlarged a bit and then an adapter intake should be possible to use a bigger bore 2 needle Walbro or ZAMA carb with an adapter intake spacer that makes use of the rubber tubes to the front and rear intake ports. I will try something along this line of thinking when I get to it. These engines have turned into a tangent hobby. I have two RC airplanes, glo versions, and I haven't flown either one in a long time. You mentioned a 28cc McCulloch, the first engine I converted is a 32cc Mac. The ports are decent sized as is, I used a 5/8" Walbro and get close to 8000 RPMs with a 20-6 prop. Of course I added a 5/8" pipe to the muffler also. I like the 32cc Macs, I have a couple more of them, but they are around 5 lbs.

RE: Who is converting Toro trimmers?
 

The best way i have found to deal with the reed valves is to close the holes and remove them. Do not use the rubber hoses at all. It would be a bear to make an intake to utilize them. I make new intakes after I increase the intake size. I also turn the carb the correct way for RC use. I then run a remote pulse line to the carb. It is the only way to do it if you turn the carb. 1 intake bolt lines up with the pulse hole on the carb so no way to run a channel. A good way to tell if you have the good 2bbl engine is the color. The thin one is very bright silver. Also if you look on the back you will see 3 gussets in a triangular pattern. They look as if they could be drilled and tapped for somthing. If your fins are even all the way accross, you have the good engine. If there is a circular dip in the middle of the triangle pattern then it is the thin one. If it is the thicker one it can be made to do well over 8000 rpm when broke in. If the thin I think 8000 may be the max. I run an 11mm Walbro twin needle carb on my conversions. That and an aluminum pits style muffler. A velocity stack will pick up 300 or so RPM on this engine and actually the stock muffler only reduced the RPM by a couple hundered but was very quiet. Strange I thought.

RE: Who is converting Toro trimmers?
 

Scott, It remains to be seen with modifying some of these 2 bbl Toros. If there is not enough metal around the main intake port to open it sufficently?, maybe the only way to get enough power is to find a method to use the front and rear Reed controlled ports? I haven't really looked at this system closely. I haven't pulled a cylinder completely off yet. It might be possible to cut down the height of the original carb spacer/intake maniflold and make an adapter to center a single bbl Walbro on it? I don't see the need to turn the original plastic manifold yet, I will study it more. These engines are light enough to consider them for twins. The pull starter will add about 5 ounces and could probably be retained if a modeler wanted to do that. One other point, obviously a lot of money was spent on research and development to design these engines. The basic mechanical design is very sound and a lot of the money was no doubt spent on emissions. A lot of the small 2 cycle engine companys now seem to be concentrating on 4 cycle designs, for emissions, so some 2 cycle bargains, like these Toros, are showing up as surplus.

RE: Who is converting Toro trimmers?
 

sorry to jump in on your guys conversation but is the same engine your talkin bout????

[link]http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7707022525&rd=1&sspage name=STRK%3AMEWA%3AIT&rd=1[/link]

RE: Who is converting Toro trimmers?
 

Maybe, there are two versions, a one and a two barrel.

I'm not sure which one Scott is converting, and the guy selling these doesn't know which one he has.

RE: Who is converting Toro trimmers?
 

Hello,
The engine that Junkman is selling is the piston port engine with a clutch. The engines Scott is converting are the so called two barrel version. They are the same except for the cylinders. The two barrel version has reed valves built in to the transfer ports. The one on ebay would be a good engine for a MT.

Dave

RE: Who is converting Toro trimmers?
 

You will have to ask Junkman which he is sending. He doesn't know which he has unless he looks. He has both the 1 and 2 bbl versions. All the engines I have are from him. He is a very nice guy to deal with. Buy 40 at a crack and he gives an even better deal :)
I just test ran 2 tonight that i sold. These i put a 9/16 id exahust pipe on instead of a 1/2 id. Both turned an APC 16x8 at 8100 rpm. That is very good. I use a laser tach accurate to .05%. All of the other ones I converted started around 7800 RPM. The best part is they will pick up 800 to 1000 rpm when broke in. If that holds true they should do that prop at 8900 to 9100 rpm. If that ain't a G26 I don't know what is. They make a Homelite look lika a terd :)

RE: Who is converting Toro trimmers?
 

