O.S. fs 200s gas conversion
 

Hi.

I'm planning on converting an fs 200s I've got laying around to gas and I've ordered the ignition, spark plug and what have you from justengines. I've added another cylinder head gasket to lower the compression, and while doing so I realized that the 200 doesn't have th bronze valve seats like the older O.S. four strokes!? Is this gonna be a show stopper with regards to the gas convertion? It looks like the valve seats are just machined in the cast aluminum head??

Also, I had planned to use the glow carb, but I realised I've got an Poulan 25 with a walbro carb laying around as well, maybe I could make an adapter and fit the walbro to the 200?

Any advise would be appeciated!

Thanks

RE: O.S. fs 200s gas conversion
 

The Saito gas engines do not have bronze valve seats either. They are chromed onto aluminum.

Lets hope that OS didn't try to use nickle?

RE: O.S. fs 200s gas conversion
 

This conversion of your engine and this one would be much alike. You should read this

http://www.rcuniverse.com/forum/m_9218106/tm.htm

RE: O.S. fs 200s gas conversion
 

Thanks, I've seen that thread before, so I figured if it works with an SC it should work with an O.S.:)

What do you think with regards to the carb?

RE: O.S. fs 200s gas conversion
 

I would use the Walbro WT-456 like in the Saito 150 conversion thread

http://www.rcuniverse.com/forum/m_93..._7/key_/tm.htm



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RE: O.S. fs 200s gas conversion
 

I'll probably be converting my FS-200 also. Why did you decide to lower compression ratio? It's not high to begin with.

Greg

RE: O.S. fs 200s gas conversion
 

I've read that it is recommended to lower the ratio a bit when converting to gas. It may work without doing so I guess, but you might have to adjuste the timing a few degrees back.

RE: O.S. fs 200s gas conversion
 

The Saito FG-20 actually has a higher compression ratio than the Saito 125

RE: O.S. fs 200s gas conversion
 

It all depends on how sensitive the combustion chamber design is to knock, and the type of fuel being used. Reducing compression ratio was recommended back when Saito produced engines with upwards of 15:1 CR. The OS will be ~8:1. I haven't measured mine yet.

RE: O.S. fs 200s gas conversion
 

Ok, maybe I should take the extra gasket out then? I think I'm going to try with the glow carb for starters, I'd like to keep it simple.

RE: O.S. fs 200s gas conversion
 

When using the glow Carb. with gas, some have narrowed the taper on the High speed needle so it would not be so sensitive.

Personally I'd buy a new needle and try it so I'd have a good needle to go back to.

RE: O.S. fs 200s gas conversion
 

I think I'm gonna leave the needle as it is for now, if it turns out be over sensitive on the needles I'll take it from there.
Should I shoot for 28 degrees on the timing without the extra shim?

RE: O.S. fs 200s gas conversion
 

One shim in that engine isn't going to change compression ratio significantly. I doubt you will even notice a difference.

RE: O.S. fs 200s gas conversion
 

I guess you're right. thanks!

RE: O.S. fs 200s gas conversion
 

Well, the conversion is on. Got the gear from Just engines yesterday, and started fiddeling today. Fixing the hall sensor to the crank case got me thinking though. How thick is this material? I certainly don't want to risk drilling away into the front bearing! I'm planning on going with M3 screws to fix the sensor to the crank case. The drive hub on the 200 is not exactly ideal for mounting a magnet either. Hopefully it's doable, I don't want to make a custom one unless I really have to.

RE: O.S. fs 200s gas conversion
 

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RE: O.S. fs 200s gas conversion
 

Ok, the conversion is complete, and I tried to start it the other day. I struggled a while to even get a stutter from the engine. After a bit of fiddeling about with the needle it started to fire up, but I couldn't make it run for long. The thing also backfires quite a lot, and I've ruined three propellers allready! Just like the thing was with nitro. Could the timing be set too early?

RE: O.S. fs 200s gas conversion
 

Does it back fire through the exhaust or the carb?

Back fires happen when the plug fires with a valve open.

To early and it back fires through the Carb. To late and it back fires through the exhaust.

RE: O.S. fs 200s gas conversion
 

Ralph hit it on the head. Sounds like the timing is off. Also, when I converted my Saito 180, the timing needed to be around 34 to 36 for best power. My converted two strokes including the little SuperTigre 51 all the way up to my DL50 have all ran best at 28 degs. I've moved the timing around quite a bit on the two strokes and they lose power if I retard it and don't gain anything if I advance it plus they idle much worse advanced any more than that. My Saito 91 and the 180 run great and make their best power around 34 to 36 degs advanced.

RE: O.S. fs 200s gas conversion
 

It back fires through the carb, so it's probably to early then. It's at 28 deg at the moment, or the magnet is exactly under the sensor at 28 deg. I suspect it sparks at an earlier stage, like immediately when the magnet meets the sensor? In that case it would fire before 28 deg. I'll have to fiddle a bit more, need to get a few new props first though! :(

RE: O.S. fs 200s gas conversion
 

When setting up EI it is important to actually turn the engine over to see where it sparks.

It does fire before the magnet goes under the censor.

RE: O.S. fs 200s gas conversion
 

Got it dialed in now. The engine runs great on gas and 5% racing oil! I cant believe how lean it runs though! 1/2 a turn out on the needle seems to be the magic spot. I had no problems making it run smoothly with the stock carb. It's well sensitive, but no problem. The carb has no low needle, just the "main" needle. It'll hopefully see some serious airtime this Easter!

Cheers, and thanks for all the help!

Tor