What's the problem?

[ohmygahitscoby]

Hey guys,

I'm trying to break in my STS, but I have a problem. I sealed everywhere except the fuel inlet. I get temperatures as high as 300. When it runs it sounds lean, (Unusually idles at a high RPM that a lean engine would sound, but goes away when I give it throttle. Comes back soon after that.) but when I richen it up, it bogs down and dies. I thought it was my idle but the gap is set to 1mm. Could there be a an air leak somewhere?

-Coby

 

[MotoGod]

It's possible, but if it's a new motor it's probably unlikely. Is it new or rebuilt?

 

[ohmygahitscoby]

New. I think it may be coming from the tank. It's an MGT tank. I think I'll try using the stock HPI tank. Sucks that I have to tune at half tank though.

 

[samrsnow]

I have a feeling its the tank or the pipe. When my STS dissagreed with a pipe it would start running at like 271F and wouldn't come down no matter what i did.

So. If you have a differen't pipe to use like the stock plastic one i would try that.

 

[Scrogg]

If you moved the HSN fuel inlet, chances are it 's leaking there. Had that problem on all my STS engines.

 

[ohmygahitscoby]

I have moved it. I'll try to seal up the inlet. Gonna be hard though since it's a new style.

I happened to check the exhaust and the gaskets are all flattened and oily. I am guessing I'm going to need new ones. I'll pick them up at the LHS today. Will the .21 gaskets fit or I have to get one that says .28 because they don't have any.

 

[samrsnow]

I happened to check the exhaust and the gaskets are all flattened and oily. I am guessing I'm going to need new ones. I'll pick them up at the LHS today. Will the .21 gaskets fit or I have to get one that says .28 because they don't have any.

The .21 gaskets are a perfect fit. Nothing to worry about

 

[ohmygahitscoby]

Awesome. Will let you guys know how it's going. I went back and sealed the HSN inlet.

 

[Racer 1966]

I found the same problem on my STS. The fuel inlet banjo fitting is flat,most carb makers put a flat on the carb mount to allow for a seal to work. STS does not have this flat on the carb.

I can mod it for you if you want,but sealant will work too.

 

[ohmygahitscoby]

Well the sealant just ripped off, lol. Do you charge? PM me. Really interested.

 

[Scrogg]

Degrease it better, the oil/fuel residue probably kept it from bonding properly. Then tighten the HSN housing up good. Then poor the sealant to it. It'll hold, just give it 24 hours to dry.

 

[Lessen]

The fuel inlet banjo fitting is flat,most carb makers put a flat on the carb mount to allow for a seal to work. STS does not have this flat on the carb.

I'm having trouble visualizing this. I think I know what the "banjo fitting" is, but what part of it that is usually flat I'm not sure of.

 

[Racer 1966]

This is not an STS carb, but should explain the problem.

 

[Rolex]

This is the closest I have to a photo that would help explain it.
It's just to the right of the arrow indicating the idle screw, and the fuel line connects to it. If you loosen the hex on the base of the HSN setup, you can turn it to any angle to make the fuel line connection convenient. If you remove the entire HSN stem and brass HSN mount, the Banjo fitting will lift off. Flat on the top, against the brass mount, and flat on the bottom, against the carb. With the fuel tube removed, it will resemble a tiny banjo but with no membrane stretched on the body, just hollow through the center where the HSN meters the fuel flow.

EDIT:
(It's all in the timing. Out drawn by Racer.)

 

[Lessen]

Ohhh, I see. The carb body has a flat section milled. I thought you were talking about the banjo part. That makes sense. So the STS is just a hole tapped right into that curved body section eh? That's dumb.

 

[ohmygahitscoby]

STS also doesn't have a seal on it.

 

[Scrogg]

Ohhh, I see. The carb body has a flat section milled. I thought you were talking about the banjo part. That makes sense. So the STS is just a hole tapped right into that curved body section eh? That's dumb.

Cheap was their goal, as with the rest of the components. Yes it is dumb.

 

[olds97_lss]

I took my HSN assembly off, cleaned it with DA, put RTV on it everywhere contact was made... and the STS30 still ran like yours to the letter. No matter how I tuned, I would get a lean bog and very high idle with minimal power throughout the RPM range, or so rich it would stall, while still having the lean idle issue. Ran around 260-280 no matter how I tuned it.

Mine was with an OFNA 125cc buggy tank which has made all my engines hold a perfect tune top to bottom.

I also rtv'd the carb neck, cinch bolt and backplate. No change.

On a side note, I ran a MGT tank on my savage for about 2 quarts and the LRP just didn't tune right. Rich or lean but almost always lean with flaky idle. Took it off, put the OFNA tank on, runs like a top, but not for very long as the LRP is thirsty!

 

[Scrogg]

The STS .28 and .30 are really different as far as the sleeves go. The .30 has a paper thin sleeve and will crack and/or warp very easily. The .28 can take a lot more abuse without failing.

 

[ohmygahitscoby]

I think I found the word I'm trying to explain. Is it "stalling"? The way my engines acts is it'll idle fine for a few seconds, then start to idle at higher RPM that sounds like it's lean.