Hi Scott,
The one I got from Junkman was the piston port type. It has the small transfers without much beef around them. I wrongly assumed that that was all he had. Your engines with the milled out transfers are the best choice.

Dave

RE: Who is converting Toro trimmers?
 

I think they may be all worth a try. When I mill them the ports are still no bigger than a Homey or Poulan 25cc. There is just somthing about the engine that is makes power. I suppose the twin ring helps. Plus they are ballanced so well. Very little vibration at all. All the toro's should make a good conversion. Some types may have a little more potential but I think they will all be good. I would like to see some numbers on an engine like yours. It may suprise you.

RE: Who is converting Toro trimmers?
 

I made a couple of prop hubs and ran a single bbl and a 2 bbl Toro, both with a Master Airscrew Classic prop. I used this same prop to test the 21 and 25cc engines I have done. The 2 bbl toro gave 7300 to 7400 RPM. I use a ACE Tachmaster that I modified and added 3 extra scales to along with a 2 or 3 blade selector switch. As long as the Sun is out, I have a 5k, 10k, 15k, 20k, and the 25k RPM range. I still have the article to do this somewhere, if anyone is interested in the modifications. OK so the 2 bbl put out around 7300 to 7500 RPM and I could see it was not going to go much higher so I concentrated on adjusting the idle, THE ONLY ADJUSTMENT, and it would idle nicely around 2200 RPM or so. These are still new engines with very little time. The throttle response is very quick. The single bbl engine idled great, but sagged above 3/4 throttle and I was running out of time today for this. It was obvious that the single bbl carb has problems. I will take it apart out of curiosity to see if I can find the problem. The way these carbs are designed, they are Walbros by the way, it is very difficult to "bore" them bigger. There is wire that moves into out of a plastic tube, when the barrel rotates. The wire doesn't look like it can easily be removed to work on the bbl. I would try this if possible because of the excellent throttle response. I now am going to make a carb spacer adapter and try a 13mm Zama (9/16") to replace the single bbl. I haven't given up on the 2bbl engine. I am going to look at the ports on both engines also to see if they can be opened. I think an aluminum plate adapter is possible for the existing 2bbl carb spacer to adapt a 13mm carb to it also. I am going to modify the existing 2 bbl carb spacer/manifold also. I think the main intake port can be opened some and I am going to leave the secondary Reed ports in place and in operation to see how this works. I think there could be some potential with using the Reed ports, after all there are already there, and before I defeat them, I want to satisfy my curiosity. One other point about these engines, I think a aluminum plate mount bolted to the rear of the engine is well worth the trouble. 1/8" is thick enough, and this gives you a larger footprint for mounting along with strengthing the rear of the case, in my opinion, for not that much weight. I use a 3" x 4" plate with the engine centered. I counter sink for the 10-32 mounting screws, but not all the way flush. If you leave them a bit high, your firewall will keep the screws from backing out. Another small point is that the muffler on the engine can work out very well for a side mounted engine. The screen "spark arrestor" (I guess that is what it is for) is easy to pry off and then an exhaust hose could be used. I tested with the original mufflers and they are pretty quiet. When you examine them, it doesn't look as though they would restrict the engine too much and they are not overly heavy. Until the next chapter of the Toro saga.

RE: Who is converting Toro trimmers?
 

Hi,
Could you post some pictures of those reed valves?

Dave

RE: Who is converting Toro trimmers?
 

Hi Dave, I intend to post some pictures when I figure out how. My digital camera and it's software is part of the problem. I got too many irons in the fire. I also had to put a new hard drive in and lost a bunch of stuff on the old drive. You know, everything happens at once. I have done some more testing, I used a new 14mm carb on a single bbl Toro with a new carb manifold I made to match, the results were not spectacular, but the way it was running I now think the magneto must be defective. It was not running steady, I thought it might be too much carb, but this is the engine that ran the same way with the original carb. It still turned 7500 RPMs with a 16-8 and I think it will do much better. This is the same ZAMA carb as the one that gave me close to 8k with the 25cc Weedeater, so I will resume testing with another magneto. I plan on posting photos also, I took some photos already.

