Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Needle Valve setting on Jett 50 FIRE

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Old 11-09-2007, 10:31 PM
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hooaa
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Default Needle Valve setting on Jett 50 FIRE

I am going out in the a.m. with a new 40 Shrike with a Jett 50 FIRE. Ihave the needle valve mounted remotely. I always have trouble getting the mixture right, usually flown too lean. I'd like to know approx. how many turns the valve should be set to for starting, and approx. where it likes to run (19+K, 8.75 x 8.75, 15%).

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Old 11-09-2007, 11:59 PM
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daven
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Default RE: Needle Valve setting on Jett 50 FIRE

Turn the needle all the way in, and then back out 5 full turns. Start the motor up and slowly turn the needle in until the rpms max out (a tach helps) and then shut it off. Wait about 10 minutes, open it a half turn and restart. Slowly turn the needle in until it jumps on to the pipe, at that point, open it back up about a 1/4 turn and you should be about 500 rpm off peak and good to go.

Its tough to tell someone how to do this, without actually being there to help. It should be slightly off the last stage of the pipe giving the motor room to unload. If you are consistently running lean, start off on the richer side, and after every flight slowly lean it out till it comes into an area the motor is happy (you will know).

It is ALWAYS better to miss to the rich side, and after 10 or so runs you will know where to leave the needle before launching.

My first run of the day never leaves the ground, it is just a test to find out peak rpm, and then I try to sneak up on it on future runs.

Good luck, nice looking plane.
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Old 11-10-2007, 02:06 AM
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Default RE: Needle Valve setting on Jett 50 FIRE

Dave, That is exactly the info I needed. I've had fairly good results when the needle valve was directly behind the motor. In this case it is 3" apart and the delay causes me to vary the mixture all over the spectrum.
Thank you!
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Old 11-10-2007, 09:58 AM
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Default RE: Needle Valve setting on Jett 50 FIRE

You shouldn't see that much of a difference with the remote needles. You want it just on that edge of getting on and falling off the pipe when you take off.
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Old 11-10-2007, 03:46 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

Hooaa:

Listen to the "Master" here closely and you will always be a few rpm above the rest in flight where it counts. One thing about high performance engines you need to stay away from and thats running them lean even when tuneing. If you do, pack up cause you are done for the day. Not going to run right and on top for the rest of the day. Read through Dub Jetts web site and you will see the same thing. Once you OVERHEAT the engine, clearances will not come back to design for some time. You are much better off on the first run of the day following the "Masters" directions, afterall, he is almost tretcherous, reserved for the older folk.
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Old 11-10-2007, 05:19 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

rmenke,
Sadly I did it all wrong last weekend. I started rich and slowly went toward lean. At one point it came on the pipe. I kept leaning it thinking that I'd better be certain that I was 500 revs below peak. It nearly died so I quickly richened it but it didn't get on the pipe. At one point I asked my hand launcher to pick it up off of the stand and toss it. It was not nearly peak but he tossed it. Five feet later it died and I made a decent recovery. I want to do it right next time. I didn't have a helper today so no chance to try the procedure out.
In earlier days I had lots of KB 40 FIRE and macs pipes on quickies. They were far less fussy. Just find the peak, back off and let go. They'd be on the pipe before the first pylon. I know that these Jetts have much more power, I just need to get used to Dubb's way of treating them.
This motor has been on two previous birds RIP. How do I know that if through misunderstanding I have already damaged it? Perhaps that is part of why I had problems setting the valve.
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Old 11-10-2007, 10:26 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

Just keep practicing and starting rich.

I like to back the needle 1/2 a turn back after each run, and then slowly bringing it leaner.

Remember the needle position from the last flight, and if you were too rich (or lean) adjust by an 1/8 turn. In my opinion, with these types of motors, once you get it TOO hot, it will never cool down and run right. You have to start rich, and slowly bring it in to an optimal setting.

Running sport planes you can get away with this tactic, and its good on the motor. Unfortunately, it takes a lot of discipline to do that on race day
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Old 11-11-2007, 04:03 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

Hooaa:

Ok, something is off here, a K & B needles easier than the Jett, never, period. Back to basics. Pull engine, check back plate and head for correct torque and no leaks at carb. Pipe seal fresh and tight? Find something with wheels that will take the Jett and pipe correctly. Add break-in prop, apc 10 X 6, and start per "Master Daven". You gotta have a tack now, and a decent one at that, the TNC is good and reasonable for the quality. Lean until she comes on the pipe. Check rpm's, should be at least 17,500. You can lean a little more but not past peak. How do you get to peak and not pass into the toooo lean area? Get that good tack and use it on each run with all your engines until you can hear 17,500, or very close. Unless you are tone deaf, its a acquired skill. If possible go to a few q-500 or formula races. You may see the guy that brings his engine to near peak, and then pinch the fuel line to kick it all the way up, and then back off to his "spot". This is a art form at work, watch and listen and most of all, learn. This is a difficult process to describe correctly. Anyway, if you are not getting 17,500, pack engine and pipe and send in to Dub Jett with a description of what is going on. It will come back giving the rpm at a reasonable cost. Fly it a few times until you are cumfortable with the engine. Do you have "club races?" If so, there is always the one or two guys that end up on top, almost all the time. See what prop they are running. Watch and listen when they start up and tune. Watch how they run their lines around the pylons and how their plane behaves in the corners and down the streight. Usually, their elevator is limited to a nice tight consistant turn at full throw, the ailerons slow enough to go into the corners the same way each and every turn, very consistant, seldom a mestake. "Learn from the best, and beat the rest". When you race at the national level, one small error us usually enough to let the Davens's get by. Keepworking at it, they all get old. ENJOY
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Old 11-11-2007, 06:24 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

Roger,

not sure if you heard, but Rusty won the NMPRA champ race today with a perfect score.

Beat out all the hot young guns
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Old 11-12-2007, 11:11 AM
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Default RE: Needle Valve setting on Jett 50 FIRE

You normally would have no issue finding peak rpm..... the long pipe sometimes makes it tricky, expecially it it is tuned for higher rpm... more narrow of a range. But it still should not be a chore.

Some good proceedure above....

Always good to error rich. You can creep up on the needle each flight.

With the sport engines, no real reason to back the needle out for starting between flights... its not like the racing engines.

I never touch the sport needles one they are set.. other than for slightly adjustments based on the conditions. The engine starts just fine at idle, warm it up at a slightly high idle for 20 seconds, then proceed to a full throttle warm up.

I rarely do much more than listen to the engine ..... briefly watch the tach during a test run to find out approximate needle position where the engine peaks out (and what it sounds like). Then back down from there where there is a notible rpm drop, and perhaps a bit of a rich "crackle".

On the full size pipe, you will be backing down probably closer to 600-800 rpm.

If the engine completely falls off the pipe too easily, or is in any way difficult to needle ------ use a lighter prop. Once you have it running properly and have a few flights in, you can try the original prop again.

If the engine can not get to the tuned point on the pipe, its just not going to run right. You CAN set the engine with a short pipe, but you have to know how it runs normally first (setting a short pipe is what we basically do for the racing engines..... the hairy edge)

Changing the prop is the easiest way of adjusting pipe length

Bob
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Old 11-12-2007, 12:38 PM
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Default RE: Needle Valve setting on Jett 50 FIRE

D:

Great for Rusty, perfect, wow. Keep trying to tell you to watch out for those old guys. he he he. ENJOY
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