Crash Master

I just bought a couple of new Thunder Tiger F-91S 4-strokes (1 goes into a new VF 66" Edge and the other is going into a new Dragon Lady). Anyway, I opened the box and found it came with lot's of little goodies (wrenches, extra o-rings, etc.) and something that I have never seen before - A CHOKE VALVE ASSEMBLY.

Now, I am a newbie when it comes to 4 strokes (I have only owned an ASP 61FS and a Mag 52FS) and know nothing about these choke valve assemblies. My first questions is, it is necessary? My second question is, what is it's purpose (I'm betting it's for cold starting)?

My last question pertains to the extra parts. I find a couple of small oval (well elongated might describe it better) pieces of metal and can't figure out what they are or might be used for. They are solid and about 1/8" thick and 1/4" long. Anybody got any idea's what these are and/or what they are used for?

Thanks for any idea's suggestions, etc.,

Checklst

The choke helps when starting it, nice to choke it and get it a little wet, my TT91 like to start wet. The oval metal parts you found are prop back plate locking(Keys)! they lock the crank shaft to the prop back plate.

I have always run with the choke assembly on so I can't tell you for sure if she will run good without it ,but from what I have read on this site they do not run vary good without the assembly, you will notice the choke assembly has the shape of carburetor velocity stack and I can tell you Velocity Stacks did increase HP on early car engines, it improves air flow by increasing air speed.[8D]

pikebishop

use the choke assembly that comes with the engine. it has a venturi effect and aids fuel draw. they won't run right without it even if you don't actually choke it.

Crash Master

I knew I could get answers here!

Thanks guys. I will put the choke assembly on both of them and get them running (if the weather ever warms up around here).

Checklst, the locking keys, are what I have in the extra parts bag spares or do I need to put them in/on when I put the spinner and prop to it?

You guys are da bomb ,

hobbyflyer

My Feedback: (10)

A caution about the choke asseembly.
It should be used, but on my engine the choke would over-travel when applied so that the venturi was about 1/2 open when I thought the choke was actually applied. Couldn't get started until I figured this out. The solution is to put a stop on the actuation rod. I just used a wheel locating collar.

Lynn19531

any pictures of the choke assembled and install with the stops?

pikebishop

the choke is pretty simple, you should have no problem putting it on. if the key isn't in your crankshaft the prop backplate will easily slip foreward and off. if it is tight and you can,t just pull it off easily it is probably installed. tt always seems to give you a few extras with their engines. I really appreciate the spare o rings they give you as every engine eventually needs these replaced. by the way the tt 91 fs in my opinion is a real powerhouse, the only drawback is they are heavy. be careful about overtightening the rocker cover bolt as this stripps easily. like all fourstrokes make sure to lube it up liberally before your first run.

Crash Master

Again I appreciate all the advice and suggestions.

I have already pulled the back plate and sprayed the crap out of it with some cheapo brake cleaner to make sure nothing was left in during machining. Blew it out and put about a gallon of after run in to make sure everything is coated real good.

Glad to hear that it's a powerhouse even if I do have to sacrifice a bit of weight. For what they cost me, the $ saving will outweigh the slight weight loss.

Thanks again,