RE: Who is converting Toro trimmers?
 

Hi,
I think 14mm is way to much carb. This the size used on 45-50cc motors. Scott E. has gotten great results with a 11mm walbro, which is the size that almost everyone uses on a 25cc. You may have an air leak in the cylinder base gasket or somrting causing uneven RPM. Mine is almost ready to run with an 11mm carb. I just need to get a small diameter hub with 8x1.0mm thread for the shaft. I think that the port timing is limiting your Rpm. Good job so far.

Dave

RE: Who is converting Toro trimmers?
 

davewallace, your reference to 14mm probably being too much carb is only because you haven't seen my 25cc Weedeater run with a duplicate carb. The weedeater runs as good as you can get one of these things to run, very smooth, good idle, and good throttle response, and it seems to running clean enough that carbon should not be a problem.
I think we are really talking about 14mm being too much carb for the Toro, but the engine ran the same way with the original carb, then I suspected the carb, now I am going to try a different magneto. After the running session was over and I thought it over, it sounded like it could be an electrical problem, and there is only one electrical part. (By the way a good tool for setting magneto gaps is a piece of Aluminum flashing, flashing is usually around 12 to 15 thousands thick.) The Toro has higher compression than the weedeater and I will probably open the ports on the Toro like I did the weedeater. By looking at some of the good references for Walbro and Zama that were posted by other here, you can see that most of these carbs have a pretty wide cc range. I sure am going to try again with this carb. It was not running any worse than the original carb and if carburization was the original problem with this particular engine, I would expect a bigger carb to aggravate the problem further. Did you get the 3 photos I sent you?

One last point, it is hard most of the time to get the intake big enough to fully use the capability of a larger carb as I am doing. This carb has a 9/16" bore but I was only able to open the carb spacer on the Weedeater, for example, to 1/2" diameter. This is one of those things I think we can "get away with".

RE: Who is converting Toro trimmers?
 

Hi,
I haven't recieved any pictures. How did you send them? I check my e-mail frequently and my private messages. If you look at some of my earlier posts in this thread you will find Toro carb insulator bored to 5/8" and modified for standard carb pulse port. I up loaded one.

Dave

RE: Who is converting Toro trimmers?
 

I did some work on engines I am testing, a single bbl and a 2 bbl. The 2 bbl intriqued me some so I studied it. The primary bore and secondary bores, in nominal sizes, are 3/8" and 9/32" diameters, respectively. In total they are pretty large as far as area is concerned, but the secondary only feeds the small Reed ports. Now the Reed ports also feed the directional ports ("directional" porting using the same ideas used in model aircraft engines), but these directional ports also are the main and only ports so the Reed ports are piggy backed into the main ports and mounted into the covers for the main ports. These are the covers that Scott removes to mill out the port transfer areas. (A mill is great for this and I don't have one.) That is some background info for what I did. I enlarged the main port as much as it can be enlarged and still use the original carb spacer which I retained and modified. I enlarged the main port through the carb spacer. Then to a depth of 250", I cut through the web seperating the two bores in the carb spacer, alowing both bores to feed both the main porting and the Reed ports. So far I left the Reed Ports in place. I opened up the ports into the cylinders somewhat, maybe 10 to 20 percent and opened the transfer passages from the crancase to the cylinder as much as I could with a file. This altogether gave me 8000 RPMs, which I didn't think was too shabby with the original 2 bbl carband the idle is still very good at 2100 to 2500. This engine is still not broken in. Maybe I should remove the Reed ports alltogether? The single bbl engine with a Zama carb only gave me 7500 RPMs. I runs nice and idles well, but it needs more work. Need to work on posting pictures now. A safety note: The carb spacer smeels like bakelite, asbestos, when working on one don't breath the dust, wear a mask, and wash away the dust with water occasionally.

