"Don't forget Stihl"
08-12-2008, 01:12 PM
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"Don't forget Stihl"
I have converted a couple of the Silhl engines and find them to be lite, powerfull engines with fantastic quality. I'll be doing several so i thought a stihl only thread might be in order. Buck & Capt. can you tell me the CC's of the two before ripping apart. Ones an FS74 & the other FS80.
08-12-2008, 08:10 PM
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RE: "Don't forget Stihl"
FS74 is a 25.4 actual[26].I have one right now i just need to get rings for.Ill go look for the 80.
FS80 is also a 25.4.Both of these are the commercial grade of trimmers.Supposibly better than my 28cc wich is an ocasional use trimmer.Heres a pic of all 3.Left to right:
22cc-I have 2 of these.
25.4cc-have 1 tore apart for new rings.
28cc3-1/2 lbs RTF,with prop,muffler,and ignno battery.17x8APC [email protected] was a used engine i bought from an auction.This one has the rail mount if ya can see it.It also has a 3 point mount on the back in the shape of a triangle.
FS80 is also a 25.4.Both of these are the commercial grade of trimmers.Supposibly better than my 28cc wich is an ocasional use trimmer.Heres a pic of all 3.Left to right:
22cc-I have 2 of these.
25.4cc-have 1 tore apart for new rings.
28cc3-1/2 lbs RTF,with prop,muffler,and ignno battery.17x8APC [email protected] was a used engine i bought from an auction.This one has the rail mount if ya can see it.It also has a 3 point mount on the back in the shape of a triangle.
08-13-2008, 07:59 AM
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RE: "Don't forget Stihl"
Hey buck thanks, The FS80 (i have two) is the one I'm working on from the other post. It turned a 16x8 MAS at 8050. Both these will hit the parts washer soon.
08-13-2008, 08:51 AM
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RE: "Don't forget Stihl"
I'm putting EI on this Stihl. This is a 24cc that i thought would make a great motor. Very light, Dual rings, Large ports. Cut the center of the flywheel which gives me the tapered and "Keyed" section for a solid base for prop hub and a base for the adjustable timing collar. I tapered a peice of 1/2" Ali to match the crank taper-chucked that in the Lathe and trued it up. Also made the prop hub.
Added the pix with the adjustable collar for timing.
Added the pix with the adjustable collar for timing.
08-13-2008, 08:50 PM
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RE: "Don't forget Stihl"
Well that just about proves that theory.Somone had said that the 25.4 where better than the 28cc because they come from the pro series of trimmer.I think with those numbers compared against my 28cc that it proves it in at least my way of thinking.
08-14-2008, 10:32 AM
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RE: "Don't forget Stihl"
Did you run it last night? Here is the completed 25.4 Stihl FS80. Came out to 2lb-10oz as shown. Muffler is a little more than needed. The small hole in the muffler is were i installed a tube made from ALI for smoke-No idea if it works. This is the one that turns 8050 with a 16x8 MAS classic. Are you saying the 28 won't do it.
08-14-2008, 02:44 PM
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RE: "Don't forget Stihl"
I'm assuming the FS80 you have is the old engine with the mikuni carb and point ignition? I have one of those, never did get that mikuni working...
08-14-2008, 03:01 PM
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RE: "Don't forget Stihl"
Yes-i have two of these, the trimmers were real heavy duty and great quality, nothing plastic on them. The FS74 was the same type of trimmer.
08-14-2008, 07:58 PM
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RE: "Don't forget Stihl"
Im sure the 28 would do it ill put a 16x8 on it and see what happens.I had a 17x8 APC on my 28 and was getting 72-7400 if i remember right .Ill try a few runs this weekend.
08-15-2008, 07:37 AM
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RE: "Don't forget Stihl"
My Giant Big Stik arrived yesterday (my test bed plane). Bought it on scratch & Dent from Tower for 112. Damaged wings (cracked ribs)which i fixed in a couple hours. Should be able to test the 25cc and above with it. I made a plate that mounts to the firewall yet has mounting hole for different size engines, so swapping will be easy. First to go on will be the 25.4 Stihl.
