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Hello, I have a Rossi .21 power head on my K&B drive with a silver bullet pipe. I have this mounted on the back of my Prather lap cat. It used to be screaming fast until I cleaned the carb. See, I screwed up by not counting my needle adjustments before disassembling the carb and I just can't get it to run right anymore. My HSN (high speed needle) is set at 2 1/3 open and is rich (it takes a couple seconds at full throttle to start two stroking) however my idle screw is out 5 1/4 and it seam lean in the water but I can't really tell for sure. When you pull the throttle back in a turn the RPM just rolls off and the engine dies. I do notice when it is out of the water it it seams to be running rich at idle but that is without a load or cooling water. I think it is spitting drops of fuel from the pipe before I put it in the water which makes me think it is rich at idle. However when fatten up the HSN then it doesn't die when i pull the throttle back, the problem is when the HSN is that rich it just 4 strokes at full throttle and leaves a con trail of smoke. I finished my last gallon of 30% and swithed over to my new gallon of 30% and the fuel made no change (so I am sure the fuel is good) I don't know what the factory carb settings so I am writing here to see if anyone can tell me where to start. When I got the engine new I only had to make a small adjustment to lean the high speed needle and the engine screamed. Let me know if any of you can help,

Thank you,
Cameron

advanced builder

You may have lost or damaged a o-ring, Sucking air. Make sure you put a little pressure downward on the carb as you are tighten the carb down. There are 2 rings ,one on the high speed one on the outer dia on the carb. Clean them carefully ,also CK them for damage. Some solvents don't like rubber, and make them brittle with heat. SOME CARBS have 3 rings ,one on the low speed. Go to there web site and CK the parts layout. Ther are 2 Rossi's Nova Rossi ,Rossi manufacturer You may need to add a few drops of oil on the carb barrel if a older carb. Replace all OLD LINES. CK you fuel tank for air leak

amax

It sounds like you have the LSN way To Rich. I would Start by Leaning it while the boat is Idling or as close to Idle as you can keep it until it Will Idle without you needing to Rev it a lot, Then Run it on the pond and start getting the HSN dialed in.

advanced builder

Amax I had to learn the hard way on the carbs. I had no one to ask. I'm still asking questions, myself on engines. Good post. my engine tuning has come a long way. It's good to ask. still .
I had a old buddy that tweaked his engine to the max, but the engine got to be a tuning night mare. Every run he messed with his needle. Never ran right. over modified. Sorry just mt 2 cents

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Amax, I understand what you are saying but that is a bit difficult. I have to turn the screw toward lean which also puts pressure on the barrel toward close. I have tried doing this by holding the throttle arm and turning the screw and it seams to always close the barrel enough to kill the engine. Wait, while I am typing to you I thought, I should just turn the idle rpm screw up so the barrel can't close. Then I can turn the idle mix screw. I have it backed off so I can use my trim to kill the engine. Sometimes you just have to talk it out to see the answer. I will also check the O-rings because that could cause me fits too.
So, do any of you know where the initial settings should be? 1 1/2 turns, 3 turns on the HSN and 4 turns on the LSN?
It would be nice to start somewhere close to the correct settings.
Thank you all for the input,
Cameron

lipdaddy

This is how I set my LSN on all my nitro engines. Adjust the LSN until you can get the engine to idle, then pinch the fuel line feeding the carb. It should run 3-5 seconds, if not lean it or add fuel until it does. I like mine closer to 4 seconds. Once I have the LSN set I rarely touch it again. Not everyone likes this way, but it seems to work for me. Good luck.

amax

What is the throttle position when your Checking to see how many turns out?? Is it All the way closed Or partially Open??

It should be Completely Closed, Then turn the needle in until it just touches the Jet, Then back out 2 to 3 Full revolutions\turns from there. Start the engine and adjust the needle if needed to get it to Idle, Only adjust it an 1\8 of a revolution at a time, Rev the engine slightly if you need to while Adjusting the screw,, Then try to let it Idle again.
Definitely Make Sure your O-Rings are in Good Shape,, they Will Definitely cause you Fits if there Not. Put a Light Coat of grease on them when you install the needle in the carb so they Don't Stick when trying To Tune the engine. Tuning a Nitro Engine is a Full Time Job, it will change every time the weather does, the higher the engines performance the more it takes to Keep it In Tune.
If you have to use the Throttle Trim on your remote to open the carb more then 1\4 turn to get it to stay running then your to rich, If you have to Trim the carb almost all the way closed to idle it down then your To Lean. It's better to stay on the Rich Side and Open the carb up with the trim to Idle Up. I like to have it idling around 1\8 open on the throttle\carb.
Using the Throttle\Brake to Kill the engine is Always A Good Idea, never use "That screw" as an "Idle Screw" to hold the carb open, use the throttle trim to do that,, That's what It's for.