RE: Who is converting Toro trimmers?
 

davewallace, I used my digital camera software to email photos to your email address. I thought they went out, but now that I know you didn't get them, I will check in to what I am doing. I remember the picture of the carb spacer you show here, but it didn't register, I guess it looked too big to be a Toro spacer. I am going to look at mine again to see if it looks like yours. The intake port on a 1 bbl Toro is huge, I don't think it needs to be enlarged at all, but the exhaust port seems as though it can use a bit of help, so I worked the exhaust over on the one I am testing. I checked the gaskets as you reminded me of, I had looked at them before, they wern't leaking, but I noticed that the cylinder base gasket could ft better so I made a new one. After I put the cylinder back on, I wondered if I shouldn't have put some Form a Gasket at the "T" of the base and case gaskets. Anyhow it wasn't leaking and the magneto seemed to be giving me trouble. After a while, it quit, I changed it and ran again. It only gives me 7500 RPMs but idles well and transitions well with the Zama carb that you thought could be too big, but the same carburetor works great on two 21cc and one 25cc Weeedeaters and they run great. This particular engine seems to have too much end play on the crank, I need to look at that. I have a couple of 5/8" Walbros, maybe I will try one to see what the results are. These engines have the porting and the compression is high, maybe they can handle more carburetation?? I have been using Poulan oil at 32:1 so far. Have you seen any recommendations on the ratio of oil for these Toros? By the way, the 2 bbl engine has a domed piston, not real high, but still not flat.

RE: Who is converting Toro trimmers?
 

The mix ratio for the Toro is 50:1. Try that oil mix. You should get better numbers. 32:1 is way too much oil.

RE: Who is converting Toro trimmers?
 

I have motorcycle and chainsaw experence and was told years ago, about 20, that 50 to 1 was a smog thing,
and that 32 to 1 was the wise mixtute.

I run oil that is rated at 100 to 1, but I run it at 75 to 1.

Am I out of touch.

RE: Who is converting Toro trimmers?
 

On the Toro the tolorences are close. Thus 50:1 is all the oil that is needed. On a cheeper engine like a Weedeater they are not as close, so therefore 40:1 and on alot of the cheeply made pocket bikes and chineese chainsaws the ration is 25:1. They also meet EPA standards but the tolorences are not as close so they need more oil to run well. Just like in the 70's 100,000 miles was alot on a car engine. Moset didn't make it that long. Now with closer tolerences in machining they go much longer on avarage. If you run an engine that should have 50:1 at a higher oil content all you will do is cause excess carbon to build up which will lead to premature wear and overheating.

RE: Who is converting Toro trimmers?
 

I had not seen any recommended info on the oil ratio for Toros. I suspected maybe 40:1, but I already had some 32:1 so I tried it. I also guessed a bit more oil wouldn't hurt for break-in. I am surprised a bit at 50:1 because 32:1 runs pretty clean. I did some more work on both engines, the single bbl and the two bbl. The 7500 RPM number for the single bbl is probably not valid and I was surprised that it was not higher. While preparing a larger carb yet to try, I discovered that I had the 14MM carb on wrong, the pump was not working. It was one of those " how in the world did I do that?" deals. I noticed that the needles were not reacting normally, but it did run. Probably because the carb has a 14mm throttle bore and a 3/4" top opening but the venturi is about 3/8" in diameter, so I guess it pulled the fuel in. I will retest that carb and the 5/8" bore carb, I have, which has the same kind of relationship between the bore and venturi. There is a lot to these 2 cycle carbs. I worked over the exhaust opening on the single bbl and reworked all the ports again on the two bbl, now that I found out my idea of opening up the intake manifold for the 2 barrel carb worked out. The throttle response was good, the idle was good, and I now think it will go over 8000 RPMs. 50:1 oil and some break in time will also help. Now I think(?) I can post some photos in another post, so this one doesn't time out.

RE: Who is converting Toro trimmers?
 

Here is a photo, it shows a 21/64" drill bit, as a gauge, in an intake port on the 2 bbl to show direction also. A 13/32" drill was used the same way on the intake manifold. You really couldn't drill the intake without ruining it. It has a countoured passage. The other photos should match the text in previous posts. Photos didn't upload. Will try again.

