Hey guys, I got my ST running great! Great transitions, top end, idle, etc. BUT when I pull it into a hover and hold it there about 20 seconds it starts to lean out and won't catch till i point the nose down! It does the same thing when you "punch it" to pull out of a hover and winds up in a tail slide! I've already plugged one exhaust outlet and I'm running a header tank setup.. This is a ST G2300... i'm afraid I'll have to shell out for a pump! anyone got a link toa good pump if it turns out i have to get one?

If you decide to go pump use the cline regulator. I don't think you need it unless your tank is to far back. My ST 3250 did the same thing. I read on here how to fix it and it worked. I went up one size on the fuel tubing. I also got the next size bigger brass and used it for the tank stopper. I also drilled out the clunk in the tank and the nipple on the carb. Then to be safe I used a zip tie to hold the line on the carb and the clunk on the line in the tank. I have a third fill line that I left with the stock line and brass. This made a big difference on mine. You are basicly increasing the volume not the pressure.


David

DO you have a link as to what size fuel tubing, brass tubing ect?

I'm going to suggest the klunk may be too close to the back of the tank. It needs to be at least 3/8" away.

Dr.1

If you're going to be doing much hovering you should get a Cline regulator or Ironbay regulator. They completely do away with typical glow engine fuel draw problems. Your engine will love the constant fuel supply, no lean runs near the end of the tank. No loss of power when the tank is full from running rich. You will conserve a lot of fuel having a constant fuel draw. The advantages are many. I agree that large tubing and clunks, etc help but the only real solution is the fuel regulator. Pumps work ok when the tank is close to the engine but my experience is that the regulators work the best. Especially if you have a tank that's on the CG.

>>> You will conserve a lot of fuel having a constant fuel draw. >>>...

Now that is interesting! Is this by eliminating the intermittent rich spots with unregulated pressure?

Ernie

Hear is the link to the cline page.

http://www.billsroom.com/pcfs/produc...uelsysdesc.htm

Also check this out

http://members.cox.net/moorman1/Bigtigre.htm

David

If your going to do a lot of nose up, hovering etc. set the carb mix with the nose pointing up and put the tank as close to the firewall as possible. If it has the large round plug on the front of the tank, bore a hole in the firewall large enough to stick it through. makes it easier to hook up the fuel lines too.

Yep I noticed this when I removed the regulator. I kept my timer set to the same time and almost had an empty tank when I landed. I normally have around 3-4 ounces to spare. I think the reason is that I had to set the engine so rich to keep it from leaning out at the end of the tank. Also it had to be rich so it would not lean out in a vertical upline or hover. There might be other reasons too but the fact is that it definitely used more fuel without the regulator.

I really dont want to drill for crankcase pressure... is there a Pump option that would work here? I have no experience with either pumps or regulators[&:]

you dont need to drill for the cline, it works off the muffler pressure and utilizes a check valve in the pressure hose to the tank. here is my setup.

That's not the ST motor he has. That's a 4 stroke and developes more pressure in the exhaust than an ST 2 stroke. The ST might work off muffler pressure but it also might not. You'll just have to try it out.

hmmmm.... I always heard people surmise that 4 strokes developed LESS muffler pressure....

Woops forgot I had this post My ST develops VERY LITTLE muffler pressure.. So I think i'd have to drill into the case which i DO NOT want to do..[&o] ANyway what about the pump option?

I have heard the same and will post the muffler pressure of a 91 Saito on Thursday. Must pick up a header that was broken.

Generally I am finding 45 size two strokes to develop from 12 t o17 column inches of water (about 1/2 to 3/4 psi) depending upon the muffler.

Bill

This is just my theory but I think the 4-strokes deliver only half the amount of exhaust pressure pulses than that of 2-strokes but each one is much stronger than the 2-stroke. So because of the check valve, the average pressure in the tank will be higher on a 4-stroke (if they both use exhaust pressure).

Out of curiosity I wrote to the folks at Cline, and they stated that 4 stroke muffler pressure works good, but 2 strokes needed crankcase pressure.

Is anyone using 2 stroke muffler pressure with good results anyway?

Ernie

I tried it on a G51... doesn't work... at least not at the rpm I was running it at (Zinger 12x4). Maybe at 16000 rpm the muffler gives adequate pressure...

Case pressure work just fine. Also very easy to "prime the tank"... on muffler pressure you may have a bit of a problem to build up pressure in the tank before you start the engine, but with case pressure you just have to flip the prop 2 or 3 times on a full tank, and that's it.

Muffler pressure on a Saito 80 measured at the field late today was 13 column inches (+/-1”) of water. At first blush four-stroke pressure seems to be stronger than two stroke pressure at idle to mid rpm. More test time is needed to be sure. An ST 90 two stroke with standard old style muffler measured 7 1/4” to 8” at full rpm and the pressure at idle was zero. The ST pressure was much less than that seen on other two strokes. The transition on the ST was reported to be marginal to bad.

Saito 80 =13”
ST 90 = 7 1/2”
OS 50 = 12”
Royal w standard muffler = 12”
Royal w Macs muffler = 15” to 17”

Bill

I am sure the Cline people are smart and know what works best with their product. However the measured pressure on two strokes appears to be in the same range as four strokes. Maybe volume is important with regulated pressure. Maybe higher pressures at lower RPM are important.

Bill

I put a MACS one piece muffler on my Tower 46 one time. Sure made it easy to adjust the engine but it knocked 400 rpm off the top end. It had a lot more pressure to the tank than the stock muffler.

Enjoy

Jim

I think you have hit the nail on the head, Bill.

Ernie

Jim,

The Macs muffler was far too expensive, but looked sexy, and it was too late to consider performance. After a number of hard landings … err crashes … breaks the muffler mounting tabs, clamp on Mac mufflers became a remedy of last resort.

It is very good to know that a decrease in top RPM should be expected. Thanks.

Bill

Another thing to consider is engine rpm. A lighter prop load will increase fuel draw and muffler pressure making the mixture vary less with attitude.