i have a homelite engine i do not know the size of. i have looked all over and cannot find anything about what size i have. it is a ST-145 model. UT number is UT-20556A. i am guessing it is a 21 cc model. i want to convert it for RC flight.

Hi carlosponti,
I looked it up at outdoor distributors and it is a standard Homey engine. Either 25cc or 30cc. The size of the engine is molded into the cylinder flange to the right of the carb mount. You can also check the exhust port, after removing the muffler. If it has a bridge in the middle of the port, it is a 25cc, if not it is a 30cc. The best size carb is 11mm. Also don't forget to tap and plug the hole above the exhust port with a 10-32 0r 10-24 screw. This will boost compression and power. There is a ton of tips on conversion and hopup of these engines at RCU and elsewhere on the web.

Regards, Dave

thanks that is real helpful. i looked in several places and couldnt find a size on the engine. those are helpful tips too. i had it all apart last night which was a bear to get certain parts off. before any hopups i was told to get the timing and how to do it, do you think all that is necesary with those hopups you recommended.

Hi Carlos,
I am glad that I could help. Like all things, it is good to take one step at a time. Look at some of the pictures and get an idea on how to reduce the weight. Buy a light weight pitts muffler, such as B&B or Wackerengines.com. Use a resister plug, such as a RDJ7Y, available at auto parts store. Plug the hole in the cylinder. Get a short shaft 5/16x24 prop hub from Wacker and make a mounting plate from scrape aluminum. Use a 16x10 or 18x6 prop and test it. Later you can add an 11mm Walbro carb, which will have a 28 molded in the inlet on the venturi. If you don't know what you are doing timing changes can destroy the engine. You can also raise compression later.
I u sed to live in Moore in the seventies. Does 1204 north norman still exist, That was my old house? I think that it was taken out years ago in a tornado. It was close to I35.

Regards Dave

Dave,

norman oklahoma or norman road. there have been several housing additions near i-35 that have been destroyed and rebuilt. i live near 19th and eastern. all of the tornadoes have been on or around 12th street and cut northeast to midwest and del-city. the reason i asked about timing is that a site i came accross said you need to measure timing if you are messing with the porting which i dont want to do. also i have a plastic back plate that was originally on the engine. do i need to make a new one with a recess to fill the space that the old backplate had? one place detailed making one on its instructions.

thanks a bunch
Joe

ps carlos is my nick. Carlo Ponti is a photographer and filmmaker married to sophie loren.

update:

i have two of these engines both had no marks imprinted to say what size however they did have a bridge in the exhaust port up the middle. also only one had a hole above the exaust port that needed plugging as suggested. one has been lightened already now all i need is a lighter muffler for both and a prop hub for both.

Dave i also tried going down near where your house would have been but i didnt see it. so i think it maybe gone. one street over has older houses and another street nearby had new houses so i imagine the damage was sparatic after the may 9th tornado. thought you would want to know.

Hi Carlos,
Thanks for the update on my old house. I sold it in 1978 and moved to Del City. I left OK in 1984.
The size numbers a real deep into the fins on the cylinder. Since you have a bridge, it is safe to say that you have two 25cc engines. The plastic back plate is fine after triming and sanding the back flat. I removed 100 thousands (about 3/32") from the back of the case to reduce its volume. Don't remove the bridge, or your ring will catch in the port and break.

Later, Dave

Hi

I'm new at this and trying my first conversion. Fly glow but always wanted to try gas. I was given a homelite engine, no numbers except a (YS) imprinted on the base of the head. It has no bridge in the exhaust so I am guessing 30cc. I am in the process of cutting away all that extra metal. I pulled the flywheel off and punched out the starter spring mounts. By the way now that I have the flywhell off, I suppose I will be completly out of time. So how do I set up for correct timeing? I told you I was new at this. Cant wait to get this thing in something and fly it. I am thinking a big stick type airplane.

i put mine on a test stand and got around 7500 rpm on it. on those homelites if you pull the magneto wheel it is keyed to a certain position even if you take the key out and remove the crankshaft when you put back in reset the key the magneto should go back into position where it needs to be. somewhere on here there is a picture where the magneto needs to be in relation to the pistion. it will be on a recent posting.