Important note: This drill size gauge idea turned out to probably be too large. When you look at the port with the top surface of the piston bisecting the diameter of the port, the top uncoverd half of the port looks really small and my drill gauge idea looks reasonable, but it seems that by me reffectively raising the intake ports, about .040" to maybe .060" (this is difficult to measure), I went to far and you can here this difference when you flip the prop. If you want to work a bit on these ports, I would suggest increasing the width a bit, but remember it is easy to go too far.
I am going to lower the cylinder around .020" of an inch to correct a bit of my excessiveness. The engine still runs well enough as it is, it idles well at 2k and has a top around 7500 plus. The next thing I am going to do with it is change the carb to a 2 needle Zama and forget the rotary Walbro, even though my "slotted" intake manifold did show some promise. We do need the reliability and adjustability of a 2 needle carb. A hint for working on ports with a file: fashion a piece of aluminum flashing 2" wide and about 3/4 of the cylinder diameter, to insert into the cylinder to protect the cylinder wall from the tip of the file. Clean up the edges of the flashing guard also. Without protection, you will probably scratch the cylinder wall.

RE: Who is converting Toro trimmers?
 

Photos uploaded, but I don't know to where? Computer said they were uploaded successfully? The second photo shows the bottom of a 2 bbl cylinder. The two openings on the sides are the transfers from the crankcase to the directional ports where the Reeds are also located. I see now that I can upload a few pictures at a time. the 2 bbl engine is verysuprising because the piston only uncovers 1/2 of the intake ports to take in the fuel charge. Now that I knew my modification of the 2 bbl intake worked, I went ahead and opened up the intake ports some more and I concentrated on the top side of the port that the piston uncovers. To look at these engines you would think the single bbl has more potential because of port sizes. I also guessed that the 2 bbl carb had more potential because the second barrel was only feeding the Reeds and probably had enough flow to add some to the primary port to the crankcase, it looks as though it does. There is no Sun out today for my Tack and I have to run some errands, but I am ready to test again. I will post the intake manifold photo etc. next.

RE: Who is converting Toro trimmers?
 

Hi Rollmyown,
You done good. I can see where these 2bbl engines have potential. I would like to get one to play with.

Dave

RE: Who is converting Toro trimmers?
 

hi davewallace,
The 2bbl carb is what is working for me so far. I figured that the way it is designed, there is no adjusting of it except for idle, could be put to use. The secondary bore doesn't open until the primary is pretty far off the idle so I guessed it wouldn't flood and stumble and was worth trying. You don't know if something like this will work at all unless you try it. The carb is a Walbro and is not junky, so I wasn't going to just discard it. My original idea was a plate on top of a cut down intake, cut down 1/4", so I made a 1/4" cut down into the dividing web and could cut down the rest of it if it didn't work. This two barrel carb is fairly large, but it works well, and I am going to stick with it. I will post the photo of the modified carb intake /spacer for everyone to see, but I got to run now. I sent you the first photo by email as a test, did you get it? Added photo, 8-31-05

Note: This slotted intake idea did show some promise, until I went a bit further on opening up the intake ports. (I think that is what happened, but if you change a couple of things at a time as I probably did, even small changes, this can happen.) Sometimes it doesn't take much to skew your experimentation off the course you think you are on. I just want to point out that this has possibilities, but it is not 100% perfectly perfected.

RE: Who is converting Toro trimmers?
 

To continue with photos, here is a side by side of a stock 2 bbl manifold system and my modified intake spacer alongside an unmodified one. There is more of an increase in the bore size of my modified one than is apparent in the photo. the hole of the modified port is perpindicular wheras the unmodified one has a contoured bend shape to its bore. The size of the modified bore in the intake manifold limits how big you can go with the matching port in the engine. You can only go so big in the carb spacer and still get a gasket to work. The directional ports and the transfer passages need worked on also. I am ready to test the second enlarging of them. I now have them as large as they probably can go. I will get some photos of them also.

RE: Who is converting Toro trimmers?
 

To continue with photos. Reed valves this time.