900 STX Carb Conundrum

[twacker]

This is making me crazy.. I have a 1998 Kawasaki 900 STX that I have done the following to.
1.) New SBT Engine
2.) Pulled fuel tank, cleaned all lines, petcock, etc.
3.) Replaced impeller, jet pump bearing seals, etc.
4.) Rebuilt carbs.
5.) New battery

It runs like crap. Only stays running when you hold the throttle at about 2000 rpm. Will idle for awhile then shuts off. Biggest problem is that it will not spool all the way up, or even close to full throttle for that matter. Just bogs down as if it is getting too much fuel.

The original engine had 2 pulse lines and the one SBT sent out only had 1. Tech support said to just put a "T" from the single to supply the dual carb pulse inputs. Is this really the way it needs to be done??

I believe the carbs that were on it when I started may have come from a 1100, so with that in mind I bought a set that I knew were from a 900 stx off of ebay hoping that would cure the problem. Well, as you could guess, it did not.

I am really getting to the point that it would be more satisfying to just blow the SOB up and roast a marshmellow from its flaming carcuss.

What errors could I have made considering that there is not one hose that was not removed that would cause this problem. Give them all to me and I will eliminate each one.

Thanks

John

[twacker]

More Info - 900 STX Carb Conundrum

I did not replace the reeds on the initial rebuild. What are the symtoms of faulty or worn out reed valves??

[twacker]

Re: 900 STX Carb Conundrum

Tech support......Where are you?????????????

[lobo]

Re: 900 STX Carb Conundrum

Not sure if you've seen this video in forums > techincal support > SBT videos but it will give you a good idea about how they work.

This tip explains to you what a reed valve is and how it works.


I've run across many helpful videos in this section.

[Technical Support]

Re: 900 STX Carb Conundrum

Your problem is in the carbs, Did you rebuild or even open up the carbs you bought from ebay? Jetting might not even be close, Who knows what the last guy had the carbs set up for. Open them up and list the jetting for each carb, Highs and lows. start with the front / middle / rear. We will get this running. You can also call in 1877-330-0231 ask to speak to Tom .

[Technical Support]

Re: 900 STX Carb Conundrum

I looked up your jetting, Your front should be (main jet) #115 middle (main jet) #105 and (rear main jet) #110 All pilot jets should be # 78 Low speed mixture screws 1 and 1/4 turns open and high speed screws set at 3/4 turns open. See if yours matches this. Tom SBT tech.

[twacker]

Re: 900 STX Carb Conundrum

I looked up your jetting, Your front should be (main jet) #115 middle (main jet) #105 and (rear main jet) #110 All pilot jets should be # 78 Low speed mixture screws 1 and 1/4 turns open and high speed screws set at 3/4 turns open. See if yours matches this. Tom SBT tech.

This just keeps getting more bizarre. Wouldn't the main jets be #95 #85 #90 for a 1998 STX?? That is whats in the original carbs. The ebay carbs don't have the main jet in the same place. Where is it?? The location that it "should" be in the case does not exist.

The main and low needle adjustment screws on the ebay carb were ALL turned all the way in. Guess someone was bored before they shipped them out. I would hope that I would need to look no further than that for my answer. Still would like to know about the main jets # and location for the ebay carb. Each case on the ebay carb has a 835 stamp on it and the main bodies have a 495, if that helps. Keihin of course. Can send pics if that would help..

[Technical Support]

Re: 900 STX Carb Conundrum

Give me a call when you get time, Tom SBT tech. 1877-330-0231.

[twacker]

Re: 900 STX Carb Conundrum

Well here we go. The main jets are on the backside of the case plate. The reason I didn't see them was THEY WERE NOT THERE!!!!! Leason learned. I mistaking thought the carb's from ebay were "virgins" and had not be tampered with. (My wife told me the same story) They showed no signs at first look.

Pulled the jets from the old carb, replaced diaphragms, set valve needles, and viola. Seems to run fine. Will lake test ASAP. I feel confident it will run strong.

Thanks Tom for pointing me in the right direction!!!

[twacker]

Re: 900 STX Carb Conundrum

I looked up your jetting, Your front should be (main jet) #115 middle (main jet) #105 and (rear main jet) #110 All pilot jets should be # 78 Low speed mixture screws 1 and 1/4 turns open and high speed screws set at 3/4 turns open. See if yours matches this. Tom SBT tech.

Lake tested and still ran poorly. Problem was the low and high mixture screw setting you gave were backwards. Just a FYI for anyone else looking at this thread. Thanks again Tom for getting me focused in the right direction

John

[Technical Support]

Re: 900 STX Carb Conundrum

the factory manual has it listed 1 1/4 low speed and 3/4 high speed, the low speed is the lowest one on the carb and the high speed is the one closest to the air box. Is this how you have them adjusted? Tom SBT tech.