08-21-2008, 07:51 AM
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RE: "Don't forget Stihl"
Just finished the Stihl 24cc, very impressed with the power, turned 8160 peak on 16x8 MAS and 8100 on a 15x10 APC. I used an 11mm carb and open exhaust. Compression is real good, no need for rings on this one. Timing was set at 29 deg. and i used 80/1 synth. oil mix. The only thing that bothered me was heavy vibration at around 4500 to 4700. Can timing effect this?
08-21-2008, 10:39 AM
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RE: "Don't forget Stihl"
frenchie, Is the engine sounding rich at the viabration level? Also you might try the prop in a different position. Maybe check the balance of prop when you have it off engine. Even try a different prop may help. If you have the flywheel that was on that engine..check its balance. Maybe it had more weight in a certain spot to balance engine!!! I have seen bolt on bob weights that said right on them...make sure to reinstall in same position. Good Luck Capt,n
08-21-2008, 11:19 AM
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RE: "Don't forget Stihl"
The flywheel had the center cut, but will check out the rest. It does seem a little rich at mid range but i've adjusted the low and high about as lean as i dare. May try a different carb. The 15x10 APC did make a slight difference over the MAS 16x8-both are balanced spot on. More testing and work. The little engine spools up fast and has lots of power. I will play with the timing a see if it vibrates at same RPM at 28 and 30 to 31 deg. If i can't get the vibration down it goes in a box! The 26 runs smoother and has about the same power-it could use new rings and that may bring it up. I wonder where these engines are happiest regarding RPM-stock porting??
I will flip the prop a 1/4 turn and see-good idea to start.
I will flip the prop a 1/4 turn and see-good idea to start.
09-09-2008, 09:34 AM
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RE: "Don't forget Stihl"
Buck-I measured the bore and stroke on the FS74 and keep coming up with 21-22cc. You mentioned it was 25-26cc ??. The stroke is very hard to measure, did it several ways and come out close to the same. Did you check yours?
09-10-2008, 12:14 AM
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RE: "Don't forget Stihl"
Well i went to the stihl site and searched and came up with nothing on the FS-74.So i guess youd have to call a service center.Im sure i read it there but maybe they took it off there site.I have one thats 25.4 and its supposed to come off of that saw.I also have a SG-75 thats supose to be 25.4.
09-10-2008, 02:27 PM
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RE: "Don't forget Stihl"
I guess I'll get it running and see what prop will work. Here are a few shots of the engine.(FS74) The flywheel is thin and light, lightest i've had so far. To bad the Mag is out, can't get no spark and other engines don't match up. It would make a real light Mag/flywheel setup. For those that have this engine or can get one go for it.
09-15-2008, 09:32 AM
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RE: "Don't forget Stihl"
I cranked up the FS74 this weekend, the smoothest running Stihl so far. Set the timing at 28 and then 30 deg. Ran it with a 15x8 APC and #24 carb. Ran very smooth at 8200. Tryed a smaller #20 carb and lost 600 RPMs but low speed and transition seemed better. Overall this FS74 is a solid platform and good running engine.
09-15-2008, 09:53 AM
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RE: "Don't forget Stihl"
ORIGINAL: frenchie79
I cranked up the FS74 this weekend, the smoothest running Stihl so far. Set the timing at 28 and then 30 deg. Ran it with a 15x8 APC and #24 carb. Ran very smooth at 8200. Tryed a smaller #20 carb and lost 600 RPMs but low speed and transition seemed better. Overall this FS74 is a solid platform and good running engine.
I cranked up the FS74 this weekend, the smoothest running Stihl so far. Set the timing at 28 and then 30 deg. Ran it with a 15x8 APC and #24 carb. Ran very smooth at 8200. Tryed a smaller #20 carb and lost 600 RPMs but low speed and transition seemed better. Overall this FS74 is a solid platform and good running engine.